CN107946560B

CN107946560B - Carbon-limited domain metal or metal oxide composite nano-structure material and preparation method and application thereof

Info

Publication number: CN107946560B
Application number: CN201711103670.6A
Authority: CN
Inventors: 麦立强; 刘子昂; 孟甲申; 王选朋
Original assignee: Wuhan University of Technology WUT
Current assignee: Wuhan University of Technology WUT
Priority date: 2017-11-10
Filing date: 2017-11-10
Publication date: 2020-09-08
Anticipated expiration: 2037-11-10
Also published as: CN107946560A

Abstract

The invention relates to a carbon-limited domain metal or metal oxide composite nano-structure material and a preparation method thereof, and the material can be used as an electrode material of an electrochemical energy storage and conversion device. The material is characterized in that metal or metal oxide nanocrystals are stacked to form a specific shape, a carbon layer is uniformly coated on the surface of the metal or metal oxide nanocrystals, the diameter of the nanocrystals is 8-50 nanometers, mesopores formed by stacking the metal or metal oxide nanocrystals are uniformly distributed on the surface and inside of the material, and the material has a specific surface area of 50-120 m²g^‑1. The invention has the beneficial effects that: A) a variety of MOF-coated nanostructured materials can be obtained; B) the thickness of the MOF coating layer can be easily controlled by the holding time; C) the carbon layer is uniformly coated on the surface of the nano structure, and the morphological characteristics of the precursor are well maintained; D) the invention has the characteristics of cheap raw materials, simple and environment-friendly process, high yield and excellent electrochemical performance of the material.

Description

Carbon-limited domain metal or metal oxide composite nano-structure material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of nano materials and electrochemical devices, and particularly relates to a carbon confinement metal or metal oxide composite nano-structure material and a preparation method thereof.

Background

In the current society, the problem of environmental pollution has become an important issue in social life, and finding a novel clean energy source capable of replacing fossil energy and achieving efficient energy storage has become a hot problem in scientific research. Therefore, efficient energy storage and conversion devices such as electrocatalytic water decomposition, fuel cells, air cells, lithium ion batteries, and the like have been developed. However, many key problems still exist with these devices and need to be solved. In the aspect of energy conversion, water decomposition is taken as an example, and a cheap and efficient electrocatalytic water decomposition catalyst is in urgent need of development. At present, reach the industryElectrocatalytic water decomposition catalysts with standard chemocatalytic activity are mostly expensive iridium-based and platinum-based materials, and the precious metal materials with extremely low reserves and extremely high cost limit the large-scale application of the electrocatalytic water decomposition catalysts; in the aspect of energy storage, the hard carbon (372 mAh g theoretical capacity) is widely used at present^-1) Lithium ion batteries as anode materials are in the bottleneck in capacity. Therefore, the development of high energy density electrode materials for lithium ion batteries is becoming more important.

Researchers find out through a large number of experiments that: metals or metal oxides with high abundance of some elements can meet the above requirements. In order to fully exert the electrochemical activity, the electrode material needs to be designed into a proper structure to meet the requirements of different occasions. In general, desirable electrode materials require high stability, high electronic and ionic conductivity, high specific surface area, and the like. In order to meet the above requirements, it is a common practice to design a nanostructure having a complex internal structure and to compound an electrode material with a carbon material. However, until Metal Organic Framework (MOF) materials are synthesized, simple and efficient methods for large-scale synthesis of good carbon-based composite materials have not been found.

By coordination reactions of metal ions or ion clusters with organic ligands, one can easily obtain MOF materials with long-range order. The material has the characteristics of abundant pore structures, ultrahigh specific surface area and uniform interval distribution of organic ligands and metal ions. Due to the unique properties, the MOF material has a very wide application prospect in the field of energy storage and transformation. At present, the synthesis of high-quality in-situ carbon composite materials by taking MOF materials as precursors is the most common application of the MOF materials in the field of energy storage and conversion. However, a simple and efficient method for using MOF materials in the design and construction of complex nanostructures has not yet been found.

Disclosure of Invention

The invention aims to provide a carbon-limited domain metal or metal oxide composite nano-structure material with simple process, easy popularization and excellent performance and a controllable preparation method thereof, and the obtained material can be used as an electrode material of an electrochemical energy storage and conversion device.

In order to achieve the purpose, the technical scheme of the invention is as follows: the carbon-confined metal or metal oxide composite nano-structured material is characterized in that metal or metal oxide nanocrystals are stacked to form a specific shape, a carbon layer is uniformly coated on the surface of the carbon-confined metal or metal oxide composite nano-structured material, the diameter of the nanocrystals is 8-50 nanometers, mesopores formed by stacking the metal or metal oxide nanocrystals are uniformly distributed on the surface and inside of the carbon-confined metal or metal oxide composite nano-structured material, and the specific surface area of the carbon-confined metal or metal oxide composite nano-structured material is 50-120 m²g^-1。

According to the scheme, the carbon layer is obtained by carbonizing a uniform metal organic framework MOF coating layer.

According to the scheme, the metal or metal oxide nanocrystals are stacked to form a nanowire array, a nanorod, a nanosheet, a nanotube or a hollow nano cube.

According to the scheme, the metal nanocrystalline comprises: a CoNi alloy or a CoSn alloy; the metal oxide nanocrystal is as follows: CoO&MnO, ZnO or ZnO&ZnMoO₃。

The preparation method of the carbon-limited domain metal or metal oxide composite nano-structure material comprises the following steps:

s1 preparing a metal oxide or metal hydroxide precursor by adopting a hydrothermal method, a solvothermal method, an electrostatic spinning method or a coprecipitation method;

s2, simultaneously placing the metal oxide or metal hydroxide precursor and the corresponding ligand in a vacuum oven, and vacuumizing the system to 100-150 Pa;

s3, performing heat preservation treatment on the set temperature of the vacuum oven according to the selected organic ligand;

s4, setting corresponding heat preservation time according to the required thickness of the metal organic framework MOF coating layer to obtain the MOF coated metal oxide or metal hydroxide nano structure;

s5, sintering the MOF-coated metal oxide or metal hydroxide nanostructure obtained in the step S4 in a reducing, inert or/and air atmosphere to obtain the carbon-limited domain metal or metal oxide composite nanostructure material, wherein the morphology of the metal oxide or metal hydroxide precursor is maintained.

According to the scheme, the metal oxide precursor is CoO&NiO mesoporous nanowire array and MnCo₂O₄Mesoporous nanotubes, ZnO nanorods or Zn₃Mo₂O₉Nanosheets, the metal hydroxide being CoSn (OH)₆Hollow cubic nanometer.

According to the scheme, the ligand is 2-methylimidazole or terephthalic acid, and a nitrogen-doped or nitrogen-undoped carbon layer is obtained correspondingly.

According to the scheme, the temperature of the oven is 60-220 ℃, and the heat preservation time is 40 min-24 h.

According to the scheme, the sintering temperature is 200-900 ℃, and the sintering time is 1-5 h.

The carbon-limited domain metal or metal oxide composite nano-structure material is applied as an electrode material of an electrochemical energy storage and conversion device.

The key to the implementation of the strategy of the invention lies in the selection of metal ions and corresponding organic ligands and the setting of low-pressure vapor deposition conditions (temperature, pressure and holding time). Compared with liquid reaction, the gaseous organic ligand molecule has higher diffusion capacity and reaction activity. Therefore, the organic ligand can easily enter the pore structure of the precursor of the nano-structure to react with the precursor of the metal oxide or the hydroxide, and finally uniform MOF coating is obtained, and then a further sintering process is carried out to obtain the uniform carbon confinement nano-structure.

The invention has the beneficial effects that:

A) by regulating the coordination relation between metal ions and organic ligands in metal oxides or hydroxides and a simple low-pressure vapor deposition technology, various MOF-coated nano-structure materials can be obtained; B) the thickness of the MOF coating layer can be easily controlled by the holding time; C) the carbon layer is uniformly coated on the surface of the nano structure, and the morphological characteristics of the precursor are well maintained; D) the method has the characteristics of cheap raw materials, simple and environment-friendly process, high yield and excellent electrochemical performance of the material, provides a universal strategy for preparing the carbon-limited domain metal or metal oxide nano-structured material, and has the potential of large-scale application.

Drawings

Fig. 1 is a diagram of the mechanism of formation of carbon-confined metal or metal oxide nanostructures (a) and sem (b) and tem (e) of the corresponding precursors, (c) and tem (f) of the coated zeolitic imidazolate-like framework compounds (ZIF) and sem (d) and tem (g) of the carbon-confined metal nanostructures;

FIG. 2 is a plot of XRD (a), BET (b), BJH (c), FT-IR (d), XPS (e) and EDS spectra (f) before and after ZIF coating in example 1;

FIG. 3 is TEM (a) and HRTEM (b-c) images and TEM-EDS spectra (d-i) after coating ZIFs of example 1;

FIG. 4 is the LSV curve (a), Tafel slope (b) and constant current long cycle curve (c) for CoNi @ NC OER performance, and the LSV curve (d) for CoNi @ NC HER performance, Tafel slope (e) and constant current long cycle curve (f) for example 1;

FIG. 5 is a set-up plot of the CoNi @ NC water splitting full reaction performance test of example 1 (a), constant current long cycle performance (b) and LSV curves before and after cycling (c);

FIG. 6 shows MnCo of example 2₂O₄ZIF coated SEM (a), EDS (b) and XRD (c) and sintered carbon limited domain CoO&SEM (d), TEM (e) and XRD (f) for MnO @ NC structures;

FIG. 7 is CoO of example 2&MnO @ NC at 0.2mV s^-1The voltage range of the CV curve under sweep speed is 0.01-3V (a)0.1A g^-1A charge-discharge curve (b) and a multiplying power performance test (c) under the current density;

FIG. 8 is CoO of example 2&MnO @ NC at 2Ag^-1Long cycle performance;

FIG. 9 is SEM (a), EDS (b) and XRD (c) of ZIF-coated ZnO nanorods of example 3, and TEM (d-e) and XRD (f) of sintered carbon-limited-domain CoO & MnO @ NC structure;

FIG. 10 is Zn of example 4₃Mo₂O₉SEM (a), EDS (b) and XRD (c) after ZIF is coated by nanosheet, and carbon-limited domain CoO after sintering&TEM (d-e) and XRD (f) of MnO @ NC structure;

FIG. 11 shows CoSn (OH) in example 5₆After hollow cubes coated with ZIFSEM (a), EDS (b) and XRD (c) and sintered carbon-limited domain CoO&TEM (d-e) and XRD (f) of MnO @ NC structure;

FIG. 12 shows CoSn (OH) of example 6₆SEM (a) after hollow cubic coating of MOF, EDS (b) and XRD (c) and carbon-limited domain CoO after sintering&TEM (d-e) and XRD (f) of MnO @ NC structure.

Detailed Description

In order to better understand the present invention, the following examples are further provided to illustrate the present invention, but the present invention is not limited to the following examples.

Example 1:

1) ultrasonically cleaning the carbon cloth for 30min by using dilute hydrochloric acid;

2) cleaning the carbon cloth obtained in the step 1) with acetone, deionized water and absolute ethyl alcohol sequentially for several times, and removing residual hydrochloric acid;

3) 1mmol of Co (NO) was weighed out separately₃)₂·6H₂O，1mmol Ni(NO₃)₂·6H₂O, 6mmol of urea, and simultaneously adding the urea into 40mL of deionized water, and magnetically stirring the mixture for 10min at normal temperature to completely dissolve the urea;

4) cutting the carbon cloth obtained in the step 2) into square blocks of 2cm multiplied by 2cm, and immersing the square blocks into the solution obtained in the step 3);

5) transferring the carbon cloth obtained in the step 4) and the solution together into a 50mL Teflon reaction kettle, and carrying out hydrothermal treatment at 120 ℃ for 6 h;

6) cleaning the carbon cloth obtained in the step 5) with deionized water for 4 times, and then placing the carbon cloth in an oven at 70 ℃ for drying to obtain a precursor of the CoO & NiO mesoporous nanowire array;

7) putting the precursor obtained in the step 6) and excessive 2-methylimidazole into a vacuum oven at the same time, and vacuumizing the system (about 100 Pa);

8) setting the vacuum oven at 90 deg.C, 120 deg.C and 150 deg.C respectively, and allowing the temperature to stabilize;

9) setting the vacuum oven to keep warm for 3h to obtain CoO & NiO @ ZIF;

10) and (3) transferring the carbon cloth obtained in the step 9) into a tube furnace, and sintering at 500, 600 and 700 ℃ for 3h in a hydrogen atmosphere to obtain CoNi @ NC-500, CoNi @ NC-600 and CoNi @ NC-700 (products).

The forming process of the carbon confinement metal nano structure array comprises the following steps: as shown in FIG. 1, first, at a low pressure and a high temperature, the organic ligand is converted into a gas to fill the entire reaction system. Then, the gaseous organic ligand enters the pore structure of the precursor by means of gas diffusion to react with the CoO & NiO on the surface of the precursor, so that the metal on the surface of the material and the organic ligand are subjected to coordination reaction to form ZIF (fig. 1c), and the reaction equation is as follows:

CoO&NiO(s)+2MIM(g)→CoO&NiO@ZIF(s)+H₂O(g)

it is evident from fig. 1f that the surface of the mesoporous nanowire is uniformly coated with a thin ZIF layer, and the surface of the nanoparticle becomes rough, which proves that the organic ligand diffuses into the mesopores to react with the material. Gaseous water generated in the reaction process is separated from the reaction system. The homogeneous gaseous reaction environment ultimately results in the formation of a homogeneous MOF coating layer.

Subsequent XRD (fig. 2a) and FT-IR (fig. 2d) both demonstrate the formation of ZIF structures. Meanwhile, XRD results show that crystalline CoO and NiO still remain in the structure. The BET (FIGS. 2b-c) results show that the nanostructure has a size of 106.1m²g^-1About the specific surface area of the ZIF-uncoated CoO&Three times (36 m) of specific surface area of NiO nano structure²g^-1) This, together with the presence of N in the EDS spectrum (fig. 2f), laterally demonstrates the formation of ZIF structures. TEM images (FIGS. 3a-c) directly show that ZIFs are distributed on both the nanostructure surface and in the mesopores. And finally obtaining the nitrogen-doped carbon in-situ coated cobalt-nickel alloy (CoNi @ NC) nanostructure through a hydrogen sintering process, wherein the nitrogen-doped carbon is uniformly distributed on the surface of the nanostructure and in the mesopores. XPS (FIG. 2e) and transmission EDS spectra (FIG. 3d-i) illustrate the presence and uniform distribution of Co, Ni, O, N, C elements.

Applying a CoNi @ NC nanowire array structure to an electrocatalytic Oxygen Evolution Reaction (OER) catalyst material, and preparing an active material: the mass ratio of 72R is 5: 5 preparing ink, wherein the solution is isopropanol: deionized water: the volume ratio of Nafion is 15: 4: 1. dropping ink on the surface of a platinum-carbon disc electrode, and carrying out electrochemical test in a 1M KOH solution with the area load of 2.0mg cm^-2. The linear voltage sweep curve (FIG. 4a) indicates that CoNi @ NC-600 has the same polarity as IrO₂Electrocatalytic activity comparable to that of/C. Meanwhile, compared with a pure CoNi-600 mesoporous nanowire array, the CoNi @ NC-600 mesoporous nanowire array structure modified by a layer of nitrogen-doped carbon shows obviously improved OER reaction activity. In particular, a significant increase in current density at the same potential, a reduction in the peak potential, and a significant reduction in the Tafel slope (FIG. 4 b). The CoNi @ NC mesoporous nano-wire obtained by comparing different sintering temperatures reaches 10mAcm^-2Current density of CoNi @ NC-500, CoNi @ NC-600, CoNi @ NC-700, IrO₂The overpotentials of 371, 353, 366 and 320mV are needed for the/C respectively. At 10mAcm^-2After 40000s at current density of (1), IrO₂both/C and CoNi-600 showed excellent stability with voltage degradation of 61.6mV and 71mV, respectively (FIG. 4C). In contrast, CoNi @ NC-500, CoNi @ NC-600, and CoNi @ NC-700 exhibited voltage degradation of 53.9mV, 6.5mV, and 17.9 mV. The sintering temperature of 600 ℃ is the optimal sintering temperature, and the OER activity and stability are excellent.

The structure is applied to an electrocatalytic Hydrogen Evolution Reaction (HER) catalyst, and the electrochemical performance (1M KOH) of the catalyst is tested. To reach-10 mA cm^-2The current densities of Pt/C, CoNi-600, CoNi @ NC-500, CoNi @ NC-600, and CoNi @ NC-700 required over-potentials of 71, 264, 244, 132, 224mV, respectively (FIG. 4 d). It can be seen that CoNi @ NC-600 still shows better HER activity, although there is still some gap from commercial platinum carbon. Again, despite the Tafel slope (109.1 mVdec) of CoNi @ NC-600^-1) Relative to commercial platinum carbon (45.9mV dec)^-1) Higher, but significantly lower than CoNi-600 (197.4mV dec)^-1),CoNi@NC-500(151.7mV dec^-1) And Tafel slope of CoNi @ NC-700 (141.0mV dec)^-1) (FIG. 4 e). At-10 mA cm^-2The current density of (D) was continuously working at 40000s, CoNi @ NC-600 showed the best cycling stability, with a voltage degradation of only 29.5mV, lower than 36mV for commercial platinum carbon (FIG. 4 f).

The excellent OER and HER activity of the nitrogen-doped carbon confinement CoNi @ NC-600 are closely related to the structure of the nitrogen-doped carbon confinement CoNi @ NC-600. The electron conductivity test of the four-probe method shows that compared with unmodified CoNi-600, the carbon modified CoNi @ NC-600 has significantly improved electron conductivity, and the characteristic ensures that the electrocatalytic activity of the electrochemical active site is fully exerted. Meanwhile, the ultrathin carbon modification layer plays a key role in limiting the agglomeration of active materials and slowing down the catalyst poisoning, and thus the improvement of the cycling stability of the electrode material is greatly promoted.

In view of the excellent electrochemical properties of the CoNi @ NC-600 material, the performance (1M KOH) of the material actually applied to the electrocatalytic water splitting full reaction was measured by the two-electrode method (FIGS. 5 a-c). The results showed that 10mA cm was reached^-2The reaction system required a voltage of 1.678V. After the current is kept for 70000s, the voltage is kept at 1.727V, and the good stability is shown.

The result shows that the nitrogen-doped carbon-limited domain CoNi @ NC-600 mesoporous nanowire has excellent OER and HER performances, and is closely related to the nitrogen-doped carbon coating structure. The structure has great potential and practical application value in the field of electrocatalytic water decomposition.

Example 2:

1) according to the mass ratio of 3: 2: 1, weighing low molecular weight polyvinyl alcohol, medium molecular weight polyvinyl alcohol and high molecular weight polyvinyl alcohol, and dissolving the low molecular weight polyvinyl alcohol, the medium molecular weight polyvinyl alcohol and the high molecular weight polyvinyl alcohol in 20mL of deionized water to prepare a solution with the mass fraction of 9.5%;

2) 3mmol of Co (CH)₃COO)₂·4H₂O and 1.5mmol Mn (CH)₃COO)₂·4H₂Dissolving O in the solution obtained in the step 1), and stirring in a water bath at 80 ℃ for 5 hours to prepare an electrospinning precursor solution;

3) carrying out electrostatic spinning on the solution obtained in the step 2) at a high voltage of 12 kV;

4) placing the electrostatic spinning nanowires obtained in the step 3) in a forced air drying oven at 80 ℃ for drying for 12 hours;

5) transferring the dried electrospun nanowire obtained in the step 4) into a muffle furnace for 1 ℃ min^-1Heating up to 500 ℃ at the heating rate, and keeping the temperature for three hours to obtain MnCo₂O₄A mesoporous nanotube precursor;

6) subjecting the MnCo obtained in the step 5) to₂O₄Simultaneously placing the mesoporous nanotube and the excessive 2-methylimidazole in a vacuum oven, and vacuumizing the system (E ^ E)100Pa)；

7) Setting the vacuum oven at 150 ℃ until the temperature is stable;

8) setting the vacuum oven for heat preservation for 3 hours to obtain MnCo₂O₄@ZIF；

9) And (3) transferring the product obtained in the step 8) to a tubular furnace, sintering for 1h at 500 ℃ in an argon atmosphere, then placing the product in a muffle furnace, and sintering for 2h at 280 ℃ in an air atmosphere to obtain the CoO & MnO @ NC mesoporous nanotube (product).

MnCo obtained in this example₂O₄@ ZIF mesoporous nanotubes, as shown in FIG. 6a, are uniform in nanotube size, with a diameter of about 150 nm. The presence of C element in EDS spectrum (fig. 6b) and the presence of ZIF peak in XRD spectrum (fig. 6C) after low pressure vapor deposition indicate the presence of ZIF in the structure. Nitrogen-doped carbon confinement CoO prepared after subsequent sintering&TEM results of MnO @ NC mesoporous nanotubes indicate that the structure of the nanotubes is well maintained (FIG. 6 d-e). The XRD pattern indicated the presence of CoO and MnO phases (fig. 6 f).

Adding CoO&MnO @ NC is used as a lithium ion battery anode material for carrying out half-cell test. At 0.2mV s^-1And carrying out cyclic voltammetry test on the battery at a voltage range of 0.01-3V at the sweep speed of (2). In the first charge-discharge cycle, two pairs of redox peaks corresponding to CoO and MnO appeared, and the curves of the second and third circles almost completely coincided, showing better stability (fig. 7 a). Comparative 0.1Ag^-1Charge and discharge performance of lower cell, carbon limited CoO&MnO @ NC compared with simple MnCo₂O₄Higher specific capacity with first coulombic efficiency and better cycling stability were exhibited (fig. 7 b). Wherein after 200 cycles of charge and discharge, CoO is added&MnO @ NC shows up to 1153mAh g^-1The specific capacity (retention rate 91.1%) is far higher than that of MnCo₂O₄534mAh g of^-1(retention ratio 53.9%). In addition, CoO&The multiplying power performance test of MnO @ NC shows that when the current density is from 0.1, 0.2, 0.5, 1, 2 and 5Ag^-1Back to 0.1Ag^-1After, CoO&The capacity recovery of MnO @ NC was as high as 100%, showing excellent rate performance (fig. 7 c). At the same time, CoO&MnO @ NC at 2A g^-1Current density lower cycle ofAfter 1000 cycles, the capacity was still stable with almost no capacity fade (fig. 8).

The results show that the nitrogen-doped carbon confinement CoO & MnO @ NC mesoporous nanotube has excellent lithium storage performance. This fully demonstrates the positive effect of the in-situ carbon composite structure on improving the electrochemical activity and stability of the material. Meanwhile, the structure has great potential in the field of energy storage.

Example 3:

1) weighing 0.55g Zn (CH)₃COO)₂·2H₂O and 0.1g cetyltrimethylammonium bromide (CTAB) were dissolved in 40mL of ethylene glycol;

2) adding 30mL of 85% hydrazine hydrate into the solution obtained in the step 1), and magnetically stirring for 1 h;

3) transferring the solution obtained in the step 2) to a 100mL Teflon reaction kettle, and heating the solvent at 160 ℃ for 6 h;

4) washing the precipitate obtained in the step 3) with absolute ethyl alcohol for 3 times, and then placing the precipitate in a forced air drying oven at 70 ℃ for drying for 6 hours to obtain a ZnO nanorod precursor;

5) putting the ZnO nano-rod obtained in the step 4) and excessive 2-methylimidazole in a vacuum oven at the same time, and vacuumizing the system (about 100 Pa);

6) setting the vacuum oven at 150 ℃ until the temperature is stable;

7) setting the vacuum oven to preserve heat for 3 hours to obtain ZnO @ ZIF;

8) and (3) transferring the product obtained in the step 7) to a tube furnace, and sintering at 550 ℃ for 3h in an argon atmosphere to obtain the nitrogen-doped carbon confinement ZnO @ NC nanorod (product).

The nitrogen-doped carbon-confined ZnO @ NC nanorod obtained in the embodiment is shown in FIG. 9. The ZnO nanorod coated with the ZIF is uniform in appearance, and an EDS (electron-discharge spectroscopy) spectrum shows uniformly distributed Zn, C and N elements. The XRD pattern indicated the presence of ZIF and ZnO phases. After sintering, the appearance can be better maintained. The XRD pattern after sintering showed the product to be pure phase ZnO.

Example 4:

1) 1mmol (NH)₄)Mo₇O₂₄·4H₂Dissolving O in 100mL of deionized water;

2) adding 8-12 mL of NH₃·H₂Adding O (2M) into the solution obtained in the step 1) at room temperature while stirring;

3) weighing 7mmol Zn (NO)₃)₂·6H₂Dissolving O in 50mL of deionized water;

4) dropwise adding the solution obtained in the step 3) into the solution obtained in the step 2), and stirring for 2 hours;

5) washing the precipitate obtained in the step 4) with deionized water and ethanol for 3 times respectively, and drying in a forced air drying oven at 70 ℃ for 6 hours to obtain Zn₃Mo₂O₉A nanosheet precursor;

6) zn obtained in the step 5)₃Mo₂O₉Placing the nanosheet and excessive 2-methylimidazole in a vacuum oven at the same time, and vacuumizing the system (about 100 Pa);

7) setting the vacuum oven at 150 ℃ until the temperature is stable;

8) setting the vacuum oven to keep the temperature for 3 hours to obtain Zn₃Mo₂O₉@ZIF；

9) Transferring the product obtained in the step 8) into a tube furnace, and sintering for 3h at 500 ℃ in an argon atmosphere to obtain the nitrogen-doped carbon confinement ZnO&ZnMoO₃@ NC nanosheet (product).

The nitrogen-doped carbon confinement ZnO obtained by the embodiment&ZnMoO₃@ NC, as shown in FIG. 10. Zn after ZIF coating₃Mo₂O₉The nanosheets are uniform in appearance, and the EDS energy spectrum shows Mo, C and N elements which are uniformly distributed. An XRD pattern shows ZIF and Zn₃Mo₂O₉The presence of a phase. After sintering, the appearance can be better maintained. The XRD pattern after sintering shows that the products are ZnO and ZnMoO₃Mixed phases of (1).

Example 5:

1) weighing 1mmol of CoCl₂6H2O and 1mmol sodium citrate, dissolved in 35mL deionized water;

2) weighing 1mmol SnCl₄·5H₂Dissolving O in 5mL of ethanol;

3) adding the solution obtained in the step 2) into the solution obtained in the step 1);

4) dropwise adding 5mL of 2M NaOH solution into the solution obtained in the step 3), and stirring for 1 h;

5) dropwise adding 20mL of 8M NaOH solution into the suspension obtained in the step 4), and stirring for 1 h;

6) washing the precipitate obtained in the step 5) with deionized water and ethanol for a plurality of times, and then drying in a forced air drying oven at 70 ℃ to obtain CoSn (OH)₆A hollow cubic precursor;

7) the CoSn (OH) obtained in the step 6)₆Placing the nano cube and the excessive 2-methylimidazole in a vacuum oven at the same time, and vacuumizing the system (about 100 Pa);

8) setting the vacuum oven at 220 ℃ until the temperature is stable;

9) setting the vacuum oven for heat preservation for 5h to obtain CoSn (OH)₆@ZIF；

10) And (3) transferring the product obtained in the step (9) to a tube furnace, and sintering at 550 ℃ for 3h in an argon atmosphere to obtain the nitrogen-doped carbon confinement CoSn @ NC nano cube (product).

The nitrogen-doped carbon confinement CoSn @ NC nano-cube obtained in the example is shown in FIG. 11. post-ZIF CoSn (OH) coating₆The nano cubic morphology is uniform, and the EDS energy spectrum shows uniformly distributed Co, Sn and C elements. XRD pattern spectrum shows ZIF and CoSn (OH)₆The presence of a phase. After sintering, the appearance can be better maintained. The XRD pattern after sintering showed the product to be a pure phase CoSn alloy.

Example 6:

1) adopting a coprecipitation method to prepare CoSn (OH)₆Nano-cubic precursor (same as example 5);

2) the CoSn (OH) obtained in the step 1)₆Placing the nano cube and the excessive terephthalic acid in a vacuum oven at the same time, and vacuumizing the system (about 100 Pa);

3) setting the vacuum oven at 220 ℃ until the temperature is stable;

4) setting the vacuum oven for heat preservation for 5h to obtain CoSn (OH)₆@MOF；

5) And (3) transferring the product obtained in the step 4) to a tube furnace, and sintering at 550 ℃ for 3h in an argon atmosphere to obtain the CoSn @ C nano cube (product).

The carbon-limited domain CoSn @ C nanocube obtained in this example is shown in FIG. 12. MOF coated CoSn (OH)₆The nano cubic morphology is uniform, and the EDS energy spectrum shows uniformly distributed Sn, Co and C elements. XRD pattern spectrum shows MOF and CoSn (OH)₆The presence of a phase. After sintering, the appearance can be better maintained. The XRD pattern after sintering showed the product to be a pure phase CoSn alloy.

Claims

1. The carbon-limited domain metal or metal oxide composite nano-structured material is prepared by stacking metal or metal oxide nanocrystals into a specific shape, uniformly coating a carbon layer on the surface of the carbon-limited domain metal or metal oxide composite nano-structured material, carbonizing the carbon layer by a uniform metal organic framework MOF coating layer, wherein the diameter of the nanocrystals is 8-50 nanometers, mesopores formed by stacking the metal or metal oxide nanocrystals are uniformly distributed on the surface and inside of the material, and the material has a specific surface area of 50-120 m²g^-1Which comprises the following steps:

s2, simultaneously placing the metal oxide or metal hydroxide precursor and the corresponding ligand in a vacuum oven, and vacuumizing the system to 100-150 Pa; the ligand is 2-methylimidazole or terephthalic acid, and a nitrogen-doped or nitrogen-free carbon layer is obtained correspondingly;

s3, heating the vacuum oven to a set temperature according to the selected organic ligand, and carrying out heat preservation treatment; the set temperature is 60-220 ℃, and the heat preservation treatment time is 40 min-24 h;

2. The method of preparing a carbon-confined metal or metal oxide composite nanostructured material according to claim 1, characterized in that: the metal oxide precursor is CoO&NiO mesoporous nanowire array and MnCo₂O₄Mesoporous nanotubes, ZnO nanorods or Zn₃Mo₂O₉Nanosheets, the metal hydroxide being CoSn (OH)₆Hollow cubic nanometer.

3. The method for preparing the carbon-limited domain metal or metal oxide composite nano-structure material according to claim 1, wherein the sintering temperature is 200-900 ℃ and the sintering time is 1-5 h.