Nickel electrode with multi-level structure and preparation method thereof

Abstract

The invention provides a nickel electrode with a multi-level structure and a preparation method thereof. The preparation method mainly comprises the following steps: preparing a bottom-layer concave-convex substrate structure by mixed acid dipping, and forming a middle layer and a catalyst layer structure by surface heterogeneous growth. According to the method, tight combination of the catalyst layer and the substrate is taken as a guide, the uneven nickel metal substrate is obtained through mixed acid etching aiming at the problem that the catalyst is prone to falling off, and a highly rough surface is provided for in-situ growth of a subsequent columnar middle layer. The nickel metal substrate and the nanoflower layer catalyst are connected through the middle layer, the binding force of the catalyst and the substrate is effectively increased, the catalyst is prevented from falling off, and industrial stable water electrolysis is achieved. The surface of the synthesized nickel electrode with the multi-level structure has excellent performance stability, the overpotential is only increased by 8 mV when the nickel electrode runs for 1000 hours under the current density of 500 mA cm <-2 >, and only 1.83 V is needed when the nickel electrode is in an electrolytic bath.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalytic materials, and particularly relates to a multi-level structure nickel electrode and a preparation method thereof. BACKGROUND

[0002] With the continuous improvement of people's living standards, the problem of energy shortage is becoming increasingly prominent. Hydrogen, as a renewable energy material with the highest energy density and clean properties, is expected to become the most valuable alternative to fossil fuels, which can solve the problems of sustainability, environmental emissions and energy security, and thus has attracted widespread attention from countries. Using electrocatalytic water splitting to convert water into hydrogen is a promising technology to solve the energy crisis. However, under the industrial level of large current density, the water electrolysis catalyst has a serious problem of aggregation and falling off, which leads to rapid performance decline and thus affects the structure and performance of the electrode, which seriously restricts the industrialization progress of electrocatalytic water splitting; in addition, slow material transport and diffusion make the reactants unable to be replenished in time under large current density, thereby increasing the reaction overpotential and reducing energy efficiency, which is another major bottleneck problem for the industrialization of water electrolysis.

[0003] Existing partial catalytic electrodes use organic binders such as Nafion, but such organic binders have low conductivity, which can reduce the overall activity and cause the electrocatalyst to fall off when oxygen is vigorously generated on the electrode surface under high current density. In order to solve this problem and avoid the use of binders, the concept of in-situ growth of self-supporting catalytic electrodes based on metal substrates is proposed. CN115386910A proposes a Ni-Fe-Cr@CeO2 self-supporting electrode prepared by cold pressing, sintering, heat treatment, and dealloying treatment, but the preparation steps involved in this patent are complicated, and there is a problem that the uniform loading of active materials cannot be guaranteed. CN118581512A proposes a method of in-situ growth of CoMnFeP bifunctional catalyst on a nickel foam by hydrothermal method and calcination in a tube furnace. Due to the large difference in interface compatibility between the active material and the carrier, the combination of the active material and the carrier is still not tight enough, resulting in a decrease in stability and activity. Although the above methods are all for the preparation of self-supporting catalytic electrodes, they cannot effectively solve the problem of serious aggregation and falling off of the catalyst under large current density, and the test scheme is complex, with poor repeatability and controllability, which is not suitable for the preparation of large-area electrodes in the rough industrialization.

[0004] In view of the above shortcomings, how to use a simple experimental scheme to prepare a catalytic electrode with stable performance and excellent performance is the key to the industrialization development of water electrolysis. SUMMARY

[0005] Based on the above analysis, the purpose of the present application is to etch the nickel foam with mixed acid, and then use the heterogeneous method to induce growth to form an intermediate layer and a catalyst layer, so as to obtain an industrial-grade self-supporting nickel electrode with a multi-level structure, multiple substance transmission channels and a high specific surface area nanoflower morphology.

[0006] In order to achieve the above technical effects, the present application is realized by the following technical scheme:

[0007] The present application first discloses a multi-level structure nickel electrode and a preparation method thereof, comprising:

[0008] (1) Pretreatment of nickel metal substrate:

[0009] The nickel metal substrate is ultrasonically cleaned with acetone and ethanol respectively, and then deionized water is used to remove residual solvents, and vacuum constant temperature drying is performed, to obtain a pretreated nickel metal substrate;

[0010] (2) Gradient etching of nickel substrate:

[0011] The pretreated nickel metal substrate is immersed in a constant temperature etching tank for 1-10 s, immediately washed repeatedly with deionized water until the acid is cleaned, the etching reaction is terminated, and then vacuum drying treatment is performed, after which it is sealed and stored, to obtain an acid etched nickel substrate for standby;

[0012] (3) Construction of heterogeneous interface:

[0013] The acid etched nickel substrate is vertically immersed in a growth solution, and is immersed at room temperature for 24-72 h, and then repeatedly washed with flowing deionized water to remove loose particles accumulated on the surface, and vacuum drying is performed, to obtain a multi-level structure nickel electrode.

[0014] Further, in step (1), the acetone ultrasonic cleaning is 15 min, and the ethanol ultrasonic cleaning is 15 min; the ultrasonic power is 200 W, and the frequency is 40 kHz; the vacuum constant temperature drying conditions are: vacuum degree ≤10 Pa, 50 ℃ constant temperature drying for 2 h.

[0015] Further, in step (1), the nickel metal substrate includes but is not limited to: nickel foam, nickel mesh or nickel plate.

[0016] Further, the nickel metal substrate is nickel foam.

[0017] Further, in step (2), the temperature of the constant temperature etching tank is 25±0.5℃; the vacuum drying treatment conditions are: vacuum degree ≤10 Pa, drying treatment at 50 ℃ for 2 h.

[0018] Further, in step (2), the etching solution is prepared by the following method:

[0019] Mix concentrated nitric acid, hydrofluoric acid and deionized water in a volume ratio of 1:1:1-3, stir for 1-3 min, and obtain.

[0020] Further, the volume ratio of the concentrated nitric acid, hydrofluoric acid and deionized water is 1:1:2.

[0021] Further, the growth solution in step (3) is prepared by the following method:

[0022] 1. Preparation of A liquid: dissolve 2-12 mmol of Ni(NO3)2 6H2O in 24 mL of isopropyl alcohol, magnetically stir for 30 min to form A liquid;

[0023] 2. Preparation of B liquid: dissolve 1-5 mmol of Fe(SO4)2 7H2O in 8 mL of deionized water, magnetically stir for 30 min to form B liquid;

[0024] 3. Preparation of growth solution: mix A liquid and B liquid uniformly to prepare the growth solution, and control the molar ratio of Ni to Fe in the growth solution to be 2-4:1 by controlling the concentration of A and B solutions.

[0025] Further, the water content of the isopropyl alcohol in step 1 is ≤0.01%, and the magnetic stirring speed is 500 rpm.

[0026] Further, the magnetic stirring speed in step 2 is 500 rpm.

[0027] Further, the molar ratio of Ni to Fe in the growth solution in step 3 is 3:1.

[0028] Further, the vacuum drying condition in step (3) is: vacuum degree ≤10 Pa, drying at 50℃ for 2 h.

[0029] The application also discloses a multi-level structure nickel electrode prepared by any of the above preparation methods.

[0030] The application has the following beneficial effects:

[0031] The application is guided by the close combination of the catalyst layer and the substrate, and aims at the problem of easy falling of the catalyst. The uneven nickel metal substrate is obtained by mixed acid etching, which provides a high rough surface for the in-situ growth of the subsequent columnar intermediate layer. The intermediate layer connects the nickel metal substrate and the nanoflower layer catalyst, effectively increases the bonding force between the catalyst and the substrate, prevents the falling of the catalyst, and realizes the stable industrial electrolysis of water. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1(a) SEM image of the multi-level structured nickel foam substrate electrode prepared in Example 1 at 1 pm, wherein S1 represents the nickel substrate, S2 represents the intermediate layer, and S3 represents the grown nanoflower; Figure 1 (b) is a mirror image of the nanoflower at 1 pm; Figure 1 (c) is a mirror image of the nickel substrate at 5 pm;

[0033] Figure 2 SEM images of the multi-level structured nickel plate substrate electrode prepared in Example 2, wherein Figure (a) is a 1 pm mirror image, and Figure (b) is a 10 pm mirror image;

[0034] Figure 3 Foam nickel substrate images under different acid etching times in Example 3, wherein Figure (a) represents SEM electron microscope morphology characterization of acid etching time 1 s, Figure (b) represents SEM electron microscope morphology characterization of acid etching time 10 s, Figure (c) is a description in the specification that "the hierarchical structure is not tightly combined with the foam nickel substrate", and Figure (d) represents the time data of the above-described "micron scratch experiment data of the catalyst under acid etching 4 s, 1 s, and 10 s from top to bottom";

[0035] Figure 4 Foam nickel substrate images under different Ni and Fe ratios in Example 4, wherein Figure (a) represents SEM morphology characterization of the catalyst with a molar ratio of Ni:Fe = 4:1, and Figure (b) represents a comparison of the electrocatalytic performance LSV of the catalysts with a molar ratio of Ni:Fe = 3:1 and Ni:Fe = 4:1 (wherein the catalyst with a molar ratio of Ni:Fe = 3:1 is the optimal catalyst in Example 1);

[0036] Figure 5 Foam nickel substrate images under different isopropanol and water ratios in Example 5, wherein Figure (a) represents a volume ratio of isopropanol:deionized water = 1:1, and Figure (b) represents a volume ratio of isopropanol:deionized water = 6:1;

[0037] Figure 6 Morphology characterization and performance table of 72 h immersion time in Example 6, wherein Figure (a) is SEM electron microscope morphology characterization of the catalyst after 72 h immersion, and Figure (b) is electrochemical performance characterization LSV after 24 h and 72 h immersion (wherein 24 h is the optimal catalyst performance in Example 1);

[0038] Figure 7 XRD test chart of the Ni electrode sample synthesized in Example 1;

[0039] Figure 8 Raman characterization chart of the Ni electrode sample synthesized in Example 1 before and after OER reaction;

[0040] Figure 9 Figure (a) shows the EDS characterization of the Ni electrode sample synthesized in Example 1, where Figure (b) represents the EDS elemental distribution characterization and Figure (a) shows the specific elemental proportions of the EDS test.

[0041] Figure 10 The image shows μm scratch test results for the Ni electrode sample synthesized in Example 1 and the NiFe LDH synthesized by hydrothermal method.

[0042] Figure 11 This is a comparison of the stability of the nickel electrode sample synthesized in Example 1 and the NiFe LDH synthesized by hydrothermal method.

[0043] Figure 12 This is a comparison graph showing the performance of the nickel electrode sample synthesized in Example 1 and commercial Raney nickel in an electrolytic cell. Detailed Implementation

[0044] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0045] This invention first discloses a method for preparing a multi-level nickel electrode, mainly including the preparation of a bottom uneven substrate structure by mixed acid impregnation and the formation of an intermediate layer and a catalyst layer structure by heterogeneous growth on the surface, specifically including the following steps:

[0046] (1) Nickel substrate pretreatment:

[0047] The nickel electrode body was cleaned by sequentially immersing a 10 cm × 10 cm nickel metal substrate in acetone and then in ethanol for 15 min each, using ultrasonic cleaning to effectively remove surface organic contaminants. The ultrasonic cleaner used a power of 200 W and a frequency of 40 kHz. After ultrasonic treatment, the substrate was repeatedly rinsed with deionized water to remove residual solvent and then placed in a vacuum drying oven (vacuum degree ≤10 Pa) at 50°C for 2 h to obtain a pretreated nickel metal substrate. The nickel metal substrate includes nickel foam, nickel mesh, or nickel plate, etc., and this embodiment of the invention primarily uses a nickel foam substrate.

[0048] (2) Gradient etching of nickel substrate:

[0049] (2.1) Preparation of etching solution: Prepare a mixed acid solution in a polytetrafluoroethylene container with a volume ratio of concentrated nitric acid (68% by mass): hydrofluoric acid (40% by mass): deionized water = 1:1:2, and stir with a glass rod for 1-3 minutes until the mixed acid is homogeneous. The ratio of concentrated nitric acid, hydrofluoric acid and deionized water is 1:1:1 to 3, for example, 1:1:1, 1:1:1.5, 1:1:2, 1:1:2.5, 1:1:3.

[0050] (2.2) Dynamic etching: The pretreated nickel metal substrate is placed in a constant temperature (25±0.5℃) etching bath and immersed in the etching solution for 3~5 s. Immediately after immersion, it is repeatedly rinsed with deionized water until the acid is completely removed, thus terminating the etching reaction and achieving a composite rough structure of surface pits and nanoscale protrusions (50~200 nm). If the immersion time is too long or the mixed acid concentration is too high, the nickel substrate structure will collapse. If the immersion time is too short or the acid concentration is too low, the acid etching effect will be insignificant, and it will be impossible to provide a composite structure of pits and protrusions with sufficient roughness for the subsequent growth process.

[0051] (2.3) Post-treatment: Dry in a vacuum drying oven at 50℃ (vacuum degree ≤10 Pa) for 2 h, and store in a vacuum bag to prevent surface oxidation, to obtain an etched nickel substrate for later use.

[0052] (3) Construction of heterogeneous interfaces:

[0053] (3.1) Precursor preparation:

[0054] ① Solution A: Dissolve 2~12 mmol Ni(NO3)2 6H2O in 24 mL of isopropanol (water content ≤0.01%), stir magnetically (500 rpm) for 30 min to form a blue-green transparent solution, which is solution A;

[0055] ② Solution B: Dissolve 1~5 mmol Fe(SO4)2 7H2O in 8 mL of deionized water and stir magnetically (500 rpm) for 30 min to form a light green transparent solution, which is solution B;

[0056] ③ By controlling the concentrations of solutions A and B and the subsequent mixing volume ratio, NiFe LDH with different element ratios can be synthesized in a controllable manner, with the molar ratio controlled between Ni:Fe = 2~4:1, and the performance being the best when Ni:Fe = 3:1.

[0057] (3.2) Composite growth

[0058] In a sealed container, solution A and solution B are mixed and stirred evenly at a volume ratio gradient of 1 to 5:1 to form heterogeneous insoluble yellow-green microparticles. The higher the volume ratio of solution A to solution B, the thicker the intermediate layer. When the volume ratio of solution A to solution B is 3:1, the thickness of the synthesized intermediate layer is suitable, forming a three-layer structure of substrate + intermediate layer + catalyst with the tightest bonding and the best performance. The acid-etched nickel substrate in step (2) is vertically immersed in the growth solution and left to stand at room temperature of 25°C for 24 to 72 hours. A composite structure containing an intermediate layer (height 0.5 to 2 μm) and nanoflowers formed by nanosheets (nanofiber 5 to 10 nm, diameter 0.5 to 10 μm, with the thickness and diameter of the nanoflowers gradually increasing from the intermediate layer to the surface) will be formed on the surface of the acid-etched nickel substrate.

[0059] (3.3) Post-processing

[0060] The composite structure was repeatedly washed with flowing deionized water to remove loose particles accumulated on the surface, and then vacuum dried in a vacuum drying oven at 50℃ (vacuum degree ≤10Pa) for 2 h to maintain the integrity of the multi-level structure.

[0061] Example 1

[0062] A multi-level nickel electrode and its preparation method

[0063] (1) Nickel substrate pretreatment:

[0064] A 10 cm × 10 cm nickel foam substrate was subjected to ultrasonic treatment with acetone and ethanol for 15 min each (ultrasonic power 200 W, ultrasonic frequency 40 kHz), followed by rinsing with deionized water and drying in a 50℃ constant temperature vacuum drying oven (vacuum degree ≤10 Pa) for 2 h.

[0065] (2) Gradient etching of nickel substrate:

[0066] ① Preparation of etching solution: Concentrated nitric acid: hydrofluoric acid: deionized water are mixed in a volume ratio of 1:1:2 and stirred for 2 min to obtain the etching solution;

[0067] ② Dynamic etching: The pretreated nickel metal substrate is placed in an etching bath at 25°C and immersed in the etching solution for 4 seconds. Immediately rinsed repeatedly with deionized water to terminate the etching reaction, forming pits and nano-protrusions (50-150 nm).

[0068] ③ Dry the substrate in a vacuum drying oven at 50℃ (vacuum degree ≤10 Pa) for 2 h, and store it in a vacuum bag to prevent surface oxidation, thus obtaining an etched nickel substrate for later use.

[0069] (3) Construction of heterogeneous interfaces:

[0070] (3.1) Precursor preparation:

[0071] ① Preparation of solution A: Dissolve 6 mmol Ni(NO3)2·6H2O in 24 mL anhydrous isopropanol (stir at 500 rpm for 30 min) to obtain solution A for later use;

[0072] ②Preparation of solution B: Dissolve 2 mmol FeSO4·7H2O in 8 mL of deionized water (stir at 500 rpm for 30 min) to obtain solution B for later use;

[0073] ③ Composite growth: Mix solution A and solution B at a volume ratio of 3:1 and vertically immerse them at room temperature of 25°C for 24 h to obtain a composite structure;

[0074] (3.2) Post-treatment: The composite structure is repeatedly washed with flowing deionized water to remove loose particles accumulated on the surface, and then vacuum dried in a vacuum drying oven at 50℃ (vacuum degree ≤10Pa) for 2 h to obtain the final product.

[0075] Results: The intermediate layer was approximately 0.8 μm thick, the surface nanoflowers had a diameter of 1-3 μm, and the nanosheets were 20 nm thick. The hierarchical structure was dense, resulting in optimal catalytic performance. When the prepared sample was applied to water electrolysis, the current density reached 500 mA cm⁻¹. -2 The OER overpotential is 428 mV. The specific polarization curve of the sample is attached. Figure 4 b and appendix Figure 6 The red circle in b indicates this.

[0076] Example 2

[0077] Change the nickel substrate

[0078] The steps in Example 2 are the same as in Example 1, except that the nickel substrate is changed from nickel foam to a nickel plate. The result is also a three-layer structure grown on the nickel plate substrate. However, the pit and protrusion structure of the Ni substrate is more pronounced, as shown in the attached figure. Figure 2 As shown.

[0079] Example 3

[0080] Change etching time

[0081] The steps in Example 3 are the same as in Example 1, except for the acid etching time, which is controlled to be 1s and 10s respectively. The resulting morphology images of the etched nickel foam substrates are shown in the attached figures. Figure 3 a and appendix Figure 3 As shown in Figure b, when the etching time is 1 s, the resulting pit and protrusion structure is not obvious enough; when the etching time is 10 s, the morphology of the formed nickel foam substrate collapses. In summary, both excessively long and excessively short etching times reduce the roughness of the etched nickel foam substrate, ultimately leading to insufficient bonding between the hierarchical structure and the nickel foam substrate, as shown in the attached figure.Figure 3 c. Appendix Figure 3 Figure d shows the μm scratch experiment under different acid etching times, which can reflect the strength of the bonding between the catalytic hierarchical structure and the nickel foam substrate. The larger the value, the stronger the obtained three-layer structure. From top to bottom, the etching times are 4 s (Ni sample in Example 1, critical force is 6.31 N), 1 s (critical force is 3.05 N), and 10 s (critical force is 4.03 N).

[0082] Example 4

[0083] Changing the elemental ratio of Ni and Fe

[0084] The steps in Example 4 are the same as in Example 1, except for the elemental ratio of Ni and Fe in step (3). Solution A: 8 mmol of Ni(NO3)2·6H2O is dissolved in 24 mL of anhydrous isopropanol, and solution B: 2 mmol of FeSO4·7H2O is dissolved in 8 mL of deionized water. The resulting tertiary structure remains basically unchanged, but the nanoflowers on the surface collapse, as shown in the attached figure. Figure 4 a. This structure is not conducive to the transport of multiple substances, such as reactants and products. Furthermore, increasing the proportion of Ni and Fe elements will lead to a decrease in water-solubilizing performance (see appendix). Figure 4 (b) The prepared sample was applied to water electrolysis at a current density of 500 mA cm⁻¹. -2 The OER overpotential is 560 mV. The specific polarization curve of the sample is attached. Figure 4 b is shown in the green box.

[0085] Example 5

[0086] Changing the volume ratio of isopropanol to water

[0087] The steps in Example 5 are the same as those in Example 1, except that the volume ratio of isopropanol to deionized water in step (3) is different.

[0088] Isopropanol:Deionized water = 1:1

[0089] ① Preparation of solution A: Dissolve 18 mmol Ni(NO3)2·6H2O in 24 mL anhydrous isopropanol (stir at 500 rpm for 30 min) to obtain solution A for later use;

[0090] ②Preparation of solution B: Dissolve 2 mmol FeSO4·7H2O in 8 mL of deionized water (stir at 500 rpm for 30 min) to obtain solution B for later use;

[0091] ③ Composite growth: Mix solution A and solution B at a volume ratio of 1:1 and vertically immerse them at room temperature of 25°C for 24 h to obtain a composite structure;

[0092] Isopropanol:Deionized water = 6:1

[0093] ① Preparation of solution A: Dissolve 3 mmol Ni(NO3)2·6H2O in 24 mL anhydrous isopropanol (stir at 500 rpm for 30 min) to obtain solution A for later use;

[0094] ②Preparation of solution B: Dissolve 2 mmol FeSO4·7H2O in 8 mL of deionized water (stir at 500 rpm for 30 min) to obtain solution B for later use;

[0095] ③ Composite growth: Mix solution A and solution B at a volume ratio of 6:1 and vertically immerse them at room temperature of 25°C for 24 h to obtain a composite structure.

[0096] The resulting tertiary structures, obtained by controlling the volume ratios of isopropanol:water to 1:1 and 6:1 respectively, are shown in the attached figure. Figure 4 a and appendix Figure 4 As shown in b. When isopropanol:water = 1:1, the thickness of the intermediate layer decreases, and there is almost no intermediate layer present. (See attached image.) Figure 5 a. When the ratio of isopropanol to water is 6:1, the thickness of the intermediate layer increases, as shown in the attached figure. Figure 5 b. The thickness of the intermediate layer is approximately 2 μm.

[0097] Example 6

[0098] Change soaking time

[0099] The steps in Example 6 are the same as in Example 1, except that the immersion time in step (3) is extended to 72 h. The surface nanoflowers grow as a whole and connect with each other to be uniformly loaded on the nickel foam substrate. The overall morphology is shown in the attached figure. Figure 6 As shown in figure a. The prepared sample was applied to water electrolysis, achieving a current density of 500 mA cm⁻¹. -2 The OER overpotential is 468 mV. The specific polarization curve of the sample is attached. Figure 6 b is shown in the blue box.

[0100] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A multi-level nickel electrode and its preparation method, comprising: (1) Pretreatment of nickel metal substrate: The nickel metal substrate was ultrasonically cleaned with acetone and ethanol respectively, and the residual solvent was removed with deionized water. After vacuum constant temperature drying, the pretreated nickel metal substrate was obtained. (2) Gradient etching of nickel substrate: The pretreated nickel metal substrate was placed in a constant temperature etching bath and immersed in the etching solution for 1-10 seconds. It was then rinsed repeatedly with deionized water until the acid was cleaned, thus terminating the etching reaction. After vacuum drying, the substrate was sealed and stored to obtain the acid-etched nickel substrate for later use. (3) Construction of heterogeneous interfaces: A nickel substrate etched by acid is vertically immersed in the growth solution and left to stand at room temperature for 24-72 hours. It is then repeatedly washed with flowing deionized water to remove loose particles accumulated on the surface and dried under vacuum to obtain a multi-level nickel electrode.

2. The preparation method according to claim 1, wherein: In step (1), the acetone ultrasonic cleaning is performed for 15 min, and the ethanol ultrasonic cleaning is performed for 15 min. The ultrasonic power is 200 W and the frequency is 40 kHz; The vacuum constant temperature drying conditions are: vacuum degree ≤10 Pa, constant temperature drying at 50 ℃ for 2 h.

3. The preparation method according to claim 1, wherein: The nickel metal matrix in step (1) includes: nickel foam, nickel mesh or nickel plate.

4. The preparation method according to claim 1, wherein: The temperature of the constant temperature etching bath in step (2) is 25±0.5℃; The vacuum drying conditions are: vacuum degree ≤ 10 Pa, drying at 50 ℃ for 2 h.

5. The preparation method according to claim 1, wherein: The etching solution in step (2) is prepared by the following method: In a polytetrafluoroethylene container, concentrated nitric acid, hydrofluoric acid, and deionized water are mixed and stirred for 1 to 3 minutes in a volume ratio of 1:1:1~3.

6. The preparation method according to claim 5, wherein: The volume ratio of concentrated nitric acid, hydrofluoric acid, and deionized water is 1:1:

2.

7. The preparation method according to claim 1, wherein: The growth solution in step (3) is prepared by the following method: ① Preparation of solution A: Dissolve 2~12 mmol Ni(NO3)2 6H2O in 24 mL isopropanol and stir magnetically for 30 min to form solution A; ② Preparation of solution B: Dissolve 1~5 mmol Fe(SO4)2 7H2O in 8 mL of deionized water and stir magnetically for 30 min to form solution B; ③ Preparation of growth solution: Mix solution A and solution B evenly to prepare growth solution. Control the concentration of solutions A and B to control the molar ratio of Ni to Fe in the growth solution to be 2~4:

1.

8. The preparation method according to claim 7, wherein: The isopropanol in step ① has a water content ≤0.01%, and the magnetic stirring speed is 500 rpm; The magnetic stirring speed in step ② is 500 rpm; The molar ratio of Ni to Fe in step ③ is 3:

1.

9. The preparation method according to claim 1, wherein: The vacuum drying conditions described in step (3) are: vacuum degree ≤ 10 Pa, drying at 50 ℃ for 2 h.

10. A multi-level nickel electrode prepared by any one of the preparation methods according to claims 1 to 9.

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