A metal oxide nanosheet, its preparation method and application

Abstract

This invention relates to a metal oxide nanosheet, its preparation method, and its application, belonging to the field of electrocatalysis technology. The preparation method of this invention involves heating and mixing a cobalt source, a molybdenum source, a manganese source, a nickel source, and an iron source with urea to obtain a eutectic solvent (DESs); the obtained eutectic solvent DESs is then heated and reacted under an inert atmosphere to obtain the metal oxide nanosheet. The preparation method of this invention is simple to operate, has low preparation cost, and a short reaction time, yielding ultrathin CoMoMnNiFeO nanosheets. x High-entropy metal oxide nanosheets have regular morphology and good crystal structure and electrocatalytic activity.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, and in particular to a metal oxide nanosheet, its preparation method and application. Background Technology

[0002] The escalating global warming and the gradual depletion of fossil fuels have spurred the urgent need to develop green and renewable energy sources. Hydrogen energy, with its high energy density and zero-emission combustion, has become an ideal alternative to traditional fossil fuels. Electrochemical water splitting for hydrogen production is a highly promising method for large-scale hydrogen production. In traditional electrocatalytic processes, the water splitting reaction consists of the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. The OER reaction involves four electron transfers and has relatively slow kinetics, limiting hydrogen production efficiency. Compared to traditional water oxidation reactions, urea is easily oxidized at the anode. The theoretical potential required for electrochemical water splitting via the urea oxidation reaction (UOR) is 0.37 V, far lower than the 1.23 V required for OER. Therefore, UOR is a feasible alternative to OER for hydrogen production. Urea, a common pollutant in water bodies, poses a threat to the environment. Electrolytic treatment of urea-rich wastewater can both produce hydrogen and degrade the wastewater. However, the UOR process is complex, involving six-electron transfer and numerous intermediate adsorption-desorption processes, resulting in slow reaction kinetics. Although noble metal catalysts such as RuO2 and IrO2 exhibit excellent catalytic performance in OER and UOR, their high cost limits their large-scale application. Therefore, developing inexpensive and efficient OER and UOR electrocatalysts is of great significance.

[0003] In recent years, high-entropy alloys (HEAs) have attracted widespread attention as novel catalytic materials in the field of energy conversion. These materials are composed of five or more metallic elements in near equimolar ratios, and their unique structural features include significant high-entropy effects, slow atomic diffusion characteristics, strong lattice distortion, and multi-component synergistic effects. These special structural properties typically endow the materials with excellent durability and corrosion resistance. Unlike traditional binary or ternary alloy systems, high-entropy alloys effectively modulate the electronic structure of active sites by forming special dd orbital hybridization, thus exhibiting superior performance in electrocatalytic reactions. However, dd orbital hybridization has limitations in the range of band structure and electronic structure modulation. Excessive dd orbital hybridization may lead to the continuous adsorption of reaction intermediates by active sites, thereby forming a surface layer that hinders electron transfer and catalytic reactions. Introducing light elements (such as nitrogen, carbon, oxygen, phosphorus, and sulfur) into alloy materials can effectively promote the interaction between metals and nonmetals. This interaction stems from the overlap of orbital spaces and the similarity of electronic state energy distributions, which can spontaneously induce dp orbital hybridization effects. This unique electronic hybridization phenomenon provides flexible and diverse optimization methods for modulating the electronic structure of materials. However, due to the problem of element segregation in the preparation of high-entropy materials, the adsorption effect of metal elements and reaction intermediates is still not satisfactory. Summary of the Invention

[0004] To address the above technical problems, this invention provides a metal oxide nanosheet, its preparation method, and its applications. The preparation process of this invention is simple, the conditions are mild, the preparation cost is low, and it is environmentally friendly. The obtained ultrathin CoMoMnNiFeO nanosheets... x High-entropy metal oxide nanosheet composites exhibit excellent electrocatalytic activity because the adsorption energy of reaction intermediates can be effectively adjusted through dp orbital hybridization between the metal and oxygen.

[0005] The present invention achieves its objective through the following scheme: The first objective of this invention is to provide a method for preparing metal oxide nanosheets, comprising the following steps: 1) Cobalt, molybdenum, manganese, nickel, and iron sources are heated and mixed with urea to obtain a eutectic solvent, DESs. 2) The obtained eutectic solvent DESs was heated under an inert atmosphere to react and obtain the metal oxide nanosheets.

[0006] In some embodiments of the present invention, the cobalt source is selected from one or more of cobalt chloride, cobalt nitrate, and cobalt sulfate; The molybdenum source is selected from one or more of molybdenum chloride, molybdenum nitrate, and molybdenum sulfate; In some embodiments of the present invention, the manganese source is selected from one or more of manganese chloride, manganese nitrate and manganese sulfate.

[0007] In some embodiments of the present invention, the nickel source is selected from one or more of nickel chloride, nickel nitrate and nickel sulfate.

[0008] In some embodiments of the present invention, the iron source is selected from one or more of ferric chloride, ferric nitrate and ferric sulfate.

[0009] In some embodiments of the present invention, the amounts of the cobalt source, molybdenum source, manganese source, nickel source, and iron source are independently 5wt%-35wt%, and the molar ratio of the mixed metal source material to urea is 1:1-10.

[0010] In some embodiments of the present invention, the heating and mixing temperature is 40~100 °C, and the inert gas in the inert atmosphere is selected from nitrogen and / or argon.

[0011] In some embodiments of the present invention, the heating reaction is carried out at a temperature of 500-900 °C for 0.5-8 h, and the heating rate is 1-20 °C / min. -1 .

[0012] A second objective of this invention is to provide a metal oxide nanosheet obtained by the aforementioned preparation method, wherein the metal oxide nanosheet comprises CoMoMnNiFeO x The orbital hybridization between metal and oxygen can regulate the adsorption strength of reaction intermediates, where x is a value based on charge balance and actual oxygen content, ranging from 7 to 9, and also includes non-stoichiometry caused by oxygen vacancies and metal vacancies.

[0013] A third objective of this invention is to provide the application of the aforementioned metal oxide nanosheets in electrocatalytic oxygen evolution and urea oxidation.

[0014] The technical solution of the present invention has the following advantages compared with the prior art: The preparation method described in this invention is simple to operate, has low preparation cost, and short reaction time, yielding CoMoMnNiFeO. x The material has a regular morphology and good crystal structure. Furthermore, the hybridization between dp orbitals can effectively regulate the adsorption energy of reaction intermediates, thereby improving the catalytic activity of the material. Attached Figure Description

[0015] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 The Fourier transform infrared spectrum (FT-IR) of the eutectic solvent prepared in Example 1 of this invention. Figure 2The X-ray powder diffraction (XRD) patterns of the materials prepared in Example 1 and the comparative example of this invention are shown below. Figure 3 The images shown are scanning electron microscope (SEM) images of the materials prepared in Example 1 and the comparative example of the present invention; wherein, (a) the material obtained in Example 1; (b) the material obtained in Comparative Example 1; (c) the material obtained in Comparative Example 2; and (d) the SEM image of the material obtained in Comparative Example 3. Figure 4 These are transmission electron microscope (TEM) and atomic force microscope (AFM) images of the material prepared in Example 1 of the present invention; wherein, (a) is an AFM image; (b) is a TEM image; (c) is an HRTEM image; and (di) is an elemental distribution map. Figure 5 The Co 2p XPS spectrum of the material prepared in Example 1 of this invention; Figure 6 The Mo 3d XPS spectrum of the material prepared in Example 1 of this invention; Figure 7 The Mn 2p XPS spectrum of the material prepared in Example 1 of this invention; Figure 8 The Ni 2p XPS spectrum of the material prepared in Example 1 of this invention; Figure 9 The Fe 2p XPS spectrum of the material prepared in Example 1 of this invention; Figure 10 The O 1s XPS spectrum of the material prepared in Example 1 of this invention; Figure 11 The urea oxidation curves of the materials obtained in the embodiments and comparative examples of this invention are shown below. Figure 12 The Tafel curves of the materials obtained in the embodiments and comparative examples of this invention are shown below. Figure 13 The materials obtained in the embodiments and comparative examples of this invention are at 10 mA·cm –2 Comparison of overpotentials under current density; Figure 14 The oxygen evolution and urea oxidation curves of the materials obtained in the embodiments of the present invention are shown. Figure 15 The oxygen evolution and urea oxidation Tafel curves of the material obtained in Example 1 of this invention are shown. Figure 16 The stability test curve of the material obtained in Example 1 of this invention; Figure 17The results are the theoretical calculation (DFT) results of Example 1 of the present invention; where (a) is the d-band center position of Co2Mo3O8 in Example 1 and (b) and the corresponding projected density of states; (c) is the charge analysis of Example 1 and Co2Mo3O8; and (d) is the standard free energy diagram of the oxygen evolution reaction process of Example 1 and Co2Mo3O8. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0017] Example 1 This embodiment provides a method for preparing metal oxide nanosheets, as detailed below: Accurately weigh out CoCl₂·6H₂O, MoCl₅, MnCl₂·4H₂O, NiCl₂·6H₂O, FeCl₃·6H₂O, and urea in a molar ratio of 1:1:1:1:1:10. Stir continuously in an oil bath at 70 °C to form DESs. Transfer the resulting DESs to a quartz boat and place it in the center of a tube furnace. In a nitrogen atmosphere, heat at 5 °C·min. -1 The temperature was raised to 650 °C and calcined for 4 h. After cooling to room temperature in a tube furnace, CoMoMnNiFeO was obtained. x Nanosheets. The obtained CoMoMnNiFeO x The nanosheets were structurally characterized, where x ranged from 7 to 9. The results are shown in Table 1 and [Table 2]. Figure 1 .

[0018] Comparative Example 1 This comparative example provides a method for preparing metal oxide nanosheets, as detailed below: Accurately weigh CoCl2·6H2O, MoCl5, MnCl2·4H2O, NiCl2·6H2O, and urea in a molar ratio of 1:1:1:1:10. Stir continuously in an oil bath at 70 °C to form DESs. Transfer the resulting DESs to a quartz boat and place it in the center of a tube furnace. Incubate under a nitrogen atmosphere at 5 °C / min. -1 The temperature was raised to 650 °C and calcined for 4 h. After cooling to room temperature in a tube furnace, CoMoMnNiO was obtained. x Nanosheet materials.

[0019] Comparative Example 2 This comparative example provides a method for preparing metal oxide nanosheets, as detailed below: Accurately weigh CoCl2·6H2O, MoCl5, MnCl2·4H2O, and urea in a molar ratio of 1:1:1:10. Stir continuously in an oil bath at 70 °C to form DESs. Transfer the resulting DESs to a quartz boat and place it in the center of a tube furnace. In a nitrogen atmosphere, heat at 5 °C / min. -1 The temperature was raised to 650 °C and calcined for 4 h. After cooling to room temperature in a tube furnace, CoMoMnO was obtained. x Nanosheet materials.

[0020] Comparative Example 3 This comparative example provides a method for preparing metal oxide nanosheets, as detailed below: Accurately weigh CoCl2·6H2O, MoCl5, and urea in a molar ratio of 1:1:10, and continuously stir in an oil bath at 70 °C to form DESs. Transfer a certain amount of DESs to a quartz boat and place it in the center of a tube furnace. In a nitrogen atmosphere, heat at 5 °C·min. -1 The temperature was raised to 650 °C and calcined for 4 h. After cooling to room temperature in a tube furnace, CoMoO was obtained. x Nanosheet materials.

[0021] Structural characterization The CoMoMnNiFeO obtained in Example 1 x The nanosheets were structurally characterized, and the results are shown in the figure. Figures 1-5 See Table 1.

[0022] CoMoMnNiFeO synthesized in Example 1 x The nanosheets were characterized for morphology and structure. FT-IR was used to confirm that the synthesized precursor solution was DESs, SEM and TEM were used to observe the product morphology, XRD and XPS were used to identify the product composition and crystal form, and UOR was used to test the properties of the synthesized sample.

[0023] Table 1 shows the CoMoMnNiFeO prepared in Example 1 of this invention. x Inductively coupled plasma emission spectroscopy data of nanosheets Example 1 Co (at.%) Mo (at.%) Mn (at.%) Ni (at.%) Fe (at.%) <![CDATA[CoMoMnNiFeO x ]]> 22.01% 23.99% 17.16% 19.22% 17.62% As shown in Table 1, the molar ratio between the metal elements is approximately 1:1:1:1:1, further proving that the synthesized sample is a high-entropy oxide.

[0024] Figure 1 The FT-IR spectrum of the precursor synthesized in Example 1 of this invention is shown. The interaction between the mixtures was demonstrated by FT-IR spectroscopy at 1500 cm⁻¹. -1 ~2000 cm -1 The peak position shifts after the metal chloride and urea form a mixture, at 3000 cm⁻¹.-1 ~3500 cm -1 The broadening of the peak shape of the mixture indicates that there is an interaction between the metal chloride and urea after they form a mixture, and the resulting mixture solution is DESs.

[0025] Figure 2 The images show the X-ray powder diffraction (XRD) patterns of the metal oxide nanosheet materials prepared in Examples 1 and Comparative Examples 1-3 of this invention. The crystal structure of the prepared samples was analyzed by XRD, revealing CoMoMnNiFeO... x CoMoMnNiO x CoMoMnO x and CoMoO x Crystal structure such as Figure 2 As shown, by comparing with the standard card, the corresponding card is Co2Mo3O8 (JCPDF no. 34-0511).

[0026] Figure 3 These are scanning electron microscope (SEM) images of the metal oxide nanosheet materials prepared in Example 1 and Comparative Examples 1-3 of this invention. As can be seen from the images, with the gradual introduction of elements such as Mn, Ni, and Fe, the morphology of the catalyst changes significantly, gradually forming a sheet-like structure from an initially rough surface, and finally transforming into ultrathin nanosheets.

[0027] Figure 4 Transmission electron microscopy (TEM) and atomic force microscopy (AFM) images of the metal oxide nanosheet material prepared in Example 1 of this invention. The AFM images show that the synthesized nanosheets are only 1.5 nm thick. TEM confirms the presence of CoMoMnNiFeO. x It is composed of nanosheets.

[0028] Figure 5-10 The X-ray photoelectron spectroscopy (XPS) spectrum of the material prepared in Example 1 of this invention further confirms the synthesis of CoMoMnNiFeO. x .

[0029] Performance testing The metal oxide nanosheet materials obtained in Example 1 and the comparative example were subjected to electrocatalytic oxygen evolution and urea oxidation tests. The experimental steps are as follows: In a three-electrode cell, electrochemical parameters for the oxygen evolution reaction (OER) and urea oxidation reaction (UOR) were set using an electrochemical (PARSTAT® 3000) workstation. Graphite rods and silver / silver chloride were used as the counter and reference electrodes, respectively, in electrolytes of 1 M potassium hydroxide (OER) and 1 M potassium hydroxide plus 0.33 M urea (UOR). The working electrode was fabricated from high-entropy oxide nanosheets coated on nickel foam NF. Experimental results are shown in […]. Figure 11-16 .

[0030] Figure 11-16 The figures show the urea oxidation performance of the materials prepared in Example 1 and the comparative example of this invention. From the performance curves, it can be concluded that the synthesis of ultrathin CoMoMnNiFeO... x Nanosheets possess the best UOR properties.

[0031] Figure 17 The results are the theoretical calculations (DFT) of the materials prepared in Example 1 and the comparative example of this invention. Analysis of the results shows that the adsorption energy of the reaction intermediate is adjusted between the metal and oxygen in the formed pentagonal high-entropy metal oxide through dp orbital hybridization.

[0032] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing metal oxide nanosheets, characterized in that, Includes the following steps: 1) Cobalt source, molybdenum source, manganese source, nickel source, iron source and urea are heated and mixed to obtain eutectic solvent DESs; 2) The obtained eutectic solvent DESs was heated and reacted under an inert atmosphere to obtain the metal oxide nanosheets; The cobalt source is selected from one or more of cobalt chloride, cobalt nitrate, and cobalt sulfate; The molybdenum source is selected from one or more of molybdenum chloride, molybdenum nitrate, and molybdenum sulfate; The manganese source is selected from one or more of manganese chloride, manganese nitrate and manganese sulfate; The nickel source is selected from one or more of nickel chloride, nickel nitrate, and nickel sulfate; The iron source is selected from one or more of ferric chloride, ferric nitrate and ferric sulfate; The temperature of the heating reaction is 500 ~ 900 ℃.

2. The preparation method according to claim 1, characterized in that, The amounts of cobalt, molybdenum, manganese, nickel, and iron sources are independently 5wt%-35wt%, and the molar ratio of the mixed metal source material to urea is 1:1-10.

3. The preparation method according to claim 1, characterized in that, The heating and mixing temperature is 40~100 ℃, and the inert gas in the inert atmosphere is selected from nitrogen and / or argon.

4. The preparation method according to claim 1, characterized in that, The heating reaction time is 0.5–8 h, and the heating rate is 1–20 °C·min. -1 .

5. A metal oxide nanosheet, characterized in that, The metal oxide nanosheets obtained by the preparation method according to any one of claims 1 to 4 include CoMoMnNiFeO x , where x is a value based on charge balance and actual oxygen content, ranging from 7 to 9.

6. The application of the metal oxide nanosheets according to claim 5 in electrocatalytic oxygen evolution and urea oxidation.

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