Material of super-stable ni nanoparticle reducing inlaid in nickel molybdate nanorod and preparation method and application thereof

Abstract

The application provides a material with super-stable Ni nanoparticles reduced and inlaid on a nickel molybdate nanorod and a preparation method and application thereof. The preparation method is as follows: under stirring, a nickel source, a molybdenum source and an organic ligand are mixed in a solvent, a foamed nickel is added, and then heating reaction is carried out to obtain a precursor grown on the foamed nickel; and annealing is carried out to obtain the material with super-stable Ni nanoparticles reduced and inlaid on the nickel molybdate nanorod. The catalytic performance of the material in hydrogen evolution reaction, urea oxidation reaction and urea total decomposition reaction is far better than that of commercial Pt / C and RuO2, and the material has good catalytic capacity and super-high cycle stability.

Description

Technical Field

[0001] This invention belongs to the fields of inorganic nanomaterials and catalyst preparation research, specifically the material of ultrastable Ni nanoparticles reduced and embedded on nickel molybdate nanorods, its preparation method and application; by using a hydrothermal followed by annealing method, Ni nanoparticles are reduced and embedded on NiMoO4 nanorods, which can be used to promote the trifunctional reactions of HER, UOR and urea total decomposition, and have high catalytic activity. Background Technology

[0002] Hydrogen, as a renewable and green fuel, plays a crucial role in alleviating the energy crisis and environmental problems. Currently, some industrial hydrogen production methods still rely heavily on fossil fuels and emit greenhouse gases such as carbon dioxide. Water electrolysis for hydrogen production has gained widespread attention as a zero-carbon emission method. Alkaline water electrolysis is particularly popular due to its inexpensive equipment requirements and effective avoidance of acid mist and corrosion. Electrochemical water splitting consists of two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Pt has long been considered the best electrocatalyst for HER due to its excellent activity and high current density. Currently, commercially used OER catalysts are still made of precious metals, including Ru-based materials. Unfortunately, the scarcity, high cost, and limited functionality of precious metals hinder their large-scale application.

[0003] The oxygen evolution reaction (OER) at the anodic kinetics is slow and requires a relatively high overpotential, resulting in high energy consumption. To address this issue, replacing the OER with other, more readily occurring anodic reactions is significant for reducing the potential for hydrogen production and overall energy costs. The theoretical voltage of the urea oxidation reaction (UOR) at 0.37V is significantly lower than that of the water oxidation reaction at 1.23V. Improving the catalytic kinetics of the anodic reaction can accelerate the overall water splitting reaction, effectively increasing hydrogen production efficiency. Urea, a common substance in industry, agriculture, and daily life, also offers promise for purifying urea-rich wastewater through its oxidation reaction as a substitute for the OER. However, the urea oxidation reaction involves a six-electron transfer process, producing N2 and CO2, and while its thermodynamic potential is low, its inherent reaction rate is slow. Therefore, the development of highly efficient catalysts is urgently needed for energy-efficient hydrogen production and the purification of urea-rich wastewater using the UOR reaction.

[0004] Currently, there are few highly efficient catalysts that can achieve hydrogen evolution reaction, urea oxidation reaction and total urea hydrolysis reaction. Summary of the Invention

[0005] The purpose of this invention is to provide a material and preparation method of ultrastable Ni nanoparticles reduced and embedded on nickel molybdate nanorods. The method utilizes a hydrothermal followed by annealing and high-temperature hydrogen reduction to reduce and embed Ni nanoparticles on NiMoO4 nanorods. The preparation method is simple and low in cost.

[0006] Another objective of this invention is to provide the application of materials with ultrastable Ni nanoparticles reduced and embedded in nickel molybdate nanorods as highly efficient catalysts for hydrogen evolution reaction, urea oxidation reaction, total water splitting and total urea hydrolysis reaction.

[0007] The specific technical solution of this invention is as follows:

[0008] A method for preparing a material with ultrastable Ni nanoparticles reduced and embedded in nickel molybdate nanorods includes the following steps:

[0009] 1) Nickel source, molybdenum source and organic ligand are mixed in a solvent, nickel foam is added and heated to react, and a precursor grown on nickel foam is obtained;

[0010] 2) Annealing of the product from step 1) yields a material in which ultrastable Ni nanoparticles are reduced and embedded in nickel molybdate nanorods.

[0011] In step 1), the molar ratio of the nickel source, molybdenum source, organic ligand and solvent is (10-30):(1-5):(5-20); more preferably, it is 15:2:12.

[0012] In step 1), the nickel source is a soluble nickel salt; preferably nickel nitrate hexahydrate Ni(NO3)2·6H2O;

[0013] In step 1), the molybdenum source is a soluble molybdenum salt; preferably ammonium molybdate tetrahydrate (NH4)6Mo7O 24 ·4H2O;

[0014] In step 1), the organic ligand is selected from 2-methylimidazole;

[0015] In step 1), the solvent is selected from water, preferably deionized water;

[0016] In step 1), the concentration of the nickel source in the solvent is 0.05-0.2M;

[0017] In step 1), the heating reaction is carried out at a temperature of 60℃-150℃ for 5h-24h; preferably, it is carried out at 90℃ for 8h.

[0018] In step 1), after the heating reaction is completed, and the reaction is allowed to cool naturally, the nickel foam with the product on it is taken out, washed with deionized water and ethanol 3-5 times to remove impurities, and then dried naturally to obtain a light yellow precursor, which is kept for later use.

[0019] In step 2), the annealing refers to annealing in a mixed atmosphere containing hydrogen and argon, with a heating rate of 1-5℃ / min, heating to 450-550℃, and an annealing time of 2-3 hours; the hydrogen volume percentage is 5%-15%; the preferred annealing conditions are: a heating rate of 5℃ / min, heating to an annealing temperature of 500℃, and an annealing time of 2 hours; in the mixed atmosphere of hydrogen and argon, the hydrogen volume percentage is 5%; if reduction is carried out in pure Ar gas, the performance will be extremely poor.

[0020] In step 2), the product after annealing and natural cooling is black.

[0021] The material provided by this invention, in which ultrastable Ni nanoparticles are reduced and embedded in nickel molybdate nanorods, is prepared by the above-described method. The ultrastable Ni nanoparticles are reduced and embedded in nickel molybdate nanorods; the length of the nanorods ranges from 10 to 30 μm, and they are needle-shaped nanorods, thin at one end and thick at the other, with a width of about 200-300 nm in the middle; the size of the ultrastable Ni nanoparticles is 10-60 nm, preferably 30-40 nm.

[0022] The present invention provides the application of ultrastable Ni nanoparticles reduced and embedded in nickel molybdate nanorods in the hydrogen evolution reaction (HER) of water electrolysis; specifically, the overpotential of the hydrogen evolution reaction in 1M KOH electrolyte solution is much lower than that of commercial Pt / C catalysts, and the lower the overpotential, the better the catalytic performance.

[0023] The present invention relates to the application of the material provided by the reduction of ultrastable Ni nanoparticles embedded in nickel molybdate nanorods in the urea oxidation reaction (UOR) in urea solution.

[0024] The application of the ultrastable Ni nanoparticles embedded in nickel molybdate nanorods provided by this invention in the complete hydrolysis of water and urea.

[0025] This invention employs a hydrothermal followed by annealing method to reduce and embed Ni nanoparticles onto NiMoO4 nanorods. The first step, hydrothermal growth on nickel foam produces smooth, needle-shaped nanorods, with the resulting NiMoO4·xH2O primarily exhibiting nanorod or nanoarray morphology. The second step, high-temperature hydrogen-argon annealing, reduces some Ni elements to Ni particles and embeds them onto the nanorods, while simultaneously roughening the nanorod surface. This in-situ growth method on conductive nickel foam effectively reduces the charge transfer resistance between the electrocatalyst and the electrolyte, thereby enhancing electron transport efficiency. The resulting nanoparticle-nanorobar structure with high surface roughness not only exposes abundant active sites but also avoids catalyst aggregation during the catalytic process, thus improving the catalyst's catalytic activity and stability. Furthermore, it exhibits a significant advantage in catalytic efficiency compared to commercial noble metal catalysts. This invention reduces and embeds Ni nanoparticles onto NiMoO4 nanorods; the nanorod-nanoparticle structure effectively prevents catalyst aggregation during the catalytic process, enhancing material stability and ensuring that Ni-NiMoO4 maintains both high activity and high stability.

[0026] Compared with existing technologies, this invention utilizes a two-step reaction process—hydrothermal followed by annealing—to first synthesize smooth, needle-shaped nanorods. Then, embedded nanoparticles are grown onto these nanorods. High-temperature annealing transforms the nanorod surface from smooth to highly rough, increasing the catalyst surface area and exposing more catalytic active sites. The catalyst preparation method of this invention is simple, requiring no precious metal raw materials. The catalyst exhibits excellent performance in HER catalysis, urea oxidation (UOR) catalysis, and urea hydrolysis catalysis; it demonstrates good catalytic activity for various reactions and possesses extremely high cycle stability. For the alkaline HER catalytic reaction, the main reaction step is the Volmer reaction: H₂O + e⁻. - →OH - +H*, Heyrovsky reaction: H2O + H* + e- - →OH - +H2, Tafel reaction: 2H*→H2. For the basic UOR-catalyzed reaction, the reaction involved is: CO(NH2)2 + 6OH- - →N2 + 5H2O + CO2 + 6e - The overall reaction equation for the electrolysis of alkaline urea is: CO(NH2)2 + 2OH- - →3H2+N2+CO2. HER, UOR, and alkaline urea electrolysis reactions require different catalyst performances, and the Ni-NiMoO4 material of this application exhibits high catalytic performance for all of these reactions. Attached Figure Description

[0027] Figure 1This is a scanning electron microscope image of Ni nanoparticles synthesized in Example 1 embedded in NiMoO4 nanorods.

[0028] Figure 2 This is a transmission electron microscope image of Ni nanoparticles synthesized in Example 1 embedded in NiMoO4 nanorods.

[0029] Figure 3 The X-ray diffraction (XRD) pattern of the reduced Ni nanoparticles embedded in NiMoO4 nanorods synthesized in Example 1 is shown.

[0030] Figure 4 Scanning electron microscope image of NiMoO4·xH2O needle-shaped nanorods prepared in Comparative Example 1;

[0031] Figure 5 Transmission electron microscopy image of the NiMoO4·xH2O needle-shaped nanorods prepared in Comparative Example 1;

[0032] Figure 6 Polarization curves of the nanomaterials prepared in Example 1 and Comparative Example 1, bare nickel foam, and commercial Pt / C in 1M KOH solution;

[0033] Figure 7 Polarization curves of the nanomaterials prepared in Example 1 and Comparative Example 1, bare nickel foam, and commercial RuO2 in 1M KOH (+0.33M Urea) solution;

[0034] Figure 8 The polarization curves are those of the product of Example 1 in a 1M KOH solution for the total water hydrolysis catalytic reaction and in a 1M KOH + 0.33M Urea solution for the total urea hydrolysis catalytic reaction.

[0035] Figure 9 The stability of the product of Example 1 in 1M KOH solution.

[0036] Figure 10 The polarization curves of the products of Examples 1, 2, and 3 in 1M KOH solution are shown.

[0037] Figure 11 Scanning electron microscope image of the material prepared in Comparative Example 2;

[0038] Figure 12 Scanning electron microscope image of the material prepared in Comparative Example 3;

[0039] Figure 13 Scanning electron microscope image of the material prepared in Comparative Example 4;

[0040] Figure 14 Scanning electron microscope image of the material prepared in Comparative Example 5;

[0041] Figure 15 This is a high-magnification transmission electron microscope image of the material prepared in Example 1;

[0042] Figure 16 This is a high-magnification scanning electron microscope image of the material prepared in Comparative Example 2;

[0043] Figure 17 This is a high-magnification scanning electron microscope image of the material prepared in Comparative Example 3;

[0044] Figure 18 This is a high-magnification scanning electron microscope image of the material prepared in Comparative Example 4;

[0045] Figure 19 Polarization curves of the products of Comparative Examples 1, 2, 3 and Example 1 in 1M KOH solution for HER catalytic reaction. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0047] Example 1

[0048] A method for preparing a material with ultrastable Ni nanoparticles reduced and embedded in nickel molybdate nanorods includes the following steps:

[0049] 1) Preparation of precursors for nickel foam: First, under stirring, 2 mmol Ni(NO3)2·6H2O and 0.25 mmol (NH4)6Mo7O were added. 24 ·4H2O and 1.2 mmol 2-methylimidazole were added sequentially to 15 mL of deionized water, and the mixture was magnetically stirred for 5 minutes to form a uniform green solution. The solution was then transferred to a polytetrafluoroethylene autoclave, and a piece of nickel foam, 2 cm × 3 cm in size, was added to it. The autoclave was then sealed and treated at 90 °C for 8 hours. After the reaction cooled naturally, the nickel foam with the product was removed, rinsed 5 times with deionized water and ethanol to remove impurities, and then allowed to dry naturally for later use.

[0050] 2) Preparation of Ni-NiMoO4 catalyst: The nickel foam containing the precursor after the above reaction was annealed in a 5% H2 / Ar mixed atmosphere, with H2 accounting for 5% by volume, the heating rate was 5℃ / min, the temperature was raised to the annealing temperature of 500℃, the annealing time was 2h, and it was then naturally cooled for later use.

[0051] Nickel foam with Ni nanoparticles embedded in NiMoO4 nanorods, prepared according to the above method, was analyzed by scanning electron microscopy and transmission electron microscopy. Figure 1 , Figure 2Observation of its morphology confirmed that it is a structure of embedded Ni nanoparticles grown on needle-shaped NiMoO4 nanorods. X-ray diffraction was also performed. Figure 3 Further evidence confirms that the material consists of Ni nanoparticles grown on needle-shaped NiMoO4 nanorods, with XRD results showing Ni and NiMoO4. This demonstrates the successful preparation of Ni-NiMoO4 material by this invention.

[0052] Example 2

[0053] A method for preparing a material with ultrastable Ni nanoparticles reduced and embedded in nickel molybdate nanorods includes the following steps:

[0054] 1) Preparation of precursors for nickel foam: First, under stirring, 2 mmol Ni(NO3)2·6H2O and 0.25 mmol (NH4)6Mo7O were added. 24 • 4H₂O and 1.5 mmol of 2-methylimidazole were added sequentially to 15 mL of deionized water, and the mixture was magnetically stirred for 5 minutes to form a homogeneous green solution. The solution was then transferred to a polytetrafluoroethylene (PTFE) autoclave, and a piece of nickel foam (2 cm × 3 cm) that had been pre-washed with hydrochloric acid, anhydrous ethanol, and deionized water was added. The autoclave was then sealed and treated at 90 °C for 8 hours. After the reaction cooled naturally, the nickel foam with the product was removed, rinsed repeatedly with deionized water to remove impurities, and then allowed to air dry for later use.

[0055] 2) Preparation of Ni-NiMoO4 catalyst: The nickel foam containing the precursor after the above reaction was annealed in a mixed atmosphere of H2 and Ar with a volume ratio of 5% H2. The annealing temperature was 500℃, the heating rate was 5℃ / min, and the annealing time was 2h. After natural cooling, it was ready for use.

[0056] Example 3

[0057] A method for preparing a material with ultrastable Ni nanoparticles reduced and embedded in nickel molybdate nanorods includes the following steps:

[0058] 1) Preparation of precursors for nickel foam: First, 2.5 mmol Ni(NO3)2·6H2O and 0.18 mmol (NH4)6Mo7O were stirred. 24 • 4H₂O and 1.2 mmol of 2-methylimidazole were added sequentially to 15 mL of deionized water, and the mixture was magnetically stirred for 5 minutes to form a homogeneous green solution. The solution was then transferred to a polytetrafluoroethylene autoclave, and a piece of nickel foam (2 cm × 3 cm) that had been pre-washed with hydrochloric acid, anhydrous ethanol, and deionized water was added. The autoclave was then sealed and treated at 90°C for 8 hours. After the reaction cooled naturally, the nickel foam with the product was removed, rinsed repeatedly with deionized water to remove impurities, and then allowed to air dry for later use.

[0059] 2) Preparation of Ni-NiMoO4 catalyst: The nickel foam containing the precursor that has undergone the above reaction is annealed in a mixed atmosphere of H2 and Ar with a volume ratio of 5% H2. The annealing temperature is 500℃, the heating rate is 5℃ / min, and the time is 2h. After natural cooling, it is ready for use.

[0060] Comparative Example 1

[0061] The process was carried out according to Example 1, except that only the first step of the hydrothermal reaction was performed to obtain nickel foam with needle-like NiMoO4·xH2O nanorods.

[0062] The needle-shaped NiMoO4·xH2O nanorods prepared according to the above method were analyzed by scanning electron microscopy and transmission electron microscopy. Figure 4 , Figure 5 Its morphology was observed and determined to be a smooth nanorod structure.

[0063] Comparative Example 2

[0064] The process was carried out according to Example 1, except that the annealing temperature was 600°C.

[0065] Comparative Example 3

[0066] The annealing was carried out according to Example 1, except that the annealing temperature was 400°C.

[0067] Comparative Example 4

[0068] The process was carried out according to Example 1, except that the gas atmosphere during annealing was changed from H2 / Ar to pure Ar.

[0069] Comparative Example 5

[0070] The procedure was carried out according to Example 1, except that the solvent water was replaced with methanol.

[0071] Figure 11 Scanning electron microscope image of the material prepared in Comparative Example 2; Figure 12 Scanning electron microscope image of the material prepared in Comparative Example 3; Figure 13 Scanning electron microscope image of the material prepared in Comparative Example 4; Figure 14 Scanning electron microscope image of the material prepared in Comparative Example 5; Figure 16 This is a high-magnification scanning electron microscope image of the material prepared in Comparative Example 2; Figure 17 This is a high-magnification scanning electron microscope image of the material prepared in Comparative Example 3; Figure 18 Here is a high-magnification scanning electron microscope (SEM) image of the material prepared in Comparative Example 4; The SEM image of a portion of the product from Comparative Example 2, annealed at 600℃, is shown below. Figure 16The morphology is no longer that of nanorods supporting nanoparticles. Excessive temperature caused morphological collapse, resulting in significant gaps between the formed nanoparticles, which hinders electron transport and thus affects performance. Comparative Example 3 shows a product annealed at 400℃; a magnified SEM image of this product is shown below. Figure 17 The morphology showed only nanorod structures without nanoparticle loading, indicating that the low annealing temperature prevented the reduction of Ni nanoparticles, thus affecting performance. Comparative Example 4 was annealed under pure Ar conditions, and local magnified SEM images were added. Figure 18 In terms of appearance Figure 17 Similarly, the reason for this morphology is that Ar has no reducing properties, so it cannot reduce Ni nanoparticles, thus affecting performance.

[0072] Application Example 1

[0073] The application of Ni nanoparticles embedded in NiMoO4 nanorods as catalysts in the hydrogen evolution reaction is as follows:

[0074] The 1cm × 1cm nickel foams prepared in Example 1 and Comparative Example 1, and bare nickel foams, were used for performance testing. 4mg of commercial Pt / C, 2mg of carbon black, and 1mg of PVDF were weighed, mixed and ground evenly, then 50μL of N-methylpyrrolidone was added and stirred further before being coated onto cleaned nickel foam for comparison. A three-electrode system was used in the test, employing a CHI760 workstation. A carbon rod was used as the counter electrode, the different nickel foam electrodes were used as the working electrodes, and a silver chloride electrode was used as the reference electrode. The electrolyte was a 1M potassium hydroxide solution. HER performance curves were obtained through polarization curves (LSV). Figure 6 As shown; the stability of the catalyst in Example 1 was measured by constant voltage (it). In the hydrogen evolution reaction (HER), at a current density of 10 mA cm⁻¹ -2 At that time, the overpotential of the catalyst prepared in Example 1 was only 27 mV, while the overpotential of the needle-shaped NiMoO4·xH2O nanorod catalyst prepared in Comparative Example 1 was 284 mV, the overpotential of the Pt / C catalyst was 50 mV, and the overpotential of the bare nickel foam was 243 mV. A constant voltage was set to maintain the initial current density at 10 mA cm⁻¹. -2 At that time, the catalyst prepared in Example 1 showed no significant change in current density after 200 hours of testing. The overall HER polarization curve showed that the catalyst with Ni nanoparticles embedded on NiMoO4 nanorods exhibited a lower potential at high current densities, indicating better catalytic performance. The it curve (… Figure 9 It can be seen that the catalyst grown by embedding Ni nanoparticles on NiMoO4 nanorods has excellent stability, and the current hardly decays after 200 hours.

[0075] Figure 10 The figures show the hydrogen evolution polarization curves of the products from Examples 1, 2, and 3 in 1M KOH solution. It can be seen that all three products prepared according to this invention exhibit good catalytic performance at a current density of 10 mA cm⁻¹. -2 At that time, the voltage level of Example 1 was 27mV, the voltage level of Example 2 was 33mV, and the voltage level of Example 3 was 31mV.

[0076] The polarization curves of the products of Comparative Examples 1, 2, 3 and Example 1 in 1M KOH solution for HER catalytic reaction are shown below. Figure 19 The overpotential of Example 1 was 27mV, the overpotential of Comparative Example 2 was 48mV, the overpotential of Comparative Example 3 was 239mV, and the overpotential of Comparative Example 4 was 216mV. Therefore, the overpotential of Example 1 was 27mV.

[0077] Application Example 2

[0078] The application of Ni nanoparticles embedded in NiMoO4 nanorods as catalysts in urea oxidation reaction is as follows:

[0079] The 1cm × 1cm nickel foams prepared in Example 1 and Comparative Example 1, and bare nickel foams, were used for performance testing. 3mg of commercial RuO2, 2mg of carbon black, and 1mg of PVDF were weighed, mixed and ground evenly, then 50μL of N-methylpyrrolidone was added and stirred further before being coated onto cleaned nickel foam for comparison. A three-electrode system was used in the test, employing a CHI760 workstation. A platinum sheet was used as the counter electrode, the nickel foam electrode as the working electrode, and a silver chloride electrode as the reference electrode. The electrolyte was a 1M KOH + 0.33M urea solution. The UOR curve was obtained through cyclic polarization curve (LSV), as shown below. Figure 7 As shown. In the urea oxidation reaction (UOR), at a current density of 10 mA cm⁻¹ -2 At that time, the potential of the catalyst prepared in Example 1 was 1.338V, the potential of the needle-shaped NiMoO4·xH2O nanorod catalyst prepared in Comparative Example 1 was 1.347V, the potential of the RuO2 catalyst was 1.396V, and the potential of the bare nickel foam was 1.353V.

[0080] The overall UOR polarization curves show that the catalyst grown by embedding Ni nanoparticles on NiMoO4 nanorods has a lower potential at high current densities and better catalytic performance.

[0081] Application Example 3

[0082] Application of Ni nanoparticle-embedded NiMoO4 nanorod catalyst in urea hydrolysis reaction: Application method: Two 1cm × 1cm nickel foam pieces of the catalyst from Example 1 were used as the cathode and anode, respectively. The electrolyte was 1M KOH + 0.33M MUrea solution. Testing was performed using a CHI760 workstation, and the urea hydrolysis performance curve was obtained through polarization curve (LSV). Figure 8 As shown. At a current density of 10 mA cm⁻¹ -2 At that time, the potential of the catalyst prepared in Example 1 was 1.364V.

[0083] The low-cost, highly active, and highly stable multifunctional catalyst provided by this invention effectively realizes the hydrogen evolution reaction, urea oxidation reaction, and total urea hydrolysis reaction, and is an effective way to simplify the catalyst system and reduce catalytic efficiency. The raw materials of this invention are readily available, the preparation is simple, and the cost is low, which is beneficial for industrial production.

[0084] The above-described detailed description of a method for promoting the three functional applications of HER, UOR, and urea decomposition by embedding Ni nanoparticles on NiMoO4 nanorods is illustrative rather than limiting. Several embodiments may be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a material with ultrastable Ni nanoparticles reduced and embedded in nickel molybdate nanorods, characterized in that, The preparation method includes the following steps: 1) Nickel source, molybdenum source and organic ligand are mixed in a solvent under stirring. After adding nickel foam, the mixture is heated to react and a precursor grown on nickel foam is obtained. 2) Annealing of the product from step 1) yields a material in which ultrastable Ni nanoparticles are reduced and embedded in nickel molybdate nanorods; In step 1), the organic ligand is selected from 2-methylimidazole; In step 2), the annealing refers to annealing in a mixed atmosphere containing hydrogen and argon, at an annealing temperature of 450-550 ℃, for a annealing time of 2-3 hours. The ultrastable Ni nanoparticles are reduced and embedded on nickel molybdate nanorods. The length of the nanorods ranges from 10 to 30 μm, and they are needle-shaped nanorods with a width of 200 to 300 nm in the middle. The size of the ultrastable Ni nanoparticles is 10 to 60 nm.

2. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of the nickel source, molybdenum source and organic ligand is (10~30):(1~5):(5~20).

3. The preparation method according to claim 1, characterized in that, In step 1), the nickel source is a soluble nickel salt; the molybdenum source is a soluble molybdenum salt.

4. The preparation method according to claim 1 or 3, characterized in that, In step 1), the nickel source is nickel nitrate hexahydrate; the molybdenum source is ammonium molybdate tetrahydrate.

5. The preparation method according to claim 1, characterized in that, In step 1), the concentration of the nickel source in the solvent is 0.05-0.2M.

6. The preparation method according to claim 1, characterized in that, In step 1), the heating reaction refers to the reaction at a temperature of 60℃-150℃ for 5h-24h.

7. A material in which ultrastable Ni nanoparticles are reduced and embedded in nickel molybdate nanorods prepared by the preparation method according to any one of claims 1-6.

8. The application of a material prepared by the method according to any one of claims 1-6, in the reduction and embedding of ultrastable Ni nanoparticles on nickel molybdate nanorods, in the hydrogen evolution reaction of water electrolysis and the urea oxidation reaction in urea solution.

9. The application of a material prepared by the method according to any one of claims 1-6, in which ultrastable Ni nanoparticles are reduced and embedded on nickel molybdate nanorods, in the urea electrolysis reaction.

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