Synthesis of nitrogen-doped carbon-coated multi-metal nanosheet arrays and its application in water electrolysis

Abstract

The application discloses a synthesis method of nitrogen-doped carbon-coated multi-metal nanosheet array and application of the multi-metal nanosheet array in water electrolysis, and relates to a method for synthesizing a precursor nanosheet array through foam nickel pretreatment and a one-step hydrothermal method, converting the precursor nanosheet array into a precursor ZIF, and pyrolyzing the precursor ZIF to obtain a final product, wherein the precursor nanosheet array comprises a seven-element Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array or a six-element Fe-Cr-Al-Co-Zn-Ni high-entropy nanosheet array. The multi-metal catalyst prepared by the method has unique advantages in a complex reaction system, and has high catalytic activity and stable electrocatalytic performance.

Description

Technical Field

[0001] This invention belongs to the technical field of polymetallic nanopowders, and in particular relates to a method for synthesizing nitrogen-doped carbon-coated polymetallic nanosheet arrays and their application in water electrolysis. This method is low in cost and has a simple synthesis process. Background Technology

[0002] With the continuous development of the global economy, human demand for energy is constantly increasing. Hydrogen, as a highly promising heat-generating raw material in the energy field, avoids the drawbacks of traditional fossil fuels that pollute the environment and emit large amounts of greenhouse gases. At the same time, hydrogen production technology by water electrolysis has been rapidly and widely applied and promoted globally due to its relatively simple process, high product purity, and near-zero carbon emission hydrogen production process driven by renewable energy electricity.

[0003] Electrocatalytic water splitting technology can produce renewable and clean hydrogen energy. Compared to the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER) requires the simultaneous transfer of four electrons and involves the breaking and formation of multiple chemical bonds. From a kinetic perspective, this multi-electron transfer process results in a higher reaction energy barrier, meaning a significant energy obstacle needs to be overcome. This implies that the OER requires a highly efficient catalyst to help lower the activation energy and accelerate the reaction.

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

[0005] Nitrogen-doped carbon-coated structures are composite materials with unique structures and properties, generated from nitrogen-containing precursors and carbon source materials through processes such as pyrolysis and doping. This transition metal-based electrocatalyst not only satisfies the requirements of high catalytic efficiency, high stability, and conductivity, but also boasts a simple synthesis process, abundant raw materials, and affordable cost. Furthermore, thanks to the protective effect of the NC-supported framework, this catalyst exhibits superior OER electrocatalytic stability.

[0006] Since the electrode reaction is a dynamic equilibrium process, a slow oxygen evolution reaction leads to 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 proceed at its optimal efficiency due to charge accumulation at the anode and changes in the electric field, ultimately affecting the kinetics and overall efficiency of the entire water splitting process. Therefore, it is necessary to invent a highly efficient catalyst to improve the oxygen evolution reaction rate. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention provides a method for synthesizing nitrogen-doped carbon-coated multimetal nanosheet arrays and their application in water electrolysis. The method involves pretreatment with nickel foam, followed by a one-step hydrothermal synthesis of the precursor nanosheet array, which is then converted into the precursor ZIF (high-entropy zeolite imidazole ester framework material). Finally, pyrolysis yields the final product. The resulting multimetal catalyst exhibits unique advantages in complex reaction systems, demonstrating not only high catalytic activity but also stable electrocatalytic performance. To achieve the above objectives, the technical solution provided by this invention is as follows:

[0008] On one hand, the present invention provides a method for synthesizing nitrogen-doped carbon-coated multimetal nanosheet arrays, comprising the following steps:

[0009] S1, Pretreatment of nickel foam: Place the nickel foam in acetone and sonicate to remove organic matter from the surface of the nickel foam; sonicate with distilled water, and then sonicate with dilute hydrochloric acid solution to remove the oxide layer on the surface; finally, sonicate and wash several times with deionized water to complete the pretreatment.

[0010] S2, Synthesis of High-Entropy Nanosheet Arrays: High-entropy nanosheet arrays were synthesized using a one-step hydrothermal method with metal salts. First, metal salts were weighed and dissolved in deionized water, stirred evenly at room temperature to form solution A. Then, urea was weighed and added to solution A, stirred evenly at room temperature to form precursor solution B. The pretreated nickel foam from step S1 was placed in the polytetrafluoroethylene liner of a high-pressure reactor. Subsequently, precursor solution B was transferred to the liner of the high-pressure reactor and sealed. The reactor was heated to react and then cooled to room temperature to obtain catalyst-loaded nickel foam. The catalyst-loaded nickel foam was washed with deionized water and ethanol and then dried to obtain high-entropy nanosheet arrays.

[0011] The metal salt is selected from nitrates, sulfates, and metal chlorides; phosphates are mostly insoluble and not feasible. In this invention, metal nitrates are preferred.

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

[0013] In step S2, the reaction conditions are heating in an oven at 120°C for 12 hours.

[0014] The drying conditions were vacuum drying at 40℃ for 12 hours.

[0015] The molar ratios of ferric nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, cobalt nitrate, and zinc nitrate are 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 total nitrate to urea is 0.3:2.4.

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

[0017] In some embodiments of the present invention, heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheets were synthesized. Preferably, the molar ratio of ferric 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, hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy nanosheets were synthesized. Preferably, the molar ratio of ferric nitrate, chromium nitrate, aluminum nitrate, cobalt nitrate, and zinc nitrate was 0.075:0.075:0.075:0.075:0.075:0.7.

[0019] S3, Preparation of high-entropy ZIF: The heptagonal or hexa-entropy nanosheet array prepared in S2 is reacted with 2-methylimidazole by heating to convert it into high-entropy ZIF; specifically, 2-methylimidazole is dissolved in deionized water and then transferred to a container. The high-entropy nanosheet array prepared in step S2 is placed in the container and fixed. The container is installed on a heating device, and the mixture is heated and stirred at the same time. After heating, the mixture is washed with methanol and dried under vacuum to obtain the precursor.

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

[0021] The reaction conditions were: heating and stirring at 100°C for 6 hours.

[0022] S4, Preparation of high-entropy nanosheet array high-performance catalyst with nitrogen-doped carbon coating: The high-entropy ZIF prepared in step S3 is converted into high-entropy nanomaterials with nitrogen-doped carbon coating by pyrolysis. Specifically, the precursor obtained in step S3 is heated in a tube furnace and cooled to room temperature to obtain the final product.

[0023] Preferably, in step S4, the temperature is 5℃·min -1 The heating rate was adjusted so that the temperature was increased from room temperature to 500°C in a tube furnace, held at that temperature for 2 hours, and then allowed to cool naturally to room temperature before the final product was obtained.

[0024] Further optimization at 5℃·min -1 The heating rate was adjusted so that the temperature was increased from room temperature to 500°C in a tube furnace, held for 2 hours, and then allowed to cool naturally to room temperature before the final product was obtained.

[0025] Secondly, the present invention provides the product obtained by the method for synthesizing the nitrogen-doped carbon-coated multimetal nanosheet array.

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

[0027] This invention is achieved through:

[0028] (1) Constructing nanostructures provides more contact area for the catalyst to adsorb hydroxide ions in the first step of the anodic 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 active sites, optimizing the adsorption of reactants and the desorption of products, thereby improving catalytic activity.

[0030] In this embodiment of the invention, the product testing results, TEM and SEM images, visually demonstrate that the material constructs a nanostructure. This nanostructure possesses a high specific surface area, which can increase the number of active sites and improve the reaction rate. XRD pattern analysis shows that the diffraction peaks differ between embodiments due to variations in the types and proportions of metals used. LSV curve comparison reveals that the different material compositions and structures in each embodiment result in different electrochemical behaviors, such as initial potential and current intensity, in the same electrolyte. This indicates that the combination of multiple metals affects the electrochemical reactivity 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 also has stronger electrocatalytic stability due to the characteristics of nitrogen-doped carbon coating.

[0032] The key feature of this product lies in its use of multi-metal catalysts, which differ significantly from single-metal and binary metal catalysts in their preparation. Regarding raw material selection and proportioning, single-metal catalysts do not have a specific metal ratio issue; determining the ratio of two metals in binary metal catalysts is relatively simple; however, determining the ratio of each metal in multi-metal catalysts requires considering the synergistic effects between multiple metals, necessitating extensive experimental and theoretical calculations for optimization to achieve optimal performance. In terms of synthesis processes, single-metal catalysts are relatively simple to synthesize, requiring only a few steps such as precipitation or impregnation; multi-metal catalysts are more complex, requiring pretreatment with nickel foam, a one-step hydrothermal synthesis of precursor nanosheet arrays, conversion to the precursor ZIF, and finally pyrolysis to obtain the final product. These differences give multi-metal catalysts unique advantages in complex reaction systems.

[0033] The synthesis principle of nitrogen-doped carbon-coated multimetal nanosheet materials is explained as follows: Nickel foam pretreatment is necessary because the nickel foam is not pure before the experiment; its surface contains organic matter and an oxide layer. The presence of organic matter hinders subsequent reactions, preventing them from occurring smoothly on the nickel foam surface. The oxide layer affects the conductivity of the material and the exposure of active sites, reducing catalyst performance. A one-step hydrothermal method dissolves and stirs metal nitrates and urea to form a solution, where a specific reaction occurs. This method allows for the uniform dispersion of multiple metal ions in the solution, and under hydrothermal conditions, the reactivity of each substance is enhanced, directly generating seven- or six-membered high-entropy nanosheet arrays with specific structures. The process is relatively simple, achieving uniform distribution of multiple metals and construction of nanosheet arrays in a single reaction step, simplifying the synthesis process. The precursor nanosheets are converted into the precursor ZIF, and the properties of ZIF are used to further optimize the material properties. For example, the ordered crystal structure of ZIF provides a stable framework for subsequent pyrolysis, making structural changes during the process more controllable; the abundant pores of ZIF increase the specific surface area of ​​the material, providing more active sites for catalytic reactions and improving catalytic efficiency; the transformation from precursor nanosheets to precursor ZIF and then to nitrogen-doped carbon-coated multimetallic nanosheets significantly improves material stability. During pyrolysis, raising and holding the temperature causes ZIF to decompose and undergo structural transformation, forming nitrogen-doped carbon-coated nanomaterials. The pyrolysis process can further adjust the microstructure of the material, allowing metal particles to be better dispersed in the carbon coating layer, optimizing the distribution of active sites, and improving catalytic activity.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

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

[0036] (2) The high-entropy nanomaterials provided by the present invention have a stable structure, which ensures stable electrocatalytic performance; at the same time, the present invention utilizes the synergistic effect between multiple metals to propose a better ratio and improve product performance. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

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

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

[0040] Figure 3 LSV curves of the comparative products of Example 1 of the present invention and 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 in Example 1 of this invention.

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

[0043] Figure 6 TEM and SEM images of the nitrogen-doped carbon-coated heptagonal high-entropy nanomaterials in Example 1 of this invention. Detailed Implementation

[0044] Nitrogen-doped carbon coating: This involves coating the surface of a carbon material with a layer of nitrogen material, forming a core-shell structure. In the preparation process, metal nitrates and urea are used as precursors. Under heating conditions (120℃, 12h), these precursors react simultaneously on the surface of nickel foam, directly generating heptagonal and hexa-membered high-entropy nanosheet arrays, i.e., nitrogen-doped carbon-coated heptagonal and hexa-membered high-entropy nanosheet materials.

[0045] Multimetal nanosheet materials: sheet-like structures with nanoscale thickness composed of multiple metals. The nanosheets provided by this invention are arranged in an array in a vertically grown sheet-like manner.

[0046] This invention provides a method for preparing a highly efficient catalyst—nitrogen-doped carbon-coated polymetallic nanosheet material—and its application in water electrolysis. The reaction involved is the oxygen evolution reaction in water electrolysis: under acidic conditions, the reaction is 2H₂O = O₂ + 4H₂O. + +4e— Under alkaline conditions, the reaction is 4OH⁻. — =O2 + 2H2O + 4e — The oxygen evolution reaction (OER) involves a four-electron transfer and the breaking and formation of multiple chemical bonds, resulting in a slow reaction. Therefore, it is desirable to prepare a high-performance catalyst to accelerate the OER. The preparation method includes the following steps:

[0047] (1) Synthesis of high-performance catalysts with nitrogen-doped carbon-coated seven-membered and six-membered high-entropy nanosheet arrays. The first step of synthesis was to pretreat nickel foam; the second step was to synthesize seven-membered and six-membered high-entropy nanosheet arrays using a one-step hydrothermal method; the third step was to convert the prepared seven-membered and six-membered high-entropy nanosheet arrays into seven-membered and six-membered high-entropy ZIFs (high-entropy zeolite imidazole ester framework materials); the fourth step was to convert the prepared seven-membered and six-membered high-entropy ZIFs into nitrogen-doped carbon-coated seven-membered and six-membered high-entropy nanomaterials through pyrolysis.

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

[0049] The instruments used in this experiment were: 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 microscopy (SEM) images were acquired using a JEOL JSM-6700F SEM. Transmission electron microscopy (TEM) images were acquired using a JEM-2100F field emission 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 analyses were performed using a ThermoFischer Talos F200X instrument. The atomic ratios of the metals were determined using inductively coupled plasma optical emission spectrometry (ICP-OES) on a Perkin Elmer Optima 7300DV instrument. X-ray photoelectron spectroscopy (XPS) analysis was performed using a VGESCALAB MKII X-ray photoelectron spectrometer with Mg Kα = 1253.6 eV as the excitation source. The products obtained from the electro-oxidation reaction of glycerol were characterized by nuclear magnetic resonance (NMR) spectroscopy, and qualitative and quantitative analyses and calculations of relevant parameters were performed.

[0050] 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, and are not intended to limit the scope of the claims of the present invention.

[0051] A method for preparing a highly efficient catalyst made of nitrogen-doped carbon-coated multimetal nanosheet material includes the following steps:

[0052] Place the nickel foam (2×3.7cm) into a beaker, add acetone, and sonicate for 5 minutes to remove organic matter from the surface. Sonicate with distilled water for one minute, then sonicate with a 1% dilute hydrochloric acid solution for 5 minutes to remove the oxide layer. Finally, wash several times with deionized water using ultrasound to complete the pretreatment.

[0053] Example 1

[0054] The first step involved preparing a nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst. In the first synthesis step, a one-step hydrothermal method was used to synthesize the seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array. First, 0.06 mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O, and 0.7 mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80 ml of deionized water. The solution was stirred at room temperature to form solution A. Then, 2.4 mmol of urea was weighed and added to solution A, and the solution was stirred at room temperature to form solution B. Nickel foam was placed in a 100 ml high-pressure reactor lined with polytetrafluoroethylene (PTFE). Precursor solution B was then transferred into the liner and sealed. The reactor was heated in a 120 °C oven for 12 h, and then cooled to room temperature. The catalyst-loaded nickel foam was washed three times with deionized water and ethanol, and then vacuum-dried at 40 °C for 12 h to obtain a uniform heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array. In synthesis step two, the prepared heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array was converted into a heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy ZIF. 8.2 g of 2-methylimidazole was dissolved in 50 ml of deionized water and then transferred to a 100 ml flask. A heptagonal high-entropy nanosheet array was placed in the flask and fixed with a pipette. The flask was mounted on an oil bath heating device and heated at 100 °C with stirring for 6 h. After heating, the nanosheets were washed three times with methanol and dried under vacuum at 40 °C for 12 h. In the third synthesis step, the prepared heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy ZIF was converted into nitrogen-doped carbon-coated heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanomaterials via pyrolysis. The obtained heptagonal high-entropy ZIF precursor was then subjected to pyrolysis in a tube furnace at 5 °C·min. -1 The heating rate was adjusted so that the temperature was increased from room temperature to 500°C in a tube furnace, held for 2 hours, and then allowed to cool naturally to room temperature before being removed to obtain a high-performance catalyst of nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array.

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

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

[0057] The fourth step is the performance testing of the product. The nitrogen-doped carbon-coated seven-membered 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 synthesis step, a hydrothermal general-purpose oven or muffle furnace is used.

[0059] In the third step of the synthesis, 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 discovered that when the temperature for preparing catalyst-loaded nickel foam in a high-pressure reactor is below 120°C, the carbon structure is not easily formed, which means that the nanosheet array morphology 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 involved preparing a nitrogen-doped carbon-coated hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst. In the first synthesis step, a one-step hydrothermal method was used to synthesize the hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy nanosheet array. First, 0.075 mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Co(NO3)2·6H2O, and 0.7 mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80 ml of deionized water. The solution was stirred at room temperature to form solution A. Then, 2.4 mmol of urea was weighed and added to solution A, and the solution was stirred at room temperature to form solution B. Nickel foam was placed in a 100 ml high-pressure reactor lined with polytetrafluoroethylene (PTFE). The precursor solution B was then transferred to the liner and sealed. The reactor was heated in a 120 °C oven for 12 h and then cooled to room temperature. The catalyst-loaded nickel foam was washed three times with deionized water and ethanol, and then vacuum dried at 40℃ for 12 h to obtain a uniform hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy nanosheet array. In the second synthesis step, the prepared hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy nanosheet array was converted into a hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy ZIF. 8.2 g of 2-methylimidazole was dissolved in 50 ml of deionized water and then transferred to a 100 ml flask. The hexa-membered high-entropy nanosheet array was placed in the flask and fixed with a pipette. The flask was mounted on an oil bath heating device and heated and stirred at 100℃ for 6 h. After heating, the nanosheets were washed three times with methanol and vacuum dried at 40℃ for 12 h. In the third synthesis step, the prepared hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy ZIF was converted into nitrogen-doped carbon-coated hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy nanomaterials via pyrolysis. The obtained precursor was subjected to inert atmosphere in a tube furnace at 5 °C·min. -1 The heating rate was adjusted so that the temperature was increased from room temperature to 500°C in a tube furnace, held for 2 hours, and then allowed to cool naturally to room temperature before being removed to obtain a high-performance catalyst of nitrogen-doped carbon-coated hexa-membered high-entropy nanosheet array.

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

[0064] The third step was performance testing of the product. The nitrogen-doped carbon-coated hexa-membered Fe-Cr-Al-Co-Zn-Ni high-entropy nanomaterial catalyst was immersed in 0.1M glycerol electrolyte (1M KOH), and its LSV curve was measured.

[0065] Example 3

[0066] The first step involved preparing a nitrogen-doped carbon-coated hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy nanosheet array high-performance catalyst. In the first synthesis step, a one-step hydrothermal method was used to synthesize the hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy nanosheet array. First, 0.075 mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O, and 0.7 mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80 ml of deionized water. The solution was stirred at room temperature to form solution A. Then, 2.4 mmol of urea was added to solution A and stirred at room temperature to form solution B. Nickel foam was placed in a 100 ml high-pressure reactor lined with polytetrafluoroethylene (PTFE). The precursor solution B was then transferred to the liner and sealed. The reactor was heated in a tube furnace at 120 °C for 12 h and then cooled to room temperature. The catalyst-loaded nickel foam was washed three times with deionized water and ethanol, and then vacuum-dried at 40°C for 12 h to obtain a uniform hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy nanosheet array. In the second synthesis step, the prepared hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy nanosheet array was converted into a hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy ZIF. 8.2 g of 2-methylimidazole was dissolved in 50 ml of deionized water and then transferred to a 100 ml flask. The hexa-membered high-entropy nanosheet array was placed in the flask and fixed with a pipette. The flask was mounted on an oil bath heating device and heated and stirred at 100°C for 6 h. After heating, the nanosheets were washed three times with methanol and vacuum-dried at 40°C for 12 h. In the third synthesis step, the prepared hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy ZIF was converted into nitrogen-doped carbon-coated hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy nanomaterials via pyrolysis. The obtained precursor was subjected to inert atmosphere in a tube furnace at 5 °C·min. -1 The heating rate was adjusted so that the temperature was increased from room temperature to 500°C in a tube furnace, held for 2 hours, and then allowed to cool naturally to room temperature before being removed to obtain a high-performance catalyst of nitrogen-doped carbon-coated hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy nanosheet array.

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

[0068] The third step was performance testing of the product. The nitrogen-doped carbon-coated hexa-membered Fe-Cr-Al-Ce-Zn-Ni high-entropy nanomaterial catalyst was immersed in 0.1M glycerol electrolyte (1M KOH), and its LSV curve was measured.

[0069] Example 4

[0070] The first step involved preparing a nitrogen-doped carbon-coated hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst. In the first synthesis step, a one-step hydrothermal method was used to synthesize the hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy nanosheet array. First, 0.075 mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O, and 0.7 mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80 ml of deionized water. The solution was stirred at room temperature to form solution A. Then, 2.4 mmol of urea was added to solution A and stirred at room temperature to form solution B. Nickel foam was placed in a 100 ml high-pressure reactor lined with polytetrafluoroethylene (PTFE). The precursor solution B was then transferred to the liner and sealed. The reactor was heated in a tube furnace at 120 °C for 12 h and then cooled to room temperature. The catalyst-loaded nickel foam was washed three times with deionized water and ethanol, and then vacuum dried at 40℃ for 12 h to obtain a uniform hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy nanosheet array. In the second synthesis step, the prepared hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy nanosheet array was converted into a hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy ZIF. 8.2 g of 2-methylimidazole was dissolved in 50 ml of deionized water and then transferred to a 100 ml flask. The hexa-membered high-entropy nanosheet array was placed in the flask and fixed with a pipette. The flask was mounted on an oil bath heating device and heated and stirred at 100℃ for 6 h. After heating, the nanosheets were washed three times with methanol and vacuum dried at 40℃ for 12 h. In the third synthesis step, the prepared hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy ZIF was converted into nitrogen-doped carbon-coated hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy nanomaterials via pyrolysis. The obtained precursor was subjected to inert atmosphere in a tube furnace at 5 °C·min. -1 The heating rate was adjusted so that the temperature was increased from room temperature to 500°C in a tube furnace, held for 2 hours, and then allowed to cool naturally to room temperature before being removed to obtain a high-performance catalyst of nitrogen-doped carbon-coated hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy nanosheet array.

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

[0072] The third step was performance testing of the product. The nitrogen-doped carbon-coated hexa-membered Fe-Cr-Ce-Co-Zn-Ni high-entropy nanomaterial catalyst was immersed in 0.1M glycerol electrolyte (1M KOH), and its LSV curve was measured.

[0073] Comparative Example 1

[0074] The first step involved preparing a nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst. In the first synthesis step, a one-step hydrothermal method was used to synthesize the seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array. First, 0.06 mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O, and 0.7 mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80 ml of deionized water. The solution was stirred at room temperature to form solution A. Then, 2.4 mmol of urea was weighed and added to solution A, and the solution was stirred at room temperature to form solution B. Nickel foam was placed in a 100 ml high-pressure reactor lined with polytetrafluoroethylene (PTFE). Precursor solution B was then transferred into the liner and sealed. The reactor was heated in a tube furnace at 130 °C for 12 h, and then cooled to room temperature. The catalyst-loaded nickel foam was washed three times with deionized water and ethanol, and then vacuum-dried at 40 °C for 12 h to obtain a uniform heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array. In synthesis step two, the prepared heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array was converted into a heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy ZIF. 8.2 g of 2-methylimidazole was dissolved in 50 ml of deionized water and then transferred to a 100 ml flask. A heptagonal high-entropy nanosheet array was placed in the flask and fixed with a pipette. The flask was mounted on an oil bath heating device and heated at 100 °C with stirring for 6 h. After heating, the nanosheets were washed three times with methanol and dried under vacuum at 40 °C for 12 h. In the third synthesis step, the prepared heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy ZIF was converted into nitrogen-doped carbon-coated heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanomaterials via pyrolysis. The obtained heptagonal high-entropy ZIF precursor was then heated in a tube furnace under an inert atmosphere at 5 °C·min. -1 The temperature was increased at a high rate and heated from room temperature to 500°C in a tube furnace. The temperature was held for 2 hours and then allowed to cool naturally to room temperature before being removed to obtain a high-performance catalyst of nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array.

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

[0076] The third step is the performance testing of the product. The nitrogen-doped carbon-coated seven-membered 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 involved preparing a nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array high-performance catalyst. In the first synthesis step, a one-step hydrothermal method was used to synthesize the seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array. First, 0.06 mmol of Fe(NO3)3·9H2O, Cr(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O, and 0.7 mmol of Zn(NO3)2·6H2O were weighed and dissolved in 80 ml of deionized water. The solution was stirred at room temperature to form solution A. Then, 2.4 mmol of urea was weighed and added to solution A, and the solution was stirred at room temperature to form solution B. Nickel foam was placed in a 100 ml high-pressure reactor lined with polytetrafluoroethylene (PTFE). Precursor solution B was then transferred into the liner and sealed. The reactor was heated in a tube furnace at 120 °C for 12 h, and then cooled to room temperature. The catalyst-loaded nickel foam was washed three times with deionized water and ethanol, and then vacuum-dried at 50 °C for 12 h to obtain a uniform heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array. In synthesis step two, the prepared heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array was converted into a heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy ZIF. 8.2 g of 2-methylimidazole was dissolved in 50 ml of deionized water and then transferred to a 100 ml flask. A heptagonal high-entropy nanosheet array was placed in the flask and fixed with a pipette. The flask was mounted on an oil bath heating device and heated at 100 °C with stirring for 6 h. After heating, the nanosheets were washed three times with methanol and dried under vacuum at 40 °C for 12 h. In the third synthesis step, the prepared heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy ZIF was converted into nitrogen-doped carbon-coated heptagonal Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanomaterials via pyrolysis. The obtained heptagonal high-entropy ZIF precursor was then heated in a tube furnace under an inert atmosphere at 5 °C·min. -1 The heating rate was adjusted so that the temperature was increased from room temperature to 500°C in a tube furnace, held for 2 hours, and then allowed to cool naturally to room temperature before being removed to obtain a high-performance catalyst of nitrogen-doped carbon-coated seven-membered Fe-Cr-Al-Ce-Co-Zn-Ni high-entropy nanosheet array.

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

[0080] The third step is the performance testing of the product. The nitrogen-doped carbon-coated seven-membered 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] Results analysis:

[0082] Depend on Figure 1 , 3 It is evident that the products from Examples 1 to 4 exhibit different performance characteristics. The graph shows that the diffraction peak intensities differ between Examples 4 and 1, indicating varying crystallinity, with Example 3 exhibiting relatively higher crystallinity. The diffraction peak intensities also change with increasing temperatures in steps S1 and S2, demonstrating that the properties of the products vary with experimental temperature. Figure 3 It is evident 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 differ among the different examples, suggesting variations in the ease 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 in Example 1 in the glycerol electrolyte is faster and the reaction proceeds more fully. Furthermore, the current intensity changes with increasing temperatures in steps S1 and S2, indicating that the properties of the product differ with variations in experimental temperature. Such differences caused by changes in experimental temperature are undesirable. As the experimental temperature increases, the particles become larger, leading to a reduction in active sites. This means that the number of catalytically active centers that reactant molecules can access decreases, thereby reducing the reaction rate, which is detrimental to the production of highly efficient catalysts. Moreover, the temperature and time set in the experimental scheme are uniquely determined; changing the temperature or time will alter the properties of the generated substances, leading to differences in product performance testing.

[0083] like Figure 2 As shown, the initial potential of the electrolyte with glycerol is approximately 1.22V, while the initial potential of the electrolyte without glycerol is approximately 1.39V. This indicates that the electrochemical reaction begins at a lower potential after the addition of glycerol, meaning that the addition of glycerol lowers the initial potential of the reaction, making it easier for the reaction to occur. Furthermore, within the same potential range, the relative current intensity of the electrolyte with glycerol is higher than that without glycerol, indicating that the electrode reaction rate is faster and the reaction proceeds more completely after the addition of glycerol.

[0084] TEM and SEM images of the precursor nanosheets in Example 1 of this invention are as follows: Figure 4As shown, TEM reveals that the nanosheets are roughly hexagonal in shape; 3D SEM images show numerous nanosheets aggregated together, exhibiting a certain degree of packing. TEM and SEM images of the precursor ZIP from Example 1 are shown below. Figure 5 As shown, TEM images reveal multiple aggregated granular structures, with some particles appearing to have connections or coating relationships. Three-dimensional SEM images show a large amount of granular material. TEM and SEM images of the nitrogen-doped carbon-coated heptagonal high-entropy nanomaterials in Example 1 are shown below. Figure 6 As shown, TEM reveals that the nitrogen-doped carbon-coated heptagonal high-entropy nanomaterials exhibit a more complex structure; 3D SEM shows that the nitrogen-doped carbon-coated heptagonal high-entropy nanosheets exhibit a needle-like or rod-like stacked state.

[0085] The electrocatalytic stability of the product obtained by this invention is reflected in the following two aspects:

[0086] 1. Current stability and onset potential stability: As can be seen from the LSV curve of the product test, if the current intensity of Example 1 fluctuates little during long-term or multiple scans and does not decrease significantly with time or number of scans, it indicates that the electrocatalytic reaction of the material can continue to proceed stably within this potential range, reflecting good electrocatalytic stability.

[0087] 2. Structural and morphological stability: TEM and 3D SEM images show 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, the structure did not undergo significant collapse, dissolution, or phase transition, and still maintained a relatively complete morphology and structural characteristics; its morphology also did not change significantly, which is conducive to maintaining stable electrocatalytic performance.

[0088] Based on the multi-metal effect, the interaction between multiple metals enhances the stability of the system. TEM and 3D SEM images show 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, the structure did not undergo significant collapse, dissolution, or phase transitions, maintaining a relatively intact morphology and structural characteristics. Its morphology also did not change significantly, which is beneficial for maintaining stable electrocatalytic performance. In multi-metal catalysts, electrons transfer between different metals, changing the electron cloud density of active sites, optimizing reactant adsorption and product desorption processes, thereby improving catalytic activity. XRD analysis shows that the different types and proportions of metals used in the examples lead to differences in diffraction peaks in different embodiments. LSV curve comparison reveals that due to the different material compositions and structures in each embodiment, they exhibit different electrochemical behaviors such as initial potential and current intensity in the same electrolyte, indicating that the combination of multiple metals affects the electrochemical reactivity and selectivity of the material.

[0089] In the preparation of nitrogen-doped carbon-coated multi-metal nanosheet array catalysts, the proportions of each material have a critical impact on product performance. The ratio of urea to metal nitrates relates to the nitrogen doping and carbon coating processes, affecting the catalyst structure and stability. Changes in the proportion of different metal nitrates affect the multi-metal synergistic effect, influencing active sites and electron cloud density, thereby altering catalytic activity. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for synthesizing a nitrogen-doped carbon-coated multimetal nanosheet array, characterized in that, Includes the following steps: S1, Pretreatment of nickel foam; S2, Synthesis of high-entropy nanosheet arrays: High-entropy nanosheet arrays were synthesized by a one-step hydrothermal method using metal salts; S3, Preparation of high-entropy ZIF: The high-entropy nanosheet array prepared in step S2 is reacted with 2-methylimidazole by heating to convert it into high-entropy ZIF; S4, Preparation of high-entropy nanosheet array high-performance catalyst with nitrogen-doped carbon coating: The high-entropy ZIF prepared in step S3 is converted into nitrogen-doped carbon coated high-entropy nanomaterials by pyrolysis. In step S2, firstly, metal salts are weighed and dissolved in deionized water, stirred evenly to form solution A. Then, urea is weighed and added to solution A, stirred evenly at room temperature to form precursor solution B. The pretreated nickel foam from step S1 is placed in the polytetrafluoroethylene liner of a high-pressure reactor. Subsequently, precursor solution B is transferred to the liner of the high-pressure reactor and sealed. The reactor is heated to react and then cooled to room temperature to obtain 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. In step S2, the reaction conditions are heating in an oven at 120 °C for 12 h; the drying conditions are vacuum drying at 40 °C for 12 h. In step S3, 2-methylimidazole is dissolved in deionized water and then transferred to a container. The high-entropy nanosheet array prepared in step S2 is placed in the container and fixed. The container is installed on a heating device and heated while stirring. After heating, the mixture is washed with methanol and dried under vacuum to obtain the precursor. In step S3, the heating device is an oil bath heating device; the reaction conditions are to maintain the temperature at 100 °C with stirring for 6 hours. In step S4, the precursor obtained in step S3 is heated in a tube furnace and cooled to room temperature to obtain the final product. In step S4, at 5 ℃·min -1 The heating rate was set at 500 °C in a tube furnace, and the temperature was maintained for 2 hours. After natural cooling to room temperature, the product was removed to obtain the final product. The molar ratio of the metal salts ferric nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, cobalt nitrate, and zinc nitrate is 0.06~0.075:0.06~0.075:0.06~0.075:0.06~0.075:0.7, and the molar ratio of the total amount of nitrate to urea is 0.3:2.

4.

2. The method for synthesizing nitrogen-doped carbon-coated multimetal nanosheet arrays according to claim 1, characterized in that, Ferric nitrate, chromium nitrate, aluminum nitrate, cerium nitrate, and cobalt nitrate are added in equal molar amounts.

3. The product obtained by the method for synthesizing nitrogen-doped carbon-coated polymetallic nanosheet arrays according to any one of claims 1 to 2.

4. The application of the product obtained by the synthesis method of nitrogen-doped carbon-coated polymetallic nanosheet array according to any one of claims 1-2 in water electrolysis, characterized in that, The product obtained by the method of synthesizing nitrogen-doped carbon-coated multimetal nanosheet arrays is used as a working electrode for water electrolysis.

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