Preparation method and application of core-shell structure nickel hydroxide / nickel nanowire

Abstract

The application discloses a preparation method of core-shell structure nickel hydroxide / nickel nanowire and application thereof, and the preparation method comprises the following steps: mixing a nickel source, an alkali source, a dispersing agent, a reducing agent and a solvent, and performing a heating reaction under the action of a magnetic field to obtain nickel nanowire; then dispersing the nickel nanowire in a modifier to perform a surface modification reaction, so that nickel hydroxide is generated on at least part of the surface of the nickel nanowire, and the core-shell structure nickel hydroxide / nickel nanowire is obtained; and the modifier comprises at least one of water, an ammonia water solution or a nickel source aqueous solution. The nickel nanowire is prepared firstly, then the nickel nanowire is dispersed in the modifier to perform a surface modification reaction, a nickel hydroxide / nickel nanowire heterostructure is formed, the problem that the nickel nanowire is prone to aggregation is effectively solved, the dispersivity and the specific surface area of the nickel nanowire are increased, the number of exposed active sites is increased, and therefore the nickel nanowire has excellent electrocatalytic oxygen evolution and hydrogen evolution performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite materials, and particularly relates to a preparation method of nickel hydroxide / nickel nanowire with a core-shell structure and application thereof. BACKGROUND

[0002] In recent years, the demand for energy by humans has shown a linear upward trend, and the consumption of non-renewable energy sources such as fossil fuels has caused serious pollution to the environment, and it is imperative to develop clean energy. Hydrogen energy, as a new type of energy with zero emissions and no pollution, has attracted widespread research and reports. Developing an efficient electrocatalytic water splitting catalyst with abundant earth resources is a prerequisite for realizing a hydrogen energy society, and a high activation energy is required for the electrolysis of water. Therefore, in order to improve the efficiency of hydrogen production, a suitable catalyst needs to be found.

[0003] Electrocatalytic water splitting includes two half-reactions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and the theoretical decomposition voltage is 1.23 V, but due to the high overpotential required for the reaction on the electrode, a decomposition voltage of 1.8 V or higher is required in the actual decomposition process. The higher the overpotential, the higher the voltage that should be applied, and the more energy consumed. Therefore, it is crucial to develop a high-efficiency hydrogen evolution catalyst that can significantly reduce the hydrogen evolution overpotential. Currently, the main commercial catalysts are noble metals such as platinum (Pt) and palladium (Pb), which are expensive and scarce, seriously affecting large-scale use, and there is an urgent need to develop electrocatalysts with high catalytic performance and low cost.

[0004] Nickel-based nanomaterials are widely used as electrocatalytic hydrogen production catalysts due to their advantages of abundant reserves, low cost, high electrical conductivity, good chemical stability, and strong magnetic responsiveness. Nickel nanowires are self-assembled from zero-dimensional nanoparticles, avoiding the drawbacks of nanoparticle ripening, and the high aspect ratio and large specific surface area effectively improve the electron conduction rate. However, the current nickel nanowires have the problem of magnetic agglomeration, which greatly limits their reaction activity. In addition, nano-nickel hydroxide is also a kind of nickel-based nanomaterial with good performance, but its in-situ growth is mostly carried out in the high-temperature environment of a hydrothermal kettle, which has the problems of complex production process and high energy consumption, making it difficult to mass-produce. SUMMARY

[0005] In order to overcome at least one problem existing in the prior art, one of the purposes of the present application is to provide a preparation method of nickel hydroxide / nickel nanowire with a core-shell structure, which can prepare a composite material with uniform morphology and good dispersity.

[0006] The second purpose of the present application is to provide a nickel hydroxide / nickel nanowire prepared by the above preparation method.

[0007] The third purpose of the present application is to provide an application of the above nickel hydroxide / nickel nanowire.

[0008] To achieve the above object, the technical scheme adopted by the present application is:

[0009] The first aspect of the present application provides a preparation method of core-shell structured nickel hydroxide / nickel nanowires, comprising the following steps: mixing a nickel source, an alkali source, a dispersing agent, a reducing agent and a solvent, and performing a heating reaction under the action of a magnetic field to obtain nickel nanowires; then dispersing the nickel nanowires in a modifier to perform a surface modification reaction, so that nickel hydroxide is generated on at least part of the surface of the nickel nanowires to obtain the core-shell structured nickel hydroxide / nickel nanowires; the modifier comprises at least one of water, an ammonia water solution or a nickel source aqueous solution.

[0010] In some specific embodiments of the present application, the modifier does not contain sodium ions.

[0011] The nickel nanowires prepared in the present application are dispersed in a specific modifier, a surface modification reaction can occur, and nickel hydroxide is generated on the surface of the nickel nanowires, thereby effectively improving the catalytic performance of the material; however, it should be noted that the modifier cannot contain sodium ions, which will inhibit the formation of nickel hydroxide on the surface of the nickel nanowires.

[0012] Preferably, the modifier is at least one of water, an ammonia water solution or a nickel source aqueous solution; the modifier is water; more preferably, the modifier is deionized water.

[0013] The water, ammonia water solution and nickel source aqueous solution in the present application all contain water, which can promote the generation of nickel hydroxide on the surface of the nickel nanowires, and ammonia water and nickel source will not inhibit the formation of nickel hydroxide.

[0014] Preferably, the nickel hydroxide is in a flower-like structure; the flower-like structure is formed by assembling a plurality of nickel hydroxide nanosheets.

[0015] Preferably, the nickel source aqueous solution comprises a nickel chloride aqueous solution, a nickel nitrate aqueous solution or a combination thereof; further preferably, the nickel source aqueous solution is selected from a nickel chloride aqueous solution; more preferably, the nickel source aqueous solution comprises a nickel chloride hexahydrate aqueous solution.

[0016] Preferably, the temperature of the surface modification reaction is 40-80℃; further preferably, 45-70℃; more preferably, 48-60℃.

[0017] Preferably, the time of the surface modification reaction is 4-30h; further preferably, 5-20h; more preferably, 6-15h; more preferably, 10-14h.

[0018] The time of the surface modification reaction affects the morphology and structure of the composite material, and the surface modification is performed within the specific time range of the present application, so that a better surface modification effect can be obtained, especially a nickel hydroxide / nickel nanowire with moderate length and uniform dispersion, which has more excellent electrocatalytic activity.

[0019] Preferably, the nickel source comprises nickel chloride, nickel nitrate or a combination thereof; further preferably, the nickel source is selected from nickel chloride; more preferably, the nickel source is selected from nickel chloride hexahydrate.

[0020] Preferably, the alkali source comprises sodium hydroxide, potassium hydroxide or a combination thereof; further preferably, the alkali source is selected from sodium hydroxide.

[0021] Preferably, the dispersant comprises polyvinylpyrrolidone, sodium citrate or a combination thereof; further preferably, the dispersant is selected from polyvinylpyrrolidone.

[0022] Preferably, the reducing agent comprises hydrazine hydrate; further preferably, the reducing agent is selected from hydrazine hydrate.

[0023] Preferably, the solvent comprises water, an alcohol solvent or a combination thereof; further preferably, the solvent comprises water and an alcohol solvent.

[0024] Preferably, in the solvent, the volume ratio of water to alcohol solvent is 1:(5-20); further preferably, 1:(8-15).

[0025] Preferably, in the solvent, the alcohol solvent is selected from ethylene glycol.

[0026] Preferably, the mass ratio of the nickel source to the alkali source is 1:(4-10); further preferably, 1:(5-8); more preferably, 1:(6-7).

[0027] Preferably, the mass ratio of the nickel source to the dispersant is 1:(4-10); further preferably, 1:(5-8); more preferably, 1:(6-7).

[0028] Preferably, the mass ratio of the nickel source to the reducing agent is 1:(4-10); further preferably, 1:(4.5-8); more preferably, 1:(5-6).

[0029] Preferably, the dosage ratio of the nickel source to the solvent is 1g:(30-100)mL; further preferably, 1g:(35-80)mL; more preferably, 1g:(40-60)mL.

[0030] Preferably, the temperature of the heating reaction is 70-100℃; further preferably, 75-90℃; more preferably, 78-85℃.

[0031] Preferably, the heating reaction time is 20-60 min; more preferably 25-50 min; and even more preferably 28-40 min.

[0032] Preferably, the mixing order of the nickel source, alkali source, dispersant, reducing agent, and solvent is as follows: after mixing the nickel source, alkali source, dispersant, and solvent, the reducing agent is added for further mixing; more preferably, the mixing order of the nickel source, alkali source, dispersant, reducing agent, and solvent is as follows: the nickel source is mixed with a portion of the solvent, and the alkali source is mixed with the remaining solvent to obtain a nickel source solution and an alkali source solution, respectively; then the nickel source solution and the alkali source solution are mixed to obtain a mixed solution; then the dispersant and reducing agent are added sequentially to the mixed solution for further mixing.

[0033] A second aspect of the present invention provides a core-shell structured nickel hydroxide / nickel nanowire prepared by the preparation method described in the first aspect of the present invention.

[0034] Preferably, the average length of the core-shell structured nickel hydroxide / nickel nanowires is 15–25 μm; more preferably, it is 18–22 μm.

[0035] Preferably, the average diameter of the core-shell structured nickel hydroxide / nickel nanowires is 350–450 nm; more preferably, it is 380–420 nm.

[0036] A third aspect of the present invention provides the application of core-shell structured nickel hydroxide / nickel nanowires as described in the second aspect of the present invention in the catalytic electrolysis of water reaction.

[0037] Preferably, the water electrolysis reaction is a water electrolysis reaction under an alkaline environment.

[0038] The nickel hydroxide / nickel nanowires of this invention exhibit better performance in catalyzing water electrolysis under alkaline conditions, particularly demonstrating superior electrocatalytic oxygen and hydrogen evolution properties in alkaline environments.

[0039] The beneficial effects of this invention are as follows: First, under the action of a magnetic field, a nickel source is reduced by a reducing agent to obtain nickel nanowires. Then, by dispersing the nickel nanowires in a modifier, a surface modification reaction can occur to form a nickel hydroxide / nickel nanowire heterostructure, which effectively improves the problem of easy aggregation of nickel nanowires. At the same time, it increases the dispersion and specific surface area of ​​nickel nanowires and increases the number of exposed active sites, thereby exhibiting excellent electrocatalytic oxygen evolution and hydrogen evolution performance.

[0040] Specifically, compared with the prior art, the present invention has the following advantages:

[0041] 1. The method provided by the application can simply and at low cost produce flower-shaped nickel hydroxide / nickel nanowires with core-shell structure. Compared with the mainstream method for preparing flower-shaped nickel hydroxide, i.e. the hydrothermal method which needs to provide a high-temperature and high-pressure environment, the application can stably produce nickel hydroxide under low-temperature conditions, is green and environmentally friendly, and is conducive to large-scale production.

[0042] 2. The nickel hydroxide / nickel nanowires with core-shell structure prepared by the application have a flower-shaped structure on the surface, the nickel hydroxide nanosheets are coated on the surface of the nickel nanowire "core" as a "shell layer", and the nickel hydroxide two-dimensional nanosheets can self-assemble to form a flower-shaped structure and form a rich heterogeneous micro-nano interface with the nickel nanowire. The composite material has uniform morphology, good dispersity and stability, and has good catalytic effect in the water electrolysis reaction, especially excellent electrocatalytic oxygen evolution and hydrogen evolution performance in an alkaline electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The XRD pattern of Examples 1-4 and Comparative Example 1.

[0044] Figure 2 The SEM pattern of Example 2.

[0045] Figure 3 The SEM pattern of Example 4.

[0046] Figure 4 The SEM pattern of Comparative Example 1.

[0047] Figure 5 The XPS spectrum of Example 2.

[0048] Figure 6 The linear scan curve of the oxygen evolution reaction of Examples 1-4 and Comparative Example 1.

[0049] Figure 7 The linear scan curve of the hydrogen evolution reaction of Examples 1-4 and Comparative Example 1. DETAILED DESCRIPTION

[0050] The content of the application will be further described in detail through specific examples. It should also be understood that the following examples are only used to further illustrate the application and cannot be understood as limiting the protection scope of the application. Some non-essential improvements and adjustments made by those skilled in the art according to the principles set forth in the application all belong to the protection scope of the application. The following example specific process parameters are only one example in the appropriate range, i.e. those skilled in the art can make appropriate selection within the range through the description herein, and are not limited to the specific data of the following examples. The raw materials, reagents or devices used in the following examples and comparative examples can be obtained from conventional commercial channels, or can be obtained by existing known methods, unless otherwise specified.

[0051] Example 1

[0052] A preparation method of a core-shell structure nickel hydroxide / nickel nanowire, the specific steps are as follows:

[0053] (1) Measure 50 mL of ethylene glycol into a 100 mL beaker, weigh 0.3 g of nickel chloride hexahydrate into the beaker, and magnetically stir until the added nickel chloride hexahydrate is completely dissolved, and the solution turns light green.

[0054] (2) Weigh 2 g of sodium hydroxide in a glass bottle, add 2 mL of water to dissolve completely, and then transfer to the solution obtained in step (1), and magnetically stir for 1-2 min.

[0055] (3) Weigh 2 g of polyvinylpyrrolidone, slowly add to the solution obtained in step (2), magnetically stir for 30 min, and ultrasonic for 15 min to ensure that the polyvinylpyrrolidone is completely dissolved.

[0056] (4) Add 2 mL of 80% mass fraction of hydrazine hydrate to the solution in step (3), magnetically stir until the solution turns light blue, and remove the magnet from the beaker.

[0057] (5) Place a 150x100x25mm magnet on both sides of the 80℃ water bath to provide a constant magnetic field, transfer the beaker to the center of the water bath, and let it stand for 30 min. After the solution turns from blue to colorless, the product nickel nanowire floats above the solution.

[0058] (6) Transfer the product nickel nanowire to a centrifuge tube, wash it with ethanol and deionized water for 4-6 times, and collect the solid.

[0059] (7) Add 2 mL of deionized water to the washed solid product, shake well, and transfer to an oven for reaction at 50℃ for 6h, and cool to room temperature.

[0060] (8) Centrifuge the reacted product, collect the solid, and freeze-dry for 6h to obtain a black powder.

[0061] Example 2

[0062] A preparation method of a core-shell structure nickel hydroxide / nickel nanowire, the specific steps are as follows:

[0063] (1) Measure 50 mL of ethylene glycol into a 100 mL beaker, weigh 0.3 g of nickel chloride hexahydrate into the beaker, and magnetically stir until the added nickel chloride hexahydrate is completely dissolved, and the solution turns light green.

[0064] (2) Weigh 2 g of sodium hydroxide in a glass bottle, add 2 mL of water to dissolve completely, and then transfer to the solution obtained in step (1), and magnetically stir for 1-2 min.

[0065] (3) Weigh 2 g of polyvinylpyrrolidone and slowly add it to the solution obtained in step (2), magnetically stir for 30 min, and ultrasonic for 15 min to ensure that the polyvinylpyrrolidone is fully dissolved.

[0066] (4) Add 2 mL of 80% hydrazine hydrate to the solution in step (3) and magnetically stir until the solution turns light blue, then remove the magnet from the beaker.

[0067] (5) Place a 150x100x25mm magnet on each side of the 80°C water bath to provide a constant magnetic field, transfer the beaker to the center of the water bath, and let it stand for 30 min after the solution turns from blue to colorless. The product nickel nanowires float above the solution.

[0068] (6) Transfer the product nickel nanowires to a centrifuge tube and wash them with ethanol and deionized water for 4-6 times, and collect the solid.

[0069] (7) Add 2 mL of deionized water to the washed solid, shake well, and transfer to an oven for reaction at 50°C for 12 h, and cool to room temperature.

[0070] (8) Centrifuge the product after reaction, collect the solid, and freeze-dry for 12 h to obtain a black powder.

[0071] Example 3

[0072] A method for preparing a core-shell structure of nickel hydroxide / nickel nanowires, the specific steps are as follows:

[0073] (1) Measure 50 mL of ethylene glycol into a 100 mL beaker, weigh 0.3 g of nickel chloride hexahydrate into the beaker, and magnetically stir until the added nickel chloride hexahydrate is completely dissolved, and the solution turns light green.

[0074] (2) Weigh 2 g of sodium hydroxide in a glass bottle, add 2 mL of water to dissolve completely, and then transfer to the solution obtained in step (1), and magnetically stir for 1-2 min.

[0075] (3) Weigh 2 g of polyvinylpyrrolidone and slowly add it to the solution obtained in step (2), magnetically stir for 30 min, and ultrasonic for 15 min to ensure that the polyvinylpyrrolidone is fully dissolved.

[0076] (4) Add 2 mL of 80% hydrazine hydrate to the solution in step (3) and magnetically stir until the solution turns light blue, then remove the magnet from the beaker.

[0077] (5) Place two magnets of 150 x 100 x 25 mm on both sides of the water bath at 80 °C to provide a constant magnetic field. Transfer the beaker to the center of the water bath. After 30 min of reaction, the solution changes from blue to colorless, and the product nickel nanowires float above the solution.

[0078] (6) Transfer the product nickel nanowires to a centrifuge tube and wash them with ethanol and deionized water for 4-6 times. Collect the solid.

[0079] (7) Add 2 mL of deionized water to the washed solid, shake well, and transfer to an oven for reaction at 50 °C for 18 h. Cool to room temperature.

[0080] (8) Centrifuge the product after reaction, collect the solid, and freeze-dry for 12 h to obtain a black powder.

[0081] Example 4

[0082] A preparation method of a core-shell structured nickel hydroxide / nickel nanowire is as follows:

[0083] (1) Measure 50 mL of ethylene glycol into a 100 mL beaker, weigh 0.3 g of nickel chloride hexahydrate into the beaker, and magnetically stir until the added nickel chloride hexahydrate is completely dissolved. The solution changes to light green.

[0084] (2) Weigh 2 g of sodium hydroxide into a glass bottle, add 2 mL of water to dissolve, and then transfer to the solution obtained in step (1). Magnetically stir for 1-2 min.

[0085] (3) Weigh 2 g of polyvinylpyrrolidone and slowly add to the solution obtained in step (2). Magnetically stir for 30 min and ultrasonic for 15 min to ensure that the polyvinylpyrrolidone is completely dissolved.

[0086] (4) Add 2 mL of 80% mass fraction of hydrazine hydrate to the solution in step (3). Magnetically stir until the solution changes to light blue, and remove the magnet from the beaker.

[0087] (5) Place two magnets of 150 x 100 x 25 mm on both sides of the water bath at 80 °C to provide a constant magnetic field. Transfer the beaker to the center of the water bath. After 30 min of reaction, the solution changes from blue to colorless, and the product nickel nanowires float above the solution.

[0088] (6) Transfer the product nickel nanowires to a centrifuge tube and wash them with ethanol and deionized water for 4-6 times. Collect the solid.

[0089] (7) Add 2 mL of deionized water to the washed solid, shake well, and transfer to an oven for reaction at 50 °C for 18 h. Cool to room temperature.

[0090] (8) The product after reaction was centrifuged, the solid was collected, and freeze-dried for 12 h to obtain a black powder.

[0091] Comparative Example 1

[0092] A preparation method of nickel nanowires, the specific steps are as follows:

[0093] (1) 50 mL of ethylene glycol was measured and added into a 100 mL beaker, 0.3 g of nickel chloride hexahydrate was weighed and added into the beaker, and magnetic stirring was performed until the added nickel chloride hexahydrate was completely dissolved, and the solution turned light green.

[0094] (2) 2 g of sodium hydroxide was weighed in a glass bottle, 2 mL of water was added to dissolve it thoroughly, and then it was transferred to the solution obtained in step (1), and magnetic stirring was performed for 1-2 min.

[0095] (3) 2 g of polyvinylpyrrolidone was weighed and slowly added to the solution obtained in step (2), and magnetic stirring was performed for 30 min and ultrasonic treatment was performed for 15 min to ensure that the polyvinylpyrrolidone was completely dissolved.

[0096] (4) 2 mL of 80% hydrazine hydrate was added to the solution in step (3), and magnetic stirring was performed until the solution turned light blue, and the magnet in the beaker was removed.

[0097] (5) Two 150x100x25mm magnets were placed on both sides of an 80℃ water bath to provide a constant magnetic field, the beaker was transferred to the center of the water bath, and after standing for 30 min, the solution turned from blue to colorless, and the product nickel nanowires floated above the solution.

[0098] (6) The product nickel nanowires were transferred to a centrifuge tube and washed with ethanol and deionized water for 4-6 times, the solid was collected, and freeze-dried for 12 h to obtain a gray-black powder.

[0099] Comparative Example 2

[0100] A preparation method of core-shell structured nickel hydroxide / nickel nanowires, which is different from Example 2 in that deionized water is replaced by an equal amount of sodium chloride aqueous solution in step (7), and the other steps and raw materials are the same as those of Example 2.

[0101] The results show that the product nickel nanowires are surface-modified by sodium chloride aqueous solution in Comparative Example 2, and nickel hydroxide nanosheets cannot be generated on the surface of the product nickel nanowires, which is speculated to be that sodium ions inhibit the formation and growth of nickel hydroxide nanosheets.

[0102] Performance test

[0103] (1) X-ray diffraction characterization

[0104] Figure 1The XRD patterns of Examples 1-4 and Comparative Example 1 are shown in Figure 1. As can be seen from the figure, the diffraction peaks of Comparative Example 1 at 2θ of 44.5°, 51.8° and 76.4° correspond to the (111), (200) and (220) crystal planes of nickel, respectively, indicating that the product is pure nickel; while in addition to the diffraction peaks of nickel, the diffraction peaks of Examples 1-4 at 2θ of 33.1°, 38.6°, 59.1° and 62.7° correspond to the (100), (101), (110) and (111) crystal planes of nickel hydroxide, respectively, and the intensity of the diffraction peaks of nickel hydroxide in the products of Examples 1-4 is different, indicating that the products have different contents of nickel hydroxide.

[0105] (2) Electron scanning microscope (SEM) characterization

[0106] Figure 2 Figure 2 is the SEM images of Example 2, wherein (a) is a low-magnification SEM image and (b) is a high-magnification SEM image. As can be seen from the figure, the nickel hydroxide / nickel nanowire composite product prepared in Example 2 has a core-shell structure, in which the nickel nanowire is the core and the flower-like nickel hydroxide self-assembled as the shell layer, and the flower-like nickel hydroxide / nickel nanowire has a length of about 20 μm and a diameter of about 400 nm, and has a uniform morphology and good dispersibility.

[0107] Figure 3 Figure 3 is the SEM images of Example 4. As can be seen from the figure, the length of the nickel nanowire is about 10 μm and the diameter is about 500 nm, indicating that the nickel nanowire is broken and the average length is shortened with the increase of the heating time.

[0108] Figure 4 Figure 4 is the SEM images of Comparative Example 1. As can be seen from the figure, the length of the nickel nanowire is about 30 μm, indicating that the nickel nanowire is easily aggregated due to the strong magnetism and has poor dispersibility.

[0109] (3) X-ray photoelectron spectroscopy (XPS) characterization

[0110] Figure 5 Figure 5 is the XPS spectrum of Example 2. As can be seen from the figure, the spectrum of Ni 2p shows two satellite peaks of Ni 2p 3 / 2 and Ni 2p 1 / 2 The peaks of Ni 2p 3 / 2 (855.6 eV) and Ni 2p 1 / 2 (873.1 eV) are derived from the Ni-OH bond, further confirming that the shell layer of the flower-like substance is nickel hydroxide.

[0111] (4) Test of the performance of catalyzing water electrolysis reaction

[0112] The specific steps are as follows:

[0113] Working electrode preparation: 30 mg of the sample prepared in Example 1-4 and Comparative Example 1 and 120 μL of 5% Nafion solution were dispersed in 3 mL of methanol solution under ultrasonic for 1 h, ensuring the powder was uniformly dispersed in the solvent to obtain a catalyst slurry, which was loaded into a spray gun liquid storage chamber, N2 was connected to the spray gun as a carrier gas, a clean hydrophilic carbon paper was used as a substrate, the slurry was uniformly sprayed onto the surface of the hydrophilic carbon paper, and dried by an infrared lamp to obtain a working electrode.

[0114] The water electrolysis oxygen evolution reaction (OER) was carried out by a three-electrode test system, using a Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, 1M KOH solution as the electrolyte, and a scan rate of 50 mV / s to measure the linear sweep voltammetry curve.

[0115] The water electrolysis hydrogen evolution reaction (HER) was carried out by a three-electrode test system, using a Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, 1M KOH solution as the electrolyte, and a scan rate of 50 mV / s to measure the linear sweep voltammetry curve.

[0116] Figure 6 are the linear sweep (LSV) curves of the oxygen evolution reaction of Example 1-4 and Comparative Example 1. As can be seen from the figure, compared with Comparative Example 1, after coating the nickel nanowires with flower-shaped nickel hydroxide, the overpotential at the same current density of Example 1-2 is significantly reduced, and the electrocatalytic oxygen evolution performance is improved. In addition, by adjusting the loading amount and effective specific surface area of nickel hydroxide on the surface of nickel nanowires through heating time, the OER overpotential can be synergistically reduced, and the electrocatalytic oxygen evolution activity can be improved. Table 1 lists the OER overpotential of Example 1-4 and Comparative Example 1 at a current density of 10 mA / cm 2 , and it can be seen that the overpotential of Example 2 is only 160 mV, which is significantly lower than that of Comparative Example 1 and other examples.

[0117] Table 1 OER overpotential of Example 1-4 and Comparative Example 1 at a current density of 10 mA / cm 2

[0118] Sample 10 mA / cm 2 OER overpotential at current density (mV) Example 1 336 Example 2 160 Example 3 430 Example 4 454 Comparative Example 1 366

[0119] Figure 7 are the linear sweep (LSV) curves of the hydrogen evolution reaction of Example 1-4 and Comparative Example 1, and Table 2 is the HER overpotential of Example 1-4 and Comparative Example 1 at a current density of 10 mA / cm 2 . As can be seen, when the current density reaches 10 mA / cm 2 , the HER overpotential of Example 1 is 208 mV, the overpotential of Example 2 is 174 mV, the overpotential of Example 3 is 209 mV, and the overpotential of Example 4 is 230 mV, indicating that the electrocatalytic hydrogen evolution activity of Example 2 is optimal. ​

[0120] Table 2 HER overpotential of Examples 1-4 and Comparative Example 1 at 10 mA / cm 2 HER overpotential at current density

[0121] Sample 10 mA / cm 2 HER overpotential at current density (mV) Example 1 208 Example 2 174 Example 3 209 Example 4 230 Comparative Example 1 229

[0122] As the length of the nickel nanowire is longer, the charge transmission is more favorable, and the electrocatalytic effect is better, and it can be seen from the comparison of Example 2 and Comparative Example 1 that the nickel hydroxide coated on the surface of the nickel nanowire can effectively improve the electrocatalytic activity of the material, and a rich heterojunction structure is formed at the contact interface of the two, which effectively promotes the charge transfer and the transition of the carrier, so that the material with a shorter length (about 20 μm) in Example 2 can obtain a better electrocatalytic activity than the material with a longer length (about 30 μm) in Comparative Example 1. Although the electrocatalytic activity of Example 3 and Example 4 is not as good as that of Example 2, it is because the material is broken during the preparation process, resulting in a shorter length, but it still has good electrocatalytic activity. In Example 4, the HER overpotential is basically the same as that of Comparative Example 1 (about 30 μm) even though the length is shorter (about 10 μm), which shows that the nickel hydroxide / nickel nanowire heterojunction structure constructed by the present application has excellent electrocatalytic activity.

[0123] The preparation method in the embodiments of the present application has low cost, low energy consumption, simple process, low requirement for equipment, and does not require high-temperature and high-pressure resistant equipment in the preparation process. The preparation of nickel hydroxide uses nickel nanowires as a nickel source, does not require the addition of any chemical reagent, and can form flower-shaped nickel hydroxide nanosheets in deionized water independently, improves the atomic utilization rate, does not produce other industrial waste, meets the green and environmental protection requirements, and is convenient for large-scale industrial production.

[0124] Compared with the current nickel / nickel hydroxide composite material which mostly uses foam nickel as a substrate, the composite material prepared in the embodiments of the present application uses nickel nanowires, and the large specific surface area of the nickel nanowires increases the loading capacity of the composite material by several times.

[0125] The flower-shaped nickel hydroxide / nickel nanowire with a core-shell structure prepared in the embodiments of the present application has uniform morphology and good dispersity, has the advantages of nickel and nickel hydroxide, the contact interface of the two forms a rich heterojunction structure, which is helpful for charge transfer and carrier transition. The self-assembly of the nickel hydroxide nanosheets into a flower-shaped structure can provide a larger specific surface area and more active sites, and has a broad development prospect in the fields of energy storage and catalysis.

[0126] To sum up, the application firstly reduces the nickel source by a reducing agent under the action of a magnetic field to obtain nickel nanowires, and then disperses the nickel nanowires in a modifier to enable a surface modification reaction, that is, to coat the nickel nanowires with flower-shaped nickel hydroxide nanosheets to form a nickel hydroxide / nickel nanowire heterostructure, effectively improving the problem that the nickel nanowires are prone to aggregation, and the flower-shaped structure can increase the dispersity and specific surface area of the nickel nanowires and increase the number of exposed active sites, thereby having excellent electrocatalytic oxygen evolution and hydrogen evolution performance.

Claims

1. A method for preparing core-shell structured nickel hydroxide / nickel nanowires, characterized in that, The process includes the following steps: mixing a nickel source, an alkali source, a dispersant, a reducing agent, and a solvent, and heating the mixture under a magnetic field to obtain nickel nanowires; then dispersing the nickel nanowires in a modifier to perform a surface modification reaction, causing nickel hydroxide to form on at least a portion of the surface of the nickel nanowires, resulting in the core-shell structured nickel hydroxide / nickel nanowires; the modifier includes at least one of water, an ammonia solution, or an aqueous solution of a nickel source; the nickel hydroxide has a flower-like structure; the flower-like structure is formed by assembling several nickel hydroxide nanosheets; the surface modification reaction temperature is 40~80℃; and the surface modification reaction time is 4~30h.

2. The preparation method according to claim 1, characterized in that, The nickel source includes nickel chloride, nickel nitrate, or a combination thereof; And / or, the alkali source includes sodium hydroxide, potassium hydroxide, or a combination thereof; And / or, the dispersant comprises polyvinylpyrrolidone, sodium citrate, or a combination thereof; And / or, the reducing agent includes hydrazine hydrate; And / or, the solvent includes water, alcohol solvents, or combinations thereof.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the nickel source to the alkali source is 1:(4~10). And / or, the mass ratio of the nickel source to the dispersant is 1:(4~10); And / or, the mass ratio of the nickel source to the reducing agent is 1:(4~10); And / or, the ratio of the nickel source to the solvent is 1 g : (30~100) mL.

4. The preparation method according to claim 1, characterized in that, The temperature of the heating reaction is 70~100℃; And / or, the heating reaction time is 20~60 min.

5. A core-shell structured nickel hydroxide / nickel nanowire prepared by the preparation method according to any one of claims 1 to 4.

6. The core-shell structured nickel hydroxide / nickel nanowires according to claim 5, characterized in that, The average length of the core-shell structured nickel hydroxide / nickel nanowires is 15~25 μm; And / or, the average diameter of the core-shell structured nickel hydroxide / nickel nanowires is 350~450 nm.

7. The application of a core-shell structured nickel hydroxide / nickel nanowire as described in claim 5 or 6 in a catalytic water electrolysis reaction.

8. The application according to claim 7, characterized in that, The water electrolysis reaction is a water electrolysis reaction under alkaline conditions.

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