Method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nano material based on iron foam and application

Abstract

The invention provides a method for in-situ preparation of a Ni-Fe7S8 / MoS2 heterojunction nano material based on iron foam and application of the Ni-Fe7S8 / MoS2 heterojunction nano material, and belongs to the technical field of nano material synthesis. Comprising the following steps: dissolving thioacetamide, sodium molybdate and nickel nitrate in deionized water, and fully stirring until the thioacetamide, the sodium molybdate and the nickel nitrate are completely dissolved to obtain a mixed reaction solution; transferring the mixed reaction solution into a high-pressure reaction kettle, then adding iron foam as a Fe source and a framework, and heating and preserving heat until the reaction is finished; and after the high-pressure reaction kettle is cooled to the room temperature, the iron foam is taken out and washed and dried, and the Ni-Fe7S8 / MoS2 heterojunction nanometer material is obtained. According to the method, the Ni-doped Fe7S8 / MoS2 heterojunction nano material is grown on the iron foam in situ by adopting a one-step hydrothermal method, so that the problems of high raw material cost, difficult synthesis and poor electrode stability are solved, low-cost and efficient synthesis is realized, the electrode stability is improved, and the preparation method is suitable for industrial production. And the excellent catalytic performance of low overpotential, fast dynamics and high charge transfer rate in hydrogen preparation through electrochemical catalysis of water decomposition is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterial synthesis, and particularly to a method for in-situ preparing Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam and applications thereof. Background Art

[0002] Due to the increasing energy consumption and environmental pollution, traditional energy will inevitably be replaced by more environmentally friendly new energy. As an important secondary energy source, hydrogen energy has attracted much attention because of its many advantages such as rich sources, environmental friendliness, high combustion calorific value, diverse utilization forms, and wide application fields, and is regarded as the cleanest energy source with the greatest development potential in the 21st century.

[0003] At present, the main hydrogen production routes include traditional fossil energy hydrogen production and renewable energy hydrogen production based on water, solar energy, wind energy, and biomass energy. Producing hydrogen through electrolysis technology is the most environmentally friendly hydrogen production process without environmental pollution and has broad development space in the future. The electrolytic water hydrogen production technology changes the redox potential of water by electrolysis and decomposes it to produce O2 and H2. At room temperature, the overall reaction equation for water electrolysis is 2H2O + electricity → 2H2 + O2. This process consists of two half-reactions, namely the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). At room temperature and standard atmospheric pressure, the minimum theoretical voltage required to drive the hydrogen evolution reaction and the oxygen evolution reaction is 1.23V, ΔG = 274.2kJ / mol. Therefore, the reaction must have additional energy to occur. The cathodic HER is a relatively easy two-electron process and can proceed at a low overpotential. However, the anodic OER, as the electron donor of HER, is a more complex four-electron process with the disadvantage of slow kinetics and requires a higher overpotential to drive the reaction, which limits the overall electrolytic water efficiency and seriously hinders the practical application of electrolytic water. Therefore, developing new strategies to obtain high-performance OER catalysts remains one of the most important tasks in the field of electrolytic water research. Noble metal-based materials (such as iridium / ruthenium oxides) are the most effective OER electrocatalysts. However, their high cost and low abundance limit their applications.

[0004] In addition, the low price of non-noble metals is more conducive to development and utilization. Transition metal dichalcogenides (TMDs) can exhibit different phases: 1T (tetragonal), 2H (hexagonal), and 3R (trigonal lattice). And they have a unique graphite-like layered structure, are relatively more flexible in morphology, and can better combine with dopants. In addition, there are various synthesis methods for TMDs. Therefore, TMDs are expected to play an important role in the field of electrocatalysis. Among them, MoS2 has a unique two-dimensional structure, multiple crystal phases, and can achieve mutual transformation. Its 2H phase with semiconductor properties can be chemically transformed into the metastable metallic 1T phase, improving the catalytic performance. Therefore, it is considered a promising catalyst. Compared with other transition metal dichalcogenides, iron-based sulfides have significant advantages. First, iron sulfide is the most widely distributed sulfide in the earth's crust and can form in various geological structures. Second, iron has the lowest price among non-noble metals. Third, iron-sulfur clusters are catalytically active sites for some chemical reactions, such as proton reduction and nitrogen reduction. Therefore, iron-based sulfides are also often used in the synthesis of catalysts.

[0005] To further improve the activity of electrocatalysts, constructing heterogeneous interfaces to increase the defects of materials, increase the active sites of catalysts, and optimize the adsorption and desorption of intermediates has been considered an effective strategy for preparing electrocatalysts. Qi et al. successfully designed and prepared freestanding, defect-rich heterogeneous MoS2 / NiS2 nanosheets and used them as bifunctional electrocatalysts for overall water splitting. The resulting MoS2 / NiS2 interface has abundant defects and a disordered structure, which can modify the electronic interaction, promote the movement of electrons, and is beneficial to the electrocatalytic reaction. Element doping can trigger phase transformation and change the electron density, which is also a commonly used strategy for catalyst preparation. Zhu et al. studied the hydrothermal synthesis method of W-doped MoS2 with environmental stability and a high concentration of the 1T phase. The proportion of the 1T phase in the prepared molybdenum disulfide can be as high as 80%, the environmental stability can reach more than one year, and it has excellent HER performance; combining the construction of heterogeneous interfaces and element doping can further adjust the electron cloud density of the heterogeneous interface and thus improve the catalytic activity. Ge et al. developed a bifunctional electrocatalyst Co-FeS / MoS2 through a simple two-step solvothermal method. The prepared catalyst inherits the structural characteristics of the original MOF, maintains a large surface area and abundant active sites, and Co doping induces the redistribution of the electric field at the FeS and MoS2 heterojunction interface, optimizing the adsorption ability of reaction intermediates, thus showing excellent electrocatalytic activity. The above research shows that the simultaneous application of heterogeneous structures and doping means can effectively improve the OER performance of catalysts. Although the above progress has been made, the methods for synthesizing catalysts are still relatively complex, mostly two-step methods or even multi-step methods, which are time-consuming, have poor repeatability, are prone to waste of raw materials, and increase costs. Moreover, the synthesized powder electrocatalysts need to be loaded on conductive electrodes using binders such as Nafion. Since a large amount of gas is generated on the electrode surface during water electrolysis, the catalyst is prone to fall off, making it difficult to achieve stable catalysis at high currents for a long time. Therefore, it is a significant but challenging task to prepare high-performance transition metal-based heterojunction nanomaterial electrocatalysts for catalytic water splitting using a simplified catalyst synthesis route.

[0006] In summary, the existing technologies have various defects and deficiencies, specifically: noble metal-based catalysts are not suitable for large-scale production due to their high price and low reserves; the synthesis route of electrocatalysts is too complex, time-consuming and laborious, with poor repeatability and prone to waste of raw materials; electrocatalysts often need to be loaded on conductive electrodes using binders such as Nafion, and have poor stability. Summary of the Invention

[0007] To overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method and application for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam. By using a one-step hydrothermal method to in-situ grow Ni-doped Fe7S8 / MoS2 heterojunction nanomaterials on iron foam, the problems of high raw material cost, difficult synthesis, and poor electrode stability are solved, realizing low-cost and efficient synthesis, improving electrode stability, and obtaining excellent catalytic performance with low overpotential, fast kinetics, and high charge transfer rate in the electrochemical catalytic water splitting for hydrogen production.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] One of the purposes of the present invention is to provide a method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam, including the following steps:

[0010] S1. Dissolve thioacetamide, sodium molybdate, and nickel nitrate in deionized water, and stir thoroughly with a magnetic stirrer until completely dissolved to obtain a mixed reaction solution;

[0011] S2. Transfer the mixed reaction solution to a high-pressure reaction kettle, then add pretreated iron foam as the Fe source and act as the skeleton, and heat and keep warm until the reaction ends;

[0012] S3. After the high-pressure reaction kettle is cooled to room temperature, take out the iron foam, wash and dry the iron foam to obtain Ni-Fe7S8 / MoS2 heterojunction nanomaterials.

[0013] Preferably, in step S1, the mass of thioacetamide is 125-250 mg, the mass of sodium molybdate is 81-162 mg, and the molar ratio of sodium molybdate to thioacetamide is 1:5; the mass of nickel nitrate is 5-20 mg, the volume of deionized water is 30-60 mL, and the ratio of sodium molybdate to deionized water in g:mL is 81:35000.

[0014] Preferably, in step S2, the pretreatment process of the iron foam is: successively clean the iron foam with hydrochloric acid, deionized water, and ethanol, and finally dry it; the specification of the iron foam is 4 cm * 1 cm * 0.1 cm to 6 cm * 3 cm * 0.1 cm, and the ratio of the iron foam to sodium molybdate in cm 3 :mmol is 4:3.

[0015] Preferably, in step S2, the heating and insulation is to transfer the high-pressure reaction kettle to a heating device and heat it to 150-230 °C, and the insulation time is 12-24 h.

[0016] Preferably, in step S3, the process of washing and drying the iron foam is as follows: taking out the iron foam from the autoclave, then washing it several times alternately with deionized water and absolute ethanol, and finally drying it in a vacuum drying oven for 8 - 12 h.

[0017] The second object of the present invention is to provide a Ni - Fe7S8 / Mo S2 heterojunction nanomaterial prepared by the above - mentioned method.

[0018] The third object of the present invention is to provide an electrode prepared from the Ni - Fe7S8 / Mo S2 heterojunction nanomaterial prepared by the above - mentioned method.

[0019] The fourth object of the present invention is to provide a battery prepared from the Ni - Fe7S8 / Mo S2 heterojunction nanomaterial prepared by the above - mentioned method.

[0020] The fifth object of the present invention is to provide a catalyst prepared by the above - mentioned method.

[0021] The sixth object of the present invention is to provide an application of the Ni - Fe7S8 / Mo S2 heterojunction nanomaterial prepared by the above - mentioned method in electrochemically catalytic water splitting for hydrogen production.

[0022] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0023] (1) In the selection of raw materials, the present invention uses Mo - and Fe - based materials rich in the earth as raw materials, which are inexpensive and easy to obtain. Compared with using noble - metal - based catalysts, it has a significant cost advantage.

[0024] (2) The present invention synthesizes the catalyst by a one - step hydrothermal method. Compared with the multi - step method, the operation is simple, the production time can be significantly shortened, the raw material loss can be reduced, and the repeatability is good, reducing the production complexity and cost.

[0025] (3) The present invention directly uses iron foam as the iron source and conductive electrode, which improves the conductivity, avoids adding an additional iron source, and saves raw materials; the generated Fe7S8 by sulfidation has good OER performance and can effectively induce high - efficiency OER catalytic activity; at the same time, avoiding the use of binders such as Nafion improves the electrode stability, enabling it to stably catalyze for a long time at a large current density, and showing excellent performance in electrochemically catalytic water splitting for hydrogen production. For example, at a current density of 100 mA / cm 2 the over - potential is as low as 260.1 mV, the Tafel slope is low, and the charge transfer rate is fast. Description of the Drawings

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0027] Figure 1 Flow chart of a method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam according to the present invention;

[0028] Figure 2 SEM spectrum of the Ni-Fe7S8 / MoS2 heterojunction nanomaterials provided by the present invention;

[0029] Figure 3 Sample morphology diagram of the Ni-Fe7S8 / MoS2 heterojunction nanomaterials provided by the present invention, showing nanoflowers supported on nanosheets;

[0030] Figure 4 Electrochemical performance comparison diagram of the Ni-Fe7S8 / MoS2 heterojunction nanomaterials prepared in Examples 1-3 of the present invention;

[0031] Figure 5 Tafel slope (Tafel) comparison diagram of the Ni-Fe7S8 / MoS2 heterojunction nanomaterials prepared in Examples 1-3 of the present invention;

[0032] Figure 6 Impedance (EIS) comparison diagram of the Ni-Fe7S8 / MoS2 heterojunction nanomaterials prepared in Examples 1-3 of the present invention. Detailed implementation manners

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0034] To make the above objects, features, and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0035] As Figure 1 shown, the present invention provides a method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam, including the following steps:

[0036] S1. Dissolve thioacetamide, sodium molybdate and nickel nitrate in deionized water, and stir well with a magnetic stirrer until completely dissolved to obtain a mixed reaction solution;

[0037] S2. Transfer the mixed reaction solution to a high-pressure reactor, then add iron foam as the Fe source and act as the skeleton, and heat and keep warm until the reaction ends;

[0038] S3. After the high-pressure reactor cools to room temperature, take out the iron foam, wash and dry the iron foam to obtain the Ni-Fe7S8 / MoS2 heterojunction nanomaterial.

[0039] Among them, in step S1, the mass of thioacetamide is 125-250 mg, the mass of sodium molybdate is 81-162 mg, and the molar ratio of sodium molybdate to thioacetamide is 1:5; the mass of nickel nitrate is 5-20 mg, the volume of deionized water is 30-60 mL, and the ratio of sodium molybdate to deionized water in g:mL is 81:35000.

[0040] In step S2, the specifications of the iron foam are 4 cm * 1 cm * 0.1 cm to 6 cm * 3 cm * 0.1 cm, and the ratio of the iron foam to sodium molybdate in cm 3 :mmol is 4:3. The heating and heat preservation is to transfer the high-pressure reactor to a heating device and heat it to 150-230 °C, and the heat preservation time is 12-24 h.

[0041] In step S3, the process of washing and drying the iron foam is as follows: take out the iron foam from the high-pressure reactor, then wash it several times alternately with deionized water and absolute ethanol, and finally place it in a vacuum drying oven and dry it for 8-12 h.

[0042] Figure 2 This is the SEM image of the Ni-Fe7S8 / MoS2 heterojunction nanomaterial provided by the present invention. Refer to Figure 2 It can be seen that the Ni-Fe7S8 / MoS2 heterojunction nanomaterial has a uniform microstructure; Figure 3 This is the sample morphology diagram of the Ni-Fe7S8 / MoS2 heterojunction nanomaterial provided by the present invention, which is a nanosheet-supported nanoflower diagram. Refer to Figure 3 It can be seen that the morphology of the Ni-Fe7S8 / MoS2 heterojunction nanomaterial is a structure of nanoflowers supported on nanosheets.

[0043] As a possible implementation manner of the present invention, the Ni-Fe7S8 / MoS2 heterojunction nanomaterial prepared by the above method can be used to prepare an electrode.

[0044] As a possible implementation mode of the present invention, the Ni-Fe7S8 / MoS2 heterojunction nanomaterial prepared by the above method can be used to prepare a battery.

[0045] As a possible implementation mode of the present invention, the Ni-Fe7S8 / MoS2 heterojunction nanomaterial prepared by the above method can be used to prepare a catalyst.

[0046] As a possible implementation mode of the present invention, the Ni-Fe7S8 / MoS2 heterojunction nanomaterial prepared by the above method can be applied to the electrochemical catalytic decomposition of water to produce hydrogen.

[0047] The technical solution of the present invention will be further elaborated below through specific examples.

[0048] Example 1

[0049] In this example, the preparation method process of the Ni-Fe7S8 / MoS2 heterojunction nanomaterial is as follows: First, weigh 81 mg of sodium molybdate, 125 mg of thioacetamide, and 5 mg of nickel nitrate, and add 35 mL of deionized water. Stir with a magnetic stirrer at room temperature for 30 min to obtain a mixed reaction solution. Subsequently, transfer the well-stirred mixed reaction solution to a stainless steel autoclave with a Teflon liner, and add iron foam pretreated and dried with hydrochloric acid, deionized water, and ethanol. The specification of the iron foam is 4.4 cm * 1 cm * 0.1 cm; then place the stainless steel autoclave in an oven and keep it at 200 °C for 18 h. Finally, wait for it to cool to room temperature, take out the reacted iron foam, and at this time, the surface of the iron foam is covered with a uniform black product. Finally, wash the iron foam several times alternately with deionized water and ethanol, and then place it in a vacuum drying oven at 60 °C for 12 h. The obtained product is the Ni-Fe7S8 / MoS2 heterojunction nanomaterial, where the molar ratio of Ni:Mo is 1:20.

[0050] Example 2

[0051] In this embodiment, the preparation method process of the Ni-Fe7S8 / MoS2 heterojunction nanomaterial is as follows: First, weigh 81 mg of sodium molybdate, 125 mg of thioacetamide, and 10 mg of nickel nitrate, and add 35 mL of deionized water. Stir with a magnetic stirrer at room temperature for 30 min to obtain a mixed reaction solution. Subsequently, transfer the well-stirred mixed reaction solution to a stainless-steel autoclave lined with Teflon, and add iron foam pretreated and dried with hydrochloric acid, deionized water, and ethanol. The specification of the iron foam is 4.4 cm * 1 cm * 0.1 cm. Then, place the stainless-steel autoclave in an oven and maintain it at 200 °C for 18 h. Finally, wait for it to cool to room temperature, take out the reacted iron foam, and at this time, the surface of the iron foam is covered with a uniform black product. Finally, wash the iron foam several times alternately with deionized water and ethanol, and then place it in a vacuum drying oven at 60 °C for 12 h. The obtained product is the Ni-Fe7S8 / MoS2 heterojunction nanomaterial, where the molar ratio of Ni:Mo is 1:10.

[0052] Example 3

[0053] In this embodiment, the preparation method process of the Ni-Fe7S8 / MoS2 heterojunction nanomaterial is as follows: First, weigh 81 mg of sodium molybdate, 125 mg of thioacetamide, and 20 mg of nickel nitrate, and add 35 mL of deionized water. Stir with a magnetic stirrer at room temperature for 30 min to obtain a mixed reaction solution. Subsequently, transfer the well-stirred mixed reaction solution to a stainless-steel autoclave lined with Teflon, and add iron foam pretreated and dried with hydrochloric acid, deionized water, and ethanol. The specification of the iron foam is 4.4 cm * 1 cm * 0.1 cm. Then, place the stainless-steel autoclave in an oven and maintain it at 200 °C for 18 h. Finally, wait for it to cool to room temperature, take out the reacted iron foam, and at this time, the surface of the iron foam is covered with a uniform black product. Finally, wash the iron foam several times alternately with deionized water and ethanol, and then place it in a vacuum drying oven at 60 °C for 12 h. The obtained product is the Ni-Fe7S8 / MoS2 heterojunction nanomaterial, where the molar ratio of Ni:Mo is 1:5.

[0054] Example 4

[0055] For the three products prepared according to Examples 1 to 3 respectively, an electrochemical workstation using a standard three-electrode system was used at room temperature to conduct electrochemical tests on the three product samples in 1.0 M KOH. The working electrode on the iron foam (IF) was made of Ni-Fe7S8 / MoS2@IF. It was calibrated with reference and converted to the reversible hydrogen electrode (RHE) through the formula.

[0056] E RHE = E (Hg / HgO)+0.89;

[0057] Before each OER test, the three - electrode system was bubbled with high - purity oxygen for 30 minutes. To explore the OER activity, linear sweep voltammetry tests were carried out at a rate of 5 mV / s in the voltage range of 0 V to 1.8 V. EIS measurements were obtained in the frequency range of 0.01 - 10 5 Hz and were fitted by Zview software. The Hg / HgO electrode in 1 M aqueous KOH solution was used as the reference electrode.

[0058] After the above - mentioned electrochemical tests were completed, the test data were analyzed, and the results were as Figures 4 to 6 shown. From the performance comparison of the Ni - Fe7S8 / MoS2 heterojunction nanomaterials prepared in Example 1, Example 2, and Example 3 in Figure 4 , it can be seen that for the catalyst prepared with the addition of 10 mg of nickel nitrate, that is, the molar ratio of Ni:Mo is 1:10, its electrochemical performance is better than that when the addition amount of nickel nitrate is 5 mg, that is, the molar ratio of Ni:Mo is 1:20, and 20 mg, that is, the molar ratio of Ni:Mo is 1:5. Especially at a current density of 100 mA / cm 2 , the over - potential of this catalyst is only 260.1 mV, showing excellent electrochemical performance. Figure 5 is the Tafel slope comparison chart of the Ni - Fe7S8 / MoS2 heterojunction nanomaterials prepared in Example 1, Example 2, and Example 3. It was found by comparison that when 10 mg of nickel nitrate was added, that is, the molar ratio of Ni:Mo was 1:10, the Tafel slope was the lowest, indicating that this catalyst has a faster kinetics during the reaction and can promote the reaction more efficiently. Looking at Figure 6 the impedance diagrams of the catalysts obtained from different examples, the catalyst prepared in Example 2 has the smallest impedance. This means that in the electrochemical reaction, the catalyst in Example 2 has a faster charge transfer rate and can transfer electrons more quickly, further improving the catalytic efficiency. Comprehensive Figures 4 to 6 results fully prove the advantages of the catalyst prepared with the addition of 10 mg of nickel nitrate in terms of electrochemical catalytic performance when preparing Ni - Fe7S8 / MoS2 heterojunction nanomaterials, and also provide an important basis for the optimization of this material in practical applications.

[0059] Through Figures 4 to 6 comparative analysis of the electrochemical performance, Tafel slope, and impedance of the Ni - Fe7S8 / MoS2 heterojunction nanomaterials prepared in Example 1, Example 2, and Example 3, the influence of different addition amounts of nickel nitrate on the material performance has been visually presented. To more clearly and comprehensively display these performance differences, the specific data are summarized in Table 1. Table 1 records the material at 100 mA / cm under different Ni:Mo molar ratios 2Key performance indicators such as overpotential and Tafel slope at current density. See Table 1:

[0060] Table 1 Performance comparison data

[0061]

[0062] From the data in Table 1, it can be seen that when 10 mg of nickel nitrate is added, that is, when the Ni:Mo molar ratio is 1:10, the advantages of the prepared Ni-Fe7S8 / MoS2 heterojunction nanomaterial in terms of various performances are as follows, which is Figures 4 to 6 completely consistent with the trend reflected, and further provides strong data support for the performance research and application of the prepared Ni-Fe7S8 / MoS2 heterojunction nanomaterial.

[0063] Therefore, the above method for in-situ preparing Ni-Fe7S8 / MoS2 heterojunction nanomaterial based on iron foam and its application, by using a one-step hydrothermal method to in-situ grow Ni-doped Fe7S8 / MoS2 heterojunction nanomaterial on iron foam, solves the problems of high raw material cost, difficult synthesis and poor electrode stability, realizes low-cost and efficient synthesis, improves electrode stability, and obtains excellent catalytic performance with low overpotential, fast kinetics and high charge transfer rate in electrocatalytic water splitting for hydrogen production.

[0064] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0065] Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam, characterized in that: The following steps are involved: S1, dissolving thioacetamide, sodium molybdate and nickel nitrate in deionized water, and stirring them fully with a magnetic stirrer until they are completely dissolved to obtain a mixed reaction solution; S2, transferring the mixed reaction liquid to a high-pressure reactor, then adding the pretreated iron foam as an Fe source and serving as a skeleton, and heating and keeping warm until the reaction is completed; S3. After the high-pressure reactor is cooled to room temperature, the iron foam is taken out, and the iron foam is washed and dried to obtain Ni-Fe7S8 / MoS2 heterojunction nanomaterials.

2. The method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam according to claim 1, characterized in that: In step S1, the mass of the thioacetamide is 125-250 mg, the mass of the sodium molybdate is 81-162 mg, and the molar ratio of the sodium molybdate to the thioacetamide is 1:5; the mass of the nickel nitrate is 5-20 mg, the volume of the deionized water is 30-60 mL, and the ratio of the sodium molybdate to the deionized water is 81:35000 in g:mL.

3. The method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam according to claim 1, characterized in that: In step S2, the pretreatment process of the iron foam is: using hydrochloric acid, deionized water, and ethanol to wash the iron foam in sequence, and finally drying; the specifications of the iron foam are 4cm*1cm*0.1cm~6cm*3cm*0.1cm, and the iron foam and sodium molybdate are mixed at a ratio of cm 3 :mmol, the ratio is 4:

3.

4. The method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam according to claim 3, characterized in that: In step S2, the heating and heat preservation is to transfer the high-pressure reactor to a heating device and heat it to 150-230° C. for a heat preservation time of 12-24 hours.

5. The method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam according to claim 1, characterized in that: In step S3, the process of washing and drying the iron foam is as follows: the iron foam is taken out from the high-pressure reactor, then washed alternately with deionized water and anhydrous ethanol for several times, and finally placed in a vacuum drying oven for drying for 8 to 12 hours.

6. A Ni-Fe7S8 / MoS2 heterojunction nanomaterial prepared by the method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterial based on iron foam as described in any one of claims 1 to 5.

7. An electrode prepared from Ni-Fe7S8 / MoS2 heterojunction nanomaterials prepared by the method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam as described in claim 6.

8. A battery prepared with Ni-Fe7S8 / MoS2 heterojunction nanomaterials prepared by the method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam as described in claim 6.

9. A catalyst prepared by the method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam as described in any one of claims 1 to 5.

10. An application of Ni-Fe7S8 / MoS2 heterojunction nanomaterials prepared by the method for in-situ preparation of Ni-Fe7S8 / MoS2 heterojunction nanomaterials based on iron foam as described in any one of claims 1 to 5 in electrochemical catalytic decomposition of water to produce hydrogen.

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