CN114590774A - Magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O and preparation method thereof - Google Patents

Magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O and preparation method thereof Download PDF

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CN114590774A
CN114590774A CN202210433483.9A CN202210433483A CN114590774A CN 114590774 A CN114590774 A CN 114590774A CN 202210433483 A CN202210433483 A CN 202210433483A CN 114590774 A CN114590774 A CN 114590774A
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hydrogen
hydrogen storage
mgh
storage material
magnesium hydride
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孙立贤
桑振
徐芬
张晨晨
夏永鹏
康莉
荚鑫磊
刘昭宇
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Guilin University of Electronic Technology
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Abstract

The invention discloses a magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O, which is prepared by mixing magnesium hydride and hierarchical porous microspheres Ti-Nb-O and mechanically ball-milling; the hierarchical porous microsphere Ti-Nb-O is prepared by a solvothermal method and a calcining method; the diameter of the material is 1-2 mu m, the microscopic morphology is spherical, and the specific surface area is 27.63 m2(ii) a pore size distribution of 38-40 nm. The preparation method comprises the following steps: 1, grading porous microsphere Ti-Nb-O precursorPreparing a precursor; 2, preparing a graded porous microsphere Ti-Nb-O; and 3, preparing the magnesium hydride hydrogen storage material based on the hierarchical porous microsphere Ti-Nb-O. As an application in the field of hydrogen storage: the initial hydrogen release temperature of the system is reduced to 189 ℃, and the hydrogen release amount reaches 6.96 wt%; the isothermal complete hydrogen release temperature is 300 ℃, and the hydrogen release amount reaches 6.82wt% in 60 min; the hydrogen absorption is 1.78 wt% in 60 min under the condition that the isothermal hydrogen absorption temperature is 50 ℃. The activation energy of catalytic hydrogen evolution is Ea(des)=92.7 kJ/mol, the activation energy for catalytic hydrogen absorption is Ea(abs)=26.0 kJ/mol; enthalpy change of desorption reaction
Figure 666268DEST_PATH_IMAGE002
Hd=69.6 kJ/mol. The cycle retention was 92.3%.

Description

Magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O and preparation method thereof
Technical Field
The invention relates to the technical field of hydrogen storage materials of new energy materials, in particular to a magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O and a preparation method thereof.
Background
Traditional fossil energy such as petroleum and coal is increasingly exhausted along with continuous use of human beings, so that the energy crisis caused by the depletion restricts the development of the human society, and the search for green, efficient and renewable new energy to replace the fossil energy is a common consensus of all human beings and a great deal of research results are obtained. The hydrogen energy has the advantages of rich raw material sources, high energy density, environment-friendly products, renewability and the like, and becomes one of the most potential alternative energy sources at present. At present, the development and utilization of hydrogen energy mainly face three key problems of production, storage and transportation. Among them, how to safely and efficiently use hydrogen energy as an on-vehicle energy storage carrier is currently the most challenging and commercially valuable research topic. The traditional high-pressure liquid and gaseous hydrogen storage method has low efficiency, high production energy consumption and low use safety, restricts the commercial use of vehicle-mounted hydrogen storage, and the solid hydrogen storage technology has great research potential as a safe and efficient hydrogen storage method, and is a hydrogen storage method which is most likely to be used on a large scale in the future.
Magnesium hydride (MgH)2) Has higher hydrogen storage capacity (7.6 wt%) and good reversibility, is considered to be one of the most potential solid hydrogen storage materials, but has high thermal stability and slow kinetic speed, and seriously restricts the use of the solid hydrogen storage material as an on-vehicle energy storage carrier.
In recent years, researchers improve MgH in modes of doping modification, nanocrystallization, composite system construction, confinement and the like2The hydrogen storage performance of the method is that the hydrogen absorption and desorption temperature is reduced, and the hydrogen absorption and desorption dynamics and reversibility are improved. Among them, doping modification, i.e., addition of carbon-based materials and various transition metal compounds (oxides, chlorides, nitrides, and the like), has been studied more. Carbon-based materials are reported to catalyze MgH2The carrier (e.g. MWCNT, etc.) of the hydrogen storage catalyst has almost no catalytic effect, and the transition metal compound, such as TiO2、NiCl2、Nb2O5And TiN etc. as a catalyst are effective in improving MgH2But they do not have a special morphology as a support to further improve MgH2Hydrogen storage performance of (1).
Among the above dopants, it has been found that oxides of higher valence metals can produce better catalytic effects, especially Nb2O5And TiO2。
Addition of 0.5 mol% Nb was observed by Barkhordarian et al2O5Thereafter, the mixture was heated at 300 ℃ for 90 seconds from MgH2With 7 wt.% H being liberated2 [Barkhordarian G, Klassen T, Bormann R. Effect of Nb2O5 content on hydrogen reaction kinetics of Mg. J. Alloys Compd. 2004, 364, 242–246.]. Subsequent studies showed uniform distribution over MgH2The Nb-based species in the matrix is an effective way to facilitate hydrogen transport.
Similarly, TiO2For improving MgH2The hydrogen storage kinetics of (a) is very efficient. Croston et al prepared TiO by sol-gel method2Based oxide materials, studies have shown the addition of TiO2Then from MgH2The initial temperature of The intermediate desorption of hydrogen is reduced from 360 ℃ by more than 100 ℃ [ Croston DL, Grant DM, Walker, GS. The catalytic effect of titanium oxide based additions on The reduction and hydrogenation of milled MgH2. J. Alloys Compd. 2010, 492, 251–258.]
In summary, either Nb-or Ti-based materials alone can be effective as catalysts for improving MgH2Hydrogen storage performance of (1).
In recent years, research on complex metal oxides has been receiving increased attention due to concerted catalytic action.
For example, Zhang et al prepared a series of ferrites (MnFe) by calcination2O4、ZnFe2O4And CoFe2O4) And indicates CoFe2O4Has higher catalytic effect [ Zhang J, Shan JW, Li P, Zhai F Q, Wan Q, Liu ZJ, Qu XH. Dehydrogenation mechanism of ball-millied MgH2 doped with ferrites (CoFe2O4, ZnFe2O4, MnFe2O4 and Mn0.5Zn0.5Fe2O4) nanoparticles. J. Alloys Compd. 2015, 643, 174–180.]。
In addition, yellow and the like prepared TMTiO by a sol-gel and calcination method3Wherein NiTiO is used3Doping with MgH2The system was found to achieve approximately 12-fold dehydrogenation rates at 235 [ Huang X, Xiao XZ, Wang XC, Wang CT, Fan XL, Tang ZC, Wang CY, Wang QD, Chen LX. Synergistic catalytic activity of porous rod-like TMTiO [ ]3 (TM = Ni and Co) for reversible hydrogen storage of magnesium hydride. J. Phys. Chem. C 2018, 122, 27973–27982.]。
In addition, the ternary oxide VNbO prepared by the solid method by Antonio Valentoni et al5Doping with MgH2It was found that VNbO was circulated at 275 ℃ with a hydrogen capacity of 5wt%5Modified MgH2At 70 times, little capacity loss was observed [ Valentoni A, Mulas G, Enzo S, Garroni S. Remarkable hydrogen storage properties of MgH2 doped with VNbO5. Phys. Chem. Chem. Phys. 2018, 20, 4100–4108.]。
In conclusion, the research on complex metal oxides shows that MgH can be improved by the concerted catalysis between metals2Hydrogen storage performance of (1).
In addition, Zhang et al prepared a series of ferrites (MnFe) by calcination2O4、ZnFe2O4And CoFe2O4) However, by comparison, ZnFe was found2O4、MnFe2O4、Mn0.5Zn0.5Fe2O4Doping with MgH2The dehydrogenation kinetics of the hydrogen storage material is higher than that of CoFe2O4Doping with MgH2Hydrogen storage materials [ Zhang J, Shan JW, Li P, ZHai F Q, Wan Q, Liu ZJ, Qu XH. Dehydrogenation mechanism of ball-milled MgH2 doped with ferrites (CoFe2O4, ZnFe2O4, MnFe2O4 and Mn0.5Zn0.5Fe2O4) nanoparticles. J. Alloys Compd. 2015, 643, 174–180.]. Shows that the synergistic effect of different metals on the improvement of MgH2The kinetic and thermodynamic effects of the metal oxide are different, so that the composite transition metal oxide is expected to be used as a precursor to create a multi-element and multi-valence chemical environment in situ through a synergistic effect between metals so as to obtain a higher catalytic effect.
For Ti and Nb complex metal oxides, such as Yuan and the like, a novel polypyrrole-chemical vapor deposition (PPy-CVD) method is used for synthesizing an amorphous Ti-Nb-O material, and the amorphous Ti-Nb-O material is proved to have high discharge density for a lithium ion battery.
The above reportsDoping to MgH with Nb base and Ti base respectively2Modified, or co-catalyzed to improve MgH2Hydrogen storage capacity of (2), but MgH2The hydrogen storage performance of hydrogen storage materials still does not meet the actual requirements, and further improvement is urgently needed. Therefore, there are also problems to be solved:
1. the carrier of the catalyst has no better catalytic performance;
2. the catalyst has no characteristics of both a carrier and a loading object;
3. the catalyst has catalytic performance but no special appearance, and the special appearance of the catalyst is opposite to MgH2The effect of hydrogen storage performance of (c);
in the prior art, a solvent heating and calcining method is adopted to prepare a graded porous Ti-Nb-O microsphere material, and the microsphere with a three-dimensional porous structure consisting of cross-linked nano particles has a larger specific surface area and rich electron transfer channels, and can effectively improve MgH2Hydrogen storage performance of (1). In addition, it improves MgH as a catalyst2The catalyst with hydrogen storage performance not only has special appearance, but also has the characteristics of a carrier and a load, and simultaneously the synergistic effect of Ti and Nb elements improves MgH2Hydrogen storage performance of (1).
Disclosure of Invention
The invention aims to provide a magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O and a preparation method thereof, which can obviously improve MgH2The hydrogen absorption and desorption performance of the fuel cell can further promote the process of applying the hydrogen energy to the vehicle-mounted fuel cell in a large scale.
The inventor researches and discovers that:
1) for solid-state catalysis, catalytic efficiency is critically dependent on the dispersion of the catalytic species in the system;
2) metal oxide with MgH2The reaction is easily reduced to low-valent substances or even zero-valent metals which are actual catalytic active sites;
3) the multivalent chemical environment proved to be advantageous for improving MgH by accelerating electron transfer between Mg and H2Dehydrogenation kinetics of (2).
Aiming at the technical problems in the prior art, the invention adopts the following modes to solve the problems:
1. firstly, a simple dissolution thermal method is combined with calcination treatment, and a novel titanium niobium oxide (Ti-Nb-O) microsphere with a three-dimensional porous structure consisting of cross-linked nano particles is reasonably constructed;
2. mixing Ti-Nb-O microspheres with MgH by ball milling method2Fully and uniformly mixed to ensure that the catalyst is uniformly dispersed in MgH2In the matrix, the particle size of the particles is simultaneously reduced.
The technical scheme for realizing the purpose of the invention is as follows:
a magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O is prepared by mixing magnesium hydride and hierarchical porous microspheres Ti-Nb-O and mechanically ball-milling; the hierarchical porous microsphere Ti-Nb-O is prepared by a solvothermal method and a calcining method; the diameter of the hierarchical porous microsphere Ti-Nb-O is 1-2 mu m, the microscopic morphology is spherical, and the specific surface area is 27.63 m2(ii) a pore size distribution of 38-40 nm.
A preparation method of a hierarchical porous Ti-Nb-O microsphere material doped magnesium hydride hydrogen storage material comprises the following steps:
step 1, preparing a hierarchical porous microsphere Ti-Nb-O precursor, dissolving a certain mass of P123 in absolute ethyl alcohol by a solvothermal method, violently stirring for a certain time to obtain a solution A, dissolving titanium isopropoxide and anhydrous niobium chloride in the solution A according to a certain mass ratio, and stirring for a certain time to obtain a reaction solution; then, carrying out solvothermal reaction under certain conditions, and finally washing and drying the obtained precipitate to obtain a hierarchical porous microsphere Ti-Nb-O precursor;
in the step 1, the concentration of P123 dissolved in absolute ethyl alcohol is 7.5-10 g/L, and the stirring time is 15-45 min; the ratio of the quantity of the titanium isopropoxide to the anhydrous niobium chloride in the step 1 is (1-3) to (5-15); the solvothermal condition is that the reaction temperature is 200 ℃ and the reaction time is 24 hours;
step 2, preparing a hierarchical porous microsphere Ti-Nb-O, namely calcining the hierarchical porous microsphere Ti-Nb-O precursor obtained in the step 1 under a certain condition by a calcining method to obtain the hierarchical porous microsphere Ti-Nb-O;
the calcining condition in the step 2 is that the calcining temperature is 800 ℃ and the calcining time is 1.5h under the argon condition;
step 3, preparing the magnesium hydride hydrogen storage material based on the hierarchical porous microsphere Ti-Nb-O, mixing the hierarchical porous microsphere Ti-Nb-O obtained in the step 2 and magnesium hydride according to a certain mass ratio, and then carrying out ball milling under certain conditions to obtain the magnesium hydride hydrogen storage material based on the hierarchical porous microsphere Ti-Nb-O;
the mass ratio of the graded porous microsphere Ti-Nb-O to the magnesium hydride in the step 3 is (6-9) to (91-94); the ball milling conditions are that argon is used as protective atmosphere, the ball-material ratio is 200:1, the ball milling rotation speed is 250 r/min, and the ball milling time is 5 h.
When the doping amount of the catalyst is 7 wt%, the initial hydrogen release temperature of the system is reduced to 189 ℃, and the hydrogen release amount reaches 6.96 wt%; when the hydrogen is discharged isothermally, the system can completely discharge the hydrogen at 300 ℃, and the hydrogen discharge amount reaches 6.82wt% in 60 min; when the system absorbs hydrogen isothermally, the system can still absorb 1.78 wt% of hydrogen within 60 min even under the condition of the temperature as low as 50 ℃;
the activation energy of catalytic hydrogen evolution is Ea(des)=92.7 kJ/mol, the activation energy for catalytic hydrogen absorption is Ea(abs)=26.0 kJ/mol; enthalpy change of desorption reaction
Figure DEST_PATH_DEST_PATH_IMAGE002
Hd=69.6 kJ/mol；
After being recycled, the sample shows good hydrogen storage reversibility and stable cyclability, and after 15 cycles, the retention rate of the actual hydrogen capacity is equivalent to 92.3% of the first cycle capacity.
The technical effects of the invention are detected by experiments, and the specific contents are as follows:
the SEM detection shows that: the Ti-Nb-O microspheres are well distributed in the range of 1-2 mu m, and the graded microspheres are assembled by primary nano particles of 20-50 nm and are mutually connected by a porous network.
According to TEM detection, the invention can be known as follows: the Ti-Nb-O microspheres are mesoporous spheres and consist of mutually connected nanoparticles with the particle size of 20-50 nm, and the lattice spacing of the Ti-Nb-O microspheres is about 0.374 nm, 0.321 nm and 0.337 nm as measured by a high resolution image and is respectively matched with the (011), (211) and (-106) surfaces of Ti-Nb-O phases (PDF # 13-0317).
The XRD detection shows that: the phase characteristics are analyzed, and the diffraction peak of the Ti-Nb-O microsphere is well matched with the crystal face of Ti-Nb-O (PDF #13-0317), so that the purity is high and the crystallinity is high.
The Bet detection shows that: the specific surface area and the pore size distribution of the Ti-Nb-O sample are determined, and the specific surface area is 27.63 m2(ii) a pore size distribution of 38-40 nm.
The XPS detection shows that: the chemical composition and valence state of the Ti-Nb-O sample are determined, and full spectrum test shows that Ti, Nb and O elements exist in the Ti-Nb-O microsphere.
The Thermogravimetric (TG) detection shows that: when the doping amount of the catalyst is 7 wt%, the initial hydrogen discharge temperature of the system is reduced to 189 ℃, and the hydrogen discharge amount reaches 6.96 wt%.
The invention can be detected by pressure-component-temperature (PCT) to obtain the following results: when the hydrogen is discharged isothermally, the system can completely discharge the hydrogen at 300 ℃, and the hydrogen discharge amount reaches 6.82wt% in 60 min; when the system absorbs hydrogen isothermally, the system can still absorb 1.78 wt percent of hydrogen within 60 min even under the condition of the temperature as low as 50 DEG C
The invention can be known through Differential Scanning Calorimetry (DSC) detection that: catalytic MgH2The activation energy of hydrogen evolution is Ea(des)=92.7 kJ/mol。
The invention can be detected by pressure-component-temperature (PCT) to obtain the following results: the hydrogen absorption activation energy of the sample is calculated to be E through the Johnson-Mehl-Avrami (JMA) equation Arrheniusa(abs)=26.0 kJ/mol。
The invention can be detected by pressure-component-temperature (PCT) to obtain the following results: calculating the desorption reaction enthalpy change of the system hydrogen by PCT curve test and van't Hoff equation
Figure 580273DEST_PATH_DEST_PATH_IMAGE002
Hd=69.6 kJ/mol。
The invention can be known through cycle performance detection that: the cyclicity test was carried out at 300 ℃. Dehydrogenation was started from initial vacuum, and the hydrogen pressure for rehydrogenation was 5 MPa. After 15 cycles, only 0.5 wt% of capacity was lost, corresponding to a capacity retention of 92.3%, indicating a significant stability of the cycling operation.
Therefore, the experimental detection of SEM, XRD, TEM, XPS, TG, DSC, PCT and the like shows that the graded porous Ti-Nb-O microsphere doped magnesium hydride hydrogen storage material has the following advantages compared with the prior art:
the raw materials used in the invention all belong to chemical raw materials which are already industrially produced, are available in the market and are easily obtained, and the synthesis process is simple, the reaction period is short, the energy consumption in the reaction process is low, and the pollution is low.
Secondly, the multivalent chemical environment adopted by the invention is beneficial to improving MgH by accelerating electron transfer between Mg and H2Dehydrogenation kinetics of (2).
The application of the magnesium hydride hydrogen storage material effectively improves the hydrogen absorption and desorption performance of magnesium hydride, has lower initial hydrogen desorption temperature, obtains high final hydrogen desorption amount by adding a small amount of catalyst, and greatly improves the hydrogen absorption performance. When the doping amount of the Ti-Nb-O microspheres is 7 wt%, the initial hydrogen release temperature is reduced to 189 ℃, and the final hydrogen release amount reaches 6.96 wt%; when the hydrogen is discharged isothermally, the system can completely discharge the hydrogen at 300 ℃, and the hydrogen discharge amount reaches 6.82wt% in 60 min; in addition, when the hydrogen is absorbed isothermally, the system can still absorb 1.78 wt% of hydrogen within 60 min even under the condition of the temperature as low as 50 ℃.
Fourthly, the Ti-Nb-O microsphere doped magnesium hydride hydrogen storage material with hierarchical porosity has lower hydrogen absorption and desorption activation energy and catalyzes MgH2The activation energy of hydrogen evolution is Ea(des)=92.7 kJ/mol, hydrogen absorption activation energy is Ea(abs)=26.0 kJ/mol。
Fifthly, the MgH is reduced by using the hierarchical porous Ti-Nb-O microsphere doped magnesium hydride hydrogen storage material as a catalytic hydrogen production material2Enthalpy change of hydrogen desorption reaction
Figure 762993DEST_PATH_DEST_PATH_IMAGE002
Hd。
And sixthly, the hierarchical porous Ti-Nb-O microsphere doped magnesium hydride hydrogen storage material has excellent cycle performance and is tested at the temperature of 300 ℃. Dehydrogenation was started from the initial vacuum and the hydrogen pressure for the rehydrogenation was 5 Mpa. After 15 cycles, only 0.5 wt% of capacity is lost, which is equivalent to 92.3% of capacity retention rate, indicating that the cycle operation has obvious stability, improving the stability of the catalyst material, and having wide application prospect in the fields of hydrogen storage materials, fuel cells and the like.
Drawings
FIG. 1 is an X-ray diffraction chart of Ti-Nb-O in example 1;
FIG. 2 is a scanning electron microscope photograph of Ti-Nb-O in example 1;
FIG. 3 is a transmission electron microscope photograph of Ti-Nb-O in example 1;
FIG. 4 is a drawing showing the physical adsorption of Ti-Nb-O in example 1;
FIG. 5 is a photoelectron spectrum of Ti-Nb-O in example 1;
FIG. 6 shows MgH in example 12-XRD pattern of 7 wt% Ti-Nb-O hydrogen storage material;
FIG. 7 shows MgH in example 12SEM and TEM images of 7 wt% Ti-Nb-O hydrogen storage material;
FIG. 8 shows MgH in example 12-TG diagram of 7 wt% Ti-Nb-O hydrogen storage material;
FIG. 9 shows MgH in example 12Isothermal desorption (300 ℃) and adsorption (300 ℃ and 5 Mpa H of-7 wt% Ti-Nb-O hydrogen storage material2) A cycle plot;
FIG. 10 shows MgH in example 12SEM and particle distribution histogram of 7 wt% Ti-Nb-O hydrogen storage material after ball milling, 15 th isothermal hydrogen absorption, 15 th isothermal hydrogen desorption;
FIG. 11 shows MgH in example 12-XPS plots of Ti 2p orbitals, Nb 3d orbitals after 15 cycles for 7 wt% Ti-Nb-O hydrogen storage material;
FIG. 12 shows MgH in example 12-isothermal hydrogen desorption diagram of 7 wt% Ti-Nb-O hydrogen storage material at different temperatures;
FIG. 13 is MgH in example 12-isothermal hydrogen sorption patterns of 7 wt% Ti-Nb-O hydrogen storage material at different temperatures;
FIG. 14 shows MgH in example 12-7 wt% Ti-Nb-O hydrogen storage material and MgH after ball milling2DSC curve and DSC curve peak fitting graph of the sample;
FIG. 15 shows MgH in example 12-7 wt% Ti-Nb-O hydrogen storage material and MgH after ball milling2An isothermal hydrogen desorption curve, a JMA curve and an Arrhenius fitting curve chart of the sample;
FIG. 16 shows MgH in example 12-7 wt% Ti-Nb-O hydrogen storage material and MgH after ball milling2PCT curves and van't Hoff of samples at different temperatures and corresponding fitting line graphs thereof;
FIG. 17 shows MgH in example 12-XRD pattern of 7 wt% Ti-Nb-O hydrogen storage material in ball-milled, dehydrogenated and rehydrogenated state;
FIG. 18 depicts the Ti-Nb-O catalyst, ball milled MgH of example 12-XPS plots of 7 wt% Ti-Nb-O and hydrogen storage material after one hydrogen sorption and desorption cycle;
FIG. 19 shows MgH in example 1 and comparative examples 1, 2, 3, 4 and 52-TG diagram of x wt% Ti-Nb-O (x =0, 1, 3, 5, 7, 10) hydrogen storage material;
FIG. 20 shows MgH in example 1 and comparative example 127 wt% Ti-Nb-O hydrogen storage material and MgH after ball milling2A comparison graph of isothermal hydrogen desorption of the sample at 300 ℃ and isothermal hydrogen absorption at 200 ℃;
FIG. 21 shows MgH in example 1 and comparative example 12-7 wt% Ti-Nb-O hydrogen storage material and MgH after ball milling2The hydrogen absorption and hydrogen desorption of the sample are compared to the energy barrier diagram.
Detailed Description
The invention is further described in detail by the embodiments and the accompanying drawings, but the invention is not limited thereto.
Example 1
A preparation method of a magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O comprises the following steps:
step 1, preparing a hierarchical porous microsphere Ti-Nb-O precursor, dissolving 0.6 g of P123 in 60 mL of absolute ethyl alcohol by a solvothermal method, violently stirring for 15 min to obtain a solution A, then dissolving 0.568 g of titanium isopropoxide and 2.7 g of anhydrous niobium chloride in the solution A according to the mass ratio of 1:5, and stirring for 30 min to obtain a reaction solution; then transferring the reaction solution into a high-pressure reaction kettle, carrying out solvothermal reaction at the reaction temperature of 200 ℃ for 24 hours, and finally washing the obtained precipitate with deionized water and absolute ethyl alcohol and drying to obtain a hierarchical porous microsphere Ti-Nb-O precursor;
step 2, preparing the graded porous microsphere Ti-Nb-O, namely calcining the graded porous microsphere Ti-Nb-O precursor obtained in the step 1 by a calcination method under the condition of argon at the calcination temperature of 800 ℃ for 1.5h to obtain the graded porous microsphere Ti-Nb-O;
in order to confirm that the material synthesized in the above procedure was Ti-Nb-O, XRD test was performed on Ti-Nb-O. The test result is shown in figure 1, the diffraction peak of the Ti-Nb-O microsphere is well matched with the crystal face of Ti-Nb-O (PDF #13-0317), the purity is high, and the crystallinity is high, which indicates that the Ti-Nb-O is successfully synthesized.
In order to demonstrate the structural characteristics of the resulting Ti-Nb-O material, SEM and TEM tests were performed on the Ti-Nb-O. As shown in FIGS. 2 and 3, the Ti-Nb-O microspheres are well distributed within the range of 1-2 μm, and these graded microspheres are assembled from primary nanoparticles of 20-50 nm, which are interconnected by a porous network; EDS energy spectrum shows that the Ti-Nb-O microspheres have and only have Ti, Nb and O elements; the lattice spacing of the Ti-Nb-O microsphere is about 0.374 nm, 0.321 nm and 0.337 nm, which are determined by high resolution image and are respectively matched with the (011), (211) and (-106) planes of the Ti-Nb-O phase (PDF # 13-0317).
To demonstrate the specific surface area and pore size distribution of the resulting Ti-Nb-O material, a Bet test was performed on Ti-Nb-O. The test results are shown in FIG. 4, which shows a specific surface area of 27.63 m2(ii) a pore size distribution of 38-40 nm.
To demonstrate the chemical composition and valence state of the resulting Ti-Nb-O material, an XPS test was performed on Ti-Nb-O. The test results are shown in fig. 5(a-d), and the full spectrum (fig. 5(a)) test shows that only Ti, Nb and O elements exist in the Ti-Nb-O microspheres; with respect to the Ti 2p spectrum (FIG. 5(b)), the Ti 2p core level (2 p) was detected3/2458.8 eV and 2p3/2464.4 eV), the binding energy separation between the two Ti 2p core levels is 5.6 eV, corresponding toTi in Ti-Nb-O microspheres4+The ionic state, another peak at about 457 eV is attributable to Ti3+This is because Ti is added to the sample when the sample is annealed in an Ar atmosphere4+Reduction occurs; in addition, the high-resolution spectrum of Nb 3d (FIG. 5(c)) shows Nb 3d5/2(207.1 eV) and Nb 3d3/2(209.8 eV) indicating the presence of Nb in the Ti-Nb-O microspheres5+Ions; for the O1 s spectrum (FIG. 5(d)), the peak at 530.1 eV of the sample, from the O-metal bond, represents O2-State.
In conclusion, the synthesized material is Ti-Nb-O, which presents a graded porous, spherical morphology with a diameter of 1-2 μm and a specific surface area of 27.63 m2A mesoporous structure with a pore size distribution of 38-40 nm; in addition, XPS detects that only Ti, Nb and O elements exist in the Ti-Nb-O microspheres, and for the Ti element, Ti is mainly used3+、Ti4+In the form of (A), the Nb element is mainly Nb5+Is present in the form of O, the O element is mainly O2-Exist in the form of (1).
And 3, preparing the magnesium hydride hydrogen storage material based on the graded porous microspheres Ti-Nb-O, putting 0.035 g of the graded porous microspheres Ti-Nb-O obtained in the step 2 and 0.465 g of magnesium hydride into a ball milling tank under the condition of argon, carrying out ball milling under the conditions of argon as protective atmosphere, ball-material ratio of 200:1, ball milling rotation speed of 250 r/min and ball milling time of 5h to obtain the magnesium hydride hydrogen storage material based on the graded porous microspheres Ti-Nb-O with the doping amount of 7 wt%, and marking as MgH2-7 wt% Ti-Nb-O。
To prove MgH 27 wt% Ti-Nb-O hydrogen storage material phase composition for MgH2XRD testing was performed on-7 wt% Ti-Nb-O hydrogen storage materials. The test result is shown in FIG. 6, and the XRD pattern after ball milling is mainly MgH2The MgO phase was also identified, but the diffraction peak was very weak, probably MgH2And Ti-Nb-O. However, XRD did not detect the Ti, Nb images, possibly due to their poor crystallization due to high energy ball milling or relatively low concentrations.
To prove MgH2Structural characteristics of-7 wt% Ti-Nb-O hydrogen storage material, for MgH 27 wt% Ti-Nb-O hydrogen storage material was SEM and TEM testing. The results are shown in FIG. 7, at MgH 27 wt% Ti-Nb-O Hydrogen storage Material presents irregular fine particles in SEM and TEM, MgH is detected in high resolution2And simultaneously detecting four elements of Mg, Ti, Nb and O in an EDS energy spectrum as well as the Ti-Nb-O phase, wherein the proportion of the three elements of Ti, Nb and O is lower, and the quantity shown in the EDS energy spectrum is less.
In conclusion, by aiming at MgH2XRD, SEM and TEM structural characterization is carried out on the-7 wt% Ti-Nb-O hydrogen storage material, which shows that the hierarchical porous Ti-Nb-O microsphere doped magnesium hydride hydrogen storage material is successfully synthesized.
To prove MgH2Carrying out temperature rise dehydrogenation test on the obtained magnesium hydride hydrogen storage material with the Ti-Nb-O content of 7 wt% according to the hydrogen release performance of the-7 wt% Ti-Nb-O hydrogen storage material with temperature, wherein the test method comprises the following steps: a proper amount of sample (10 mg-15 mg) is weighed, the temperature is raised to 600 ℃ at the heating rate of 3 ℃/min to test the hydrogen release performance of the hydrogen storage material, the detection result is shown in figure 8, the initial hydrogen release temperature is 189 ℃, the hydrogen release amount is 6.96 wt% when the temperature is raised to 600 ℃, and the hydrogen release rate reaches 98.5% of the theoretical value.
To demonstrate the stability of the catalytically active species, towards MgH2The-7 wt% Ti-Nb-O hydrogen storage material was tested for cycle performance. The specific test method comprises the following steps: the cycle performance was tested using MH-PCT at 300 ℃ with a hydrogen pressure of 5 MPa. The results of the test analysis are shown in FIG. 9(a, b), MgH2The actual hydrogen capacity of the-7 wt% Ti-Nb-O hydrogen storage material remained at 6.26 wt% after 15 cycles, which corresponds to a capacity retention of 92.3% compared to the first cycle capacity. Description of MgH2The-7 wt% Ti-Nb-O hydrogen storage material shows a stable hydrogenation/dehydrogenation phenomenon, and has good hydrogen storage reversibility and stable cyclicity.
To prove MgH2The-7 wt% Ti-Nb-O hydrogen storage material has good hydrogen storage reversibility and stable cyclicity, and SEM test and particle size analysis are carried out on a sample after 15 cycles. The results of the test analysis are shown in FIGS. 10(a-c), MgH 27 wt% Ti-Nb-O hydrogen storage material, isothermally hydrogenated samples, and fine particles which appeared irregular after the 15 th cycle hydrogenation, the average particle size of these samplesThere were no significant differences (fig. 10(d-e)) at 297.1 nm, 338.5 nm, and 343.7 nm, respectively. Shows that the Ti-Nb-O addition can effectively prevent MgH2The particles are agglomerated, which is beneficial to the circulation stability.
To further demonstrate MgH2The-7 wt% Ti-Nb-O hydrogen storage material has good hydrogen storage reversibility and stable cyclability, and XPS test is carried out on a sample after 15 cycles. The results of the test analysis are shown in FIG. 11(a, b), and the hydrogen storage material after 15-cycle test mainly comprises metals of Ti (459.8/453.8 eV), TiO (455.8 eV) and NbO2(208.7/206.7 eV) and NbO (205.7/202.8 eV), indicating that the effective multielement and multi-valence catalytic species remain unchanged after the first desorption, thus promoting dissociation and recombination of H-H and Mg-H.
The test and analysis of the cycle performance show that MgH2The-7 wt% Ti-Nb-O hydrogen storage material has good hydrogen storage reversibility and stable cyclicity. The reasons for this are two, one is that the sample particle size does not change significantly before and after cycling, and the other is the multi-element and multi-valence catalytic environment.
To demonstrate the effect of temperature on the hydrogen evolution of magnesium hydride after Ti-Nb-O addition, MgH was added to example 12Isothermal hydrogen discharge experiments were performed on-7 wt% Ti-Nb-O hydrogen storage materials. The specific test method comprises the following steps: firstly, respectively raising the temperature of an MH-PCT furnace body to a target temperature of 225 ℃, 250 ℃, 275 ℃ and 300 ℃, then placing a sample into a sample tube in an argon environment, and finally respectively placing the sample tube into a furnace body at a temperature of 225 ℃, 250 ℃, 275 ℃ and 300 ℃ to perform isothermal hydrogen discharge test; the test results are shown in FIG. 12, and MgH of the invention increases with isothermal temperature from 225 ℃ to 300 ℃2The hydrogen release amount of the-7 wt% Ti-Nb-O hydrogen storage material is gradually increased in the same time, and the hydrogen release amount in 1 h is respectively 2.84 wt%, 5.09 wt%, 6.16 wt% and 6.82wt% at the temperature of 225 ℃, 250 ℃, 275 ℃ and 300 ℃. The above isothermal hydrogen discharge data can also be visualized by the following table 1:
TABLE 1 corresponding relation table of isothermal hydrogen release temperature and 1 h hydrogen release amount of MgH2-7 wt% Ti-Nb-O hydrogen storage material
Isothermal hydrogen evolution temperature/. degree.C 225 250 275 300
1 h hydrogen release amount/wt% 2.84 5.09 6.16 6.82
To demonstrate the effect of temperature on the hydrogen absorption of magnesium hydride after Ti-Nb-O addition, MgH was added to example 12Isothermal hydrogen absorption experiments were performed on-7 wt% Ti-Nb-O hydrogen storage materials. . The specific test method comprises the following steps: for isothermal hydrogen absorption, firstly, the furnace body is raised to 450 ℃ according to the isothermal hydrogen releasing step, hydrogen in a sample is completely released, and then the hydrogen releasing sample is subjected to a hydrogenation experiment at the given temperature of 50 ℃, 100 ℃, 150 ℃ and 200 ℃ respectively and the initial hydrogen pressure of 5 MPa. The test results are shown in FIG. 13, and MgH of the present invention increases with isothermal temperature from 50 ℃ to 200 ℃2The hydrogen release amount of the-7 wt% Ti-Nb-O hydrogen storage material is gradually increased in the same time, and the hydrogen absorption amounts in 1 h are respectively 1.37 wt%, 3.46 wt%, 4.99 wt% and 6.76 wt% at the temperature of 50 ℃, 100 ℃, 150 ℃ and 200 ℃. The above isothermal hydrogen sorption data can also be visualized by the following table 2:
TABLE 2 corresponding relationship table of isothermal hydrogen absorption temperature and 30 min hydrogen desorption amount of MgH2-7 wt% Ti-Nb-O hydrogen storage material
Isothermal hydrogen sorption temperature/. degree.C 50 100 150 200
Hydrogen absorption amount/wt% in 30 min 1.37 3.46 4.99 6.76
Comprehensive isothermal hydrogen absorption and desorption test shows MgH2The hydrogen release amount of the-7 wt% Ti-Nb-O hydrogen storage material can reach 6.82wt% in 60 min at the temperature of 300 ℃; the hydrogen release amount in 60 min can reach 6.76 wt% at 200 ℃, which shows that the MgH of the invention2The-7 wt% Ti-Nb-O hydrogen storage material has better hydrogen storage performance.
In order to prove the influence of the graded porous Ti-Nb-O microspheres on the hydrogen evolution dynamic performance of magnesium hydride, MgH is subjected2-7 wt% Ti-Nb-O hydrogen storage material and ball milled MgH2And (3) carrying out Differential Scanning Calorimetry (DSC) test on the sample, fitting the test data by using a Kissinger equation, and calculating the final activation energy. The specific test method comprises the following steps: firstly, a sample is placed in a sample tube under an argon environment, then the sample tube is placed in a differential scanning calorimeter, and finally, a program is set to heat the sample to 500 ℃ at 5 ℃/min, 10 ℃/min, 15 ℃/min and 20 ℃/min respectively for carrying out an experiment. The results of the testing and fitting are shown in FIG. 14, confirming MgH2The hydrogen evolution activation energy of the-7 wt% Ti-Nb-O hydrogen storage material was 92.7 kJ/mol.
To demonstrate the effect of graded porous Ti-Nb-O microspheres on hydrogen absorption kinetics of magnesium hydride, the isothermal hydrogen absorption curve was analyzed by Johnson-Mehl-Avrami (JMA) model to further determine MgH2-7 wt% Ti-Nb-O hydrogen storage material and ball milled MgH2Hydrogen absorption activation energy (E) of samplea(abs)). The specific test method comprises the following steps: firstly, raising the furnace body to 450 ℃ according to the step of isothermal hydrogen release, completely releasing hydrogen in a sample, then respectively carrying out a hydrogenation experiment on the sample after hydrogen release at the given temperature of 100 ℃, 125 ℃, 150 ℃ and 175 ℃ and the initial hydrogen pressure of 5 Mpa, and finally fitting an isothermal hydrogen absorption curve to obtain the hydrogen absorption activation energy. The results of the testing and fitting are shown in FIGS. 15(a-c), confirming MgH2-7 wt% Ti-Nb-O hydrogen storage material has a hydrogen absorption activation energy of 26.0 kJ/mol; in addition, isothermal hydrogen evolution was analyzed by Johnson-Mehl-Avrami (JMA) modelCurve, further identifies MgH2Hydrogen evolution activation energy (E) of 7 wt% Ti-Nb-O hydrogen storage materiala(des)). The results of the testing and fitting are shown in FIG. 15(d-e), confirming MgH2The hydrogen evolution activation energy of the-7 wt% Ti-Nb-O hydrogen storage material is 94.8 kJ/mol, which is very close to 92.7 kJ/mol of hydrogen evolution activation energy measured by DSC.
In order to prove the influence of the graded porous Ti-Nb-O microspheres on the hydrogen absorption thermodynamic performance of the magnesium hydride, a PCT curve is analyzed through PCT measurement and a van't Hoff equation, and MgH is further determined2Hydrogen release enthalpy change of-7 wt% Ti-Nb-O hydrogen storage material
Figure 542730DEST_PATH_DEST_PATH_IMAGE002
Hd. The results of the testing and fitting are shown in FIGS. 16(a-b), confirming MgH2Hydrogen release enthalpy change of-7 wt% Ti-Nb-O hydrogen storage material
Figure 141201DEST_PATH_DEST_PATH_IMAGE002
Hd=69.6 kJ/mol；
In conclusion, the pair of MgH is the graded porous Ti-Nb-O microsphere material2Hydrogen storage kinetics and thermodynamic tests show that MgH2The-7 wt% Ti-Nb-O hydrogen storage material has better hydrogen storage kinetics and thermodynamic properties.
In order to prove the object-image change of the graded porous Ti-Nb-O microsphere material in the ball milling and hydrogen storage processes, MgH at different stages is subjected to2XRD analysis was performed on-7 wt% Ti-Nb-O hydrogen storage material. The test analysis result is shown in FIG. 17, and the XRD pattern after ball milling is mainly MgH2The MgO phase was also identified, but the diffraction peak was very weak, probably MgH2And Ti-Nb-O. After dehydrogenation, MgH2The diffraction peak of (A) is replaced by the metal Mg with larger peak intensity, and MgH appears after the subsequent hydrogenation2Here, XRD did not detect the Ti, Nb images, which may be due to their poor crystallization due to high energy ball milling or relatively low concentrations. In addition, MgH after rehydrogenation2The phases show very sharp diffraction peaks indicating MgH at elevated temperatures2Recrystallization occurred.
In order to prove the existence form of Ti and Nb elements in the ball milling and hydrogen storage processes of the graded porous Ti-Nb-O microsphere material, a Ti-Nb-O catalyst and MgH after ball milling are subjected to2XPS analysis was performed on-7 wt% Ti-Nb-O and hydrogen storage material after one hydrogen absorption and desorption cycle. The results of the test analysis are shown in FIGS. 18(a-f), and for the Ti-Nb-O catalyst, the valence of Ti (FIG. 18(a)) is +4 for TiO2(464.4/458.8 eV) and +3 valence Ti3+(457.0 eV); nb with the valence of +5 (FIG. 18(d)) being the valence of Nb2O5(209.8/207.1 eV). After ball milling, the XPS peak for Ti shifts to the right (FIG. 18(b)), but still corresponds to TiO 22p of1/2And 2p3/2Spin dual orbit, while a new diffraction peak appeared clearly in the Nb XPS spectrum (fig. 18(e)), decomposing the Nb 3d XPS peak into 3d3/2And 3d5/2Spin dual orbitals, found except Nb2O5In addition, there was a pair of XPS peaks for NbO (205.7/202.8 eV). It is shown that a small amount of catalyst is reduced during the ball milling process, and the valence state of a part of Nb element is reduced to + 2. After the first hydrogen absorption and desorption cycle, the Ti element is also reduced, and the spin dual-orbit peak of the simple substance Ti appears in the Ti 2p XPS peak (figure 18(c)) of the hydrogen absorption product, which is respectively positioned at 459.8 eV (2 p)1/2) And 453.8 eV (2 p)3/2) To (3). In the Nb 3d XPS (FIG. 18(f)), Nb is shown2O5The peak disappeared and new NbO appeared2The valence of Nb is further reduced by the peak (208.7/206.7 eV), and the valence of Nb in the hydrogen absorption product is +4 and + 2.
The XPS analysis result shows that the Ti-Nb-O catalyst is reduced in the ball milling and hydrogen absorption and desorption processes, and active substances are generated in situ. MgH doped with Ti-Nb-O2The active material in the hydrogen absorption product of the sample was TiO2，Ti，NbO2Compared with a ball-milling product, Ti and Nb have more valence states, and compared with a single-valence metal oxide, the multi-valence transition metal can remarkably promote charge transfer between magnesium and hydrogen molecules and accelerate hydrogen absorption and desorption reaction, namely the multi-valence transition metal has better catalytic activity.
In order to demonstrate the effect of Ti-Nb-O as a catalyst on the hydrogen evolution performance of magnesium hydride, the catalyst was prepared byComparative example 1A magnesium hydride material having a Ti-Nb-O content of 0 wt%, denoted as-milled MgH, was prepared2。
Comparative example 1
As-milled MgH2A method for producing a hydrogen occluding material, namely, a magnesium hydride hydrogen occluding material having a Ti-Nb-O content of 0 wt%, was the same as in example 1 except that: in the above step, Ti-Nb-O is not added, that is, only 0.5 g of MgH is weighed2。
The obtained seed as-milled MgH2The hydrogen storage material was subjected to the temperature-increasing dehydrogenation test in the same manner as in example 1, and the test results are shown in fig. 19, in which the initial hydrogen-evolving temperature was 310 ℃, the hydrogen-evolving amount was 7.32 wt% when the temperature was increased to 600 ℃, and the hydrogen-evolving rate was 96.3 wt% of the theoretical value.
As can be seen from a comparison of example 1 with comparative example 1, MgH was produced21 wt% Ti-Nb-O hydrogen storage material, reducing the initial hydrogen evolution temperature of magnesium hydride from 310 ℃ to 189 ℃, and increasing the hydrogen evolution rate from 96.3% to 98.5%.
To demonstrate comparison of MgH doped with 7 wt% Ti-Nb-O catalyst at the same temperature2Hydrogen storage material and ball milled MgH2Hydrogen absorption and desorption properties of (1) for MgH in example 127 wt% Ti-Nb-O Hydrogen storage Material and ball milled MgH in comparative example 12An isothermal hydrogen absorption and desorption experiment is carried out. The specific test method comprises the following steps: when isothermal hydrogen discharge is carried out, firstly, the MH-PCT furnace body is raised to the target temperature of 300 ℃, then a sample is placed into a sample tube under the argon environment, and finally the sample tube is placed into the furnace body at 300 ℃ for isothermal hydrogen discharge test; for isothermal hydrogen absorption, firstly, the furnace body is raised to 450 ℃ according to the isothermal hydrogen releasing step, hydrogen in the sample is completely released, then the temperature is set to be 200 ℃, and the initial hydrogen pressure is 5 Mpa, so that the hydrogenation experiment is carried out on the sample after hydrogen releasing. As shown in FIG. 20, the results of the test show that MgH of the present invention is released isothermally at 300 ℃ (FIG. 20(a))2The-7 wt% Ti-Nb-O hydrogen storage material can release 6.82wt% of hydrogen in 60 min, and MgH is generated after ball milling2The sample can release 0.03wt% of hydrogen in 60 min; MgH of the present invention when absorbing hydrogen isothermally at 200 ℃ (FIG. 20(b))2Hydrogen absorption capacity of-7 wt% Ti-Nb-O hydrogen storage material in 30 minUp to 6.76 wt%, and MgH after ball milling2The hydrogen absorption of the sample is only 0.88wt% in 30 min.
By comparing the isothermal hydrogen absorption and desorption of example 1 with that of comparative example 1, MgH is prepared21 wt% of Ti-Nb-O hydrogen storage material, and increasing the hydrogen release amount of magnesium hydride from 0.03wt% in 60 min to 6.82wt% in 60 min when isothermal hydrogen release is carried out at 300 ℃; when the magnesium hydride is subjected to isothermal hydrogen release at the temperature of 200 ℃, the hydrogen release amount of the magnesium hydride is increased from 0.88wt% absorbing hydrogen in 30 min to 6.76 wt% releasing hydrogen in 30 min.
To demonstrate the dehydrogenation activation energy of ball-milled magnesium hydride, the same as-milled MgH of comparative example 1 was added2The hydrogen storage material is subjected to Differential Scanning Calorimetry (DSC) test, and the Kissinger equation is applied to fit the test data to calculate the final activation energy. The specific test method comprises the following steps: firstly, a sample is put into a sample tube under the argon environment, then the sample tube is put into a differential scanning calorimeter, and finally, a program is set to respectively heat the sample to 500 ℃ at 5 ℃/min, 10 ℃/min, 15 ℃/min and 20 ℃/min for experiment. The results of the testing and fitting are shown in FIG. 14, confirming the as-milled MgH2The hydrogen desorption activation energy of the hydrogen storage material was 158.3 kJ/mol.
By comparing the activation energy of example 1 with that of comparative example 1, MgH was produced2The hydrogen desorption activation energy of the-7 wt% Ti-Nb-O hydrogen storage material is 92.7 kJ/mol, as-milled MgH2The hydrogen desorption activation energy of the hydrogen storage material was 158.3 kJ/mol, indicating MgH2Hydrogen desorption activation energy ratio of-7 wt% Ti-Nb-O hydrogen storage material to MgH after ball milling2The hydrogen evolution activation energy is reduced by about 41.4%.
To demonstrate the hydrogen absorption activation energy of ball-milled magnesium hydride, the isothermal hydrogen absorption curve was analyzed by the Johnson-Mehl-Avrami (JMA) model to further determine the hydrogen absorption activation energy (E) of the sample of comparative example 1a(abs)). The specific test method comprises the following steps: firstly, raising the furnace body to 450 ℃ according to the step of isothermal hydrogen release, completely releasing hydrogen in a sample, then performing a hydrogenation experiment on the sample after hydrogen release at a given temperature of 150 ℃, 175 ℃, 200 ℃ and 225 ℃ respectively under an initial hydrogen pressure of 5 Mpa, and finally fitting an isothermal hydrogen absorption curve to obtain hydrogen absorption activation energy. The results of the test and fitting are shown in FIG. 15 (g)As-closed MgH was confirmed as shown by-i)2The hydrogen absorption activation energy of the hydrogen storage material was 86.7 kJ/mol; in addition, the isothermal hydrogen desorption curve is analyzed by a Johnson-Mehl-Avrami (JMA) model, and as-miled MgH is further determined2Hydrogen evolution activation energy (E) of hydrogen storage materiala(des)). The results of the testing and fitting are shown in FIG. 15(j-l), confirming as-milled MgH2The hydrogen desorption activation energy of the hydrogen storage material was 164.3 kJ/mol, which is very close to 158.3 kJ/mol, which is the hydrogen desorption activation energy measured by DSC.
By comparing the activation energy of example 1 with that of comparative example 1, MgH was produced2The hydrogen absorption activation energy of the-7 wt% Ti-Nb-O hydrogen storage material is 26.0 kJ/mol, as-milled MgH2The hydrogen absorption activation energy of the hydrogen storage material was 86.7 kJ/mol, indicating MgH2Hydrogen desorption activation energy ratio of-7 wt% Ti-Nb-O hydrogen storage material to MgH after ball milling2The hydrogen desorption activation energy is reduced by about 70.0%.
To demonstrate the change in enthalpy of hydrogen evolution of ball-milled magnesium hydride
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HdThe PCT curve was analyzed by PCT measurements and van't Hoff equation, further comparing the change in hydrogen enthalpy for the sample of example 1
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Hd. The results of the test and fitting are shown in FIG. 16(a-b), confirming as-milled MgH2Hydrogen evolution enthalpy change of hydrogen storage material
Figure 887812DEST_PATH_DEST_PATH_IMAGE002
Hd=76.7 kJ/mol；
From the comparison of the enthalpy change of hydrogen evolution between example 1 and comparative example 1, MgH was produced2Hydrogen release enthalpy change of-7 wt% Ti-Nb-O hydrogen storage material
Figure 352292DEST_PATH_DEST_PATH_IMAGE002
Hd=69.6 kJ/mol，as-milled MgH2Hydrogen evolution enthalpy change of hydrogen storage material
Figure 224433DEST_PATH_DEST_PATH_IMAGE002
Hd=76.7 kJ/mol, shows MgH2MgH of-7 wt% Ti-Nb-O hydrogen storage material after hydrogen discharge enthalpy change ratio ball milling2The enthalpy change of the hydrogen release is reduced by about 7.1 kJ/mol.
To demonstrate the effect of the addition of Ti-Nb-O as a catalyst on the hydrogen evolution performance of magnesium hydride, a magnesium hydride hydrogen storage material having a Ti-Nb-O content of 1 wt%, designated as MgH, was prepared by comparative example 22-1 wt% Ti-Nb-O。
In conclusion, the pair of MgH is the graded porous Ti-Nb-O microsphere material2Hydrogen storage kinetics and thermodynamic tests show that MgH2The activation energy ratio of hydrogen absorption and desorption of the Ti-Nb-O hydrogen storage material of 7 wt percent to MgH after ball milling2The hydrogen absorption and desorption activation energy is respectively reduced by about 70.0 percent and 41.4 percent; MgH2-7 wt% of MgH of Ti-Nb-O hydrogen storage material after ball milling of hydrogen desorption enthalpy change ratio2The enthalpy change of hydrogen desorption of (a) is reduced by about 7.1 kJ/mol. The hierarchical porous Ti-Nb-O microsphere material pair MgH can be visually shown by the following FIG. 212Hydrogen storage kinetics and thermodynamics.
To demonstrate the effect of Ti-Nb-O as a catalyst, which is added in an amount of 1 wt%, 3wt%, 5wt%, 10 wt% on the hydrogen desorption performance of magnesium hydride, comparative examples 2, 3, 4, 5 were provided.
Comparative example 2
MgH2-1 wt% Ti-Nb-O hydrogen storage material, the steps not specifically described being the same as in example 1, except that: the addition amount of the Ti-Nb-O is 0.005 g, the mass of the correspondingly weighed magnesium hydride is 0.495 g, and the obtained material is marked as MgH2-1 wt% Ti-Nb-O。
The obtained MgH2The temperature-rising dehydrogenation test was carried out on the-1 wt% Ti-Nb-O hydrogen storage material, the test method was the same as that of example 1, and the test results are shown in FIG. 19, in which the initial hydrogen-evolving temperature was 235 ℃, the hydrogen-evolving amount was 7.28 wt% when the temperature was raised to 600 ℃, and the hydrogen-evolving rate reached 96.8% of the theoretical value.
As can be seen by comparing comparative example 1 with comparative example 2, MgH was produced21% by weight of Ti-Nb-O hydrogen storage material, starting with magnesium hydrideThe hydrogen temperature is reduced from 310 ℃ to 235 ℃, and the hydrogen release rate is improved from 96.3 percent to 96.8 percent.
Comparative example 3
MgH2-3 wt% Ti-Nb-O Hydrogen storage Material preparation method, the steps not specifically described being the same as in example 1 except that: the addition amount of the Ti-Nb-O is 0.015 g, the mass of the magnesium hydride correspondingly weighed is 0.485 g, and the obtained material is marked as MgH2-3 wt% Ti-Nb-O。
The obtained MgH2The temperature-rising dehydrogenation test was carried out on the-3 wt% Ti-Nb-O hydrogen storage material, the test method was the same as that of example 1, and the test results are shown in FIG. 19, in which the initial hydrogen-evolving temperature was 221 ℃, the hydrogen-evolving amount was 7.19 wt% when the temperature was raised to 600 ℃, and the hydrogen-evolving rate reached 97.5% of the theoretical value.
As can be seen by comparing comparative example 1 with comparative example 3, MgH was produced21 wt% Ti-Nb-O hydrogen storage material, reducing the initial hydrogen evolution temperature of magnesium hydride from 310 ℃ to 235 ℃ and increasing the hydrogen evolution rate from 96.3% to 97.5%.
Comparative example 4
MgH2-5 wt% Ti-Nb-O Hydrogen storage Material preparation method, the steps not specifically described being the same as in example 1 except that: the addition amount of the Ti-Nb-O is 0.025 g, the mass of the correspondingly weighed magnesium hydride is 0.475 g, and the obtained material is marked as MgH2-5 wt% Ti-Nb-O。
The obtained MgH2The temperature-rising dehydrogenation test was carried out on the-5 wt% Ti-Nb-O hydrogen storage material, the test method was the same as that of example 1, and the test results are shown in FIG. 19, in which the initial hydrogen-evolving temperature was 208 ℃, the hydrogen-evolving amount was 7.07 wt% when the temperature was raised to 600 ℃, and the hydrogen-evolving rate reached 97.9% of the theoretical value.
As can be seen by comparing comparative example 1 with comparative example 4, MgH was produced21 wt% Ti-Nb-O hydrogen storage material, reducing the initial hydrogen evolution temperature of magnesium hydride from 310 ℃ to 235 ℃ and increasing the hydrogen evolution rate from 96.3% to 97.9%.
Comparative example 5
MgH2-10 wt% Ti-Nb-O Hydrogen storage Material preparation method, the steps not specifically described being the same as in example 1 except that:the addition amount of the Ti-Nb-O is 0.05 g, the mass of the magnesium hydride correspondingly weighed is 0.45 g, and the obtained material is marked as MgH2-10 wt% Ti-Nb-O。
The obtained MgH2The temperature-rising dehydrogenation test was carried out on the-10 wt% Ti-Nb-O hydrogen storage material, the test method was the same as that of example 1, and the test result is shown in FIG. 19, in which the initial hydrogen-evolving temperature was 177 ℃, the hydrogen-evolving amount was 6.21 wt% when the temperature was raised to 600 ℃, and the hydrogen-evolving rate reached 90.8% of the theoretical value.
As can be seen by comparing comparative example 1 with comparative example 5, MgH was produced21 wt% Ti-Nb-O hydrogen storage material, which reduces the initial hydrogen evolution temperature of magnesium hydride from 310 ℃ to 177 ℃, but the hydrogen evolution rate is reduced from 96.3% to 90.8%, probably due to MgH2The-10 wt% Ti-Nb-O hydrogen storage material partially decomposed during the ball milling process, resulting in a reduction in hydrogen content.
The results of example 1 and comparative examples 1, 2, 3, 4, 5 are shown visually in table 3 below:
TABLE 3 corresponding relationship table of catalyst amount, initial hydrogen desorption temperature, and final hydrogen desorption amount
Catalyst doping amount/wt% 0 1 3 5 7 10
Initial hydrogen evolution temperature/. degree.C 310 235 221 208 189 177
Final hydrogen evolution/wt% 7.32 7.28 7.19 7.07 6.96 6.21
The experimental results show that the addition of the hierarchical porous Ti-Nb-O microspheres obviously reduces MgH2The hydrogen desorption temperature of (1). After adding 1 wt% of Ti-Nb-O, MgH2The initial hydrogen release temperature of the ball mill is reduced from 310 ℃ to 235 ℃, compared with MgH after ball milling2The sample was reduced by 75 ℃. The hydrogen evolution temperature of the sample decreased with further increasing the amount of catalyst added until the amount of Ti-Nb-O added reached 7 wt%, although the initial temperature decreased to 189 deg.c and the amount of Ti-Nb-O added further increased to 10 wt%, the initial hydrogen evolution temperature decreased, but the effective hydrogen storage capacity of the system decreased. Comprehensively comparing hydrogen release temperature with hydrogen release amount, MgH2The-7 wt% Ti-Nb-O hydrogen storage material has the best hydrogen release performance, the initial hydrogen release temperature is reduced by 121 ℃ compared with that after ball milling, and the total hydrogen release amount is 6.96 wt%.

Claims (9)

1. A magnesium hydride hydrogen storage material based on hierarchical porous microspheres Ti-Nb-O is characterized in that: is prepared by mixing magnesium hydride and graded porous microspheres Ti-Nb-O and mechanically milling; the hierarchical porous microsphere Ti-Nb-O is prepared by a solvothermal method and a calcining method.
2. A hierarchical porous Ti-Nb-O microsphere material doped magnesium hydride hydrogen storage material is characterized in that: the diameter of the hierarchical porous microsphere Ti-Nb-O is 1-2 mu m, the microscopic morphology is spherical, and the specific surface area is 27.63 m2(ii) a pore size distribution of 38-40 nm.
3. The preparation method of the graded porous Ti-Nb-O microsphere material doped magnesium hydride hydrogen storage material according to claim 1, which is characterized by comprising the following steps:
step 1, preparing a hierarchical porous microsphere Ti-Nb-O precursor, dissolving a certain mass of P123 in absolute ethyl alcohol by a solvothermal method, violently stirring for a certain time to obtain a solution A, dissolving titanium isopropoxide and anhydrous niobium chloride in the solution A according to a certain substance amount ratio, and stirring for a certain time to obtain a reaction solution; then, carrying out solvothermal reaction under certain conditions, and finally washing and drying the obtained precipitate to obtain a hierarchical porous microsphere Ti-Nb-O precursor;
step 2, preparing a hierarchical porous microsphere Ti-Nb-O, namely calcining the hierarchical porous microsphere Ti-Nb-O precursor obtained in the step 1 under a certain condition by a calcining method to obtain the hierarchical porous microsphere Ti-Nb-O;
and 3, preparing the magnesium hydride hydrogen storage material based on the hierarchical porous microsphere Ti-Nb-O, mixing the hierarchical porous microsphere Ti-Nb-O obtained in the step 2 and magnesium hydride according to a certain mass ratio, and performing ball milling under certain conditions to obtain the magnesium hydride hydrogen storage material based on the hierarchical porous microsphere Ti-Nb-O.
4. The production method according to claim 3, characterized in that: in the step 1, the concentration of P123 dissolved in absolute ethyl alcohol is 7.5-10 g/L, and the stirring time is 15-45 min; the ratio of the quantity of the titanium isopropoxide to the anhydrous niobium chloride in the step 1 is (1-3) to (5-15); the solvothermal condition is that the reaction temperature is 200 ℃ and the reaction time is 24 h.
5. The production method according to claim 3, characterized in that: the calcining condition of the step 2 is that the calcining temperature is 800 ℃ and the calcining time is 1.5h under the argon condition.
6. The production method according to claim 3, characterized in that: the mass ratio of the graded porous microsphere Ti-Nb-O to the magnesium hydride in the step 3 is (6-9) to (91-94); the ball milling conditions are that argon is used as protective atmosphere, the ball material ratio is 200:1, the ball milling rotating speed is 250 r/min, and the ball milling time is 5 hours.
7. The application of the graded porous Ti-Nb-O microsphere material doped with magnesium hydride hydrogen storage material as the hydrogen storage field according to claim 1 is characterized in that: when the doping amount of the catalyst is 7 wt%, the initial hydrogen release temperature of the system is reduced to 189 ℃, and the hydrogen release amount reaches 6.96 wt%; when the hydrogen is discharged isothermally, the system can completely discharge the hydrogen at 300 ℃, and the hydrogen discharge amount reaches 6.82wt% in 60 min; when the system absorbs hydrogen isothermally, the system can still absorb 1.78 wt% of hydrogen within 60 min even under the condition of the temperature as low as 50 ℃.
8. The application of the graded porous Ti-Nb-O microsphere material doped with magnesium hydride hydrogen storage material as the hydrogen storage field according to claim 1 is characterized in that: the activation energy of catalytic hydrogen evolution is Ea(des)=92.7 kJ/mol, the activation energy for catalytic hydrogen absorption is Ea(abs)=26.0 kJ/mol; enthalpy change of desorption reaction
Figure DEST_PATH_IMAGE002
Hd=69.6 kJ/mol。
9. The application of the graded porous Ti-Nb-O microsphere material doped with magnesium hydride hydrogen storage material as the hydrogen storage field according to claim 1 is characterized in that: after being recycled, the sample shows good hydrogen storage reversibility and stable cyclability, and after 15 cycles, the retention rate of the actual hydrogen capacity is equivalent to 92.3% of the first cycle capacity.
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CN115259076A (en) * 2022-07-20 2022-11-01 华南理工大学 Method for improving reversible hydrogen storage performance of magnesium hydride by niobium-doped titanium dioxide catalyst
CN115259076B (en) * 2022-07-20 2024-01-23 华南理工大学 Method for improving reversible hydrogen storage performance of magnesium hydride by using niobium-doped titanium dioxide catalyst

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