Synthesis method of nitrogen-doped carbon-coated multi-metal nanosheet array and water electrolysis application of nitrogen-doped carbon-coated multi-metal nanosheet array

Abstract

The invention discloses a synthesis method of a nitrogen-doped carbon-coated multi-metal nanosheet array and an application of the nitrogen-doped carbon-coated multi-metal nanosheet array in electrolyzed water. The synthesis method comprises the following steps: pretreating foamed nickel, synthesizing a precursor nanosheet array by a one-step hydrothermal method, then converting the precursor nanosheet array into a precursor ZIF, and finally pyrolyzing the precursor ZIF to obtain a final product. The precursor nanosheet array comprises a seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array or a six-membered Fe-Cr-Al-Co-Zn-Ni high-entropy nanosheet array, and the precursor nanosheet array comprises a seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array. The prepared multi-metal catalyst shows unique advantages in a complex reaction system, not only is high in catalytic activity, but also has stable electro-catalytic performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-metal nanopowders, and in particular relates to a synthesis method of a nitrogen-doped carbon-coated multi-metal nanosheet array and its application in water electrolysis. The method has low cost and simple synthesis process. Background Art

[0002] With the continuous development of the global economy, human demand for energy continues to grow. Hydrogen, as a highly potential heat-generating raw material in the energy field, avoids the disadvantages of traditional fossil fuels that pollute the environment and emit a large amount of greenhouse gases. At the same time, the technology of hydrogen production by electrolysis of water has been rapidly widely used and promoted around the world because of its relatively simple process, high product purity, and the ability to achieve nearly zero carbon emission hydrogen production process driven by renewable energy electricity.

[0003] Electrocatalytic water splitting technology can produce renewable and clean hydrogen energy. Compared with the hydrogen evolution reaction, the oxygen evolution reaction (OER) requires the simultaneous transfer of four electrons and is accompanied by the breaking and formation of multiple chemical bonds. From a kinetic point of view, the multi-electron transfer process will lead to a higher reaction energy barrier, that is, a larger energy barrier needs to be overcome before it can proceed. This means that OER requires an efficient catalyst to help it reduce the activation energy of the reaction and make the reaction proceed faster.

[0004] Among them, the most effective hydrogen production catalysts are precious metal-based electrocatalysts, such as iridium dioxide and ruthenium dioxide. However, due to the disadvantages of high cost and low reserves, their application in water electrolysis is limited. The patent "A nitrogen-doped carbon-coated non-precious bimetallic cobalt-molybdenum oxide oxygen evolution reaction catalyst, preparation method and application" (publication number: CN112553643A) provides a nitrogen-doped carbon-coated bimetallic cobalt-molybdenum oxide oxygen evolution reaction catalyst, but there is no more research on the effect of catalysts prepared by more transition metals in oxygen evolution reaction.

[0005] The nitrogen-doped carbon-coated structure is a composite material with unique structure and properties generated by pyrolysis and doping of nitrogen-containing precursors and carbon source materials. This transition metal-based electrocatalyst not only meets the requirements of efficient catalytic performance, high stability and conductivity, but also meets the characteristics of simple synthesis process, abundant synthetic raw materials and affordable price. In addition, thanks to the protective effect of the catalyst NC support skeleton, the catalyst has super strong OER electrocatalytic stability.

[0006] Since the electrode reaction is a dynamic equilibrium process, the slow oxygen evolution reaction will cause charge accumulation on the electrode surface, thus affecting the hydrogen evolution reaction. In a two-electrode system, if the oxygen evolution reaction rate at the anode is too slow, the hydrogen evolution reaction at the cathode will not be able to proceed at the optimal efficiency due to the charge accumulation and electric field change at the anode, ultimately affecting the kinetics and overall efficiency of the entire water decomposition process. Therefore, an efficient catalyst has to be invented to increase the oxygen evolution reaction rate. Summary of the invention

[0007] In order to solve the above problems of the prior art, the present invention provides a method for synthesizing a nitrogen-doped carbon-coated multi-metal nanosheet array and its electrolytic water application, wherein the precursor nanosheet array is synthesized by a one-step hydrothermal method through nickel foam pretreatment, and then converted into a precursor ZIF (high entropy zeolite imidazolate framework material), and finally pyrolyzed to obtain the final product. The prepared multi-metal catalyst exhibits unique advantages in a complex reaction system, and not only has high catalytic activity, but also has stable electrocatalytic performance. In order to achieve the above objectives, the technical solution provided by the present invention is as follows:

[0008] In one aspect, the present invention provides a method for synthesizing a nitrogen-doped carbon-coated multi-metal nanosheet array, comprising the following steps:

[0009] S1, pretreatment of nickel foam: place the nickel foam in acetone and use ultrasonic wave to remove organic matter on the surface of the nickel foam; use distilled water ultrasonic wave, and then use dilute hydrochloric acid solution ultrasonic wave to remove the surface oxide layer; finally, use deionized water ultrasonic wave to wash several times, and the pretreatment is complete.

[0010] S2, synthesis of high entropy nanosheet arrays: metal salts are taken and synthesized by a one-step hydrothermal method. First, metal salts are weighed and dissolved in deionized water, and stirred evenly at room temperature to form solution A. Urea is then weighed and added to solution A, and stirred evenly at room temperature to form a precursor solution B. The nickel foam pretreated in step S1 is placed in a polytetrafluoroethylene liner of an autoclave, and then the precursor solution B is transferred to the autoclave liner and sealed, heated for reaction, and then cooled to room temperature to obtain a catalyst-loaded nickel foam. The catalyst-loaded nickel foam is washed with deionized water and ethanol, and then dried to obtain a high entropy nanosheet array.

[0011] The metal salt is selected from nitrates, sulfates, and metal chlorides; phosphates are mostly insoluble and unworkable. In the present invention, metal nitrates are preferred.

[0012] The nitrate is selected from at least five of ferric nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, cobalt nitrate and zinc nitrate.

[0013] In step S2, the reaction condition is heating in an oven at 120° C. for 12 h.

[0014] The drying condition was vacuum drying at 40°C for 12 h.

[0015] Among them, the molar ratio of iron nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, cobalt nitrate and zinc nitrate is 0.06-0.075:0.06-0.075:0.06-0.075:0.06-0.075:0.06-0.075:0.7, and the molar ratio of the total amount of nitrate to urea is 0.3:2.4.

[0016] Furthermore, ferric nitrate, chromium nitrate, aluminum nitrate, cerium nitrate and cobalt nitrate are added in equal molar amounts.

[0017] In some embodiments of the present invention, a seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet is synthesized, and preferably, the molar ratio of iron nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, cobalt nitrate and zinc nitrate is 0.06:0.06:0.06:0.06:0.06:0.7.

[0018] In some embodiments of the present invention, hexameric Fe-Cr-Al-Co-Zn-Ni high entropy nanosheets are synthesized, and preferably, the molar ratio of iron nitrate, chromium nitrate, aluminum nitrate, cobalt nitrate and zinc nitrate is 0.075:0.075:0.075:0.075:0.075:0.7.

[0019] S3, preparation of high-entropy ZIF: converting the seven-element high-entropy nanosheet array or the six-element high-entropy nanosheet array prepared in S2 into high-entropy ZIF by heating with 2-methylimidazole; specifically, dissolving 2-methylimidazole in deionized water and then transferring it into a container, placing the high-entropy nanosheet array prepared in step S2 into the container and fixing it, installing the container on a heating device, heating and stirring at the same time, washing with methanol after heating, and vacuum drying to obtain a precursor.

[0020] Preferably, in step S3, the heating device is an oil bath heating device.

[0021] The reaction conditions were heating at 100°C with stirring for 6 h.

[0022] S4, preparation of high-performance catalyst of nitrogen-doped carbon-coated high-entropy nanosheet array: converting the high-entropy ZIF prepared in step S3 into nitrogen-doped carbon-coated high-entropy nanomaterial by pyrolysis. Specifically, the precursor obtained in step S3 is heated in a tubular furnace, and the final product is obtained after cooling to room temperature.

[0023] Preferably, in step S4, the temperature is 5°C·min -1 The temperature was raised from room temperature to 500°C in a tube furnace, kept at this temperature for 2 hours, and then naturally cooled to room temperature before being taken out to obtain the final product.

[0024] More preferably, the temperature is 5°C·min -1 The mixture was heated from room temperature to 500°C in a tube furnace at a heating rate of , kept warm for 2 h, and then naturally cooled to room temperature before being taken out to obtain the final product.

[0025] In a second aspect, the present invention provides a product obtained by the synthesis method of the nitrogen-doped carbon-coated multi-metal nanosheet array.

[0026] In a third aspect, the present invention provides an application of a product obtained by a synthesis method of a nitrogen-doped carbon-coated multi-metal nanosheet array in water electrolysis; the product obtained by the synthesis method of the nitrogen-doped carbon-coated multi-metal nanosheet array is used as a working electrode for water electrolysis.

[0027] The present invention is achieved by:

[0028] (1) Constructing nanostructures to provide more contact area for the catalyst to adsorb hydroxide ions in the first step of the anode reaction, thereby exposing more active sites and increasing the reaction rate;

[0029] (2) Multimetal effect: The interaction between multiple metals enhances the stability of the system. In multimetal catalysts, electrons will transfer between different metals, changing the electron cloud density of the active site, optimizing the reactant adsorption and product desorption process, and thus improving the catalytic activity.

[0030] In the embodiments of the present invention, through the product test results, TEM and SEM images intuitively show that the material has constructed a nanostructure. The nanostructure has the characteristics of high specific surface area, which can increase more active sites and improve the reaction rate. XRD spectrum analysis shows that due to the different types and proportions of metals invested in the embodiments, there are differences in the diffraction peaks of different embodiments. LSV curve comparison shows that due to the different material compositions and structures of each embodiment, different electrochemical behaviors such as initial potential and current intensity are exhibited in the same electrolyte, that is, the combination of multiple metals affects the electrochemical reaction activity and selectivity of the material.

[0031] The nitrogen-doped carbon-coated seven-element high-entropy nanosheet array high-performance catalyst combines these two improvement measures and has stronger electrocatalytic stability due to its nitrogen-doped carbon coating characteristics.

[0032] The characteristic of this product is the use of multi-metal catalysts, which are significantly different from single-metal and binary metal catalysts in terms of preparation. In terms of raw material selection and ratio, there is no problem of metal ratio for single-metal catalysts; it is relatively simple to determine the ratio of two metals for binary metal catalysts; when determining the ratio of each metal for multi-metal catalysts, the synergistic effect between multiple metals must be considered, and optimization through a large number of experiments and theoretical calculations is required to achieve the best performance. In terms of synthesis process, the synthesis of single-metal catalysts is relatively simple, such as precipitation method, impregnation method, etc. It can be completed in a few steps; the synthesis of multi-metal catalysts is more complicated, requiring nickel foam pretreatment, a one-step hydrothermal method to synthesize the precursor nanosheet array, and then converted into the precursor ZIF, and finally pyrolysis to obtain the final product. These differences make multi-metal catalysts show unique advantages in complex reaction systems.

[0033] The synthesis principle of nitrogen-doped carbon-coated multi-metal nanosheet materials is explained: the reason for the pretreatment of nickel foam is that the nickel foam is not in a pure state before the experiment, and there are organic matter and oxide layers on its surface. The presence of organic matter will hinder the subsequent reaction and prevent the reaction from occurring smoothly on the surface of nickel foam; the oxide layer will affect the conductivity of the material and the exposure of active sites, reducing the performance of the catalyst. The one-step hydrothermal method dissolves and stirs metal nitrates and urea to form a solution, and a specific reaction occurs. This method can make a variety of metal ions evenly dispersed in the solution, and under the hydrothermal environment, the reaction activity of each substance is enhanced, and a seven-element or six-element high-entropy nanosheet array with a specific structure can be directly generated. The process is relatively simple, and the uniform distribution of multiple metals and the construction of nanosheet arrays can be achieved in one reaction step, simplifying the synthesis process; the precursor nanosheet is converted into a precursor ZIF, and these characteristics of ZIF are used to further optimize the material performance. For example, the ordered crystal structure of ZIF provides a stable framework for subsequent pyrolysis, making the structural changes of the material during pyrolysis more controllable; the abundant pores of ZIF increase the specific surface area of ​​the material, provide more active sites for the catalytic reaction, and improve the catalytic efficiency; the material stability is significantly improved through the transformation from precursor nanosheets to precursor ZIF and then to nitrogen-doped carbon-coated multi-metal nanosheet materials. During the pyrolysis process, the temperature is raised and kept warm to cause the ZIF to decompose and transform its structure, forming a nitrogen-doped carbon-coated nanomaterial. The pyrolysis process can also further adjust the microstructure of the material, so that the metal particles are better dispersed in the carbon coating layer, optimize the distribution of active sites, and improve the catalytic activity.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention provides a high-performance catalyst of a nitrogen-doped carbon-coated multi-element high-entropy nanosheet array, which constructs a nanostructure and utilizes the multi-metal effect to enhance the catalytic activity; at the same time, the nitrogen-doped carbon-coated structure is utilized to have a stronger electrocatalytic stability.

[0036] (2) The high entropy nanomaterial provided by the present invention has a stable structure, which ensures stable electrocatalytic performance; at the same time, the present invention utilizes the synergistic effect between multiple metals, proposes a better ratio, and improves product performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0038] Figure 1 : XRD spectra of Examples 1, 2, 3, 4 of the present invention and Comparative Examples 1 and 2;

[0039] Figure 2 : Comparison diagram of LSV properties in the electrolyte before and after adding glycerol in Example 1 of the present invention.

[0040] Figure 3 : LSV curves of Example 1 of the present invention and the comparative products of Examples 2, 3, 4 after element reduction and Comparative Examples 1 and 2 in 0.1M glycerol electrolyte.

[0041] Figure 4 : TEM and SEM images of the precursor nanosheets of Example 1 of the present invention.

[0042] Figure 5 :TEM and SEM images of the precursor ZIP of Example 1 of the present invention.

[0043] Figure 6 :TEM and SEM images of the nitrogen-doped carbon-coated seven-element high-entropy nanomaterial in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] Nitrogen-doped carbon coating: a layer of nitrogen material is coated on the surface of the carbon material to form a core-shell structure. In the preparation process, starting from metal nitrate and urea as precursors, under heating conditions (120°C, 12h), these precursors react simultaneously on the surface of nickel foam to directly generate seven-element and six-element high-entropy nanosheet arrays, that is, nitrogen-doped carbon-coated seven-element and six-element high-entropy nanosheet materials.

[0045] Multi-metal nanosheet material: a sheet-like structure composed of multiple metals and having a nanometer-level thickness. The nanosheets provided by the present invention form an array in a vertically growing sheet-like manner.

[0046] The present invention provides a method for preparing a highly efficient catalyst, a nitrogen-doped carbon-coated multi-metal nanosheet material, and its application in water electrolysis. The reaction involved is the oxygen evolution reaction of water electrolysis: under acidic conditions, the reaction is 2H2O=O2+4H + +4e— ; Under alkaline conditions, the reaction is 4OH — =O2+2H2O+4e — The reaction involves four electron transfers and is accompanied by the breaking and formation of multiple chemical bonds, which causes the oxygen evolution reaction to proceed slowly. Therefore, a high-performance catalyst is desired to achieve rapid oxygen evolution reaction. The preparation method includes the following steps:

[0047] (1) Synthesis of nitrogen-doped carbon-coated seven-membered and six-membered high-entropy nanosheet array high-performance catalysts. In the first step of the synthesis, nickel foam is pretreated; in the second step of the synthesis, the seven-membered and six-membered high-entropy nanosheet arrays are synthesized by a one-step hydrothermal method; in the third step of the synthesis, the prepared seven-membered and six-membered high-entropy nanosheet arrays are converted into seven-membered and six-membered high-entropy ZIFs (high-entropy zeolite imidazolate framework materials); in the fourth step of the synthesis, the prepared seven-membered and six-membered high-entropy ZIFs are converted into nitrogen-doped carbon-coated seven-membered and six-membered high-entropy nanomaterials by thermal decomposition.

[0048] (2) Electrochemical performance test of nitrogen-doped carbon-coated seven-element and six-element high-entropy nanomaterial catalysts: Using a CHI660 electrochemical workstation in 1M KOH+0.1M glycerol electrolyte, a three-electrode system was constructed with nitrogen-doped carbon-coated seven-element and six-element high-entropy nanomaterials as working electrodes, platinum sheets as counter electrodes, and Hg / HgO electrodes as reference electrodes. The voltage range of the cyclic voltammetry was 0.9-1.8V vs. RHE, and the scan rate was 100mV·s -1 The LSV properties of the catalyst were tested after 10 cycles.

[0049] Instruments used in this experiment: X-ray diffraction (XRD) was performed on a Philips X'Pert Pro Super diffractometer, and the X-ray source was Cu Kα radiation. Scanning electron microscope images were taken on a JEOL JSM-6700F scanning electron microscope. Transmission electron microscope images were taken using a JEM-2100F field emission electron microscope at an accelerating voltage of 200 kV. High-resolution transmission electron microscopy (HRTEM), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and corresponding elemental mapping analysis were performed on a ThermoFischer Talos F200X instrument. The atomic ratio of metals was determined on a Perkin Elmer Optima 7300DV inductively coupled plasma emission spectrometer (ICP-OES). X-ray photoelectron spectroscopy (XPS) analysis was performed using a VGESCALAB MKII X-ray photoelectron spectrometer with an excitation source of Mg Kα=1253.6 eV. The related products obtained from the glycerol electro-oxidation reaction were characterized by a nuclear magnetic resonance (NMR) spectrometer, and qualitative and quantitative analysis and calculation of related parameters were performed.

[0050] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0051] A method for preparing a nitrogen-doped carbon-coated multi-metal nanosheet material high-efficiency catalyst comprises the following steps:

[0052] Place nickel foam (2×3.7 cm) in a beaker, add acetone, and perform ultrasonic treatment for 5 minutes to remove organic matter on the surface of nickel foam. Perform ultrasonic treatment for one minute in distilled water, and then perform ultrasonic treatment for 5 minutes in 1% dilute hydrochloric acid solution to remove the oxide layer on the surface. Finally, perform ultrasonic washing several times with deionized water to complete the pretreatment.

[0053] Example 1

[0054] The first step is to prepare a nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array high-performance catalyst. Synthesis step 1: The seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array was synthesized by a one-step hydrothermal method. First, 0.06mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O and 0.7mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80ml of deionized water, stirred evenly at room temperature to form solution A, and then 2.4mmol of urea was weighed and added to solution A, stirred evenly at room temperature to form solution B. The nickel foam was placed in the polytetrafluoroethylene liner of a 100 ml high-pressure reactor, and then the precursor solution B was transferred to the liner and sealed, heated in an oven at 120 ° C for 12 hours, and then cooled to room temperature. The nickel foam loaded with the catalyst was washed three times with deionized water and ethanol, and vacuum dried at 40 ° C for 12 hours to obtain a uniform seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array; Synthesis step 2, the prepared seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array was converted into a seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy ZIF. Dissolve 8.2g of 2-methylimidazole in 50ml of deionized water, then transfer to a 100ml flask, place the seven-element high entropy nanosheet array in the flask and fix it with a straw, install the flask on an oil bath heating device, heat and stir at 100°C for 6h, wash with methanol 3 times after heating, and vacuum dry at 40°C for 12h; Synthesis step three, convert the prepared seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy ZIF into nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanomaterials by pyrolysis. The obtained seven-element high entropy ZIF precursor was heated in a tube furnace at 5°C·min -1 The temperature was raised from room temperature to 500°C in a tube furnace at a heating rate of , and kept warm for 2 h. After naturally cooling to room temperature, the nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst was obtained.

[0055] The second step is the morphological characterization of the products. TEM and SEM tests were performed on the precursor nanosheets, precursor ZIF, and nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanomaterials.

[0056] The third step is the phase characterization of the product. The XRD diffraction pattern of the nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanomaterial catalyst was tested.

[0057] The fourth step is to test the performance of the product. The nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanomaterial catalyst was immersed in 1M KOH and 0.1M glycerol electrolyte (1M KOH) respectively, and its LSV curve was measured.

[0058] In the first step of the synthesis, hydrothermal treatment is generally performed in an oven or a muffle furnace.

[0059] In the synthesis step 3, an inert atmosphere is required when heating in a tube furnace. Argon is generally used as the inert gas, but nitrogen can also be used.

[0060] The inventors have found that when the temperature of the reaction in the high-pressure reactor to prepare the nickel foam loaded with the catalyst is lower than 120°C, the carbon structure is not easy to form, which means that the morphology of the nanosheet array is damaged and it is difficult to maintain a neat and orderly array morphology, which is not conducive to the formation of the final product.

[0061] Example 2

[0062] The first step is to prepare a nitrogen-doped carbon-coated hexavalent Fe-Cr-Al-Co-Zn-Ni high entropy nanosheet array high-performance catalyst. In the first step of synthesis, a hexavalent Fe-Cr-Al-Co-Zn-Ni high entropy nanosheet array was synthesized by a one-step hydrothermal method. First, 0.075mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Co(NO3)2·6H2O and 0.7mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80ml of deionized water, stirred evenly at room temperature to form solution A, and then 2.4mmol of urea was weighed and added to solution A, stirred evenly at room temperature to form solution B. The nickel foam was placed in the polytetrafluoroethylene liner of a 100ml high-pressure reactor, and then the precursor solution B was transferred to the liner and sealed, heated in an oven at 120℃ for 12h, and then cooled to room temperature. The nickel foam loaded with catalyst was washed three times with deionized water and ethanol, and vacuum dried at 40℃ for 12h to obtain a uniform hexavalent Fe-Cr-Al-Co-Zn-Ni high entropy nanosheet array; Synthesis step 2, the prepared hexavalent Fe-Cr-Al-Co-Zn-Ni high entropy nanosheet array was converted into a hexavalent Fe-Cr-Al-Co-Zn-Ni high entropy ZIF. 8.2g of 2-methylimidazole was dissolved in 50ml of deionized water, then transferred into a 100ml flask, the hexavalent high entropy nanosheet array was placed in the flask and fixed with a straw, the flask was installed on an oil bath heating device, heated at 100℃ while stirring for 6h, washed with methanol 3 times after heating, and vacuum dried at 40℃ for 12h; Synthesis step 3, the prepared hexavalent Fe-Cr-Al-Co-Zn-Ni high entropy ZIF was converted into a nitrogen-doped carbon-coated hexavalent Fe-Cr-Al-Co-Zn-Ni high entropy nanomaterial by pyrolysis. The obtained precursor was heated in a tube furnace at 5 °C min -1 The temperature was raised from room temperature to 500°C in a tube furnace at a heating rate of , and kept warm for 2 h. After naturally cooling to room temperature, the nitrogen-doped carbon-coated hexameric high-entropy nanosheet array high-performance catalyst was obtained.

[0063] The second step is the phase characterization of the product. The XRD diffraction pattern of the nitrogen-doped carbon-coated hexavalent Fe-Cr-Al-Co-Zn-Ni high entropy nanomaterial catalyst was obtained.

[0064] The third step is to test the performance of the product. The nitrogen-doped carbon-coated hexavalent Fe-Cr-Al-Co-Zn-Ni high-entropy nanomaterial catalysts were immersed in 0.1M glycerol electrolyte (1M KOH) and their LSV curves were measured.

[0065] Example 3

[0066] The first step is to prepare a nitrogen-doped carbon-coated hexavalent Fe-Cr-Al-Ce-Zn-Ni high entropy nanosheet array high-performance catalyst. In the first step of synthesis, a hexavalent Fe-Cr-Al-Ce-Zn-Ni high entropy nanosheet array was synthesized by a one-step hydrothermal method. First, 0.075mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O and 0.7mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80ml of deionized water, stirred evenly at room temperature to form solution A, and then 2.4mmol of urea was weighed and added to solution A, stirred evenly at room temperature to form solution B. The nickel foam was placed in the polytetrafluoroethylene liner of a 100ml high-pressure reactor, and then the precursor solution B was transferred to the liner and sealed, heated in a 120℃ tube furnace for 12h, and then cooled to room temperature. The nickel foam loaded with catalyst was washed three times with deionized water and ethanol, and vacuum dried at 40°C for 12h to obtain a uniform hexavalent Fe-Cr-Al-Ce-Zn-Ni high entropy nanosheet array; Synthesis step 2, the prepared hexavalent Fe-Cr-Al-Ce-Zn-Ni high entropy nanosheet array was converted into a hexavalent Fe-Cr-Al-Ce-Zn-Ni high entropy ZIF. 8.2g of 2-methylimidazole was dissolved in 50ml of deionized water, then transferred into a 100ml flask, the hexavalent high entropy nanosheet array was placed in the flask and fixed with a straw, the flask was installed on an oil bath heating device, heated at 100°C while stirring for 6h, washed with methanol 3 times after the heating was completed, and vacuum dried at 40°C for 12h; Synthesis step 3, the prepared hexavalent Fe-Cr-Al-Ce-Zn-Ni high entropy ZIF was converted into a nitrogen-doped carbon-coated hexavalent Fe-Cr-Al-Ce-Zn-Ni high entropy nanomaterial by pyrolysis. The obtained precursor was heated in a tube furnace at 5 °C min -1 The temperature was raised from room temperature to 500°C in a tube furnace at a heating rate of , and kept warm for 2 h. After naturally cooling to room temperature, the nitrogen-doped carbon-coated hexameric Fe-Cr-Al-Ce-Zn-Ni high-entropy nanosheet array high-performance catalyst was obtained.

[0067] The second step is the phase characterization of the product. The XRD diffraction pattern of the nitrogen-doped carbon-coated hexavalent Fe-Cr-Al-Ce-Zn-Ni high entropy nanomaterial catalyst was obtained.

[0068] The third step is to test the performance of the product. The nitrogen-doped carbon-coated hexavalent Fe-Cr-Al-Ce-Zn-Ni high-entropy nanomaterial catalysts were immersed in 0.1M glycerol electrolyte (1M KOH) and their LSV curves were measured.

[0069] Example 4

[0070] The first step is to prepare a nitrogen-doped carbon-coated hexavalent Fe-Cr-Ce-Co-Zn-Ni high entropy nanosheet array high-performance catalyst. In the first step of synthesis, a hexavalent Fe-Cr-Ce-Co-Zn-Ni high entropy nanosheet array was synthesized by a one-step hydrothermal method. First, 0.075mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O and 0.7mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80ml of deionized water, stirred evenly at room temperature to form solution A, and then 2.4mmol of urea was weighed and added to solution A, stirred evenly at room temperature to form solution B. The nickel foam was placed in the polytetrafluoroethylene liner of a 100ml high-pressure reactor, and then the precursor solution B was transferred to the liner and sealed, heated in a 120℃ tube furnace for 12h, and then cooled to room temperature. The nickel foam loaded with catalyst was washed three times with deionized water and ethanol, and vacuum dried at 40℃ for 12h to obtain a uniform hexavalent Fe-Cr-Ce-Co-Zn-Ni high entropy nanosheet array; Synthesis step 2, the prepared hexavalent Fe-Cr-Ce-Co-Zn-Ni high entropy nanosheet array was converted into a hexavalent Fe-Cr-Ce-Co-Zn-Ni high entropy ZIF. 8.2g of 2-methylimidazole was dissolved in 50ml of deionized water, then transferred into a 100ml flask, the hexavalent high entropy nanosheet array was placed in the flask and fixed with a straw, the flask was installed on an oil bath heating device, heated at 100℃ while stirring for 6h, washed with methanol 3 times after heating, and vacuum dried at 40℃ for 12h; Synthesis step 3, the prepared hexavalent Fe-Cr-Ce-Co-Zn-Ni high entropy ZIF was converted into a hexavalent Fe-Cr-Ce-Co-Zn-Ni high entropy nanomaterial coated with nitrogen-doped carbon by pyrolysis. The obtained precursor was heated in a tube furnace at 5 °C min -1 The temperature was raised from room temperature to 500°C in a tube furnace at a heating rate of , and kept warm for 2 h. After naturally cooling to room temperature, the nitrogen-doped carbon-coated hexameric Fe-Cr-Ce-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst was obtained.

[0071] The second step is the phase characterization of the product. The XRD diffraction pattern of the nitrogen-doped carbon-coated hexavalent Fe-Cr-Ce-Co-Zn-Ni high entropy nanomaterial catalyst was obtained.

[0072] The third step is to test the performance of the product. The nitrogen-doped carbon-coated hexavalent Fe-Cr-Ce-Co-Zn-Ni high-entropy nanomaterial catalysts were immersed in 0.1M glycerol electrolyte (1M KOH) and their LSV curves were measured.

[0073] Comparative Example 1

[0074] The first step is to prepare a nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array high-performance catalyst. Synthesis step 1: The seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array was synthesized by a one-step hydrothermal method. First, 0.06mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O and 0.7mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80ml of deionized water, stirred evenly at room temperature to form solution A, and then 2.4mmol of urea was weighed and added to solution A, stirred evenly at room temperature to form solution B. The nickel foam was placed in the polytetrafluoroethylene liner of a 100 ml high-pressure reactor, and then the precursor solution B was transferred to the liner and sealed, heated in a 130 ° C tube furnace for 12 hours, and then cooled to room temperature. The nickel foam loaded with the catalyst was washed three times with deionized water and ethanol, and vacuum dried at 40 ° C for 12 hours to obtain a uniform seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array; Synthesis step 2, the prepared seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array was converted into a seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy ZIF. Dissolve 8.2g of 2-methylimidazole in 50ml of deionized water, then transfer to a 100ml flask, place the seven-element high entropy nanosheet array in the flask and fix it with a straw, install the flask on an oil bath heating device, heat and stir at 100°C for 6h, wash with methanol 3 times after heating, and vacuum dry at 40°C for 12h; Synthesis step three, convert the prepared seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy ZIF into nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanomaterials by pyrolysis. The obtained seven-element high entropy ZIF precursor was sintered in a tube furnace at 5°C·min under an inert atmosphere. -1 The mixture was heated at a heating rate of 500°C from room temperature in a tube furnace and kept warm for 2 h. After naturally cooling to room temperature, the mixture was taken out to obtain a nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst.

[0075] The second step is the phase characterization of the product. The XRD diffraction pattern of the nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanomaterial catalyst was tested.

[0076] The third step is to test the performance of the product. The nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanomaterial catalyst was immersed in 1M KOH and 0.1M glycerol electrolyte (1M KOH) respectively, and its LSV curve was measured.

[0077] Comparative Example 2

[0078] The first step is to prepare a nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array high-performance catalyst. Synthesis step 1: The seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array was synthesized by a one-step hydrothermal method. First, 0.06mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O and 0.7mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80ml of deionized water, stirred evenly at room temperature to form solution A, and then 2.4mmol of urea was weighed and added to solution A, stirred evenly at room temperature to form solution B. The nickel foam was placed in the polytetrafluoroethylene liner of a 100 ml high-pressure reactor, and then the precursor solution B was transferred to the liner and sealed, heated in a 120 ° C tube furnace for 12 hours, and then cooled to room temperature. The nickel foam loaded with the catalyst was washed three times with deionized water and ethanol, and vacuum dried at 50 ° C for 12 hours to obtain a uniform seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array; Synthesis step 2, the prepared seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanosheet array was converted into a seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high entropy ZIF. Dissolve 8.2g of 2-methylimidazole in 50ml of deionized water, then transfer to a 100ml flask, place the seven-element high entropy nanosheet array in the flask and fix it with a straw, install the flask on an oil bath heating device, heat and stir at 100°C for 6h, wash with methanol 3 times after heating, and vacuum dry at 40°C for 12h; Synthesis step three, convert the prepared seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy ZIF into nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanomaterials by pyrolysis. The obtained seven-element high entropy ZIF precursor was sintered in a tube furnace at 5°C·min under an inert atmosphere. -1 The temperature was raised from room temperature to 500°C in a tube furnace at a heating rate of , and kept warm for 2 h. After naturally cooling to room temperature, the nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst was obtained.

[0079] The second step is the phase characterization of the product. The XRD diffraction pattern of the nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanomaterial catalyst was tested.

[0080] The third step is to test the performance of the product. The nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanomaterial catalyst was immersed in 1M KOH and 0.1M glycerol electrolyte (1M KOH) respectively, and its LSV curve was measured.

[0081] Result analysis:

[0082] Depend on Figure 1 , 3 It can be seen that the performance of the products of Examples 1 to 4 is different. As can be seen from the figure, the diffraction peak intensities of Examples 4 to 1 are different, which means that the crystallinity of 1-4 is different, among which the crystallinity of Example 3 is relatively large. When the temperature of steps S1 and S2 is increased, the diffraction peak intensity also changes, indicating that the properties of the product will also be different as the experimental temperature changes. Figure 3 It can be seen that as the potential increases, the reaction rate accelerates and the current intensity increases. The starting potentials at which the current begins to increase significantly in different embodiments are slightly different, suggesting that there are differences in the difficulty of the electrochemical reaction in each case. At the same potential, the relative current intensity of Example 1 is higher than that of Examples 2, 3, and 4, indicating that the electrochemical reaction rate of Example 1 in the glycerol electrolyte is faster and the reaction is more fully carried out. And when the temperature of steps S1 and S2 is increased, the current intensity also changes accordingly, indicating that the properties of the product will also be different as the experimental temperature changes. And this difference caused by changing the experimental temperature is not good. When the experimental temperature increases, the particles will become larger, resulting in a decrease in active sites, which means that the number of catalytic active centers that the reactant molecules can contact is reduced, thereby reducing the reaction rate, which is not conducive to the production of efficient catalysts. And the temperature set by the experimental scheme and the time controlled are uniquely determined. When the temperature or time is changed, the properties of the generated material will change, resulting in differences in product performance tests.

[0083] like Figure 2 As shown, the starting potential of the electrolyte with glycerol added is about 1.22V, and the starting potential of the electrolyte without glycerol added is about 1.39V. This shows that after adding glycerol, the electrochemical reaction begins at a lower potential, which means that the addition of glycerol reduces the starting potential of the reaction, making the reaction easier to occur. And in the same potential range, the relative current intensity of the electrolyte with glycerol added is higher than that without glycerol added, indicating that the rate of the electrode reaction is faster after adding glycerol, making the reaction more complete.

[0084] The TEM and SEM images of the precursor nanosheets of Example 1 of the present invention are as follows: Figure 4As shown in FIG. 1 , the TEM image shows that the nanosheets are roughly hexagonal in shape; the three-dimensional SEM image shows that many nanosheets are aggregated together and have a certain stacking state. Figure 5 As shown in FIG. 1 , multiple granular structures can be seen aggregated through TEM, and some particles seem to have a certain connection or coating relationship between them; a large number of granular substances can be seen through the three-dimensional SEM image; the TEM image and SEM image of the nitrogen-doped carbon-coated seven-element high entropy nanomaterial in Example 1 are shown in FIG. Figure 6 As shown, through TEM it can be seen that the nitrogen-doped carbon-coated seven-element high entropy nanomaterial presents a more complex structure; from the three-dimensional SEM it can be seen that the nitrogen-doped carbon-coated seven-element high entropy nanosheet material presents a needle-like and rod-like stacking state.

[0085] The electrocatalytic stability of the product prepared by the present invention can be reflected in the following two aspects:

[0086] 1. Current stability and starting potential stability: It can be seen from the LSV curve of the product detection that if the current intensity fluctuates slightly during a long time or multiple scans, such as in Example 1, and does not decay significantly with time or the number of scans, it means that within this potential range, the electrocatalytic reaction of the material can proceed continuously and stably, reflecting good electrocatalytic stability.

[0087] 2. Structural stability and morphological stability: From the TEM and three-dimensional SEM images, it can be seen that from the precursor material to the precursor ZIF and then to the nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanomaterial, its structure has not undergone significant collapse, dissolution, phase change and other phenomena, and still maintains relatively complete morphology and structural characteristics; its morphology has not changed significantly, which is conducive to maintaining stable electrocatalytic performance.

[0088] According to the multi-metal effect: the interaction between multiple metals enhances the stability of the system; from the TEM and three-dimensional SEM images, it can be seen that from the precursor material to the precursor ZIF to the nitrogen-doped carbon-coated seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high entropy nanomaterial, its structure has not undergone significant collapse, dissolution, phase change and other phenomena, and still maintains relatively complete morphology and structural characteristics; its morphology has not changed significantly, which is conducive to maintaining stable electrocatalytic performance; in multi-metal catalysts, electrons will transfer between different metals, change the electron cloud density of the active site, optimize the adsorption of reactants and the desorption of products, thereby improving the catalytic activity. XRD spectrum analysis shows that due to the different types and proportions of metals invested in the embodiments, there are differences in the diffraction peaks of different embodiments. LSV curve comparison found that due to the different material composition and structure of each embodiment, it exhibits different electrochemical behaviors such as initial potential and current intensity in the same electrolyte, that is, the combination of multiple metals has an impact on the electrochemical reaction activity and selectivity of the material.

[0089] When preparing nitrogen-doped carbon-coated multi-metal nanosheet array catalysts, the ratio of each material has a critical impact on product performance. The ratio of urea to metal nitrate is related to the nitrogen doping and carbon coating process, affecting the catalyst structure and stability; changes in the ratios of different metal nitrates will affect the multi-metal synergistic effect, active sites and electron cloud density, thereby changing the catalytic activity. The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for synthesizing a nitrogen-doped carbon-coated multi-metal nanosheet array, characterized in that: The steps include: S1, pretreatment of nickel foam; S2, synthesis of high entropy nanosheet arrays: using metal salts to synthesize high entropy nanosheet arrays using a one-step hydrothermal method; S3, preparation of high entropy ZIF: converting the high entropy nanosheet array prepared in step S2 into high entropy ZIF by heating with 2-methylimidazole; S4, preparation of nitrogen-doped carbon-coated high-entropy nanosheet array high-performance catalyst: The high-entropy ZIF prepared in step S3 is converted into nitrogen-doped carbon-coated high-entropy nanomaterials by pyrolysis.

2. The method for synthesizing nitrogen-doped carbon-coated multi-metal nanosheet arrays according to claim 1, characterized in that: In step S2, first, weigh the metal salts respectively and dissolve them in deionized water, stir them evenly to form solution A, then weigh urea and add them to solution A, stir them evenly at room temperature to form a precursor solution B; put the nickel foam pretreated in step S1 into the polytetrafluoroethylene liner of the autoclave, then transfer the precursor solution B to the autoclave liner and seal it, heat it for reaction, and then cool it to room temperature to obtain a nickel foam loaded with a catalyst; wash the nickel foam loaded with the catalyst with deionized water and ethanol, and then dry it to obtain a high entropy nanosheet array.

3. The method for synthesizing nitrogen-doped carbon-coated multi-metal nanosheet arrays according to claim 1, characterized in that: The metal salt is selected from nitrates, sulfates, and metal chlorides, and the nitrate is selected from at least five of ferric nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, cobalt nitrate, and zinc nitrate.

4. The method for synthesizing nitrogen-doped carbon-coated multi-metal nanosheet arrays according to claim 3, characterized in that: The molar ratio of iron nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, cobalt nitrate and zinc nitrate is 0.06-0.075:0.06-0.075:0.06-0.075:0.06-0.075:0.06-0.075:0.7, and the molar ratio of the total amount of nitrate to urea is 0.3:2.

4.

5. The method for synthesizing nitrogen-doped carbon-coated multi-metal nanosheet arrays according to claim 3, characterized in that: Ferric nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, and cobalt nitrate are added in equal molar amounts.

6. The method for synthesizing nitrogen-doped carbon-coated multi-metal nanosheet arrays according to claim 2, characterized in that: In step S3, 2-methylimidazole is dissolved in deionized water and then transferred into a container, the high entropy nanosheet array obtained in step S2 is placed in the container and fixed, the container is installed on a heating device, heated and stirred, washed with methanol after heating, and vacuum dried to obtain a precursor.

7. The method for synthesizing nitrogen-doped carbon-coated multi-metal nanosheet arrays according to claim 6, characterized in that: In step S4, the precursor obtained in step S3 is heated in a tube furnace, and the final product is obtained after cooling to room temperature.

8. The method for synthesizing nitrogen-doped carbon-coated multi-metal nanosheet arrays according to claim 7, characterized in that: In step S2, the reaction conditions are heating in an oven at 120°C for 12 hours; the drying conditions are vacuum drying at 40°C for 12 hours; In step S3, the heating device is an oil bath heating device; the reaction conditions are heating at 100° C. and stirring for 6 hours; In step S4, the temperature was set at 5°C·min -1 The mixture was heated from room temperature to 500°C in a tube furnace at a heating rate of , kept warm for 2 h, and then naturally cooled to room temperature before being taken out to obtain the final product.

9. A product obtained by the synthesis method of nitrogen-doped carbon-coated multi-metal nanosheet arrays according to any one of claims 1 to 8.

10. Use of the product obtained by the synthesis method of nitrogen-doped carbon-coated multi-metal nanosheet arrays according to any one of claims 1 to 8 in electrolysis of water, characterized in that: The product obtained by the synthesis method of the nitrogen-doped carbon-coated multi-metal nanosheet array is used as a working electrode for electrolysis of water.

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