Nickel-iron layered double hydroxide with flaky nanoflower morphology and its preparation method and application

Abstract

The present invention relates to a nickel-iron layered double hydroxide having a flaky nanoflower morphology and its preparation method and application. The preparation method of the nickel-iron layered double hydroxide comprises the following steps: S1, dissolving nickel acetate in an organic solvent or a mixed solvent of an organic solvent and water to prepare a first solution; dissolving a ferrous salt in water to prepare a second solution; S2, mixing the first solution and the second solution to obtain a mixed solution, and obtaining the nickel-iron layered double hydroxide through standing and aging. The method is simple to operate, has mild reaction conditions, low equipment cost, and a green synthesis process; and the NiFe-LDH prepared by the above method presents a three-dimensional nanoflower structure with uniform morphology and high specific surface area, which can provide more active sites. It exhibits excellent electrocatalytic performance as a catalyst for electrolysis of water and oxygen evolution, and has broad application prospects in the fields of electrochemical energy storage, electrocatalysis, and catalytic oxidation.

Description

Technical Field

[0001] The present invention relates to the fields of nanomaterial preparation and electrocatalysis, and in particular to a nickel-iron layered double hydroxide with a flaky nanoflower morphology, and a preparation method and application thereof. Background Art

[0002] Nickel-iron layered double hydroxide (NiFe-LDH) is a two-dimensional material with a layered structure, consisting of positively charged metal hydroxide layers and interlayer anions. The metal hydroxide layers are composed of metal cations (such as Ni 2+ and Fe 3+ ) and hydroxide ions (OH - ), these metal cations are arranged in a hexagonal close-packed manner in the layer, and the interlayer anions and water molecules balance the positive charge of the metal hydroxide layer, which can be expressed by the chemical formula: [Ni 2+ 1-x Fe 3+ x (OH)2] x + (A n- ) x / n ·yH2O. Among them, A n- are exchangeable charge-compensating anions present in the interlayer region (e.g. SO4 2- 、CO3 2- 、NO3 - NiFe-LDH has a large specific surface area, abundant active sites, a unique layered structure, good compositional tunability, and low cost. It has broad application prospects in electrochemical energy storage (such as supercapacitor electrode materials), electrocatalysis (such as water electrolysis to produce hydrogen), and catalytic oxidation (such as degradation of organic pollutants).

[0003] Currently, NiFe-LDHs are typically prepared using solid solution methods such as co-precipitation, hydrothermal, and electrodeposition. Co-precipitation is the most common method, in which metal salts are co-precipitated by slowly adding a precipitant solution (such as NaOH solution or ammonia solution) with continuous stirring to adjust the pH. The desired product is obtained by controlling the reaction conditions, including temperature (60-80°C), concentration, and pH. The hydrothermal method can be used to obtain materials with better crystallinity. This method requires high temperature and high pressure to promote crystal growth and produce a more regular layered structure. A precipitant is also required to provide an alkaline environment to promote the reaction. Electrodeposition involves applying a suitable voltage to reduce anions, generating hydroxide ions, and thereby raising the pH near the cathode. When the concentrations of cations and hydroxide ions reach the solubility product constant, a precipitation reaction of hydroxides or oxides occurs, yielding the target product.

[0004] The traditional co-precipitation method is relatively simple and low-cost, but it requires the addition of additional precipitants to control the pH of the solution, making the reaction process difficult to control. Furthermore, the precipitation process can lead to uneven composition and structure of the precipitate due to variations in precipitation rate, local supersaturation, and temperature, resulting in uneven morphology and size of the resulting product. NiFe-LDH prepared by the conventional co-precipitation method typically has an overpotential of 260-320 mV at a current density of 10 mA / cm². Metal doping and composite modification are commonly used to enhance catalytic performance. NiFe-LDH prepared by the hydrothermal method can form a uniform nanostructure, but the equipment cost is high and the reaction conditions, such as high temperature and high pressure, are required, making the experimental operation more complex. The overpotential of NiFe-LDH prepared by the hydrothermal method is typically 225-350 mV at a current density of 10 mA / cm². Electrodeposition processes are challenging to control, requiring precise control of electroplating process parameters (voltage, current density, temperature, etc.) to avoid uneven deposition. The overpotential of NiFe-LDH prepared by conventional electrodeposition is typically 250-350 mV at a current density of 10 mA / cm².

[0005] In view of the problems faced by NiFe-LDHs materials such as complex preparation process and insufficient performance in electrocatalytic applications, there is an urgent need to develop a new preparation method that is both simple and efficient with excellent catalytic performance. Summary of the Invention

[0006] The present invention aims to solve the problems existing in the existing NiFe-LDHs preparation technology, such as complex process, uneven product morphology, high equipment requirements and poor catalytic performance of the obtained product.

[0007] The present invention provides a method for preparing NiFe-LDH having a flaky nanoflower morphology, which has the following characteristics: (1) the reaction can be completed at room temperature without the need for adding a precipitant to adjust the pH value; (2) the resulting product exhibits a highly uniform nanoflower morphology and a uniform composition distribution; (3) compared with traditional preparation processes, this method has the advantages of simple operation, mild reaction conditions, and environmental friendliness, effectively solving the problems of complex processes, high equipment requirements, and uneven product morphology in the prior art. This preparation method is conducive to promoting the application of NiFe-LDH in fields such as electrochemical energy storage (such as supercapacitor electrode materials), electrocatalysis (such as water electrolysis to produce hydrogen), and catalytic oxidation (such as degradation of organic pollutants).

[0008] Specifically, the following technical solutions are provided:

[0009] The first aspect of the present invention provides a method for preparing NiFe-LDH having a flaky nanoflower morphology, comprising the following steps:

[0010] S1, dissolving a nickel salt in a solvent to prepare a first solution; dissolving a water-soluble ferrous salt in water to prepare a second solution;

[0011] The solvent is an organic solvent or a mixed solvent of an organic solvent and water;

[0012] The nickel salt includes at least one of nickel acetate and nickel acetate hydrate (such as nickel acetate tetrahydrate);

[0013] S2. Evenly mix the first solution and the second solution to obtain a mixed solution, and then allow the mixed solution to stand for aging to obtain the nickel-iron layered double hydroxide.

[0014] This method uses nickel acetate as the nickel source and a water-soluble ferrous salt as the iron source. The two metal sources are dissolved and mixed uniformly in the presence of an organic solvent and water. After aging, uniform NiFe-LDH with a flaky nanoflower morphology is produced. The entire preparation process can be carried out at room temperature (15-35°C). The raw materials are readily available, the operation is simple, the conditions are mild, and no complex equipment is required, facilitating the low-cost industrial production of NiFe-LDH. The synthesis mechanism of this preparation method is as follows (ferrous sulfate is used as an example of the ferrous salt):

[0015] CH3COO - +H2O→CH3COOH+OH -

[0016] 4Fe 2+ +2H2O+O2→4Fe 3+ +4OH -

[0017] 6Ni 2+ +2Fe 3+ +16OH - +SO4 2- +7H2O→Ni6Fe2(SO4)(OH) 16 7H2O

[0018] Among them, the acetate ion (CH3COO - ) as the conjugate base of the weak acid, it will partially hydrolyze to produce OH - , Fe in the mixed solution 2+ Oxidized to Fe with the help of oxygen and water 3+ At the same time, oxygen is reduced to produce some OH - , the generated Fe 3+ and Ni 2+ As a metal center, it interacts with OH in the solution -In addition, the present invention reduces the dielectric constant of the reaction system by adding an organic solvent, thereby enhancing the electrostatic attraction between solute molecules and promoting their aggregation behavior, thereby effectively regulating the morphology of NiFe-LDH.

[0019] In addition, it should be noted that in the above preparation method, the two salts cannot be added directly to the mixed solvent, otherwise the reaction will begin before the salts are completely dissolved, resulting in uncontrollable reaction rate, low yield and easy production of other by-products; therefore, the two salts must first be dissolved separately to prepare the corresponding salt solutions, and then the two salt solutions are mixed to obtain a mixed solution in which the salts are completely dissolved and evenly mixed, thereby achieving the preparation of uniform NiFe-LDH with a flaky nanoflower morphology.

[0020] Preferably, in step S1, the organic solvent is selected from at least one of methanol, ethanol, isopropanol, ethyl acetate, and acetone.

[0021] Preferably, in step S1, the ferrous salt is selected from at least one of ferrous sulfate, ammonium ferrous sulfate, ferrous acetate, and ferrous nitrate.

[0022] During the above reaction process, the concentration of the hydrolyzed salt needs to be controlled. Too low a concentration will reduce the yield of NiFe-LDH and affect its nanomorphology, while too high a concentration will lead to the generation of a large amount of impurities.

[0023] Preferably, in step S1, the molar ratio of the nickel salt to the water-soluble ferrous salt is (1-8):1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, etc., including but not limited to the molar ratios listed above.

[0024] Preferably, in step S1, the concentration of the water-soluble ferrous salt in the second solution is 0.04-0.08 mol / L, for example, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, etc.

[0025] Preferably, in step S2, the volume ratio of the organic solvent to water in the mixed solution is 1: (1-15), for example 1: 1, 1: 2, 1: 3, 1: 4, 1, 1: 6, 1: 7, 1: 8, 1: 9, 1: 10, 1: 11, 1: 12, 1: 13, 1: 14, 1: 15, etc., including but not limited to the volume ratios listed above; the volume ratio of the organic solvent to water in the mixed solution affects the morphology and yield of the product. If the volume ratio of the organic solvent to water is too small, for example, less than 1: 15, as the proportion of water increases, the yield gradually decreases, and a product with uniform morphology cannot be formed; however, the volume ratio of the organic solvent to water should not be too large. If it is greater than 1: 1, insufficient water will prevent the hydrolysis reaction from fully proceeding, resulting in reactant residues and reducing the yield of the target product.

[0026] Preferably, in step S2, the mixing process includes ultrasound, the ultrasound power is 60-120 W, and the ultrasound time is 1-3 min.

[0027] Preferably, in step S2, the aging time is 10-36 h and the temperature is 15-35°C.

[0028] Preferably, step S2 further includes the steps of centrifuging, washing and drying the aged product.

[0029] The second aspect of the present invention provides a NiFe-LDH having a flaky nanoflower morphology prepared by the preparation method described in the first aspect.

[0030] The third aspect of the present invention provides an application of the NiFe-LDH having a flaky nanoflower morphology as described in the second aspect in the field of electrocatalysis.

[0031] Furthermore, the electrocatalytic field includes but is not limited to water electrolysis and oxygen evolution.

[0032] Beneficial effects of the present invention:

[0033] 1. This method uses nickel acetate and ferrous salt as raw materials. By simple dissolution and standing at room temperature, nano-flower-shaped NiFe-LDH with uniform composition and uniform morphology can be prepared. Compared with the coprecipitation method, there is no need to add additional alkaline solution as a precipitant to control the pH value, and there is no need to strictly control the reaction temperature. The preparation process is green and environmentally friendly, and the morphology is more regular. Compared with the hydrothermal method, the experimental operation is simple, the equipment cost is low, and the reaction conditions are milder. It can be seen that the preparation method provided by the present invention has easy-to-obtain raw materials, simple operation, easy control, mild conditions, and the prepared product has uniform morphology, which is suitable for industrial low-cost preparation of NiFe-LDH.

[0034] 2. The NiFe-LDH prepared in the present invention has a three-dimensional nanoflower morphology and is assembled from two-dimensional nanosheets. Compared with two-dimensional nanosheets (two-dimensional nanosheets are prone to stacking, resulting in some active sites being buried), the material with this morphology has a higher specific surface area and can provide more active sites. It can be used as an electrocatalyst in electrocatalytic fields such as water electrolysis and oxygen evolution.

[0035] 3. The NiFe-LDH with a flaky nanoflower morphology synthesized in this invention exhibits excellent catalytic performance as an electrocatalyst in the oxygen evolution reaction (OER) during water electrolysis. In a 1.0 mol / L KOH alkaline solution, the overpotential required to achieve a current density of 10 mA / cm² is only 220-240 mV, significantly superior to the commercial noble metal RuO catalyst (358 mV). BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a scanning electron microscope image (SEM) of the NiFe-LDH prepared in Example 1, wherein the scale bar in a is 500 nm; the scale bar in b is 200 nm;

[0037] Figure 2 This is a transmission electron microscopy (TEM) image of the NiFe-LDH prepared in Example 1;

[0038] Figure 3 The energy dispersive spectrum (EDS) test results of NiFe-LDH prepared in Example 1;

[0039] Figure 4 Elemental mapping (EDX-Mapping) of NiFe-LDH prepared in Example 1;

[0040] Figure 5 This is an SEM image of the NiFe-LDH prepared in Example 2, where the scale bar in a is 500 nm and the scale bar in b is 200 nm;

[0041] Figure 6 This is a SEM image of the NiFe-LDH prepared in Example 3, where the scale bar in a is 500 nm and the scale bar in b is 200 nm;

[0042] Figure 7 This is a SEM image of the NiFe-LDH prepared in Example 4, where the scale bar in a is 500 nm and the scale bar in b is 200 nm;

[0043] Figure 8 This is a SEM image of the NiFe-LDH prepared in Example 5, where the scale bar in a is 500 nm and the scale bar in b is 200 nm;

[0044] Figure 9The X-ray diffraction patterns (XRD) of NiFe-LDH prepared in Examples 1, 4, and 5 and the superposition of NiFe-LDH standard cards;

[0045] Figure 10 This is a SEM image of the NiFe-LDH prepared in Example 6, where the scale bar in a is 500 nm and the scale bar in b is 200 nm;

[0046] Figure 11 This is a SEM image of the NiFe-LDH prepared in Example 7, where the scale bar in a is 500 nm and the scale bar in b is 200 nm;

[0047] Figure 12 This is a SEM image of the NiFe-LDH prepared in Example 8, where the scale bar in a is 500 nm and the scale bar in b is 200 nm;

[0048] Figure 13 This is an SEM image of the NiFe-LDH prepared in Comparative Example 1, where the scale of a is 500 nm and the scale of b is 200 nm;

[0049] Figure 14 Linear sweep voltammetry (LSV) curves of NiFe-LDH prepared from nickel salt and ferrous salt in different molar ratios in Examples 1, 2, and 3 as electrocatalysts measured in 1 M KOH electrolyte;

[0050] Figure 15 LSV curves of NiFe-LDH prepared from different ferrous salts in Examples 1, 4, and 5 as electrocatalysts measured in 1 M KOH electrolyte;

[0051] Figure 16 These are the LSV curves of NiFe-LDH prepared in different organic solvent systems in Examples 1, 6, and 7 as electrocatalysts measured in 1 M KOH electrolyte. DETAILED DESCRIPTION

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "comprising" or "including" used in the present invention means that in addition to the components described, other components may also be included. The term "comprising" or "including" used in the present invention may also be replaced by the closed form "being" or "consisting of."

[0053] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0054] Example 1: This example relates to the preparation of a NiFe-LDH with a flaky nanoflower morphology, comprising the following steps:

[0055] According to the stoichiometric ratio of Ni:Fe = 6:1, 0.5375 g of nickel acetate tetrahydrate was dissolved in 6 mL of methanol, and 0.1412 g of ammonium ferrous sulfate heptahydrate was dissolved in 6 mL of deionized water. The two solutions were then mixed and thoroughly mixed by ultrasonic treatment. The resulting mixed solution was aged at room temperature for 24 h. After the reaction, the mixture was centrifuged, washed, and vacuum-dried to obtain the product NiFe-LDH.

[0056] The SEM image of NiFe-LDH prepared in this example is as follows Figure 1 As shown, Figure 1 a and b are SEM images of NiFe-LDH at different scales. It can be seen from the figure that the NiFe-LDH prepared in this example has a nanoflower morphology composed of nanosheets, a regular layered structure and a relatively regular overall morphology, and the thickness of the nanosheets is relatively thin (such as Figure 2 As shown in Figure 3), the nanoflowers are uniform in size, approximately 300-500 nm.

[0057] The EDS test results of NiFe-LDH prepared in this example are as follows: Figure 3 As shown in the figure, the product contains Ni, Fe, O, and S elements; and the EDX-Mapping diagram of the product ( Figure 4 ) shows that each element is evenly distributed in the nanosheet. In addition, Figure 9 It can be seen that in the XRD pattern of the product prepared in this example, the diffraction peaks are located at 9.99°, 20.02°, 34.19° and 60.02°, which correspond to the characteristic diffraction peaks of the (003), (006), (012) and (110) crystal planes of NiFe-LDH (PDF#42-0573), respectively, further confirming that the NiFe-LDH material was successfully prepared in this example.

[0058] Example 2: This example relates to the preparation of a NiFe-LDH with a flaky nanoflower morphology. The only difference from Example 1 is that the added amounts of nickel acetate tetrahydrate and ferrous salt are different, satisfying Ni:Fe=5:1; the other operations are the same, and a NiFe-LDH with a flaky nanoflower morphology is prepared.

[0059] Figure 5 This is the SEM image of the NiFe-LDH prepared in this example, where the scale of a is 500 nm and the scale of b is 200 nm. It can be seen from the figure that the NiFe-LDH synthesized in this example has a nanoflower morphology, is assembled from nanosheets, and has a relatively regular overall morphology.

[0060] Example 3: This example relates to the preparation of a NiFe-LDH with a flaky nanoflower morphology. The only difference from Example 1 is that the added amounts of nickel acetate tetrahydrate and ferrous salt are different, satisfying Ni:Fe=7:1; the other operations are the same, and a NiFe-LDH with a flaky nanoflower morphology is prepared.

[0061] Figure 6 This is the SEM image of the NiFe-LDH prepared in this example, where the scale of a is 500 nm and the scale of b is 200 nm. It can be seen from the figure that the NiFe-LDH synthesized in this example has a nanoflower morphology, is assembled from nanosheets, and has a relatively regular overall morphology.

[0062] Example 4: This example relates to the preparation of a NiFe-LDH with a flaky nanoflower morphology. The only difference from Example 1 is that the water-soluble ferrous salt is ferrous sulfate heptahydrate, and the amount of ferrous sulfate heptahydrate added satisfies Ni:Fe=6:1; the other operations are the same, and NiFe-LDH with a flaky nanoflower morphology is prepared.

[0063] Figure 7 The SEM image of NiFe-LDH prepared in this example, where the scale of a is 500 nm and the scale of b is 200 nm, shows that the NiFe-LDH synthesized in this example has a nanoflower morphology, which is assembled from nanosheets and has a relatively regular overall morphology. The XRD pattern of the product prepared in this example is shown in FIG. Figure 9 As shown, the diffraction peaks of the product are all attributed to NiFe-LDH (PDF#42-0573), which shows that the product prepared in this example is NiFe-LDH.

[0064] Example 5: This example relates to the preparation of a NiFe-LDH with a flaky nanoflower morphology. The only difference from Example 1 is that the water-soluble ferrous salt is ferrous acetate tetrahydrate, and the amount of water-soluble ferrous salt added satisfies Ni:Fe=6:1; the other operations are the same, and a NiFe-LDH with a flaky nanoflower morphology is prepared.

[0065] Figure 8 The SEM image of NiFe-LDH prepared in this example, where the scale of a is 500 nm and the scale of b is 200 nm, shows that the NiFe-LDH synthesized in this example has a nanoflower morphology, which is assembled from nanosheets and has a relatively regular overall morphology. The XRD pattern of the product prepared in this example is shown in FIG. Figure 9 As shown, the diffraction peaks of the product are all attributed to NiFe-LDH (PDF#42-0573), which shows that the product prepared in this example is NiFe-LDH.

[0066] Example 6: This example relates to the preparation of NiFe-LDH with a flaky nanoflower morphology. The only difference from Example 1 is that the organic solvent is ethanol, and 6 mL of methanol is replaced by a mixed solvent consisting of 1 mL of ethanol and 5 mL of deionized water. The rest of the operations are the same to prepare NiFe-LDH with a flaky nanoflower morphology.

[0067] Figure 10 This is the SEM image of the NiFe-LDH prepared in this example, where the scale of a is 500 nm and the scale of b is 200 nm. It can be seen from the figure that the NiFe-LDH synthesized in this example has a nanoflower morphology, is assembled from nanosheets, and has a relatively regular overall morphology.

[0068] Example 7: This example relates to the preparation of NiFe-LDH with a flaky nanoflower morphology. The only difference from Example 1 is that the organic solvent is isopropanol, and an equal volume of isopropanol is used to replace methanol. The other operations are the same to prepare NiFe-LDH with a flaky nanoflower morphology.

[0069] Figure 11 This is the SEM image of the NiFe-LDH prepared in this example, where the scale of a is 500 nm and the scale of b is 200 nm. It can be seen from the figure that the NiFe-LDH synthesized in this example has a nanoflower morphology, is assembled from nanosheets, and has a relatively regular overall morphology.

[0070] Example 8: This example relates to the preparation of a NiFe-LDH with a flaky nanoflower morphology. The only difference from Example 1 is that the amounts of methanol and water added are different. 4 mL of methanol is used to dissolve nickel acetate tetrahydrate, and 8 mL of deionized water is used to dissolve ammonium ferrous sulfate heptahydrate. The other operations are the same to prepare NiFe-LDH with a flaky nanoflower morphology.

[0071] Figure 12 This is the SEM image of the NiFe-LDH prepared in this example, where the scale of a is 500 nm and the scale of b is 200 nm. It can be seen from the figure that the NiFe-LDH synthesized in this example has a nanoflower morphology, is assembled from nanosheets, and has a relatively regular overall morphology.

[0072] Comparative Example 1: This comparative example relates to the preparation of NiFe-LDH. The only difference from Example 1 is that the solvent for dissolving nickel acetate tetrahydrate is deionized water, and an equal volume of deionized water is used to replace methanol. The other operations are the same to prepare NiFe-LDH.

[0073] Figure 13This is the SEM image of the NiFe-LDH prepared in this comparative example, where the scale of a is 500 nm and the scale of b is 200 nm. It can be seen from the figure that the morphology of the NiFe-LDH synthesized in this example is uneven, and there are two morphologies: flaky nanoflowers and nanospheres.

[0074] Comparative Example 2: This comparative example relates to the preparation of NiFe-LDH. The only difference from Example 1 is that the nickel salt is nickel nitrate, and the other operations are the same. No obvious precipitate is produced after the reaction, and the product NiFe-LDH cannot be synthesized.

[0075] Test Example: The NiFe-LDH synthesized in Example 1-7 was used as a catalyst to test the oxygen evolution performance of water electrolysis. The specific steps are as follows:

[0076] A standard three-electrode system was used for testing in 1.0 M KOH alkaline electrolyte. The working electrode was a glassy carbon electrode with a diameter of 5 mm, and the reference electrode and counter electrode were Ag / AgCl electrode and graphite electrode, respectively. The electrochemical characterization was completed using a Chenhua CHI760E electrochemical workstation.

[0077] Catalyst slurry preparation: 5 mg of NiFe-LDH catalyst and 2 mg of conductive carbon black were uniformly dispersed in a mixture of 970 μL of isopropanol and 30 μL of 0.5 wt% Nafion solution. Ultrasonic treatment was performed for 30 minutes to obtain a uniform dispersion. 21 μL of the slurry was added dropwise to the surface of the glassy carbon electrode in seven portions, resulting in a loading of approximately 0.5348 mg cm -2 uniform catalyst coating.

[0078] Overpotential calculation: The overpotential of the catalyst is calculated according to the Nernst equation and the reversible hydrogen electrode (RHE) is used as a reference: E RHE = E Ag / AgCl + 0.197 + 0.059 × pH. Linear sweep voltammetry (LSV) test at 5 mV s -1 The scanning rate was set at 95%, and the automatic compensation function of the electrochemical workstation was used to compensate for 95%. The polarization curve was obtained by the formula η =E RHE The calculated overpotential value is -1.23 V.

[0079] Figure 14-16 The linear sweep voltammetry (LSV) curves of different NiFe-LDH catalysts measured in 1M KOH electrolyte show the linear sweep voltammetry performance of the product NiFe-LDH under different preparation conditions. Figure 14 NiFe-LDH catalysts prepared with different molar ratios of nickel salt and ferrous salt, Figure 15 NiFe-LDH catalysts prepared corresponding to different types of ferrous salts, Figure 16 NiFe-LDH catalysts prepared in different organic solvent systems. As shown in the figure, the NiFe-LDH prepared in Examples 1-7 all exhibited excellent catalytic performance. By adjusting the ratio of nickel and iron salts, the type of ferrous salt, and the organic solvent system, the catalytic performance of the synthesized NiFe-LDH fluctuated within a narrow range. In a 1.0 mol / L KOH alkaline solution, the overpotential required to achieve a current density of 10 mA / cm² was only 220-240 mV, significantly superior to the commercial noble metal oxygen evolution reaction (OER) catalyst RuO2 (358 mV).

[0080] It can be seen from this that the sheet-like nanoflower morphology NiFe-LDH prepared by the preparation method provided by the present invention is used as a non-precious metal OER electrocatalyst, showing the industrialization potential of replacing precious metal catalysts.

[0081] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing nickel-iron layered double hydroxide having a flaky nanoflower morphology, characterized in that: The following steps are involved: S1, dissolving a nickel salt in a solvent to prepare a first solution; dissolving a water-soluble ferrous salt in water to prepare a second solution; The solvent is an organic solvent or a mixed solvent of an organic solvent and water; The organic solvent is selected from at least one of methanol, ethanol, isopropanol, acetone, and ethyl acetate; The nickel salt includes at least one of nickel acetate and nickel acetate hydrate; The molar ratio of the nickel salt to the water-soluble ferrous salt is (1-8):1; The concentration of the water-soluble ferrous salt in the second solution is 0.04-0.08 mol / L; S2. The first solution and the second solution are uniformly mixed to obtain a mixed solution, and the nickel-iron layered double hydroxide is obtained by standing and aging; the aging temperature is 15-35° C.; the volume ratio of the organic solvent to water in the mixed solution is 1:(1-15).

2. The preparation method according to claim 1, characterized in that In step S1, the water-soluble ferrous salt is selected from at least one of ferrous sulfate, ammonium ferrous sulfate, ferrous acetate, and ferrous nitrate.

3. The preparation method according to claim 1, characterized in that In step S2, the mixing step includes ultrasonic treatment, the power of the ultrasonic treatment is 60-120 W, and the time of the ultrasonic treatment is 1-3 min.

4. The preparation method according to claim 1, characterized in that In step S2, the aging time is 10-36 h.

5. A nickel-iron layered double hydroxide having a flaky nanoflower morphology, characterized in that: The product is prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the nickel-iron layered double hydroxide having a flaky nanoflower morphology according to claim 5 in the field of electrocatalysis.

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