Monatomic alloy for catalyzing MgH2 to absorb and desorb hydrogen and preparation method of monatomic alloy

Abstract

The invention discloses a monatomic alloy for catalyzing MgH2 to absorb and desorb hydrogen and a preparation method of the monatomic alloy. The method comprises the following steps: firstly, coating magnesium-based hydride powder with a metal coordination compound with an MN4 active site to obtain a metal coordination compound-magnesium-based hydride compound; the metal coordination compound-magnesium-based hydride compound is subjected to in-situ hydrogenation treatment, and monatomic alloy is obtained; the monatomic alloy includes a magnesium-based hydride and a metal monatomic-magnesium catalyst M1-Mg formed on the surface of the magnesium-based hydride, where M1 represents a metal monatomic atom, and M represents nickel, iron or cobalt. The preparation method disclosed by the invention has the characteristics of simple preparation process and easiness in industrial amplification; the monatomic alloy disclosed by the invention is relatively good in stability and excellent in hydrogen absorption and desorption performance, and has a good application prospect in the field of hydrogen storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel solid hydrogen storage materials, and in particular relates to a single-atom alloy for catalyzing the absorption and desorption of hydrogen by MgH2 and a preparation method thereof. Background Art

[0002] As a clean and renewable energy source, hydrogen has the advantages of high energy density, safety, and low cost. It has great potential as an ideal energy carrier. Therefore, hydrogen is expected to play an important role in helping to achieve carbon neutrality in the future. Compared with the storage of gaseous and liquid compressed hydrogen, solid-state hydrogen storage materials have higher weight and volume hydrogen density and higher safety. Magnesium hydride (MgH2) is one of the most representative metal hydrides because of its abundant natural resources, low cost, and high theoretical weight capacity (7.6wt%). However, the dehydrogenation temperature is high (~400°C), the kinetic barrier is high (activation energy is ~160kJ·mol -1 ) and poor cycle stability greatly limit the practical commercial application of MgH2.

[0003] The number and intrinsic activity of active sites are important factors that determine catalytic activity and selectivity. In the prior art, nanoscale catalysts have good catalytic effects on Mg / MgH2 hydrogen storage materials because small-sized catalysts can effectively expose more surface active sites and change the electronic structure. Compared with nanoscale catalysts, single-atom catalysts (SACs) can further improve the catalytic effect. This is because the active sites of SACs are highly dispersed, even up to 100%, which is unattainable by nanoparticle catalysts. In addition, these active center atoms in the form of single atoms exhibit special coordination environments and electronic structures. Single-atom catalysts may aggregate or sinter under high temperature conditions, resulting in the loss of active sites and affecting the long-term stability of the catalyst. In addition, the single-atom preparation process may involve expensive precursors or complex synthesis steps, which may lead to a higher cost of the final product and limit its commercial application. Summary of the invention

[0004] In order to solve the stability problem of MNC catalyst in the field of hydrogen storage, the present invention provides a single-atom alloy that catalyzes the absorption and desorption of hydrogen by MgH2 and a preparation method thereof. The single-atom alloy provided by the present invention catalyzes the absorption and desorption of hydrogen by MgH2 through a metal single-atom-magnesium catalyst uniformly distributed on the surface of magnesium-based hydride, thereby exhibiting excellent hydrogen absorption and desorption performance.

[0005] The present invention is implemented by the following technical solutions:

[0006] 1. A method for preparing a single-atom alloy for catalyzing the absorption and desorption of hydrogen by MgH2

[0007] The preparation method comprises the following steps:

[0008] 1) A magnesium-based hydride powder is coated with a metal coordination compound to obtain a metal coordination compound-magnesium-based hydride complex; the metal coordination compound has a metal-nitrogen (MN4) active site, in which each metal center (M) is coordinated with four nitrogen atoms (N).

[0009] The step 1) is specifically as follows: dissolving the metal coordination compound powder in an organic solvent, adding the magnesium-based hydride powder, subjecting the mixture to ultrasonic treatment at room temperature, stirring for a period of time, and vacuum drying to obtain a metal coordination compound-magnesium-based hydride complex.

[0010] The mass ratio of the metal coordination compound powder to the magnesium-based hydride powder is 1-5:95-99. The amount ratio of the metal coordination compound powder to the organic solvent is 2-10 mg:0.5-2.5 mL. The organic solvent includes tetrahydrofuran (THF) or N,N-dimethylformamide (DMF).

[0011] The stirring time is 6 to 12 hours. The vacuum drying temperature is 60 to 80° C., and the vacuum drying time is 6 to 12 hours.

[0012] Optionally, the magnesium-based hydride is magnesium hydride (MgH2) or magnesium-nickel alloy Mg2NiH4.

[0013] Optionally, the metal coordination compound is a metal phthalocyanine coordination compound, a metal tetraphenylporphyrin coordination compound, a tetraaminoporphyrin compound, a tetrapyridineporphyrin compound or a metal tetraphenylporphyrin compound. The metal center in the metal coordination compound is nickel, iron, cobalt, titanium, manganese or vanadium.

[0014] When the metal is nickel, the nickel coordination compound is in the shape of a long rod with a length of 3 to 5 μm. The size of the magnesium-based hydride powder is preferably submicron. When the magnesium-based hydride is magnesium hydride, the size of the magnesium hydride (MgH2) powder is preferably submicron, and most preferably 18 μm.

[0015] Preferably, the metal coordination compound is nickel phthalocyanine (NiPc), iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc) or nickel tetraphenylporphyrin (Ni-TPP) or the like.

[0016] Furthermore, the preparation process of the submicron magnesium hydride powder is specifically as follows: magnesium hydride and tetrahydrofuran (1g magnesium hydride corresponds to 1mL tetrahydrofuran) are mixed in a stainless steel ball mill, and stainless steel grinding balls with diameters of 6mm and 3mm are used to perform ball milling at a speed of 450-500r / min under room temperature and inert gas atmosphere. After the ball milling, the magnesium hydride powder is vacuum dried at 60-80°C for 4-6h to obtain the magnesium hydride powder. The ball milling process includes ten cycles, and each cycle is forward for 20-30min, rest for 15min, reverse for 20-30min, and rest for 15min. Among them, the total weight of the stainless steel grinding balls and the weight ratio of magnesium hydride are 40:1, and the weight ratio of the stainless steel grinding balls with a diameter of 6mm to the stainless steel grinding balls with a diameter of 3mm is 1:2.

[0017] 2) The metal coordination compound-magnesium-based hydride complex is subjected to in-situ hydrogenation treatment to obtain the single-atom alloy. The in-situ hydrogenation treatment is specifically: 6 dehydrogenation / hydrogenation reactions; each dehydrogenation / hydrogenation reaction includes one dehydrogenation reaction and one hydrogenation reaction, and the conditions of the dehydrogenation reaction are: 350-400°C, 3-5MPa for 10-30min; the conditions of the hydrogenation reaction are: 350-400°C, 0-0.1MPa for 10-30min.

[0018] In a specific implementation, the dehydrogenation / hydrogenation reaction is carried out in a PCT device.

[0019] 2. A single-atom alloy catalyzing the absorption and desorption of hydrogen in MgH2

[0020] The single-atom alloy includes a magnesium-based hydride and a metal single-atom-magnesium catalyst formed on the surface lattice of the magnesium-based hydride. Specifically, the metal single atom is embedded in the surface lattice of the magnesium-based hydride, and a metal single-atom-magnesium catalyst is formed on the surface of the magnesium-based hydride. The metal single-atom-magnesium catalyst is used to catalyze the absorption and desorption of hydrogen by the magnesium-based hydride.

[0021] The metal single atom-magnesium catalyst is mainly formed by metal single atoms M1 embedded in the surface lattice of magnesium-based hydride. The metal single atom-magnesium catalyst is represented by: M1-Mg. Among them, M1 represents a metal single atom, derived from the metal M in the metal-nitrogen site of the metal coordination compound, specifically a nickel single atom, an iron single atom, a cobalt single atom, a titanium single atom, a manganese single atom or a vanadium single atom, the subscript "1" in M1 represents the number of metal atoms, and Mg represents magnesium.

[0022] The metal single atom-magnesium catalyst is evenly distributed on the surface of the magnesium-based hydride. The mass content of the metal single atom M1 in the single atom alloy is 0.1-0.5%.

[0023] The magnesium-based hydride is magnesium hydride (MgH2) or magnesium-nickel alloy Mg2NiH4.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The preparation method of the present invention has the characteristics of simple preparation process, simple method, easy control of component structure and easy industrial scale-up.

[0026] 2. In the single-atom alloy prepared by the present invention, the metal single-atom-magnesium catalyst has good stability and has better catalytic MgH2 hydrogen absorption and desorption performance than the metal-nitrogen (MN4) site. Therefore, the single-atom alloy obtained by the present invention has good hydrogen absorption and desorption performance compared with MgH2, and has broad application prospects in the field of hydrogen storage.

[0027] 3. The single-atom alloy Ni1-MgH2 prepared by the present invention absorbs 5.1 wt% of H2 in 15 minutes at a temperature of 150°C, and dehydrogenates 6.2 wt% of H2 in 30 minutes at a temperature of 275°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The X-ray diffraction (XRD) patterns of the nickel phthalocyanine-magnesium hydride composites in Examples 1 to 3 of the present invention and a reference material are shown.

[0029] Figure 2 TEM image and energy dispersive X-ray element mapping element map of the nickel phthalocyanine-magnesium hydride composite in Example 2 of the present invention.

[0030] Figure 3 The color change of the nickel phthalocyanine-magnesium hydride complex in Example 2 of the present invention during the dehydrogenation / hydrogenation cycle.

[0031] Figure 4 This is the EDX element distribution diagram of the single-atom alloy in Example 2 of the present invention.

[0032] Figure 5 This is a high-angle annular dark field scanning TEM (HAADF-STEM) image of the single-atom alloy in Example 2 of the present invention.

[0033] Figure 6 k is the k of the nickel phthalocyanine-magnesium hydride complex in Example 2 of the present invention in the dehydrogenation / hydrogenation cycle 3 Weighted Fourier transform-EXAFS (FT-EXAFS) spectrum.

[0034] Figure 7 1 is the isothermal hydrogenation curve of the single-atom alloy in Example 2 of the present invention at different temperatures.

[0035] Figure 8 1 is the isothermal dehydrogenation curve of the single-atom alloy in Example 2 of the present invention at different temperatures.

[0036] Fig. 9 The isothermal dehydrogenation curves of the single-atom alloy, metal coordination compound and ball-milled MgH2 in Example 2 of the present invention are compared.

[0037] Fig.10 This is a graph showing the cyclic stability test results of the single-atom alloy in Example 2 of the present invention.

[0038] Fig.11 This is the Ni1-Mg HAADF-STEM image of the single-atom alloy in Example 2 of the present invention after 30 hydrogen absorption / dehydrogenation cycles.

[0039] Fig.12 This is the EDX element distribution diagram of the single-atom alloy in Example 2 of the present invention after 30 hydrogen absorption / dehydrogenation cycles.

[0040] Fig.13 The Fe 2p of the iron phthalocyanine-magnesium hydride composite and the single-atom alloy in Example 4 of the present invention is 3 / 2 XPS spectrum.

[0041] Fig.14 The Co 2p of the iron phthalocyanine-magnesium hydride complex and the single-atom alloy in Example 5 of the present invention is 3 / 2 XPS spectra.

[0042] Fig.15 It is a schematic diagram of the principle of the present invention. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] like Fig.15As shown, the present invention adopts a method of in-situ reduction under high-temperature hydrogen, based on the metal-nitrogen (MN4) active site of a high-valent metal single atom (M) coordinated with nitrogen (N), and utilizes the unstable characteristics of the MN4 active site in a hydrogen storage reduction environment, so that the MN4 active site dispersed on the surface of the magnesium-based hydride forms a metal single atom-magnesium catalyst M1-Mg in situ, and spontaneously evolves into a zero-valent metal M. The metal single atom-magnesium catalyst M1-Mg shows remarkable stability in catalyzing Mg hydrogen storage. It shows comprehensive catalytic ability in all steps of H2 entering and exiting Mg, and is more effective than the NiN4 active site in the key steps of hydrogenation and dehydrogenation reactions. In addition, the method of the present invention utilizes MN4 to be pyrolyzed in situ on the surface of MgH2, so that a layer of carbon remains on the surface, which can not only prevent metal aggregation, but also increase the specific surface area of ​​the metal.

[0045] The specific embodiments of the present invention are as follows:

[0046] Unless otherwise specified, the raw materials used in the embodiments of the present invention are obtained by commercial means. In the embodiments of the present invention, the metal coordination compound-magnesium-based hydride complex is expressed as: x wt%MZ(MD)-MgH2. Wherein, MZ represents a metal coordination compound, M represents a metal center in the metal coordination compound, Z represents a ligand in the metal coordination compound, MgH2 represents magnesium hydride, x wt% represents the mass fraction of the metal coordination compound in the metal coordination compound-magnesium-based hydride complex, and MD (Molecular Dispersion) represents the distribution state of the metal coordination compound on the surface of the magnesium-based hydride powder particles, that is, the metal coordination compound is dispersed on the surface of the magnesium-based hydride powder particles in the form of molecules.

[0047] Unless otherwise specified, in the embodiments of the present invention, the single-atom alloy is represented by: M1-MgH2, wherein M1 represents a single metal atom.

[0048] Unless otherwise specified, in the embodiments of the present invention, the metal single atom-magnesium catalyst is represented by: M1-Mg, wherein M1 represents a metal single atom.

[0049] Example 1

[0050] In this embodiment, a nickel phthalocyanine-magnesium hydride complex 1wt% NiPc(MD)-MgH2 is first prepared, and then the nickel phthalocyanine-magnesium hydride complex 1wt% NiPc(MD)-MgH2 is subjected to in-situ hydrogenation treatment to obtain a single-atom alloy 1wt% Ni1-MgH2, wherein the mass content of metal Ni in the single-atom alloy is 0.1%.

[0051] The specific process of this embodiment is as follows:

[0052] 1) Using nickel phthalocyanine to coat magnesium hydride powder to obtain a nickel phthalocyanine-magnesium hydride composite 1wt% NiPc(MD)-MgH2; the specific process is:

[0053] 1.1) Ball milling of magnesium hydride: 2g of commercially available magnesium hydride (MgH2) and 2mL of tetrahydrofuran (THF) were mixed in a 500mL stainless steel ball milling jar, using stainless steel grinding balls with diameters of 6mm and 3mm, with a weight ratio of 1:2 and a ball-to-powder weight ratio of 40:1. Ball milling was performed at room temperature and in an argon atmosphere at a speed of 500r / min. The ball milling process included ten cycles, and each cycle was as follows: forward rotation for 20min, rest for 15min, reverse rotation for 20min, and rest for 15min. After ball milling, the mixture was dried in vacuum at 80°C for 4h to obtain magnesium hydride powder;

[0054] 1.2) Nickel phthalocyanine coated magnesium hydride powder: 2 mg of nickel phthalocyanine powder (NiPc, 95%, MacLean) was dissolved in 0.5 mL of tetrahydrofuran to obtain a tetrahydrofuran solution of nickel phthalocyanine, and 198 mg of magnesium hydride powder was added to the tetrahydrofuran solution of nickel phthalocyanine. After ultrasonic treatment for 0.5 h, the solution was stirred for 12 h and vacuum dried at 60° C. for 12 h to obtain a nickel phthalocyanine-magnesium hydride complex 1 wt% NiPc(MD)-MgH2;

[0055] 2) The nickel phthalocyanine-magnesium hydride complex 1wt% NiPc(MD)-MgH2 was subjected to in-situ hydrogenation treatment to obtain a single-atom alloy 1wt% Ni1-MgH2. The in-situ hydrogenation treatment process is specifically as follows: 6 dehydrogenation / hydrogenation reactions are performed; each dehydrogenation / hydrogenation reaction includes one dehydrogenation reaction and one hydrogenation reaction, and the conditions for the dehydrogenation reaction are: 350°C, 3MPa for 10 minutes; the conditions for the hydrogenation reaction are: 350°C, 0.1MPa for 10 minutes.

[0056] Example 2

[0057] This embodiment follows the same process as that of embodiment 1. First, 6 mg of nickel phthalocyanine powder (NiPc, 95%, McLean) is dissolved in 1.5 mL of tetrahydrofuran to obtain a tetrahydrofuran solution of nickel phthalocyanine. Then, 194 mg of magnesium hydride powder is added to the tetrahydrofuran solution of nickel phthalocyanine. After ultrasonic treatment for 0.5 h, stirring for 12 h, vacuum drying at 60° C. for 12 h is performed to obtain a nickel phthalocyanine-magnesium hydride complex 3wt% NiPc (MD) -MgH2. Then, the nickel phthalocyanine-magnesium hydride complex 3wt% NiPc (MD) -MgH2 is subjected to in-situ hydrogenation reaction to obtain a single-atom alloy 3wt% Ni1-MgH2. The mass content of metal Ni in the single-atom alloy is 0.3%.

[0058] Example 3

[0059] This embodiment follows the same process as that of embodiment 1. First, 10 mg of nickel phthalocyanine powder (NiPc, 95%, McLean) is dissolved in 2.5 mL of tetrahydrofuran to obtain a tetrahydrofuran solution of nickel phthalocyanine. Then, 190 mg of magnesium hydride powder is added to the tetrahydrofuran solution of nickel phthalocyanine. After ultrasonic treatment for 0.5 h, stirring for 12 h, vacuum drying at 60° C. for 12 h obtains a nickel phthalocyanine-magnesium hydride complex 5wt% NiPc(MD)-MgH2. Subsequently, the nickel phthalocyanine-magnesium hydride complex 5wt% NiPc(MD)-MgH2 is subjected to in-situ hydrogenation reaction to obtain a single-atom alloy 5wt% Ni1-MgH2. The mass content of metal Ni in the single-atom alloy is 0.5%.

[0060] Example 4

[0061] In this example, the same process as in Example 1 was followed to first prepare an iron phthalocyanine-magnesium hydride complex 3wt% FePc(MD)-MgH2, and then the iron phthalocyanine-magnesium hydride complex 3wt% FePc(MD)-MgH2 was subjected to an in-situ hydrogenation reaction to obtain a single-atom alloy Fe1-MgH2.

[0062] Example 5

[0063] In this example, the same process as in Example 1 was followed to first prepare a cobalt phthalocyanine-magnesium hydride complex 3wt% CoPc(MD)-MgH2, and then the cobalt phthalocyanine-magnesium hydride complex 3wt% CoPc(MD)-MgH2 was subjected to an in-situ hydrogenation reaction to obtain a single-atom alloy Co1-MgH2.

[0064] Example 6

[0065] This example follows the same process as Example 1, first preparing a tetraphenylporphyrin nickel (II)-magnesium hydride complex 3wt% Ni-TPP (MD)-MgH2, and then performing an in-situ hydrogenation reaction on a cobalt phthalocyanine-magnesium hydride complex 3wt% Ni-TPP (MD)-MgH2 to obtain a single-atom alloy Ni1#2-MgH2, wherein #2 represents a molecule that also has a NiN4 active site.

[0066] See also Figure 1 , Figure 1 The X-ray diffraction (XRD) patterns of the nickel phthalocyanine-magnesium hydride complex x wt% NiPc(MD)-MgH2, x=1 (Example 1), 3 (Example 2), and 5 (Example 3) in Examples 1 to 3 of the present invention are shown. From the XRD patterns, it can be seen that magnesium hydride MgH2 is detected in the nickel phthalocyanine-magnesium hydride complex, but no crystalline NiPc is detected.

[0067] The following uses the nickel phthalocyanine-magnesium hydride composite 3wt% NiPc(MD)-MgH2 (hereinafter referred to as NiN4-MgH2) and the single-atom alloy Ni1-MgH2 obtained in Example 2 of the present invention as examples to test their performance. The test results are as follows:

[0068] See also Figure 2 , Figure 2 The TEM image and energy dispersive X-ray element mapping element map (Mg, N, Ni) of the nickel phthalocyanine-magnesium hydride composite NiN4-MgH2 in Example 2 of the present invention are shown. It can be seen that the Ni element and the N element are evenly distributed on the magnesium hydride MgH2 particles, that is, NiPc is in a molecularly dispersed state on the MgH2 particles.

[0069] See also Figure 3 , Figure 3 The color change of the nickel phthalocyanine-magnesium hydride complex NiN4-MgH2 solution in Example 2 of the present invention in six dehydrogenation / hydrogenation cycles. The NiN4-MgH2 before treatment and the products after 1, 2, 3, and 6 dehydrogenation / hydrogenation reactions are dispersed in tetrahydrofuran. The NiN4-MgH2 before treatment shows a blue color similar to the original color of the phthalocyanine solution. During the in-situ hydrogenation treatment, as the number of cycles increases, the color of the solution gradually changes from light cyan to white. It can be seen that NiPc (MD) gradually degrades in the dehydrogenation / hydrogenation cycle. In addition, phthalocyanine NiPc has excellent thermal stability at 700°C, so it cannot be thermally decomposed at a dehydrogenation / hydrogenation cycle temperature of 350°C, which also proves that the color change is caused by the reduction of NiPc by the reducing environment of Mg / MgH2 hydrogenation and dehydrogenation.

[0070] See also Figure 4 , Figure 4 : is the EDX element distribution diagram of the single-atom alloy Ni1-MgH2 in Example 2 of the present invention. Figure 4 As shown, EDX confirmed the uniform distribution of Ni, N, and C elements on Ni1-MgH2.

[0071] See also Figure 5 , Figure 5 This is a high angle annular dark field scanning TEM (HAADF-STEM) image of the single atom alloy Ni1-MgH2 in Example 2 of the present invention. Figure 5 As shown, high-angle annular dark field scanning TEM (HAADF-STEM) directly observed Ni1 single atoms on MgH2, highlighted by red circles. It can be seen that the metal single atom Ni1 is embedded in the surface lattice of magnesium hydride and forms a metal single atom-magnesium catalyst Ni1-Mg on the surface of magnesium hydride.

[0072] See also Figure 6 , Figure 6 k is the k of the nickel phthalocyanine-magnesium hydride complex in Example 2 of the present invention in the dehydrogenation / hydrogenation cycle 3 Weighted Fourier transform-EXAFS (FT-EXAFS) spectrum. The FT-EXAFS spectrum of the third cycle sample is A well-scattered Ni-N peak is shown at Another rather large peak appears at , which is longer than the Ni-Ni bond of the Ni foil and represents the Mg-Ni bond. This trend is further enhanced after 6 cycles, when NiN4 has completely decomposed. Spectral characterization shows that NiN4 is gradually reduced to Ni1-Mg on the Mg / MgH2 surface.

[0073] See also Figure 7 , Figure 7 : isothermal hydrogenation curves of the single-atom alloy Ni1-MgH2 in Example 2 of the present invention at different temperatures. It can be seen that the single-atom alloy Ni1-MgH2 obtained in Example 2 of the present invention can absorb 5.1wt% of H2 within 15min, and even at a temperature as low as 100°C, Ni1-MgH2 can still absorb 3.6wt% of H2 within 60min.

[0074] See also Figure 8 , Figure 8 The isothermal dehydrogenation curves of the single-atom alloy Ni1-MgH2 at different temperatures in Example 2 of the present invention are shown. In terms of dehydrogenation, at 275°C, Ni1-MgH2 releases 6.2wt% of H2 within 30 minutes. Even at a relatively low temperature of 225°C, Ni1-MgH2 can still release 5wt% of H2 within 360 minutes, which is far superior to the hydrogen absorption and dehydrogenation performance of MgH2 ( Fig. 9 ).

[0075] See also Fig.10 , Fig.10 The graph is a test result of the cyclic stability of the single-atom alloy in Example 2 of the present invention. A hydrogen absorption / dehydrogenation cycle test was conducted at 300°C to demonstrate the reversibility of Ni1-MgH2. In each cycle, the material absorbed H2 within 1 minute and desorbed H2 within 13 minutes. The degradation of the material was negligible throughout the 30 cycles. In addition, the kinetic properties were also well maintained. Fig.11 and Fig.12 As shown in Figure 2, the HAADF-STEM image clearly shows that Ni still maintains atomic dispersion after 30 cycles. In addition, the EDX elemental distribution map confirms the uniform distribution of Ni1 atoms over a larger range.

[0076] See also Fig.13 , Fig.13is the Fe2p of the iron phthalocyanine-magnesium hydride complex and the single-atom alloy in Example 4 of the present invention. 3 / 2 XPS spectrum. It can be seen that after six cycles of hydrogen absorption and desorption, the FePc on the MgH2 surface is reduced to zero-valent Fe1-Mg.

[0077] See also Fig.14 , Fig.14 The Co2p of the iron phthalocyanine-magnesium hydride complex and the single-atom alloy in Example 5 of the present invention 3 / 2 XPS spectrum shows that after six cycles of hydrogen absorption and desorption, the CoPc on the MgH2 surface is reduced to zero-valent Co1-Mg.

[0078] In summary, the method of the present invention uses a metal coordination compound with an MN4 active site to prepare a single-atom alloy through in-situ hydrogenation treatment, achieving good near-room temperature and high-temperature hydrogen storage performance.

[0079] The above is only an explanation of the best embodiment of the present invention, but it should not be understood as a limitation of the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. All changes made within the scope of protection of the independent claims of the present invention are within the scope of protection of the present invention.

[0080] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

Claims

1. A method for preparing a single-atom alloy for catalyzing the absorption and desorption of hydrogen by MgH2, characterized in that: The preparation method comprises the following steps: 1) using a metal coordination compound to coat a magnesium-based hydride to obtain a metal coordination compound-magnesium-based hydride complex; the metal coordination compound has a metal-nitrogen site, and the metal-nitrogen site is represented by: MN4 Wherein, M represents metal and N represents nitrogen; The magnesium-based hydride is magnesium hydride MgH2 or magnesium-nickel alloy Mg2NiH4; 2) performing in-situ hydrogenation treatment on the metal coordination compound-magnesium-based hydride complex to obtain the single-atom alloy.

2. The method for preparing a single-atom alloy for catalyzing MgH2 absorption and desorption of hydrogen according to claim 1, characterized in that: In the step 1), the metal coordination compound is a metal phthalocyanine coordination compound, a metal tetraphenylporphyrin coordination compound, a tetraaminoporphyrin compound, a tetrapyridineporphyrin compound or a metal tetraphenylporphyrin compound; the metal M in the metal coordination compound is nickel, iron, cobalt, titanium, manganese or vanadium.

3. The method for preparing the single-atom alloy for catalyzing MgH2 absorption and desorption of hydrogen according to claim 1, characterized in that: The step 1) is specifically as follows: dissolving the metal coordination compound powder in an organic solvent, adding the magnesium-based hydride powder, subjecting the mixture to ultrasonic treatment, stirring for a period of time, and vacuum drying to obtain a metal coordination compound-magnesium-based hydride complex; the mass ratio of the metal coordination compound powder to the magnesium-based hydride powder is 1-5:95-99; and the amount ratio of the metal coordination compound powder to the organic solvent is 2-10 mg:0.5-2.5 mL.

4. The method for preparing a single-atom alloy for catalyzing MgH2 absorption and desorption of hydrogen according to claim 3, characterized in that: The stirring time is 6 to 12 hours, the vacuum drying temperature is 60 to 80° C., and the vacuum drying time is 6 to 12 hours.

5. The method for preparing a single-atom alloy for catalyzing MgH2 absorption and desorption of hydrogen according to claim 1, characterized in that: In the step 1), the magnesium-based hydride is magnesium hydride, and the preparation process of the magnesium hydride powder is specifically as follows: using stainless steel grinding balls with diameters of 6 mm and 3 mm, ball milling is performed at a speed of 450-500 r / min at room temperature and in an inert gas atmosphere, and after the ball milling is completed, vacuum drying is performed to obtain the magnesium hydride powder; the ball milling process includes ten cycles, and each cycle process is forward rotation for 20-30 minutes, rest for 15 minutes, reverse rotation for 20-30 minutes, and rest for 15 minutes.

6. The method for preparing a single-atom alloy for catalyzing MgH2 absorption and desorption of hydrogen according to claim 5, characterized in that: The size of the magnesium hydride powder is submicron level.

7. The method for preparing a single-atom alloy for catalyzing MgH2 absorption and desorption of hydrogen according to claim 1, characterized in that: The in-situ hydrogenation treatment is specifically: performing 6 dehydrogenation / hydrogenation reactions; each dehydrogenation / hydrogenation reaction includes one dehydrogenation reaction and one hydrogenation reaction, and the conditions of the dehydrogenation reaction are: 350-400°C, 3-5MPa for 10-30min; the conditions of the hydrogenation reaction are: 350-400°C, 0-0.1MPa for 10-30min.

8. A single-atom alloy obtained by the method for preparing a single-atom alloy catalyzing MgH2 absorption and desorption of hydrogen according to any one of claims 1 to 7, characterized in that: The single-atom alloy includes a magnesium-based hydride and a metal single-atom-magnesium catalyst formed on the surface of the magnesium-based hydride, and the metal single-atom-magnesium catalyst is represented by: M1-Mg Among them, M1 represents a single metal atom, specifically a single nickel atom, a single iron atom, a single cobalt atom, a single titanium atom, a single manganese atom or a single vanadium atom, and Mg represents magnesium.

9. The single-atom alloy according to claim 8, characterized in that: The metal single atom-magnesium catalyst is uniformly distributed on the surface of magnesium-based hydride, and the magnesium-based hydride is magnesium hydride or magnesium-nickel alloy Mg2NiH4; the mass content of the metal single atom M1 in the single atom alloy is 0.1-0.5%.

10. The single-atom alloy according to claim 8, characterized in that: The metal single atom-magnesium catalyst is used for catalyzing the absorption and desorption of hydrogen by magnesium-based hydride.

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