Preparation method of molybdenum disulfide nano array with rich edge structure

Abstract

The invention provides a molybdenum disulfide nano array and a preparation method and application thereof. The molybdenum disulfide nano array vertically grows on the substrate, the molybdenum disulfide nano array is integrally of a dendritic structure, and the dendritic structure extends from the substrate to the edge. The molybdenum disulfide nano array has rich edges and correspondingly has rich active sites, and the dendritic structure enables the active sites of the molybdenum disulfide nano array to be fully exposed. As an independent electrode, the molybdenum disulfide nano array shows excellent catalytic hydrogen evolution performance and cycling stability.

Description

Technical Field

[0001] The present invention relates to the field of chemical preparation, and in particular to a molybdenum disulfide array, a preparation method thereof, and applications thereof. Background Art

[0002] As a clean fuel with great development potential, hydrogen energy is regarded as an ideal choice to replace traditional fossil energy. Among them, water electrolysis hydrogen production technology is not only a key way to efficiently obtain high-purity hydrogen, but also can serve as an energy storage carrier for intermittent renewable energy (such as wind energy and solar energy), providing key technical support for the realization of the hydrogen economy. Among traditional HER electrocatalysts, precious metals (such as platinum) are one of the most efficient categories. However, the scarcity and high price of precious metals greatly limit their large-scale application in the industrial field, so the development of low-cost and high-efficiency HER electrocatalysts is particularly urgent.

[0003] In recent years, molybdenum disulfide (MoS2) has been widely regarded as an ideal alternative to precious metal platinum due to its low cost, special edge configuration and excellent hydrogen evolution reaction (HER) activity. Studies have shown that the catalytic activity of MoS2 mainly comes from the active sites on its edges, but the basal plane of MoS2 is catalytically inert due to the lack of active sites. The current strategies to improve the catalytic performance of MoS2 focus on two directions: edge engineering and disorder engineering: edge engineering enhances HER performance by constructing edge-rich nanostructures, while disorder engineering focuses on activating inert basal planes. Although traditional post-processing techniques (such as plasma treatment, chemical etching, electrochemical activation and hydrogen annealing) are widely used to construct disordered structures, these methods are prone to damage to the edge structure due to excessive processing in actual operation, which in turn reduces the concentration of active sites and weakens the stability of the catalyst. Therefore, studying MoS2 nanoarrays with high-density active edges is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a molybdenum disulfide nanoarray having a high density of active edges.

[0005] Another object of the present invention is to provide a preparation method and application of molybdenum disulfide nanoarrays.

[0006] The technical solutions of the present invention are as follows:

[0007] A molybdenum disulfide nanoarray is vertically grown on a substrate. The array exhibits a dendritic structure that extends from the substrate toward the edge. The dendritic structure is characterized by the presence of a new sub-nanostructure on the vertically grown nanosheets. Furthermore, the dendritic structure is characterized by the dense presence of numerous MoS2 secondary sheets on the sides of the vertically grown nanosheets.

[0008] The edge of the molybdenum disulfide nanoarray is composed of a number of nanosheets.

[0009] The above-mentioned method for preparing a molybdenum disulfide nanoarray comprises the following steps:

[0010] S1: Place the raw materials and substrate in a sealed environment; the substrate can be carbon cloth, molybdenum mesh, tungsten mesh, or titanium mesh. During preparation, the raw materials (sulfur-containing and molybdenum-containing materials) can be placed in a crucible, and then the substrate can be placed on the inner wall of the crucible.

[0011] S2: generating a magnetic field in the closed environment and ensuring that the raw material and the substrate are placed in the magnetic field;

[0012] S3: After a certain reaction time, stop applying the magnetic field;

[0013] After cooling in step S4, the molybdenum disulfide nanoarray can be obtained, and the molybdenum disulfide nanoarray is located on the surface of the substrate;

[0014] The atomic ratio of S to Mo in the raw material is less than or equal to 2.

[0015] Wherein, the sealed environment contains a trace amount of hydrogen, and the volume percentage of the trace amount of hydrogen is 0.1-10%.

[0016] Wherein, the gas pressure of the closed environment is less than 90KPa.

[0017] Wherein, the magnetic field strength of the magnetic field is 1 mT to 10 T.

[0018] Wherein, the reaction time is 10s to 100min.

[0019] The sulfur-containing material has a sulfur content of not less than 0.1%; the sulfur-containing material is sulfur, sulfide or disulfide, or a mixture of several thereof.

[0020] The magnetic field lines are parallel to each other. This allows the MoS2 nanoarray to grow rapidly in height and width, while growing slowly in thickness, which is beneficial for growing thin layers of MoS2 nanoarrays over large areas. The magnetic field lines are aligned with the direction of the MoS2 nanoarray.

[0021] In one embodiment, the reactants are sulfur-containing materials and molybdenum sheets, which serve as both conductors (heat sources) and reactants.

[0022] In one embodiment, the reactants are a sulfur-containing substance and molybdenum oxide, wherein the molybdenum oxide is a mixture of one or both of molybdenum trioxide and molybdenum dioxide. In this case, a heat source for heating the raw materials is also included in the closed environment. The heat source is a metal conductor that can achieve heating, but other elements that can evaporate cannot be introduced into the heat source. Therefore, the heat source is preferably a molybdenum sheet. That is, when the raw materials are molybdenum trioxide and / or molybdenum dioxide, a heat source is also included during preparation. The heat source can be a molybdenum-containing conductor such as a molybdenum sheet. When the conductor is placed in a dynamic magnetic field, according to the principle of electromagnetic induction, an induced circular eddy current is generated inside the conductor, thereby achieving heating of the conductor. In the technical solution of the present invention, the sulfur-containing substance, molybdenum trioxide / molybdenum dioxide, and heat source (molybdenum sheet) are generally placed in contact, preferably, the sulfur-containing substance and molybdenum trioxide / molybdenum dioxide cover the surface of the heat source. In this way, during heating, the sulfur-containing substance can be rapidly heated by the molybdenum sheet, and the generated sulfur vapor molecules meet with molybdenum trioxide molecules on the substrate, thereby generating molybdenum disulfide. Alternatively, the sulfur-containing substance, molybdenum trioxide, and molybdenum sheet can be placed in a container, and then the container can be placed in a closed environment. The container can be a crucible, such as a porcelain crucible, a quartz crucible, or a graphite crucible. It should be noted that the molybdenum sheet, acting as a heat source, initially generates a relatively small amount of molybdenum vapor. However, since the vapor pressure of the molybdenum vapor formed by molybdenum oxide is saturated, the generation of molybdenum vapor from the molybdenum sheet is suppressed. Therefore, the molybdenum atoms generated by the molybdenum sheet and participating in the reaction in this case can be ignored.

[0023] The present invention adopts a magnetic transport competitive nucleation growth mechanism to prepare a molybdenum disulfide nanoarray with abundant edges. The present invention uses molybdenum-containing substances and sulfur-containing substances as raw material reactants, and grows the molybdenum disulfide nanoarray on a substrate in a vacuum magnetic levitation induction furnace. Utilizing the characteristic that the induced magnetic field can quickly heat metal materials, an induced magnetic field is applied to the heat source (molybdenum sheet). When the magnetic field lines intersect the molybdenum sheet, eddy currents are generated on the molybdenum sheet. The eddy currents heat the molybdenum sheet and then heat the molybdenum trioxide / molybdenum dioxide / molybdenum sheet and sulfur in the crucible. Molybdenum and sulfur are transported to the substrate surface under the constraint of a dynamic magnetic field, and molybdenum disulfide is rapidly planted and grown on the substrate surface to form a dendritic structure. Finally, a molybdenum disulfide nanoarray with abundant edges is obtained, and the molybdenum disulfide nanoarray is planted on the substrate surface.

[0024] Furthermore, when trace amounts of hydrogen are present in the reaction environment, the formation of sulfur-depleted zones can be accelerated, i.e., sulfur-depleted active interfaces are formed at the edge of the MoS2 nanostructure. This can induce the growth of the MoS2 nanosheet edges in two directions, resulting in an edge multiplication fractal phenomenon (EPM mechanism), ultimately yielding MoS2 nanoarrays with richer edges. At this point, the edges of the MoS2 grow competitively through hydrogen etching and magnetic transport, rapidly accumulating sulfur vacancies, adjusting the sulfur-to-molybdenum ratio, and proliferating in a fractal mechanism, with the degree of proliferation depending on the outcome of the competition between the two.

[0025] It should be noted here that there are many ways to generate a magnetic field in a closed environment, and here it mainly refers to the use of changing current to generate a dynamic electromagnetic field.

[0026] When a trace amount of hydrogen is contained, the gas in the enclosed space is generally a mixture of hydrogen and argon (or nitrogen). The mixed gas can be directly used to clean the vacuum chamber and adjusted to the gas pressure required for the experiment.

[0027] The beneficial effects of the present invention include:

[0028] (1) The molybdenum disulfide nanoarray of the present invention has an overall dendritic structure, which extends from the substrate to the edge. On the one hand, the molybdenum disulfide nanoarray of the present invention has abundant edges and correspondingly abundant active sites. On the other hand, the dendritic structure fully exposes the active sites of the molybdenum disulfide nanoarray of the present invention. As an independent electrode, the molybdenum disulfide nanoarray exhibits excellent catalytic hydrogen evolution performance and cyclic stability.

[0029] (2) Compared with existing preparation methods, the preparation method of the present invention requires simpler production equipment, has a shorter reaction time, and is faster to produce, with the fastest completion time being 1 minute. The preparation method of the present invention can plant molybdenum disulfide nanoarrays on a specified substrate and in a specific area.

[0030] (3) The edge structure of the obtained MoS2 nanoarray conforms to the fractal proliferation mechanism. The number of nanosheets making up the array is controllable, and the thickness can be controlled to 2-3 layers. The edge structure of the MoS2 nanoarray is realized by hydrogen infiltration, resulting in dense fractal proliferation at the edge.

[0031] (4) The preparation method of the present invention can obtain hydrogen with molybdenum disulfide nanoarrays with rich edges. The obtained nanoarrays exhibit excellent performance in the electrocatalytic hydrogen production process, including low overpotential and long service life. Compared with other methods, it is more conducive to scientific research promotion and industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the edge structure of the molybdenum disulfide nanoarray obtained in Examples 1 to 6.

[0033] Figure 2 These are the morphological characteristic diagrams of the molybdenum disulfide nanoarrays obtained in Examples 1 to 3.

[0034] Figure 3 These are the morphological characteristic diagrams of the molybdenum disulfide nanoarrays obtained in Examples 4 to 6.

[0035] Figure 4 Raman spectra of samples S1-H2, S1 and S4.

[0036] Figure 5 This is the peak intensity evolution trend of the samples from S4, S1 to S1-H2.

[0037] Figure 6 Crystal structure diagrams of samples S4, S1, S1-H2 and substrate.

[0038] Figure 7 HRTEM images of samples S1-H2.

[0039] Figure 8 The electrochemical HER performance of the MoS2 nanoarrays prepared in Examples 1 to 3.

[0040] Figure 9 The C of the MoS2 nanoarray prepared in Examples 1 to 3 dl Extract graph.

[0041] Figure 10 The electrochemical HER performance of the MoS2 nanoarrays obtained in Examples 4 to 6.

[0042] Figure 11 C of the MoS2 nanoarray obtained in Examples 4 to 6 dl Extract graph.

[0043] Figure 12 Schematic diagram of the principle of the molybdenum disulfide nanoarray of the present invention. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0045] Unless otherwise specified, the raw materials and reagents used in the present invention are commercially available.

[0046] Example 1

[0047] This embodiment is implemented in a vacuum magnetic levitation melting furnace, which uses alternating current to generate an electromagnetic field.

[0048] A method for preparing a molybdenum disulfide nanoarray comprises the following steps:

[0049] (1) Accurately weigh 40 mg of sulfur, 45 mg of molybdenum trioxide, and 5.5 g of molybdenum flakes. Place them in a crucible with the substrate (molybdenum mesh) tightly against the inner wall of the crucible. Then, place the porcelain crucible in a vacuum magnetic levitation melting furnace. The reaction raw materials are sulfur and molybdenum trioxide; the molybdenum flakes serve as the heat source.

[0050] (2) The current of the vacuum magnetic levitation melting furnace is set to 30A, and the reaction time is set to 60s. At this time, the magnetic field strength generated is approximately 0.03T.

[0051] (3) Use argon gas to clean the vacuum magnetic levitation melting furnace three times or more, maintain the gas pressure in the furnace at 10KPa, and then start the reaction for 60S.

[0052] (4) After the reaction is completed, the temperature is lowered to obtain a molybdenum disulfide nanoarray, and the obtained sample is named S4.

[0053] Example 2

[0054] The operating steps of this example are the same as those of Example 1, except that the S / Mo molar ratio in the raw material is 2 (i.e., the sulfur element is 20 mg), and the obtained sample is named S2.

[0055] Example 3

[0056] The operating steps of this example are the same as those of Example 1, except that the S / Mo molar ratio in the raw material is 1 (i.e., the sulfur element is 10 mg), and the obtained sample is named S1.

[0057] Example 4

[0058] This embodiment is implemented in a vacuum magnetic levitation melting furnace, which uses alternating current to generate an electromagnetic field. A method for preparing a molybdenum disulfide nanoarray includes the following steps:

[0059] (1) Accurately weigh 40 mg of sulfur, 45 mg of molybdenum trioxide, and 5.5 g of molybdenum flakes, respectively, and place them in a crucible with the substrate tightly attached to the inner wall of the crucible. Then, place the porcelain crucible into a vacuum magnetic levitation melting furnace.

[0060] (2) The current of the vacuum magnetic levitation melting furnace is set to 30A, and the reaction time is set to 60s. At this time, the magnetic field strength generated is approximately 0.03T.

[0061] (3) Use a mixture of 5% hydrogen and 95% argon to clean the vacuum magnetic levitation melting furnace three times or more, maintain the gas pressure in the furnace at 10Kpa, and then start the reaction for 60S.

[0062] (4) After the reaction is completed, the temperature is lowered to obtain a molybdenum disulfide nanoarray, and the obtained sample is named S4-H2.

[0063] Example 5

[0064] The operating steps of this example are the same as those of Example 4, except that the S / Mo molar ratio is 2 (i.e., the sulfur element is 20 mg), and the obtained sample is named S2-H2.

[0065] Example 6

[0066] The operating steps of this example are the same as those of Example 4, except that the S / Mo molar ratio is 1 (i.e., the sulfur element is 10 mg), and the obtained sample is named S1-H2.

[0067] Example 7

[0068] A method for preparing a molybdenum disulfide nanoarray comprises the following steps:

[0069] (1) Accurately weigh 0.32 g of sulfur and 0.96 g of molybdenum flakes, respectively, and place them in a crucible with the substrate (molybdenum mesh) tightly attached to the inner wall of the crucible. Then, place the porcelain crucible into a vacuum magnetic levitation melting furnace.

[0070] (2) The magnetic field strength generated by the vacuum magnetic levitation melting furnace is set to approximately 10T.

[0071] (3) Use argon gas to clean the vacuum magnetic levitation melting furnace three times or more, maintain the gas pressure in the furnace at 80KPa, and then start the reaction for 100 minutes.

[0072] (4) After the reaction is completed, the temperature is lowered to obtain the molybdenum disulfide nanoarray.

[0073] Example 8

[0074] A method for preparing a molybdenum disulfide nanoarray comprises the following steps:

[0075] (1) Accurately weigh 10 mg of sulfur, 38 mg of molybdenum dioxide, and 5.5 g of molybdenum flakes, respectively, and place them in a crucible with the substrate tightly attached to the inner wall of the crucible. Then, place the porcelain crucible into a vacuum magnetic levitation melting furnace.

[0076] (2) The magnetic field strength generated by the vacuum magnetic levitation melting furnace is set to approximately 1 mT.

[0077] (3) Use a mixture of 0.1% hydrogen + 99.9% argon to clean the vacuum magnetic levitation melting furnace three times or more, maintain the gas pressure in the furnace at 10KPa, and then start the reaction for 10S.

[0078] (4) After the reaction is completed, the temperature is lowered to obtain the molybdenum disulfide nanoarray.

[0079] Example 9

[0080] A method for preparing a molybdenum disulfide nanoarray comprises the following steps:

[0081] (1) Accurately weigh 19 mg of sulfur dioxide, 45 mg of molybdenum trioxide, and 2.76 g of molybdenum flakes, respectively, and place them in a crucible with the substrate tightly attached to the inner wall of the crucible. Then, place the porcelain crucible into a vacuum magnetic levitation melting furnace.

[0082] (2) The magnetic field strength generated by the vacuum magnetic levitation melting furnace is set to approximately 4T.

[0083] (3) Use a mixture of 10% hydrogen and 90% helium to clean the vacuum magnetic levitation melting furnace three times or more, maintain the gas pressure in the furnace at 30Kpa, and then start the reaction for 150S.

[0084] (4) After the reaction is completed, the temperature is lowered to obtain the molybdenum disulfide nanoarray.

[0085] Figure 1 The edge structure diagram of the molybdenum disulfide nanoarray obtained in Examples 1 to 6. Figure 1 a in the embodiment 1, Figure 1 b in the example 2, Figure 1 The sample c in the embodiment 3 is the sample.

[0086] like Figure 1 As shown in a, when the S / Mo molar ratio is 4, the MoS2 nanoarrays grow vertically on the surface of the molybdenum mesh, showing dense growth characteristics. Figure 1 As shown in Figure b, when the S / Mo molar ratio in the reactants is reduced to 2, newly generated sub-nanostructures can be observed on the surface of MoS2 nanosheets. Figure 1 As shown in Figure (c), when the molar ratio drops to 1, a large number of MoS2 secondary sheets grow densely along the sides of the nanosheets, forming a rich fractal structure in the edge area of sample S1.

[0087] Figure 2 A more detailed comparison of the morphological characteristics of samples S4, S2 and S1, where Figure 2 (ac) in the figure are the morphology images of sample S4, in which MoS2 nanosheets grow vertically on the substrate. Figure 2(df) in the figure are the morphology images of sample S2, where a small amount of secondary structures appear on the side of the MoS2 nanosheets. Figure 2 In the morphology of the (gi) sample S1, a rich fractal structure is formed at the edge of the MoS2 nanosheet. It is worth noting that when the S / Mo molar ratio drops to 2, the growth orientation of the MoS2 nanosheet changes from perpendicular to the substrate to parallel to the substrate, which may lay the foundation for the subsequent formation of the unique structure of S1. During the growth of S1, as the proportion of S in the DMF (dynamic magnetic field) transmission channel (i.e., the rapid transmission channel of gas molecules constructed by DMF) decreases, the edge area of the MoS2 nanostructure forms a sulfur-poor active interface due to the reduction of sulfur elements. When the concentration of sulfur vacancies accumulates to a certain level, the EPM mechanism (edge multiplication fractal phenomenon) is triggered, forming a rich fractal structure at the edge of S1. The newly generated structure is composed of smaller nanosheets.

[0088] Figure 1 The edge structure diagram of the molybdenum disulfide nanoarray obtained in Examples 1 to 6. Figure 1 The d in the figure is the sample of Example 4, Figure 1 The e in the figure is the sample of Example 5, Figure 1 The f in the figure is the sample of Example 6.

[0089] like Figure 1 As shown in df in Figure 3, adding hydrogen to the reaction systems of samples S4, S2, and S1 yields the micromorphological features of samples S4-H2, S2-H2, and S1-H2. It should be emphasized that adding hydrogen to the reaction system does not increase the number of reaction steps.

[0090] like Figure 1 As shown in Figure d, in the S4-H2 sample, although hydrogen was added, the EMP mechanism was not triggered, and the edges of the MoS2 nanosheets remained intact and did not bifurcate. When the sulfur content in the reactants is sufficient, a large number of sulfur molecules continuously reach the substrate surface, resulting in almost no sulfur vacancies at the edges of the MoS2 nanostructures, and no sulfur-poor active interface is formed. Even if hydrogen is added to the reaction system, even if the sulfur vacancies generated by hydrogen consumption of sulfur are quickly filled by saturated sulfur atoms, sulfur vacancies are difficult to accumulate, and the sulfur at the edges of the MoS2 nanosheets is always saturated, so the EMP mechanism can never be triggered. The morphology of the MoS2 nanosheet array in the S4-H2 sample is basically the same as that of sample S4.

[0091] like Figure 1As shown in Figure e, the edge structure of the sample S2-H2 nanosheets shows a clear fractal dense proliferation phenomenon. The top 200-300nm area is affected by hydrogen, forming a dense tree-like fractal structure. It is worth mentioning that the premise for the effectiveness of the EPM mechanism is that enough sulfur vacancies accumulate at the edge of the molybdenum disulfide nanosheets to form a sulfur-poor active area. Therefore, the higher the sulfur content reaching the substrate surface, the more difficult it is to accumulate sulfur vacancies, and the later the EPM mechanism takes effect. Only when the S / Mo molar ratio reaching the substrate surface is less than 2, the molybdenum disulfide nanosheets begin to grow fractally. Therefore, thanks to the rapid transport of molecules by the DMF transmission channel, the S element is relatively sufficient in the early growth of S2-H2, so the large logarithm of nanosheets still grows vertically. As the growth progresses, the sulfur element decreases, and hydrogen accelerates the effectiveness of the EMP mechanism, and the edge of the MoS2 nanoarray begins to fractal dense proliferation.

[0092] like Figure 1 As shown in figure f, when the S / Mo molar ratio in the reactants is further reduced to 1 (S1-H2), the edge density of the MoS2 nanoarray reaches a higher level. Due to the low sulfur content in the reactants, during the process of hydrogen accelerating the formation of sulfur-poor zones, the rapid accumulation of sulfur vacancies at the edge makes it easier to reach the threshold for the EPM mechanism to take effect. After the EPM mechanism is triggered, the newly formed MoS2 nanostructure will continue to accumulate sulfur vacancies during the growth process and continue to trigger the EPM mechanism, thereby causing a high-frequency proliferation phenomenon of the edge structure. For a more detailed comparison of the morphological characteristics of samples S4-H2, S2-H2 and S1-H2, see Figure 3 .

[0093] Figure 3 Figures ac are the morphology images of sample S4-H2, and the morphology of MoS2 nanosheets is not affected by the addition of hydrogen. Figure 3 df in the figure is the morphology of sample S2-H2. The top of the MoS2 nanosheet is affected by hydrogen and edge proliferation occurs. Figure 3 gi in the figure is the morphology of sample S1-H2, and exponential proliferation occurs at the edges of the nanosheets of the entire MoS2 nanoarray.

[0094] Figure 4 The Raman spectra of S1-H2, S1 and S4 samples are shown in the range of 350-450 cm -1 Two characteristic peaks can be observed in the range of . Among them, A originating from interlayer vibration 1g Peaks and peaks from in-plane vibrations The peak confirms the formation of MoS2. 1g Mode and The frequency difference (Δω) of the modes is usually used to determine the number of layers of MoS2. 1g and The peak position difference Δω is stable at 24.4 cm -1 This value clearly points to a 2-3 layer MoS2 nanostructure, and also shows that adjusting the S / Mo molar ratio and hydrogen treatment did not cause a change in the number of nanosheet layers in the MoS2 nanoarray.

[0095] Figure 5 The peak intensity evolution trend of samples from S4, S1 to S1-H2 is shown. 1g and The intensity of the characteristic peaks decreases in sequence, which corresponds to the gradual decrease in the size of the nanosheets in the MoS2 nanoarray. In addition, compared with the MoS2 grown on parallel substrates, the S4 and S1 samples show significantly enhanced Some studies have shown that the integral intensity ratio may be related to the local strain generated by the bending of the vertical MoS2 nanosheets during growth. The bending of the nanosheets induces strain to strengthen the interlayer vibration. The sharp decay of the intensity ratio is due to the fact that the nanosheet structure that makes up the MoS2 nanoarray becomes smaller after the addition of hydrogen, and the original bending-induced strain of the nanosheet disappears.

[0096] Figure 6 Figure a is the HRTEM image of sample S4, showing the MoS2 crystal structure observed from the

[001] direction. The HRTEM image of the S4 sample shows a complete MoS2 crystal structure along the

[001] crystal axis, with no obvious defects observed, confirming the high-quality 2H-type crystal structure of the MoS2 nanosheets. Figure 6 Figure b is the TEM image of S1, which shows a 120° step at the top edge. The edge of the MoS2 nanosheet presents a typical 120° angle feature, and its top edge profile structure is similar to the MoS2 morphology after contact with oxygen plasma, which may be related to the loss of sulfur molecules in the DMF transmission channel in the later stage of the reaction. Figure 6 Figure c is the crystal structure diagram of sample S1-H2. It can be observed that small holes less than 10 nm are generated on the S1-H2 basal plane. Figure 6 The d in the figure is that part of the molybdenum on the substrate of sample S1-H2 is reduced by hydrogen etching, resulting in the loss of molybdenum atoms as shown by the red arrows. Figure 6 As shown in Figures c and d, analysis of the S1-H2 sample found that hydrogen can accelerate the triggering of the EMP mechanism to promote high-density proliferation at the edge of MoS2 nanosheets. On the one hand, hydrogen forms nanopore structures with a diameter of less than 10nm on the basal surface of some MoS2 nanosheets. On the other hand, defects are generated by the loss of molybdenum atoms caused by hydrogen reduction reaction. The missing molybdenum atoms are marked by red arrows. Finally, the Moiré fringes ( Figure 7 ), indicating that there is a rotation angle of about 7° between adjacent MoS2 layers.

[0097] Figure 7 Moiré patterns can be observed in some parts of the HRTEM image of S1-H2, indicating that there is a slight rotation between the MoS2 layers. Figure 7 b in the figure is estimated based on SAED, and the rotation angle between MoS2 is about 7°.

[0098] The electrochemical performance test method is as follows:

[0099] Electrochemical tests were carried out using a standard three-electrode system in 0.5 M H2SO4 electrolyte.

[0100] The hydrogen evolution reaction (HER) performance of all samples in this study was tested using a CHI 760E electrochemical workstation manufactured by Shanghai Chenhua Instrument Co., Ltd. A conventional three-electrode system was used to evaluate their electrochemical properties in an argon-saturated electrolyte solution containing 0.5 M sulfuric acid. In all measurements, an Ag / AgCl electrode (containing a saturated KCl electrolyte solution) served as the reference electrode, and a graphite rod served as the counter electrode. All test samples were free-standing thin films grown on substrates, allowing for direct application to the working electrode without the need for any adhesive or conductive agent. For example, HER testing was performed on MoS2 nanoarrays grown on a Mo mesh. The mesh was 10 × 13 mm in size. During the seeding process, MoS2 nanosheets were grown only within the lower 10 × 10 mm area. During HER testing, the sample holder was clamped to the portion of the MoS2 nanoarray that was not grown, ensuring a test area of 10 × 10 mm. Before testing, the sample was briefly sonicated (<1 min) in 0.5 M sulfuric acid solution to fill the cavities within the array structure with liquid. In addition, for comparison, a Pt / C electrode was prepared by mixing commercial Pt / C (20%) with an ethanol solution of Nafion and then dropping it on a carbon fiber paper. The test was performed after vacuum drying. In this work, all potentials mentioned were calibrated and related to the reversible hydrogen electrode (RHE) by the following formula: E (RHE) =E (Ag / AgCl) +0.198+0.059×pH(V).

[0101] Electrochemical tests include the following: (1) Linear sweep voltammetry (LSV) curve: at 5 mV s -1 The LSV test is performed at a scan rate of 100 nm. By analyzing the Tafel curve obtained from the polarization curve, the Tafel slope can be further calculated to evaluate the kinetic characteristics of the hydrogen evolution reaction of the catalytic material and its reaction path. For example, when performing LSV testing on a MoS2 nanoarray planted on a molybdenum mesh surface, argon gas is passed through a 0.5 M sulfuric acid solution for 30 minutes before the test. The sample is then activated by cyclic voltammetry (CV) with a voltage range of -0.198 to -0.698 V and a scan rate of 50 mV s -1, scanning number 10 circles. LSV test conditions: magnetic stirring 520 rpm, voltage range 0~-0.698V, scanning speed 5mV s -1 Final data were obtained after iR compensation and plotted in Origin software, with voltage as the abscissa and current density as the ordinate. The Tafel slope was calculated using the formula η = a + b × log |J|, where η represents the overpotential, b is the Tafel slope, and J is the current density.

[0102] (2) Electrochemical impedance spectroscopy (EIS) test: For example, when performing EIS test on MoS2 nanoarrays planted on the surface of a molybdenum mesh, the test conditions are: the test is carried out at a potential of -0.25 V (vs. RHE), the AC amplitude is 5 mV, and the test frequency range is 100 kHz to 0.1 Hz. The solution resistance (R) of the catalytic material can be obtained by fitting the equivalent circuit using the Z View software. s ) and charge transfer resistance (R ct ). Among them, R s Reflects the impedance of the electrolyte between the working electrode and the counter electrode, R ct The charge transfer capability of the material and its electrochemical reaction kinetics can be characterized. The final data were plotted in Origin software, with Z ′ (Ωcm 2 ) as the horizontal coordinate of the image, with -Z ″ (Ωcm 2 ) as the vertical axis.

[0103] (3) Electrochemically active area (ECSA) test: ECSA and double layer capacitance (C dl ) is positively correlated, so through C dl ECSA can be evaluated. C dl It can be obtained by calculating the CV curve of the non-Faraday region at different scanning rates. For example, the C dl During the test, the test conditions of cyclic voltammetry scanning were: scanning range -0.198 ~ 0.098V, scanning number of 20 circles, and the sample was tested at five different scanning rates, which were set to 20, 40, 60, 80 and 100mV / s respectively. dl The graph was obtained by taking the data of the 20th cycle at each scanning speed and plotting it in Origin software, with voltage (V vs. RHE) as the horizontal axis and current density as the vertical axis. dlThe graph is obtained by taking the current density at a voltage of 0.05 V (V vs. RHE) at different scan rates. The scan rate is then used as the horizontal coordinate of the image, and the current density is used as the vertical coordinate to plot the graph. A linear fit is performed on the above five points, and the slope of the obtained linear function is the electrochemical active area of the sample.

[0104] The MoS2 nanoarrays grown on a molybdenum mesh substrate and the MoS2 nanoarrays grown on the molybdenum disulfide nanoarray substrate of the present invention were used as electrocatalyst systems to evaluate the hydrogen evolution reaction (HER) performance. Due to the self-supporting array structure, the MoS2 nanoarrays can be used as independent electrodes for HER without the addition of binders or conductive agents.

[0105] Figure 8 Electrochemical HER performance of MoS2 nanoarrays prepared with different S / Mo ratios. (a) is the scanning rate of 5mVs -1 (b) is the LSV curve of the current density of 10 mA cm -2 and 100mA cm -2 (c) is the Tafel slope plot. (d) is the Nyquist plot of the electrochemical impedance spectroscopy.

[0106] like Figure 8 As shown in (ab), after iR correction, the S1, S2, S4 and Mo mesh samples have a current density of 10 mA cm -2 The overpotentials (ηvs.RHE) were 234 mV, 247 mV, 256 mV and 341 mV respectively. It is worth noting that when the S / Mo molar ratio in the reactants decreases (S4→S2→S1 sequence), the catalyst -2 The overpotential of samples S4, S2, and S1 shows a step-wise decrease, which is highly consistent with the evolution trend of the edge structure density of the MoS2 nanoarray. Specifically, the significant reduction in the overpotential of samples S4, S2, and S1 is mainly due to the increase in the edge structure of the MoS2 nanoarray. Such structural features provide an efficient catalytic interface for the hydrogen adsorption / desorption process. Samples S1, S2, and S4 at 100 mA cm -2 The overpotentials at the catalytic current density were 323, 358 and 379 mV ( Figure 5-10 (ab)), which is consistent with the edge density evolution trend of MoS2 nanoarrays.

[0107] By plotting the logarithm of current density against overpotential ( Figure 8(c)), the Tafel slopes of S1, S2, S4 and Mo network were 77mV / dec, 82mV / dec, 84mV / dec and 152mV / dec respectively (corrected by iR). The Tafel slopes of samples S4, S2 and S1 showed a decreasing trend with the decrease of the S / Mo molar ratio in the reactants, indicating that the optimization of the edge structure of MoS2 nanoarrays can significantly improve the kinetic efficiency of the HER reaction. In addition, in order to further study the electrode kinetic characteristics of the HER process, the samples were tested by electrochemical impedance spectroscopy (EIS) ( Figure 8 (d)). Experimental data show that the charge transfer resistance (R ct ) shows a decreasing trend with the decrease of the S / Mo molar ratio in the reactants, which confirms that more edge active sites are successfully introduced during the increase of the edge structure density of MoS2 nanoarrays.

[0108] Through the electrochemical double layer capacitance (C dl )test( Figure 9 ), the electrochemically active specific surface area (ECSA) of the catalysts was evaluated. dl The values are 6.19mF cm -2 、9.98mF cm -2 and 11.8 mF cm -2 From S4 to S1, C dl The values show a gradual increase, and the electrochemically active specific surface area of the catalyst increases, indicating that the active sites of the MoS2 nanoarrays can be increased by reducing the S / Mo molar ratio in the reactants. Combined with the morphological analysis of S4, S2, and S1, the increased active sites mainly come from the rich fractal structure at the edge of the MoS2 nanoarrays.

[0109] Figure 10 The electrochemical HER performance of the MoS2 nanoarrays obtained in Examples 4 to 6. (a) Scan rate 5 mV s -1 LSV curve. (b) Current density is 10 mA cm -2 and 100mA cm -2 (c) Tafel slope plot. (d) Nyquist plot of electrochemical impedance spectroscopy.

[0110] like Figure 10 As shown in a and b, after iR correction, the S1-H2, S2-H2 and S4-H2 samples are -2The overpotentials (ηvs.RHE) were 182mV, 219mV and 228mV respectively. The reduction in the overpotential of samples S4-H2, S2-H2 and S1-H2 was mainly due to the fractal dense proliferation of the edge structure of the molybdenum disulfide nanoarrays achieved by the addition of hydrogen. In addition, hydrogen also introduced some defects on the basal plane of the MoS2 nanosheets, causing part of the MoS2 basal plane to be activated. The overpotentials of the samples with hydrogen added were all lower than those of the samples without hydrogen added, which shows that adding hydrogen is an effective means of reducing the overpotential. MoS2 nanoarrays showed good HER performance at high current density. Samples S1-H2, S2-H2, and S4-H2 at 100mA cm -2 At the catalytic current density of 1.5, 2.5 and 3.5 GHz, the overpotentials are 238, 278 and 293 mV, respectively.

[0111] By plotting the logarithm of current density against overpotential ( Figure 10 (c)), the Tafel slopes of S1-H2, S2-H2 and S4-H2 were 63mV / dec, 70mV / dec and 72mV / dec respectively (corrected by iR). After adding hydrogen treatment, the Tafel slopes of samples S4-H2, S2-H2 and S1-H2 also showed a decreasing trend, confirming that hydrogen can accelerate the fractal dense proliferation of the edge structure of MoS2 nanoarrays and introduce surface defects, which is beneficial to promote the rapid HER kinetic process. Figure 10 As shown in (d), further study of the electrode kinetics of the HER process revealed that the charge transfer resistances of S4-H2, S2-H2, and S1-H2 all decreased significantly, indicating that the in-situ hydrogen etching effectively increased the active edge density and surface defects of the MoS2 nanoarray.

[0112] Figure 11 C of the MoS2 nanoarray obtained in Examples 4 to 6 dl Extracted Figure. (bd) CV curves of S1-H2, S2-H2 and S4-H2 in the range of 0.1-0.2 V (vs. RHE). Electrochemical double layer capacitance test ( Figure 11 ), the electrochemical active surface area of the catalyst was evaluated. dl The values are 13.55mF cm -2 、23.39mF cm -2 and 62.24 mF cm -2 , showing a gradually increasing trend, which indicates that the ECSA of the catalyst is also gradually increasing. Among them, the S1-H2 sample with hydrogen added shows the highest C dl Value (62.24mF cm -2), reflecting that S1-H2 has an extremely high electrochemically active specific surface area, which is 10 times higher than that of S4, indicating that the active sites of MoS2 nanoarrays can be effectively increased by reducing the S / Mo molar ratio in the reactants and adding hydrogen.

[0113] The reaction mechanism of the preparation method of the molybdenum disulfide nanoarray of the present invention is shown in Figure 12 When the S / Mo molar ratio is greater than 2, the diffusion rate of sulfur in the van der Waals interlayers is greater than that between crystal planes, prompting the MoS2 nanosheets to grow perpendicular to the base, resulting in a structure similar to a smooth tree trunk planted in the ground. When the S / Mo molar ratio drops to ≤2, the edge of the MoS2 nanostructure depletes sulfur, forming a sulfur-depleted active interface. When the concentration of sulfur vacancies accumulates to a certain level, the reaction system enters a phase dominated by the EPM mechanism. New nanosheet nucleation and growth then propagate in two different directions. Secondary nucleation generates fractal structures at the nanosheet edges, leading to fractal proliferation of the MoS2 nanoarray edge structure. At this point, the MoS2 nanoarray structure resembles a dry tree with a few branches. When the MoS2 nanoarray is immersed in a hydrogen atmosphere during its growth, the hydrogen also accelerates the reduction of sulfur at the nanosheet edges, promoting the generation of sulfur vacancies and forming a sulfur-depleted active interface. Hydrogen accelerates the triggering of the EPM mechanism, leading to exponentially dense fractal growth at the edges of the MoS2 nanosheet array. Because the entire reaction system is uniformly immersed in the hydrogen atmosphere, the hydrogen also accelerates the reduction of sulfur at the nanosheet edges, promoting the generation of sulfur vacancies and forming a sulfur-depleted active interface. This hydrogen accelerates the triggering of the EPM mechanism, causing the edges of the MoS2 nanosheet array to grow densely and fractally. Whenever enough sulfur vacancies accumulate at the edge of a MoS2 nanostructure, the EPM mechanism is triggered. After the EPM mechanism is triggered, the newly formed MoS2 nanostructure will continue to accumulate sulfur vacancies during its growth process, further triggering the EPM mechanism, thereby achieving a short-term, high-density proliferation of the edge structure of the MoS2 nanoarray. The edge achieves explosive proliferation.

[0114] By optimizing the molar ratio of S / Mo in the reactants and adding hydrogen, a sulfur-poor active interface is formed at the edge of the newly generated MoS2 nanostructure, which can induce the edge of the MoS2 nanosheet to grow in two directions and show an edge multiplication fractal phenomenon (EPM mechanism). Relying on the rapid transmission capability of the DMF transmission channel, when the S / Mo in the reactants decreases, sulfur vacancies will accumulate in the edge of the MoS2 nanostructure to form an active interface, thereby triggering the EPM growth mechanism in subsequent growth. The addition of hydrogen further accelerates the accumulation rate of sulfur vacancies in the edge of the MoS2 nanostructure, promotes the triggering of the EPM growth mechanism, and thus realizes the rapid explosive proliferation of the edge structure of the MoS2 nanoarray in a short period of time. HER tests show that the optimal sample is 100mA cm -2 The overpotential at this current density is only 238 mV, and the electrode structure remains stable after 24 hours of continuous operation at this current density, demonstrating excellent catalytic durability.

[0115] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0116] Any portions not described in detail in this specification are known in the art. The above embodiments are provided for illustrative purposes only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications that do not depart from the spirit and principles of the present invention are intended to be encompassed within the scope of the present invention.

Claims

1. A molybdenum disulfide nanoarray, characterized in that: The molybdenum disulfide nanoarray grows vertically on the substrate. The molybdenum disulfide nanoarray has a dendritic structure as a whole, and the dendritic structure extends from the substrate to the edge.

2. The molybdenum disulfide nanoarray according to claim 1, characterized in that The edge of the molybdenum disulfide nanoarray is composed of several nanosheets.

3. The method for preparing a molybdenum disulfide nanoarray according to claim 1 or 2, characterized in that: The steps include: Place the raw materials and substrate in a closed environment; generating a magnetic field in the enclosed environment and ensuring that the raw material and substrate are placed in the magnetic field; After a certain reaction time, the magnetic field is stopped; the reaction time is 10s to 100min; After cooling, the molybdenum disulfide nanoarray can be obtained, and the molybdenum disulfide nanoarray is located on the surface of the substrate; The atomic ratio of S to Mo in the raw material is less than or equal to 2.

4. The method according to claim 3, characterized in that The sealed environment contains a trace amount of hydrogen, and the volume percentage of the trace amount of hydrogen is 0.1-10%.

5. The method according to claim 3, characterized in that The gas pressure of the closed environment is less than 90 KPa; and / or the magnetic field strength of the magnetic field is 1 mT to 10 T.

6. The method according to claim 3, characterized in that The magnetic field lines are parallel to each other.

7. The method according to claim 3, characterized in that The reactants are sulfur-containing substances and molybdenum sheets.

8. The method according to claim 3, characterized in that The reactants are sulfur-containing materials and molybdenum oxide, wherein the molybdenum oxide is one or a mixture of molybdenum trioxide or molybdenum dioxide, and a heat source for heating the raw materials is also included in a closed environment.

9. The method according to claim 7 or 8, characterized in that The sulfur content of the sulfur-containing material is not less than 0.1%; the sulfur-containing material is one or a mixture of sulfur, sulfide or disulfide.

10. Use of the molybdenum disulfide nanoarray according to claim 1 or 2 in hydrogen evolution reaction.

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