A nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst, its preparation method and application

Abstract

This invention relates to a nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst, its preparation method, and its application. The preparation method includes: dispersing and dissolving mesoporous carbon powder to obtain mesoporous carbon ink; drop-coating the mesoporous carbon ink onto nickel foam, drying it, and then calcining it to obtain a self-supporting mesoporous carbon precursor; preparing an electroplating solution containing nickel and molybdenum salts, placing the self-supporting mesoporous carbon precursor as a substrate in the electroplating solution; and growing nanocrystalline particulate nickel-molybdenum bimetallic alloy in situ on the surface of the self-supporting mesoporous carbon precursor substrate by constant current electrodeposition to obtain the nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen evolution catalysts, specifically relating to a nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst, its preparation method, and its application. Background Technology

[0002] With rapid global industrial development and population growth, global energy demand is increasing dramatically, projected to reach at least 10 megawatts (TW) by 2050. Traditional fossil fuels are non-renewable energy sources, and their large-scale use inevitably leads to a severe energy crisis and environmental pollution. Therefore, developing efficient and clean energy is of paramount importance. In recent years, hydrogen (H2) has attracted considerable attention due to its high energy density and the fact that its only combustion byproduct is pollution-free water, making it a promising energy carrier and a potential alternative to future low-carbon energy systems. Currently, large-scale hydrogen production in industry primarily utilizes alkaline water electrolysis. However, this technology suffers from high overpotential during the hydrogen evolution reaction (HER) at the cathode and high energy consumption. Therefore, reducing the cell voltage required for water electrolysis is crucial for achieving efficient and energy-saving hydrogen production through water electrolysis.

[0003] Studies have shown that molybdenum (Mo)-based electrocatalysts exhibit high activity and excellent stability over a wide pH range. Furthermore, the Earth's crust is rich in Mo, and the low cost of preparation makes them promising candidates to replace expensive Pt-based metal HER catalysts. In alkaline media, Ni-Mo is currently the most studied binary alloy, and its performance ranking is: Ni-Mo > Co-Mo > Fe-Mo. The d electrons in the metallic bonds of Ni-Mo alloys can be shared. The alloying of near-d-filled nickel and molybdenum with half-empty d orbitals constitutes a synergistic effect of d electrons, which can significantly improve the activity of hydrogen evolution electrocatalysis.

[0004] Currently, most hydrogen evolution catalysts are based on nickel foam, but its small specific surface area, poor conductivity, and limited number of active sites significantly restrict its development. To overcome these drawbacks, carbon materials can be used as catalyst supports, offering advantages such as high conductivity, large specific surface area, favorable metal phase reduction, and excellent alkali resistance. Therefore, developing simple and reproducible synthesis processes is crucial for preparing NiMo@C-type materials with excellent electrocatalytic hydrogen evolution performance and good stability. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing and applying a nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst, thereby solving the problems of low electrocatalytic hydrogen evolution performance, high price, poor stability, and complex preparation process of existing hydrogen evolution catalysts.

[0006] Specifically, in the first aspect, the present invention provides a method for preparing a nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst, comprising: Mesoporous carbon powder is dispersed and dissolved to obtain mesoporous carbon ink; the mesoporous carbon ink is drop-coated onto nickel foam, dried, and then calcined to obtain a self-supporting mesoporous carbon precursor. An electroplating solution containing nickel and molybdenum salts was prepared, and the self-supporting mesoporous carbon precursor was placed in the electroplating solution as a substrate. Nanocrystalline nickel-molybdenum bimetallic alloy was grown in situ on the surface of the self-supporting mesoporous carbon precursor substrate by constant current electrodeposition to obtain the nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst.

[0007] Preferably, the concentration of the mesoporous carbon ink is 1–20 mg / L, more preferably 5–10 mg / L.

[0008] Preferably, the loading of the coated mesoporous carbon on the nickel foam is controlled to be 0.1–5 mg / cm³. 2 Preferably, it is 0.25–4 mg / cm³. 2 .

[0009] Preferably, the calcination temperature is 200–1000℃, the calcination time is 1–3 h, and the heating rate is 1–4℃ / min; more preferably, the calcination temperature is 400–800℃, the calcination time is 1–2 h, and the heating rate is 2.5–3.5℃ / min.

[0010] Preferably, the calcination is carried out in an inert atmosphere, preferably an argon atmosphere; the gas flow rate in the inert atmosphere is 10-100 mL / min, preferably 50 mL / min.

[0011] Preferably, the electroplating solution is an aqueous solution containing 0.01–0.08 mol / L nickel nitrate hexahydrate, 0.001–0.05 mol / L ammonium molybdate heptahydrate, 0.1–0.5 mol / L sodium citrate and / or ammonium citrate, 0.1–0.5 mol / L sodium chloride, and 0.4–0.8 g / L saccharin; more preferably, the electroplating solution is an aqueous solution containing 0.03–0.06 mol / L nickel nitrate hexahydrate, 0.007–0.04 mol / L ammonium molybdate heptahydrate, 0.2–0.4 mol / L sodium citrate and / or ammonium citrate, 0.2–0.4 mol / L sodium chloride, and 0.5–0.8 g / L saccharin; more preferably, the concentration of saccharin in the electroplating solution is 0.6–0.7 g / L.

[0012] Preferably, the current density of the constant current electrodeposition is -60 to -150 mA / cm². 2 The electrodeposition time is 400–3000 s; preferably, the current density of the constant current electrodeposition is -80 to -120 mA / cm². 2 The electrodeposition time is 450–2700 s.

[0013] Secondly, the present invention provides a nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst obtained according to the above preparation method.

[0014] Preferably, the nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst is a multi-level rod-shaped heterostructure in which nickel-molybdenum nanoparticles are anchored on the surface of a foamed nickel substrate supported by mesoporous carbon, with a specific surface area of ​​30-45 m². 2 / g, the particle size of the nanocrystalline nickel-molybdenum bimetallic alloy is 10-30nm.

[0015] Preferably, in the nickel-molybdenum alloy self-supporting hydrogen evolution catalyst, the mass ratio of nickel to molybdenum is 20-35:3-5, and the mass ratio of the total mass of the nickel-molybdenum alloy to the mass ratio of mesoporous carbon and foamed nickel is 43-48:0.25-4:37-40.

[0016] Thirdly, the present invention also provides an application of the above-mentioned nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst in electrocatalytic hydrogen evolution.

[0017] Beneficial effects (1) The present invention uses a drop-coating-programmed temperature-increasing calcination method to prepare a self-supporting mesoporous carbon precursor substrate. After high-temperature calcination, the mesoporous carbon and the nickel foam are tightly bonded, providing higher conductivity and a larger specific surface area, which can provide more active sites for the hydrogen evolution reaction. Furthermore, using carbon as the substrate material can better induce the precipitation and reduction of the nickel-molybdenum alloy phase during the electrodeposition process, resulting in uniform nanocrystalline nickel-molybdenum alloy particles. Moreover, it has the advantages of simple and easy operation, environmental friendliness, and strong repeatability. (2) The NiMo@C / NF composite electrocatalyst prepared in this invention has a large specific surface area and its active sites are directly exposed on the surface, which improves mass transport. It exhibits more efficient hydrogen evolution activity than commercial Pt / C in alkaline media and can maintain stable performance under high current for a long time. It has broad application prospects in the field of electrocatalysis. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the self-supporting mesoporous carbon precursor electrode prepared in Example 1. Figure 2 This is a scanning electron microscope image of the nanocrystalline nickel-molybdenum alloy self-supporting catalyst prepared in Example 1; Figure 3 The above is a cathode polarization curve of the hydrogen evolution reaction of the nanocrystalline nickel-molybdenum alloy self-supporting catalyst prepared in Example 1. Figure 4 This is a schematic diagram illustrating the stability of the nanocrystalline nickel-molybdenum alloy self-supporting catalyst prepared in Example 1. Detailed Implementation

[0019] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0020] The following exemplifies the preparation method of the nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst provided by the present invention, which mainly includes the following steps.

[0021] (1) Preparation of self-supporting mesoporous carbon precursor. Mesoporous carbon powder was weighed and dissolved in a mixed solution of water and ethanol. The solution was ultrasonically dispersed to obtain a uniformly dispersed mesoporous carbon ink. Then, the mesoporous carbon ink was drop-coated onto a nickel foam substrate. Subsequently, the substrate coated with the mesoporous carbon ink was dried and placed in a tube furnace for controlled calcination in an inert atmosphere. After calcination, the substrate was cooled to room temperature, so that carbon material grew in the pores of the nickel foam or on the surface of the nickel foam skeleton, thus obtaining the self-supporting mesoporous carbon precursor.

[0022] In the water-ethanol mixture, the volume ratio of water to ethanol can be 3:2; the ultrasonic dispersion time can be 20-40 min (e.g., 30 min); the concentration of the mesoporous carbon ink can be controlled to be 1-20 mg / L, preferably 5-10 mg / L. The concentration of the mesoporous carbon ink affects the carbon loading in the catalyst material, and consequently alters the loading of the electrodeposited nickel-molybdenum alloy: excessively high ink concentration leads to increased carbon loading, which easily causes the electrodeposited nickel-molybdenum alloy in the catalyst to agglomerate, ultimately affecting the electrochemical active area and hydrogen evolution performance of the catalyst; excessively low ink concentration results in smaller and more dispersed electrodeposited nickel-molybdenum alloy particles in the catalyst, which cannot be fully loaded onto the carbon material, ultimately also affecting the hydrogen evolution performance of the catalyst.

[0023] In some preferred embodiments, the foamed nickel can be sequentially coated with 3M hydrochloric acid and V before drop-coating the mesoporous carbon ink. 1:1 The nickel foam was ultrasonically washed for 15 minutes in a mixture of acetone and ethanol, ethanol, and deionized water, and then dried at 60°C for 2 hours.

[0024] In some embodiments, the loading of coated mesoporous carbon on nickel foam can be controlled to be 0.1-5 mg / cm³. 2 Preferably 0.25–4 mg / cm³ 2Excessive carbon loading will cause the subsequently electrodeposited nickel-molybdenum alloy to agglomerate, thus affecting the electrochemical active area of ​​the catalyst and its hydrogen evolution performance; conversely, insufficient carbon loading will result in small and dispersed nickel-molybdenum alloy particles that cannot be fully loaded onto the carbon material, ultimately also affecting the catalyst's hydrogen evolution performance.

[0025] The drying temperature can be 30-100℃ (e.g., 80℃), and the time can be 0.5-4 h (e.g., 2 h). The temperature for controlled calcination can be 200-1000℃, the calcination time can be 1-3 h, and the heating rate can be 1-4℃ / min; preferably, the calcination temperature is 400-800℃, the calcination time is 1-2 h, and the heating rate is 2.5-3.5℃ / min. The inert atmosphere can be argon, and the flow rate can be 10-100 mL / min (e.g., 50 mL / min).

[0026] Temperature-controlled calcination of a nickel foam substrate coated with mesoporous carbon ink not only enhances the bonding force between the mesoporous carbon and the nickel foam substrate but also alters the hydrophobicity of the mesoporous carbon material, thus facilitating the adhesion of subsequent electrodeposited nickel-molybdenum alloy particles. Maintaining appropriate parameters for temperature control, holding time, and heating rate during calcination prevents changes in sample morphology and defects within the carbon material. This ensures a suitable specific surface area, bonding force between carbon and nickel foam, and hydrophobicity of the mesoporous carbon material in the prepared catalyst material. Otherwise, defects such as excessively large catalyst particles will directly affect its hydrogen evolution performance.

[0027] (2) Preparation of nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst (electrode). An electroplating solution containing nickel salt and molybdenum salt was prepared, and the self-supporting mesoporous carbon precursor obtained in step (1) was placed in the electroplating solution; then, nanocrystalline particulate nickel-molybdenum bimetallic alloy was grown in situ on the surface of the self-supporting mesoporous carbon precursor substrate by constant current electrodeposition to obtain the nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst.

[0028] In some embodiments, the electroplating solution may be an aqueous solution containing 0.01–0.08 mol / L nickel nitrate hexahydrate, 0.001–0.05 mol / L ammonium molybdate heptahydrate, 0.1–0.5 mol / L sodium citrate or / and ammonium citrate, 0.1–0.5 mol / L sodium chloride, and 0.4–0.8 g / L saccharin; preferably, the electroplating solution is an aqueous solution containing 0.03–0.06 mol / L nickel nitrate hexahydrate, 0.007–0.04 mol / L ammonium molybdate heptahydrate, 0.2–0.4 mol / L sodium citrate or / and ammonium citrate, 0.2–0.4 mol / L sodium chloride, and 0.5–0.8 g / L saccharin; more preferably, the concentration of saccharin is 0.6–0.7 g / L.

[0029] Sodium citrate and / or ammonium citrate are complexing agents. Adding a complexing agent to the plating bath enables the formation of stable complexes with metal ions, while also preventing the formation of hydroxide precipitates. This controls and stabilizes the concentration of free metal ions in the plating bath, ensuring the deposition reaction proceeds at a normal rate. Sodium chloride is a conductive salt; its addition enhances the conductivity of the solution, and chloride ions also promote the dissolution of the anolyte passivation film. The addition of saccharin promotes grain refinement during the electrodeposition process of the catalyst material.

[0030] Maintaining the appropriate molar concentrations of the nickel and molybdenum sources in the electroplating solution significantly impacts the hydrogen evolution performance of the catalyst sample. Insufficient concentrations of nickel and molybdenum sources in the electrodeposition solution result in incomplete electrodeposition, leading to small and dispersed alloy particles. Conversely, excessively high concentrations cause the grown nickel-molybdenum alloy particles to aggregate or cluster, resulting in poor catalyst material performance and hindering the hydrogen evolution catalytic reaction.

[0031] In some embodiments, the current density of the constant current electrodeposition can be -60 to -150 mA / cm². 2 The electrodeposition time can be 400-3000 s; preferably, the current density of the constant current electrodeposition is -80 to -120 mA / cm². 2 The electrodeposition time is 450-2700 s. If the electrodeposition current density is too low or the electrodeposition time is too short, the resulting nickel-molybdenum particles will be small and dispersed; if the electrodeposition current density is too high or the electrodeposition time is too long, the electrodeposited nickel-molybdenum alloy particles will agglomerate or even crack in some areas, ultimately affecting the hydrogen evolution performance of the catalyst material.

[0032] The nanocrystalline nickel-molybdenum alloy self-supporting catalyst obtained by the preparation method provided by this invention is a multi-level rod-shaped heterostructure in which nickel-molybdenum nanoparticles are anchored on the surface of a foamed nickel substrate supported by mesoporous carbon, with a specific surface area of ​​30-45 m². 2 / g, the nickel-molybdenum nanoparticles are grown and attached to the surface of a rod-shaped carbon framework. The particle size of the nanocrystalline nickel-molybdenum bimetallic alloy is 10-30 nm.

[0033] In some embodiments, the mass ratio of nickel to molybdenum in the nickel-molybdenum alloy self-supporting catalyst can be controlled to be 20-35:3-5, and the mass ratio of the total mass of the nickel-molybdenum alloy to the mass of carbon material and foamed nickel can be 43-48:0.25-4:37-40.

[0034] The nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst obtained by the preparation method provided by this invention utilizes a nickel foam substrate for support and grows mesoporous carbon material on the nickel foam. The mesoporous carbon material not only enhances the conductivity of the catalyst material but also promotes the growth and grain refinement of the nickel-molybdenum alloy particles. Simultaneously, it provides more active sites, creating favorable conditions for the hydrogen evolution reaction.

[0035] In the catalyst structure, nickel foam provides a good substrate, eliminating the need for binders and conductive agents; mesoporous carbon supported on the nickel foam substrate provides more active sites. The mesoporous carbon is composed of several rod-like structures, which provide good conductivity during electrodeposition and promote the growth and uniform dispersion of nanocrystalline nickel-molybdenum alloy during the electrodeposition process. The rod-like structures and large specific surface area enable the uniform growth of the nickel-molybdenum alloy on the mesoporous carbon. The numerous active sites provided by the carbon material can significantly accelerate the hydrogen evolution reaction, and the special structure and inherent properties of the mesoporous carbon material greatly enhance the stability of the catalyst, making it a promising candidate for practical production.

[0036] The preparation method provided by the present invention has the advantages of simple and efficient process, environmental friendliness and strong reproducibility. At the same time, the hydrogen evolution catalyst obtained by the preparation method shows high hydrogen evolution activity and cycle stability under alkaline conditions.

[0037] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention fall within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0038] Example 1 (1) Preparation of self-supporting mesoporous carbon precursor. Mesoporous carbon powder was weighed and dissolved in a mixed solution of water and ethanol (volume ratio of water to ethanol is 3:2). The solution was ultrasonically dispersed for 30 min to obtain uniformly dispersed mesoporous carbon ink. Then, the mesoporous carbon ink was uniformly drop-coated onto pretreated nickel foam. Subsequently, it was dried at 80 °C for 2 h. The nickel foam substrate coated with mesoporous carbon ink was placed in a tube furnace and heated to 600 °C at a rate of 3.5 °C / min in an inert Ar gas flow of 50 mL / min and held for 2 h. Then it was cooled to room temperature to obtain the self-supporting mesoporous carbon precursor, denoted as C / NF.

[0039] (2) Preparation of nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst (electrode). 50 mL of an electroplating solution containing nickel and molybdenum salts was prepared, and the self-supporting mesoporous carbon precursor obtained in step (1) was placed in the electroplating solution. The electroplating solution was an aqueous solution containing 0.05 mol / L nickel nitrate hexahydrate, 0.01 mol / L ammonium molybdate heptahydrate, 0.3 mol / L sodium citrate, 0.3 mol / L sodium chloride, and 0.6 g / L saccharin. Then, a constant current electrodeposition method was used, with a current density of -100 mA / cm². 2 Under certain conditions, nanocrystalline nickel-molybdenum bimetallic alloy was deposited for 2400 s to grow on the surface of a self-supporting mesoporous carbon precursor substrate, resulting in a nanocrystalline nickel-molybdenum alloy self-supporting catalyst, denoted as NiMo@C / NF-J.

[0040] The nanocrystalline nickel-molybdenum alloy self-supporting catalyst prepared in Example 1 has a particle size of 20 nm. The mass ratio of nickel to molybdenum in the nickel-molybdenum alloy self-supporting catalyst is 28:5, and the mass ratio of the total mass of the nickel-molybdenum alloy to the mass of carbon material and foamed nickel is 45.8:3:37.

[0041] Figure 1 This is a scanning electron microscope (SEM) image of the self-supporting mesoporous carbon precursor electrode prepared in Example 1. As can be seen from the image, the smooth-surfaced mesoporous carbon consists of rod-like structures ranging from 2 to 10 μm in diameter, and its large specific surface area is beneficial for particle growth and provides more active sites.

[0042] Figure 2 This is a scanning electron microscope (SEM) image of the nanocrystalline nickel-molybdenum alloy self-supporting catalyst prepared in Example 1. As can be seen from the image, nanocrystalline nickel-molybdenum alloy particles with a diameter of approximately 20 nm are uniformly dispersed on a self-supporting mesoporous carbon substrate, forming a heterogeneous hierarchical structure.

[0043] Figure 3 The figure shows the cathodic polarization curves of the hydrogen evolution reaction of the nanocrystalline nickel-molybdenum alloy self-supporting catalyst prepared in Example 1. As can be seen from the figure, NiMo@C / NF requires only 7 mV overpotential to reach 10 mA cm⁻¹. -2 Its current density is significantly better than that of NiMo / NF, C / NF and commercial Pt / C.

[0044] Figure 4 This is a schematic diagram illustrating the stability of the nanocrystalline nickel-molybdenum alloy self-supporting catalyst prepared in Example 1. As can be seen from the figure, under a constant current of 100 mA cm⁻¹, [the stability is achieved]. -2Under the conditions specified, the stability test conducted on the mesoporous carbon / nickel foam substrate showed a slight increase in voltage after 380 h, compared to the stability maintained for only 138 h when directly electrodeposited on the nickel foam substrate, further demonstrating that the addition of mesoporous carbon material can enhance the stability of the material.

[0045] Example 2 The preparation process in this embodiment is the same as in Example 1. The main difference is that in step (2), the electrodeposition conditions are a current density of -110 mA / cm². 2 After 1800 s deposition, nanocrystalline nickel-molybdenum bimetallic alloy was grown on the surface of a self-supporting mesoporous carbon precursor substrate, resulting in a nanocrystalline nickel-molybdenum alloy self-supporting catalyst, denoted as NiMo@C / NF-S.

[0046] The nanocrystalline nickel-molybdenum alloy self-supporting catalyst prepared by Example 2 has a particle size of 28 nm. The mass ratio of nickel to molybdenum in the nickel-molybdenum alloy self-supporting catalyst is 24:4, and the mass ratio of the total mass of the nickel-molybdenum alloy to the mass of carbon material and nickel foam is 47.3:3:39.

[0047] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst, characterized in that, include: Mesoporous carbon powder is dispersed and dissolved to obtain mesoporous carbon ink; The mesoporous carbon ink was drop-coated onto nickel foam, dried, and then calcined to obtain a self-supporting mesoporous carbon precursor. An electroplating solution containing nickel and molybdenum salts was prepared, and the self-supporting mesoporous carbon precursor was placed in the electroplating solution as a substrate. Nanocrystalline nickel-molybdenum bimetallic alloy was grown in situ on the surface of the self-supporting mesoporous carbon precursor substrate by constant current electrodeposition to obtain the nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst.

2. The preparation method according to claim 1, characterized in that, The concentration of the mesoporous carbon ink is 1–20 mg / L.

3. The preparation method according to claim 2, characterized in that, The concentration of the mesoporous carbon ink is 5–10 mg / L.

4. The preparation method according to claim 1, characterized in that, The loading of coated mesoporous carbon on nickel foam was controlled to be 0.1–5 mg / cm³. 2 .

5. The preparation method according to claim 4, characterized in that, The loading of coated mesoporous carbon on nickel foam was controlled to be 0.25–4 mg / cm³. 2 .

6. The preparation method according to claim 1, characterized in that, The calcination temperature is 200–1000℃, the calcination time is 1–3 h, and the heating rate is 1–4℃ / min.

7. The preparation method according to claim 6, characterized in that, The calcination temperature is 400–800℃, the calcination time is 1–2 h, and the heating rate is 2.5–3.5℃ / min.

8. The preparation method according to claim 1, characterized in that, The calcination is carried out in an inert atmosphere, wherein the gas flow rate in the inert atmosphere is 10–100 mL / min.

9. The preparation method according to claim 8, characterized in that, The calcination is carried out in an argon atmosphere at a flow rate of 50 mL / min.

10. The preparation method according to claim 1, characterized in that, The electroplating solution is an aqueous solution containing 0.01–0.08 mol / L nickel nitrate hexahydrate, 0.001–0.05 mol / L ammonium molybdate heptahydrate, 0.1–0.5 mol / L sodium citrate and / or ammonium citrate, 0.1–0.5 mol / L sodium chloride, and 0.4–0.8 g / L saccharin.

11. The preparation method according to claim 10, characterized in that, The electroplating solution is an aqueous solution containing 0.03–0.06 mol / L nickel nitrate hexahydrate, 0.007–0.04 mol / L ammonium molybdate heptahydrate, 0.2–0.4 mol / L sodium citrate or / and ammonium citrate, 0.2–0.4 mol / L sodium chloride, and 0.5–0.8 g / L saccharin.

12. The preparation method according to claim 11, characterized in that, The concentration of saccharin in the electroplating solution is 0.6–0.7 g / L.

13. The preparation method according to claim 1, characterized in that, The current density of the constant current electrodeposition is -60 to -150 mA / cm². 2 The electrodeposition time is 400–3000 s.

14. The preparation method according to claim 1, characterized in that, The current density of the constant current electrodeposition is -80 to -120 mA / cm². 2 The electrodeposition time is 450–2700 s.

15. A nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst obtained by the preparation method according to claim 1.

16. The nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst according to claim 15, characterized in that, The nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst is a multi-level rod-shaped heterostructure in which nickel-molybdenum nanoparticles are anchored on the surface of a foamed nickel substrate supported by mesoporous carbon, with a specific surface area of ​​30–45 m². 2 / g, the particle size of nickel-molybdenum nanoparticles is 10-30nm.

17. The nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst according to claim 16, characterized in that, In the nickel-molybdenum alloy self-supporting hydrogen evolution catalyst, the mass ratio of nickel to molybdenum is 20-35:3-5, and the mass ratio of the total mass of the nickel-molybdenum alloy to the mass ratio of mesoporous carbon and foamed nickel is 43-48:0.25-4:37-40.

18. The application of the nanocrystalline nickel-molybdenum alloy self-supporting hydrogen evolution catalyst according to claim 15 in electrocatalytic hydrogen evolution.

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