Preparation method and electrochemical application of high-entropy MOF-GO nanosheet

Abstract

The invention relates to a preparation method and electrochemical application of a high-entropy MOF-GO nanosheet, and belongs to the technical field of new materials. According to the method, graphene oxide (GO) is taken as a structure-directing agent, five metal ions of nickel, cobalt, iron, copper and zinc react with a terephthalic acid organic ligand in a mixed solvent at 140 DEG C through a one-pot method, and the high-entropy MOF-GO nanosheet with the accordion-shaped morphology is successfully prepared. By regulating and controlling key parameters, uniform heterogeneous nucleation and two-dimensional orientation growth of multi-element metal ions on the GO surface are realized; wherein the effective inhibition of the GO on the Jahn-Teller distortion of the Cu is the key for realizing the controllable growth and finally forming the single high-entropy phase. And the prepared nanosheet shows excellent performance in electro-catalytic reaction and alkaline zinc batteries.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically relating to a method for preparing high-entropy MOF-GO nanosheets and their application in the field of electrochemistry. Background Technology

[0002] Metal-organic frameworks (MOFs) are a class of crystalline porous materials formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. Due to their high specific surface area, tunable pore structure, and functionalized pore environment, they exhibit great application potential in gas adsorption and separation, catalysis, sensing, drug delivery, and energy storage and conversion. However, traditional single-metal or bimetallic MOF materials often suffer from limitations in intrinsic conductivity, structural stability, and the number of active sites in complex electrochemical applications, making it difficult to simultaneously meet the stringent requirements of high capacity, long cycle life, and high rate performance.

[0003] In recent years, the concept of high entropy—introducing five or more different metal elements into a single crystal lattice to form a homogeneous phase—has been successfully applied to the design of MOF materials, resulting in high-entropy MOFs. The "cocktail party effect" and significant lattice distortion brought about by high entropy can effectively regulate the electronic structure of materials, expose more active sites, and enhance the structural stability of materials. Therefore, high-entropy MOFs have attracted widespread attention in electrocatalysis (such as oxygen evolution reaction and oxygen reduction reaction) and electrochemical energy storage (such as supercapacitors and ion batteries), and are considered strong candidates for next-generation high-performance electrochemical materials. However, further development of high-entropy MOFs still faces the dual challenges of synthesis and morphology control. Specifically, at the synthesis level, various metal ions with different chemical properties compete for coordination during self-assembly, making it difficult to achieve uniform nucleation and pure phase growth. Furthermore, the complex nucleation and growth mechanisms are still unclear, which brings fundamental difficulties to the directional design and controllable preparation of materials. Correspondingly, at the morphological level, macroscopic bulk high-entropy MOF materials obtained by conventional hydrothermal / solvothermal methods result in most active sites being buried inside the material, while also causing problems such as long ion / electron transport paths and insufficient electrolyte wetting, which severely limit the efficient performance of their intrinsic activity.

[0004] Graphene oxide (GO), as an important two-dimensional material, possesses abundant oxygen-containing functional groups (such as hydroxyl, epoxy, and carboxyl groups) on its surface, exhibiting excellent hydrophilicity and dispersibility. Based on these properties, compositing MOFs with GO to construct heterostructures is considered an effective strategy to enhance the electrochemical performance of MOF materials. In existing technologies, GO is often used as a supporting template, theoretically guiding the heterogeneous nucleation and growth of MOF units through its surface functional groups, suppressing the disordered stacking of MOF nanosheets, and simultaneously enhancing the conductivity and structural stability of the composite material. Currently, numerous studies have reported composite materials based on single or bimetallic MOFs and GO, which typically demonstrate superior performance compared to single-component materials in applications such as supercapacitors and electrocatalysis. However, when the research scope expands from simple MOFs to high-entropy MOF systems containing five or more metal elements, the complex interactions between GO and multi-metal ions, as well as the influence mechanism of GO on the high-entropy phase crystallization pathway, remain unclear. This mechanistic uncertainty makes directly transferring the GO compositing strategy to high-entropy MOF systems a significant challenge.

[0005] In summary, developing high-entropy MOF-GO nanosheets that combine high-entropy characteristics with the synergistic advantages of GO composites is an important direction for improving their electrochemical performance. However, current research in this interdisciplinary field is still in its early stages. A series of key technical challenges remain to achieve controllable preparation of high-entropy MOF-GO nanosheets: First, thermodynamically, ensuring the uniform self-assembly of multiple metal ions to form a stable single high-entropy phase, rather than individual phases or mixtures of metal oxides, is a primary obstacle. Second, kinetically, how the presence of GO affects the coordination rate and sequence of multiple metal ions, ultimately guiding the high-entropy MOF to achieve two-dimensional directional growth rather than bulk growth, remains unclear. Finally, regarding morphology control, precisely optimizing synthesis conditions (such as the amount of GO added, reaction temperature, solvent system, etc.) to obtain nanosheets with uniform size also lacks systematic theoretical guidance and universal preparation strategies. Therefore, current technologies lack a simple and efficient method to systematically solve the above problems and achieve controllable preparation of high-performance high-entropy MOF-GO nanosheets. Summary of the Invention

[0006] To address the challenges of morphological control, unclear growth mechanism, and large-scale preparation difficulties in high-entropy MOF-GO composite materials, this invention aims to provide a "one-pot method" for the controllable and large-scale preparation of accordion-shaped high-entropy MOF-GO nanosheets, utilizing GO interface engineering to regulate the crystallization path of high-entropy MOFs. The core of this method lies in leveraging the abundant oxygen-containing functional groups on the GO surface to guide the homogeneous heterogeneous nucleation of multi-metal ions through electrostatic interactions, effectively inhibiting Cu... 2+The Jahn-Teller distortion was utilized, and by modulating the surface energy distribution, precise control was achieved throughout the entire process from nucleation and two-dimensional orientation growth to the final morphological evolution, thereby obtaining high-entropy MOF-GO nanosheets with regular structures. The method is simple, reproducible, and suitable for large-scale production. Specific steps include:

[0007] (1) Preparation of GO dispersion: GO was dispersed in deionized water and ultrasonically treated to obtain a uniform and stable dispersion.

[0008] (2) Preparation of multi-metal ion / GO mixed dispersion: Nitrates of nickel, cobalt, iron, copper and zinc are dissolved in the GO dispersion obtained in step (1) according to a preset molar ratio. The metal ions are uniformly adsorbed on the GO surface by ultrasonic treatment to form a mixed dispersion system.

[0009] (3) Preparation of accordion-shaped high-entropy MOF-GO nanosheets: The mixed dispersion obtained in step (2) was transferred to a reactor, and organic ligand terephthalic acid (BDC) and a mixed solvent composed of N,N-dimethylformamide (DMF) and ethylene glycol (EG) were added. The reaction was carried out under reflux in an oil bath at 140°C. After the reaction was completed, the product was cooled, separated, washed and dried to obtain high-entropy MOF-GO nanosheets.

[0010] Furthermore, the concentration of the GO dispersion in step (1) is a key parameter for controlling the morphology of the product, and its preferred concentration is 2 mg / mL. Under this concentration condition, the GO surface can provide a suitable amount of uniformly distributed heterogeneous nucleation sites, which is the optimal condition for realizing the accordion-like nanosheet structure.

[0011] Furthermore, in step (3), the volume ratio of DMF to EG is 1:1, the reaction temperature is 140℃, the reaction time is 10 hours, and the stirring rate is 30 rpm to ensure that the reaction proceeds fully.

[0012] Furthermore, the washing solvent in step (3) is ethanol, and the drying conditions are vacuum drying at 60°C.

[0013] Furthermore, by scaling up the amount of each material in the above steps, this synthesis method can stably achieve the preparation of high-entropy MOF-GO nanosheets on a kilogram-scale.

[0014] Another object of the present invention is to provide the application of accordion-shaped high-entropy MOF-GO nanosheets prepared by the above method in the field of electrochemistry, particularly as an electrocatalyst for oxygen evolution reaction or a cathode material for quasi-solid-state alkaline zinc batteries.

[0015] Compared with existing technologies, the advantages of this invention are as follows: it elucidates for the first time the stepwise synergistic mechanism of GO-guided high-entropy MOF crystal growth and accordion-like morphology formation, providing a simple, efficient, controllable, and easily scalable synthesis route. This method successfully achieves high-quality preparation of structurally regular and high-performance high-entropy MOF-GO nanosheets, providing new ideas for the development of other high-performance high-entropy materials. Attached Figure Description

[0016] Figure 1 The X-ray diffraction (XRD) pattern of the high-entropy MOF-GO of this invention;

[0017] Figure 2 This is a transmission electron microscope (TEM) image of the high-entropy MOF-GO of this invention;

[0018] Figure 3 Linear sweep voltammetry (LSV) curves of the oxygen evolution reaction (OER) in alkaline electrolyte using high-entropy MOF-GO as an electrocatalyst in this invention.

[0019] Figure 4 The galvanostatic charge-discharge (GCD) curves of the quasi-solid-state alkaline zinc battery assembled with high-entropy MOF-GO as the positive electrode in this invention are shown at different current densities. Detailed Implementation

[0020] The principles and features of the present invention will be described in detail below with reference to implementation. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0021] Example 1:

[0022] (1) Accurately weigh 100 mg of GO, disperse it in 50 mL of deionized water, and sonicate it for 2 hours to obtain a uniform and stable GO dispersion with a concentration of 2 mg / mL.

[0023] (2) Accurately weigh a total of 15.85 mmol of the above five metal nitrates according to the molar ratio of nickel, cobalt, iron, copper and zinc of 6:1:1:1:1, and add them to the GO dispersion prepared in step (1). Continue to sonicate the mixed solution for 1 hour to ensure that the metal ions are uniformly adsorbed on the GO surface and form a metal ion / GO mixed dispersion system.

[0024] (3) Transfer the mixed dispersion obtained in step (2) to a 500 mL three-necked round-bottom flask. Add 18 mmol of terephthalic acid (H2BDC), 120 mL of DMF, and 120 mL of EG to the flask. Place the reaction system in a 140°C oil bath and reflux the mixture under magnetic stirring (30 rpm) for 10 hours.

[0025] (4) After the reaction was completed, the product was allowed to cool naturally to room temperature. The solid product was collected by centrifugation and washed three times with DMF and anhydrous ethanol to remove unreacted raw materials and solvents. Finally, the washed product was dried in a vacuum drying oven at 60°C for 12 hours to obtain the final dark gray high-entropy MOF-GO nanosheets.

[0026] Figure 1 The diffraction characteristics exhibited are highly consistent with the Ni-BDC framework (CCDC no. 985792) structure, with sharp and intense diffraction peaks corresponding to the (200), (001), and (201) crystal planes, indicating that the material has high crystallinity and good phase purity. It was confirmed that the five metal elements Ni, Co, Fe, Cu, and Zn have been successfully and uniformly doped at the atomic level, forming a single-phase high-entropy crystal structure without any impurity phases. This result fully demonstrates that the introduction of GO did not destroy the intrinsic crystal structure of the MOF, but rather served as an effective structural guiding template, guiding the directional growth of the high-entropy MOF and forming a layered, ordered composite structure.

[0027] Figure 2 The high-entropy MOF-GO prepared by the method of this invention clearly exhibits a typical accordion-like morphology, consisting of multilayer nanosheets stacked in a highly ordered manner. High-resolution images further reveal the well-defined layered structure and uniform thickness distribution of the nanosheets. This morphological feature directly confirms the crucial regulatory role of GO in the heterogeneous nucleation and two-dimensional growth of high-entropy MOFs during synthesis, avoiding the formation of bulk crystals and successfully constructing an open layered structure conducive to electrochemical mass transfer and charge transport.

[0028] Figure 3 The OER performance of high-entropy MOF-GO nanosheets in 1.0 M KOH electrolyte is presented. LSV curves show that this catalyst achieves an OER of 10 mA cm⁻¹. -2 The overpotential required is only 213 mV at the specified current density. The superior performance is mainly attributed to the unique multi-metal synergistic effect and abundant active sites characteristic of high-entropy systems. These features collectively promote the optimization of reaction kinetics, demonstrating the material's exceptional electrocatalytic activity.

[0029] Figure 4 The GCD curve of a quasi-solid-state alkaline zinc battery assembled using high-entropy MOF-GO as the cathode material is presented. Test results show that the battery can provide a high specific capacity of 223.3 mA hg⁻¹ at a current density of 1 A g⁻¹. With increasing current density, the battery capacity retention remains at a high level, exhibiting excellent rate performance.

[0030] The above description is merely a specific embodiment of the present invention, but its protection scope is not limited thereto. Any modifications or equivalent substitutions that can be easily made by those skilled in the art within the scope of the technology disclosed in this invention should be included within the protection scope of this invention. Therefore, the protection scope of this invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing high-entropy MOF-GO nanosheets, characterized in that, Includes the following steps: (1) Preparation of graphene oxide (GO) dispersion: GO was dispersed in deionized water and ultrasonically treated to obtain a uniform and stable dispersion; (2) Preparation of multi-metal ion / GO mixed dispersion: Dissolve the metal salts of nickel (Ni), cobalt (Co), iron (Fe), copper (Cu) and zinc (Zn) in the GO dispersion obtained in step (1) according to a preset molar ratio, and form a mixed dispersion system by ultrasonic treatment; (3) Preparation of high-entropy MOF-GO nanosheets: The mixed dispersion obtained in step (2) is transferred to a reactor, and organic ligand terephthalic acid (BDC) and a mixed solvent composed of N,N-dimethylformamide (DMF) and ethylene glycol (EG) are added. The mixture is subjected to reflux under heating conditions. After the reaction is completed, the product is cooled, separated, washed and dried to obtain the final product.

2. The method according to claim 1, characterized in that, The concentration of the GO dispersion in step (1) is 2 mg / mL.

3. The method according to claim 1, characterized in that, The metal salts of Ni, Co, Fe, Cu and Zn mentioned in step (2) are nitrates, and their molar ratio is 6:1:1:1:

1.

4. The method according to claim 1, characterized in that, In step (3), the volume ratio of DMF to EG in the mixed solvent is 1:

1.

5. The method according to claim 1, characterized in that, The reaction temperature in step (3) is 140℃, the reaction time is 10 hours, and the stirring rate is 30 rpm.

6. The method according to claim 1, characterized in that, The washing solvent in step (3) is ethanol, and the drying conditions are vacuum drying at 60°C.

7. The application of high-entropy MOF-GO nanosheets prepared by any one of claims 1-6 in the field of electrochemistry.

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