Heterostructure composite material based on Ni (OH) 2 / Fe2O3 nanosheet coated nanoparticles and application of heterostructure composite material in electrocatalytic oxygen evolution reaction

Abstract

The invention provides a composite material of a derivative transition metal hydroxide based on a metal organic framework, and discloses a composite nano material of a two-dimensional layered nickel-based MOF material and a Fe2O3 nano particle structure etched under an alkaline condition and application of the composite nano material in the aspect of electro-catalytic oxygen evolution performance. A two-step synthesis technology is adopted, firstly, nickel nitrate and a 2, 6-naphthalenedicarboxylic acid organic ligand are subjected to self-assembly in a system with deionized water and N, N-dimethylformamide as solvents, and Ni-NDC of a nanosheet structure is obtained; then, ferric nitrate and Ni-NDC are used for obtaining the Ni (OH) 2 / Fe2O3 composite material with nanoparticles wrapped by nanosheets in an alkaline solution. In addition, the composite material has a large number of active sites and excellent conductivity, so that the composite material has good electro-catalytic oxygen evolution performance.

Description

Technical Field

[0001] The present invention relates to a novel composite of a nanoparticle - encapsulated heterostructure MOF - derived transition metal hydroxide with nanosheets, and is particularly applied to the electrocatalytic oxygen evolution reaction (OER). This technology belongs to the fields of electrochemical catalysts and energy storage, and is specifically used for the preparation of electrocatalysts for water decomposition to produce oxygen. Background Art

[0002] With the continuous development of society, the consumption of fossil fuels has caused a series of global energy problems and environmental problems, attracting people's attention to the development of new sustainable energy sources. Electrochemical water splitting is a convenient method for generating oxygen through the oxygen evolution reaction (OER). However, the OER process involves four - electron transfer and requires higher energy than the cathodic hydrogen evolution reaction, thus controlling the overall efficiency of electrochemical water splitting. Currently, noble - metal - based catalysts are considered the most widely used and stable OER electrocatalysts. However, due to problems such as resource scarcity and high cost, it is difficult for them to have large - scale commercial applications. Therefore, it is crucial to find non - noble - metal OER catalyst materials with rich resources, high activity, and high stability.

[0003] In recent years, metal - organic framework materials (MOFs) have become a promising OER electrocatalyst due to their high specific surface area, adjustable framework structure, and complex and diverse coordination modes. Among them, nickel - based catalysts, such as oxides and hydroxides, which are low - cost and high - activity materials, have been widely studied. In alkaline solutions, nickel - iron - based hydroxides have been proven by a large number of studies to be the most promising non - noble - metal - based OER electrocatalysts. Compared with materials containing only a single Ni or Fe element, catalyst materials with both Ni and Fe elements generally have more excellent OER activity, which benefits from the synergistic catalysis between Ni and Fe, effectively reducing the over - potential of the reaction. Therefore, designing efficient NiFe - based catalysts is of great significance for promoting the electrocatalytic water - splitting reaction.

[0004] This work aims at the technical defects and barriers existing in current electrocatalytic oxygen - evolution catalysts, and proposes a simple method of etching in an alkaline solution to treat a two - dimensional layered nickel - based MOF material (Ni - NDC), which enables metal sites to coordinate with hydroxyl groups and become highly active catalytic sites. Metal - organic framework - derived transition metal hydroxides have become one of the research hotspots in coordination chemistry and materials science due to their low cost, high activity, and application prospects in multiple fields. They have been widely regarded as potential electrode materials for the electrochemical oxygen - evolution reaction. Summary of the Invention

[0005] The present invention relates to a novel nanosheet-wrapped nanoparticle heterostructure Ni(OH)2 / Fe2O3 composite material and a preparation method thereof, aiming to enhance the stability and electrocatalytic performance of MOF-derived transition metal hydroxides through coordination of metal sites with hydroxyl groups, thereby improving their application effects in energy storage and catalytic reactions. The method of the present invention includes etching a two-dimensional layered nickel-based MOF material and a composite nanomaterial with a Fe2O3 nanoparticle structure under alkaline conditions. Finally, a nanosheet-wrapped nanoparticle heterostructure is obtained with better structural stability than the precursor, and the mutual synergy among the components endows it with excellent catalytic activity.

[0006] Based on this, the nanosheet-wrapped nanoparticle heterostructure composite material described in the present invention is prepared through a high-temperature reaction, providing an electrode material with a high specific surface area, high ion transport efficiency, and capable of effectively improving the electrocatalytic oxygen evolution performance by utilizing the electrostatic interaction between metals, and a preparation method thereof.

[0007] The technical solution of the present invention is as follows: A Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material, which is assembled from an oxide composed of iron metal elements and a transition metal hydroxide. The diameter of the nanosheets is about 1-7 μm, and the thickness of the nanosheets is about 5-10 nm.

[0008] The method for preparing the material includes the following steps: (1) Take nickel nitrate hexahydrate and 2,6-naphthalenedicarboxylic acid and dissolve them in water and N,N-dimethylformamide, and stir evenly at room temperature; (2) Transfer the mixed solution obtained in step (1) to a hydrothermal reaction kettle with a polytetrafluoroethylene liner, carry out hydrothermal reaction, and take it out and cool naturally to room temperature; (3) Centrifuge the sample obtained in step (2) to collect the precipitate, wash it by centrifugation with ethanol and water respectively, and then dry it in vacuum to obtain Ni-NDC with a nanosheet structure.

[0009] (4) Dissolve the sample obtained in step (3) and iron nitrate nonahydrate in sodium hydroxide solution, and ultrasonically disperse and mix evenly at room temperature; (5) Transfer the mixed solution obtained in step (4) to a hydrothermal reaction kettle with a polytetrafluoroethylene liner, carry out hydrothermal reaction, and take it out and cool naturally to room temperature; (6) Centrifuge the sample obtained in step (5) to collect the precipitate, wash it by centrifugation with ethanol and water respectively, and then dry it in vacuum to obtain Ni(OH)2 / Fe2O3 with a nanosheet and nanoparticle structure.

[0010] The molar mass ratio of nickel nitrate hexahydrate to 2,6-naphthalenedicarboxylic acid described in step (1) is 0.1-1:0.1-1.

[0011] The molar mass ratio of nickel nitrate hexahydrate to 2,6-naphthalenedicarboxylic acid described in step (1) is 0.1:0.12.

[0012] The volume ratio of deionized water to N,N-dimethylformamide described in step (1) is 0.1 - 1:10 - 15.

[0013] The volume ratio of deionized water to N,N-dimethylformamide described in step (1) is 1:12.

[0014] The hydrothermal reaction temperature described in step (2) is 100 - 150 °C, and the reaction time is 10 - 15 h.

[0015] The hydrothermal reaction temperature described in step (2) is 130 °C, and the reaction time is 12 h.

[0016] The vacuum drying temperature described in step (3) is 60 °C, the pressure is 10 MPa, and the time is 10 - 15 h.

[0017] The mass ratio of Ni-NDC to iron(III) nitrate nonahydrate described in step (4) is 1 - 10:0 - 10.

[0018] The mass ratio of Ni-NDC to iron(III) nitrate nonahydrate described in step (4) is 6:1.

[0019] The concentration of sodium hydroxide described in step (4) is 1 - 5 mol / L, and the volume is 10 - 20 mL.

[0020] The concentration of sodium hydroxide described in step (4) is 1 mol / L, and the volume is 16 mL.

[0021] The hydrothermal reaction temperature described in step (5) is 120 - 160 °C, and the reaction time is 10 - 15 h.

[0022] The hydrothermal reaction temperature described in step (5) is 140 °C, and the reaction time is 12 h.

[0023] A similar scheme can be used to prepare Ni(OH)2 nanosheets, and iron(III) nitrate nonahydrate is not added in step (4).

[0024] A similar scheme can be used to prepare Fe2O3 nanoparticles, and 50 mg of iron(III) nitrate nonahydrate is taken without adding Ni-NDC in step (4).

[0025] Another technical solution of the present invention is the application of the nanosheet-wrapped nanoparticle heterostructure composite material in electrocatalytic oxygen evolution. After the basic characterization of the nanosheet-wrapped nanoparticle heterostructure composite material, its oxygen evolution performance is tested. The specific method is as follows: The obtained Ni(OH)2 / Fe2O3 composite material of nanosheets and nanoparticles was used as the working electrode in a three-electrode system. A platinum sheet was used as the counter electrode, and a mercury / mercuric oxide electrode was used as the reference electrode to conduct electrocatalytic oxygen evolution performance tests in a 1 M KOH solution. It was found that the overpotential of the Ni(OH)2 / Fe2O3 composite material was lower than that of Fe2O3 and Ni(OH)2 at the same current density, and it had faster OER kinetics and good stability.

[0026] The beneficial effects of the present invention are as follows: (1) The synthesis method of this material is simple, and the raw materials for preparation are inexpensive and easy to obtain. Relatively stable nanosheets and nanoparticles with nanoscale sizes can be formed by controlling the reaction time and reaction temperature.

[0027] (2) The synthesis of the heterogeneous structure of nanoparticles wrapped by nanosheets effectively increases the specific surface area of the material, which is more conducive to electron transfer.

[0028] (3) Benefiting from the structural and compositional advantages, this material has good oxygen evolution performance. At a current density of 10 mA cm -2 , the overpotential is 273 mV, and it also has faster OER kinetics and good stability.

[0029] (4) This material better exerts the interfacial electron interaction between Fe2O3 and Ni(OH)2, ensuring fast electron transfer and good conductivity of the heterogeneous structure, making the OER performance of the Ni(OH)2 / Fe2O3 composite material with a heterogeneous structure of nanosheets wrapped around nanoparticles based on nickel foam better than that of Fe2O3 and Ni(OH)2.

[0030] (5) The method of the present invention has a simple process, is easy to operate, has low requirements for equipment, and the prepared electrode is firmly bonded to the substrate, has excellent OER performance and stability, and can be widely applied to the energy storage aspect of the electrocatalytic oxygen evolution field.

[0031] (6) The present invention provides a new idea for designing and synthesizing more electrode materials based on transition metal hydroxides to improve the electrochemical performance of energy storage and energy conversion. Description of the Drawings

[0032] Figure 1 It is the X-ray diffraction pattern of the synthesized samples in Example 2, Example 3, Example 4, Example 5 and the Ni(OH)2 sample synthesized in Example 6.

[0033] Figure 2 It is the scanning electron microscope image of the NiFe-1 sample synthesized in Example 2.

[0034] Figure 3Scanning electron microscope image of the Ni(OH)2 sample synthesized in Example 6.

[0035] Figure 4 Scanning electron microscope image of the Fe2O3 sample synthesized in Example 7.

[0036] Figure 5 CV curves of the NiFe-1 sample synthesized in Example 2 at different scan rates.

[0037] Figure 6 Overpotential comparison of the synthesized samples in Examples 2, 3, 4, and 5 at different current densities.

[0038] Figure 7 Linear sweep voltammetry comparison curves of the synthesized samples in Examples 2, 3, 4, 5, 6, and 7 at a current density of 10 mA cm -2 of. Detailed implementation mode

[0039] The present invention will be further described below in conjunction with examples, but the scope of protection required by the present invention is not limited to the scope described in the examples.

[0040] Example 1 (Preparation of NiFe-0) Take 87 mg of nickel nitrate hexahydrate and 80 mg of 2,6-naphthalenedicarboxylic acid and dissolve them in a mixed solution of 12 mL of N,N-dimethylformamide and 1 mL of deionized water. Stir at room temperature for 1 h to uniformly mix the reactants to obtain a mixed solution A.

[0041] Transfer the mixed solution A to a 25 mL polytetrafluoroethylene liner, then place it in a stainless steel container and keep it at 130 °C for 12 hours. Cool to room temperature, and finally obtain a green solid powder. Wash it three times by centrifugation with ethanol and water respectively, at a rotation speed of 8000 rpm / min and a centrifugation time of 2 min. Vacuum dry the obtained product at 60 °C for 12 hours to obtain sample B.

[0042] Dissolve 30 mg of sample B and 2.5 mg of iron nitrate nonahydrate in 16 mL of 1 mol / L sodium hydroxide solution, and ultrasonicate at room temperature for 20 min to uniformly mix the reactants to obtain a mixed solution C.

[0043] Transfer the mixture C into a 25 mL polytetrafluoroethylene liner, and then place it in a stainless-steel container and keep it at 140 °C for 12 h. Cool it to room temperature, and finally obtain a yellow solid powder. Centrifuge and wash it three times with ethanol and water respectively at a rotation speed of 8000 rpm / min for 2 min. Vacuum-dry the obtained product at 60 °C for 12 h to obtain a Ni(OH)2 / Fe2O3 heterostructure composite material with nanosheets wrapping nanoparticles, named NiFe-0.

[0044] Example 2 (Preparation of NiFe-1) Dissolve 87 mg of nickel nitrate hexahydrate and 80 mg of 2,6-naphthalenedicarboxylic acid in a mixed solution of 12 mL of N,N-dimethylformamide and 1 mL of deionized water, and stir at room temperature for 1 h to uniformly mix the reactants to obtain mixture A.

[0045] Transfer mixture A into a 25 mL polytetrafluoroethylene liner, and then place it in a stainless-steel container and keep it at 130 °C for 12 h. Cool it to room temperature, and finally obtain a green solid powder. Centrifuge and wash it three times with ethanol and water respectively at a rotation speed of 8000 rpm / min for 2 min. Vacuum-dry the obtained product at 60 °C for 12 h to obtain sample B.

[0046] Dissolve 30 mg of sample B and 5 mg of iron nitrate nonahydrate in 16 mL of 1 mol / L sodium hydroxide solution, and ultrasonically treat it at room temperature for 20 min to uniformly mix the reactants to obtain mixture C.

[0047] Transfer mixture C into a 25 mL polytetrafluoroethylene liner, and then place it in a stainless-steel container and keep it at 140 °C for 12 h. Cool it to room temperature, and finally obtain a yellow solid powder. Centrifuge and wash it three times with ethanol and water respectively at a rotation speed of 8000 rpm / min for 2 min. Vacuum-dry the obtained product at 60 °C for 12 h to obtain a Ni(OH)2 / Fe2O3 heterostructure composite material with nanosheets wrapping nanoparticles, named NiFe-1.

[0048] From Figure 1 the XRD pattern, it can be seen that after the Ni-NDC precursor is alkalized during the hydrothermal process, The positions of its diffraction peaks are in complete agreement with those of hexagonal nickel hydroxide (JCPDS Card No. 14-0117), indicating that the Ni-NDC precursor is completely transformed into Ni(OH)2 derivative material after alkalization. At the same time, the diffraction peaks of a series of NiFe-x alkalized products can all be corresponded to the diffraction peaks of nickel hydroxide (JCPDS Card No. 14-0117) and Fe2O3 (JCPDS Card No. 39-1346), indicating the successful preparation of Ni(OH)2 / Fe2O3. It can be observed from the scanning electron microscope images that Figure 3 the Ni(OH)2 material is in the form of small-sized flaky materials, Figure 4 the Fe2O3 material is in the form of large-sized granular materials, and it can be observed from Figure 2 that in the NiFe-1 material, Ni(OH)2 and Fe2O3 are closely combined, which indicates that the interfacial electronic interaction between the surface Fe and Ni metals is good, resulting in highly active catalytic sites.

[0049] Example 3 (Preparation of NiFe-2) 87 mg of nickel nitrate hexahydrate and 80 mg of 2,6-naphthalenedicarboxylic acid were dissolved in a mixed solution of 12 mL of N,N-dimethylformamide and 1 mL of deionized water, and stirred at room temperature for 1 h to uniformly mix the reactants, obtaining a mixed solution A.

[0050] The mixed solution A was transferred to a 25 mL polytetrafluoroethylene liner, and then placed in a stainless steel container and kept at 130 °C for 12 h, cooled to room temperature, and finally a green solid powder was obtained. It was centrifugally washed three times with ethanol and water respectively at a rotation speed of 8000 rpm / min and a centrifugation time of 2 min, and the obtained product was vacuum dried at 60 °C for 12 h to obtain sample B.

[0051] 30 mg of sample B and 10 mg of iron nitrate nonahydrate were dissolved in 16 mL of 1 mol / L sodium hydroxide solution, and ultrasonically treated at room temperature for 20 min to uniformly mix the reactants, obtaining a mixed solution C.

[0052] The mixed solution C was transferred to a 25 mL polytetrafluoroethylene liner, and then placed in a stainless steel container and kept at 140 °C for 12 h, cooled to room temperature, and finally a yellow solid powder was obtained. It was centrifugally washed three times with ethanol and water respectively at a rotation speed of 8000 rpm / min and a centrifugation time of 2 min, and the obtained product was vacuum dried at 60 °C for 12 h to obtain a Ni(OH)2 / Fe2O3 heterostructure composite material with nanosheets wrapping nanoparticles, named NiFe-2.

[0053] Example 4 (Preparation of NiFe-3) 87 mg of nickel nitrate hexahydrate and 80 mg of 2,6-naphthalenedicarboxylic acid were dissolved in a mixed solution of 12 mL of N,N-dimethylformamide and 1 mL of deionized water, and stirred at room temperature for 1 h to uniformly mix the reactants, obtaining a mixed solution A.

[0054] The mixed solution A was transferred to a 25 mL polytetrafluoroethylene inner liner, and then placed in a stainless steel container and kept at 130 °C for 12 h, cooled to room temperature, and finally a green solid powder was obtained. The product was centrifugally washed three times with ethanol and water respectively, at a rotation speed of 8000 rpm / min and a centrifugation time of 2 min, and the obtained product was vacuum dried at 60 °C for 12 h to obtain sample B.

[0055] 30 mg of sample B and 30 mg of ferric nitrate nonahydrate were dissolved in 16 mL of 1 mol / L sodium hydroxide solution, and ultrasonically treated at room temperature for 20 min to uniformly mix the reactants, obtaining a mixed solution C.

[0056] The mixed solution C was transferred to a 25 mL polytetrafluoroethylene inner liner, and then placed in a stainless steel container and kept at 140 °C for 12 h, cooled to room temperature, and finally a yellow solid powder was obtained. The product was centrifugally washed three times with ethanol and water respectively, at a rotation speed of 8000 rpm / min and a centrifugation time of 2 min, and the obtained product was vacuum dried at 60 °C for 12 h to obtain the Ni(OH)2 / Fe2O3 heterostructure composite material with nanosheets wrapping nanoparticles, named NiFe-3.

[0057] Example 5 (Preparation of NiFe-4) 87 mg of nickel nitrate hexahydrate and 80 mg of 2,6-naphthalenedicarboxylic acid were dissolved in a mixed solution of 12 mL of N,N-dimethylformamide and 1 mL of deionized water, and stirred at room temperature for 1 h to uniformly mix the reactants, obtaining a mixed solution A.

[0058] The mixed solution A was transferred to a 25 mL polytetrafluoroethylene inner liner, and then placed in a stainless steel container and kept at 130 °C for 12 h, cooled to room temperature, and finally a green solid powder was obtained. The product was centrifugally washed three times with ethanol and water respectively, at a rotation speed of 8000 rpm / min and a centrifugation time of 2 min, and the obtained product was vacuum dried at 60 °C for 12 h to obtain sample B.

[0059] 30 mg of sample B and 50 mg of ferric nitrate nonahydrate were dissolved in 16 mL of 1 mol / L sodium hydroxide solution, and ultrasonically treated at room temperature for 20 min to uniformly mix the reactants, obtaining a mixed solution C.

[0060] Transfer the mixture C into a 25 mL polytetrafluoroethylene liner, and then place it in a stainless-steel container and keep it at 140 °C for 12 h. Cool it to room temperature, and finally obtain a yellow solid powder. Centrifuge and wash it three times with ethanol and water respectively at a rotation speed of 8000 rpm / min for 2 min. Vacuum dry the obtained product at 60 °C for 12 h to obtain the Ni(OH)2 / Fe2O3 heterostructure composite material with nanosheets wrapping nanoparticles, named NiFe-4.

[0061] Example 6 (Preparation of Ni(OH)2) Without adding Fe2O3 and with other experimental conditions the same as in Experimental Example 1, Ni(OH)2 can be obtained.

[0062] Example 7 (Preparation of Fe2O3) Without adding Ni(OH)2 and with other experimental conditions the same as in Experimental Example 1, Fe2O3 can be obtained.

[0063] The performance test of the NiFe-1 sample prepared in Example 2 above is as Figure 7 , when the current density is 10 mA cm -2 , the overpotential is as low as 273 mV, as Figures 6-7 , linear sweep voltammetry curves of different contents of ferric nitrate nonahydrate were tested and compared. The results show that the addition of an appropriate amount of ferric nitrate nonahydrate endows it with excellent OER overpotential. As can be seen from Figure 7 , the overpotential values of the composite materials are lower than those of the individual Ni(OH)2 and Fe2O3. The results show that the interfacial electron interaction between the two metals Fe and Ni is good, and the electrocatalytic oxygen evolution performance has been greatly improved, which can effectively reduce the OER reaction overpotential and promote the electron transfer in the electrolyte.

[0064] The present invention proposes a simple hydrothermal method to synthesize nanosheets with a thickness of 5 - 10 nm that wrap nanoparticles in a heterostructure composite material. Benefiting from the advantages of the structure and composition and the interfacial electron interaction between metals, the prepared Ni(OH)2 / Fe2O3 heterostructure electrode with nanosheets wrapping nanoparticles has excellent electrocatalytic oxygen evolution performance, and has faster OER kinetics and good stability.

[0065] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The embodiments in this application and the features in the embodiments can be arbitrarily combined with each other without conflict. The protection scope of the present invention should be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, the equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A preparation method of a composite material with a heterostructure of Ni(OH)2 / Fe2O3 nanosheet-coated nanoparticles, characterized in that, It includes the following steps: (1) Take nickel nitrate hexahydrate and 2,6-naphthalenedicarboxylic acid and dissolve them in N,N-dimethylformamide solution. After stirring evenly, carry out hydrothermal reaction to obtain Ni-NDC with a nanosheet structure; (2) The sample obtained in step (1) and iron nitrate nonahydrate are dissolved in sodium hydroxide solution. After ultrasonic dispersion and mixing evenly at room temperature, carry out hydrothermal reaction to obtain Ni(OH)2 / Fe2O3 with a heterostructure of nanosheets wrapping nanoparticles.

2. The preparation method of the Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material according to claim 1, characterized in that, In step (1), the molar mass ratio of nickel nitrate hexahydrate to 2,6-naphthalenedicarboxylic acid is 0.1-1:0.1-1; the N,N-dimethylformamide solution is an N,N-dimethylformamide solution with or without water. In the N,N-dimethylformamide solution with water, the volume ratio of deionized water to N,N-dimethylformamide is 0.5-1:10-15.

3. The preparation method of the Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material according to claim 1, characterized in that, In step (1), the molar mass ratio of nickel nitrate hexahydrate to 2,6-naphthalenedicarboxylic acid is 0.1:0.12; the volume ratio of deionized water to N,N-dimethylformamide is 1:

12.

4. The preparation method of the Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material according to claim 1, characterized in that, The hydrothermal reaction temperature in step (1) is 100-150 °C, and the reaction time is 10-15 h; preferably, the hydrothermal reaction temperature is 130 °C and the reaction time is 12 h.

5. The preparation method of the Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material according to claim 1, wherein, In step (2), the mass ratio of Ni-NDC to iron nitrate nonahydrate is 1-10:0.5-10, preferably, the mass ratio of Ni-NDC to iron nitrate nonahydrate is 6:

1.

6. The preparation method of the Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material according to claim 1, characterized in that, The concentration of sodium hydroxide in step (2) is 1-5 mol / L.

7. The preparation method of the Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material according to claim 6, characterized in that, The concentration of sodium hydroxide in step (2) is 1 mol / L.

8. The preparation method of the Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material according to claim 1, characterized in that, The hydrothermal reaction temperature in step (2) is 120-160 °C, and the reaction time is 10-15 h.

9. The preparation method of the Ni(OH)2 / Fe2O3 nanosheet-wrapped nanoparticle heterostructure composite material according to claim 8, characterized in that, The hydrothermal reaction temperature in step (2) is 140 °C and the reaction time is 12 h. Application of the Ni(OH)2 / Fe2O3 composite material with a heterostructure of nanosheets wrapping nanoparticles prepared by the method according to any one of claims 1-9 in the preparation of electrocatalytic oxygen evolution.

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