Ce-doped high-entropy metal-organic framework derived multi-metal oxyhydroxide bifunctional electrode material and preparation and application thereof

Abstract

The application discloses a Ce-doped high-entropy metal organic framework derived multi-metal oxyhydroxide bifunctional electrode material and a preparation method and application thereof, and belongs to the technical field of electrocatalysis and electrochemical energy storage materials. The material is based on a foamed nickel, and a multi-metal oxyhydroxide nanosheet array composed of a Ce-doped high-entropy MOF precursor of Fe, Co, Ni, Mn and Ce is in-situ grown on the surface of the foamed nickel and is restructured by electrochemical activation. The preparation method comprises the following steps: pretreating the foamed nickel substrate; dissolving five kinds of metal salts, terephthalic acid and a surfactant in a mixed solvent, and performing a solvothermal reaction with the foamed nickel to grow the precursor; and activating and restructuring the precursor into an active material by a cyclic voltammetry method in an alkaline electrolyte. The application utilizes the synergistic effect of high-entropy multi-metals and the electronic structure regulation effect of Ce doping, and combines an electrochemical in-situ restructuring strategy, so that the obtained material does not need a binder, has excellent oxygen evolution reaction catalytic activity and supercapacitance, and can be used for water electrolysis oxygen evolution electrodes and supercapacitor electrodes.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis and electrochemical energy storage materials technology, specifically relating to a bifunctional electrode material with both excellent oxygen evolution reaction (OER) catalytic performance and supercapacitor (SC) energy storage performance, its preparation method and application. Background Technology

[0002] With the rapid development of clean energy technologies, electrocatalytic water splitting for hydrogen production and supercapacitor energy storage have become research hotspots. The oxygen evolution reaction (OER), as the anodic half-reaction in water electrolysis, suffers from slow four-electron transfer kinetics leading to high overpotentials, becoming a bottleneck restricting overall energy conversion efficiency. On the other hand, while supercapacitors possess high power density and long cycle life, their energy density is typically low. Developing bifunctional electrode materials capable of simultaneously and efficiently catalyzing the OER and storing charge is of great significance for constructing integrated energy conversion and storage systems.

[0003] High-entropy metal-organic frameworks (HE-MOFs) are considered ideal precursors for preparing high-performance electrochemical materials due to their multi-metal synergistic effects and tunable electronic structures. However, direct use of MOF materials often faces problems such as poor conductivity and deep burial of active sites. Electrochemical activation to reconstruct MOF precursors in situ into hydroxyl oxides is an effective strategy for exposing active sites and improving performance. Rare earth element Ce possesses a unique 4f electronic structure and variable valence states (Ce... 3+ / Ce 4+ Doping with oxygen can effectively modulate the electronic structure of transition metal centers and introduce oxygen vacancies, thereby enhancing the intrinsic activity and conductivity of the material.

[0004] Currently, there is a lack of methods to combine Ce doping strategies with high-entropy MOF precursors and prepare bifunctional electrode materials with both high-efficiency oxygen evolution reaction catalytic activity and excellent supercapacitor performance through electrochemical reconstruction techniques. Furthermore, the preparation methods are often complex or costly. Therefore, developing a simple and high-performance bifunctional electrode material is of great significance. Summary of the Invention

[0005] To address the shortcomings of existing bifunctional electrode materials in terms of electron transport, active site exposure, and structural stability, this invention provides a Ce-doped high-entropy metal-organic framework-derived multimetallic hydroxyl oxide bifunctional electrode material, its preparation method, and its applications. This material achieves a synergistic enhancement of oxygen evolution reaction catalytic performance and supercapacitor energy storage performance through high-entropy multimetal synergistic effects, Ce-doped electronic structure modulation, and electrochemical in-situ activation and reconstruction.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a Ce-doped high-entropy metal-organic framework-derived multimetallic hydroxyl oxide bifunctional electrode material, comprising a conductive substrate and an active material layer grown in situ on the surface of the conductive substrate; the active material layer is a multimetallic hydroxyl oxide nanosheet array containing iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn) and cerium (Ce); the active material layer is formed by electrochemical activation and in-situ reconstruction of a Ce-doped high-entropy metal-organic framework (HE-MOF) precursor containing the Fe, Co, Ni, Mn and Ce elements in an alkaline electrolyte.

[0007] Preferably, the conductive substrate is nickel foam (NF).

[0008] The Ce-doped high-entropy metal-organic framework precursor is FeCoNiMnCe-MOF with terephthalic acid as a ligand. The polymetallic hydroxyoxide is FeCoNiMnCeOOH, and the Fe, Co, Ni, Mn and Ce elements are uniformly distributed in the material.

[0009] The polymetallic hydroxyoxides have an amorphous or low-crystallinity structure, which is beneficial for exposing more active sites.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned bifunctional electrode material, comprising the following steps: S1. Pre-treat the conductive substrate; S2. Dissolve the iron source, cobalt source, nickel source, manganese source, cerium source, organic ligand and surfactant in a mixed solvent to obtain a precursor solution; S3. The pretreated conductive substrate is placed in the precursor solution and a solvothermal reaction is carried out to grow a Ce-doped high-entropy metal-organic framework precursor in situ on the surface of the conductive substrate. S4. The conductive substrate loaded with the Ce-doped high-entropy metal-organic framework precursor is placed in an alkaline electrolyte and electrochemically activated to reconstruct the precursor in situ into the bifunctional electrode material.

[0011] Preferably, in step S1, the pretreatment includes ultrasonically cleaning the nickel foam with acetone, dilute hydrochloric acid and deionized water in sequence and then drying it.

[0012] Preferably, in step S2, the iron source, cobalt source, nickel source, manganese source and cerium source are their respective nitrates, such as ferric nitrate nonahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, manganese nitrate tetrahydrate and cerium nitrate hexahydrate; the organic ligand is terephthalic acid; and the surfactant is hexadecyltrimethylammonium bromide (CTAB).

[0013] Preferably, in step S2, the molar ratio of metal ions in the iron source, cobalt source, nickel source, manganese source and cerium source is (0.2-2.3):(0.2-2.3):(0.2-2.3):(0.2-2.3):(0.2-2.3).

[0014] Preferably, in step S2, the mixed solvent includes N,N-dimethylformamide (DMF), ethanol, and water in a volume ratio of 40-60:1-10:1-10.

[0015] Preferably, in step S3, the temperature of the solvothermal reaction is 105-170°C and the time is 8-37 hours.

[0016] Preferably, in step S4, the alkaline electrolyte is a 1-3 M KOH solution; the electrochemical activation treatment is performed using cyclic voltammetry (CV) with a scan rate of 10-100 mV s⁻¹, a cycle count of 10-180, and a scan potential window of 0-0.4 V to 1-1.3 V (relative to the Hg / HgO reference electrode).

[0017] Mechanism of Invention: This invention first utilizes multiple metal ions (Fe, Co, Ni, Mn, Ce) and organic ligands to construct a high-entropy MOF precursor, forming a complex local electronic environment and structure through the high-entropy effect. After electrochemical activation in an alkaline electrolyte, the precursor undergoes in-situ reconstruction, transforming into an amorphous array of multi-metal hydroxyl oxide nanosheets. The introduction of Ce not only modulates the electronic states of active centers such as Fe, Co, Ni, and Mn, promoting the formation of high-valence active species, but also induces the generation of defects such as lattice distortion and oxygen vacancies. Simultaneously, the loose nanosheet array structure formed by reconstruction has abundant mesopores, greatly increasing the exposed area of ​​active sites and promoting the diffusion of electrolyte ions and rapid transport of interfacial charges, thereby synergistically improving the OER catalytic activity and pseudocapacitive energy storage performance of the material.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. Multi-component synergy and Ce doping effect: By constructing a pentagonal high-entropy system of Fe, Co, Ni, Mn and Ce, and introducing Ce with variable valence state and unique electronic structure, the electronic environment of the active center is effectively regulated, promoting the formation of high-valence active species and inducing lattice distortion and defects, thereby synergistically improving the intrinsic electrocatalytic activity and charge storage capacity of the material.

[0019] 2. In-situ growth and reconstruction strategy: The active material is grown directly on the conductive substrate without the need for a binder, ensuring good electrical contact and structural stability. The ordered MOF precursor is reconstructed in situ into an amorphous / low-crystallinity hydroxyl oxide nanosheet array through electrochemical activation. This process significantly increases the specific surface area and active site exposure of the material, and optimizes the ion / electron transport pathway.

[0020] 3. Dual-Effect Material: The prepared electrode material exhibits both excellent OER catalytic performance and supercapacitor energy storage performance. In the oxygen evolution reaction, the material has a low overpotential and good stability; as a supercapacitor electrode, it has a high areal capacitance and good rate performance, enabling the integration of energy conversion and electrochemical energy storage functions.

[0021] 4. Simple method and easy to scale up: The target electrode material is prepared by a conventional solvothermal reaction combined with electrochemical activation. The process is simple, the reaction conditions are relatively mild, the raw materials are readily available, and the active material can be directly grown on the surface of the conductive substrate, which facilitates subsequent electrode assembly and practical application, and has the potential for further scale-up preparation. Attached Figure Description

[0022] Figure 1 Comparison of X-ray diffraction (XRD) patterns of the FeCoNiMnCe-MOF precursor prepared in Example 1 and the FeCoNiMnCeOOH material obtained after electrochemical activation.

[0023] Figure 2 Transmission electron microscope (TEM) image of the FeCoNiMnCeOOH material prepared in Example 1.

[0024] Figure 3 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the FeCoNiMnCeOOH material prepared in Example 1.

[0025] Figure 4 The OER linear sweep voltammetry (LSV) curves of the materials in Example 1, Comparative Example 1 (FeCoNiOOH), and Comparative Example 2 (FeCoNiMnOOH) in 1 M KOH are shown.

[0026] Figure 5 The galvanostatic charge-discharge (GCD) curves (three-electrode system) of the materials in Example 1, Comparative Example 1 and Comparative Example 2 in 1 M KOH are shown.

[0027] Figure 6 The constant current charge-discharge curves are for the asymmetric supercapacitor (ASC) assembled using the material from Example 1 as the positive electrode and activated carbon as the negative electrode. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0029] Example 1: Preparation of FeCoNiMnCeOOH bifunctional electrode material 1. Pretreatment of nickel foam substrate Cut the nickel foam into rectangular sheets measuring 1 cm × 1.5 cm. Soak each sheet in acetone, 1 M hydrochloric acid solution, and deionized water using ultrasonic cleaning for 10 minutes each to thoroughly remove surface oil and oxide layers. After cleaning, dry the nickel foam in a 60°C vacuum oven for later use.

[0030] 2. Preparation of FeCoNiMnCe-MOF precursor Weigh out 0.6 mmol of ferric nitrate nonahydrate, 0.6 mmol of nickel nitrate hexahydrate, 0.6 mmol of cobalt nitrate hexahydrate, 0.7 mmol of manganese nitrate tetrahydrate, and 0.8 mmol of cerium nitrate hexahydrate, along with 4 mg of hexadecyltrimethylammonium bromide and 6 mmol of terephthalic acid. Add these to a mixed solvent consisting of 28 mL of N,N-dimethylformamide, 3 mL of ethanol, and 3 mL of deionized water, and stir until fully mixed. Transfer the mixed solution and the pretreated nickel foam to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), and react in an oven at 140 °C for 24 hours. After the reaction, allow it to cool naturally to room temperature, remove the sample, wash it repeatedly with N,N-dimethylformamide, ethanol, and deionized water, and dry it at 60 °C for 12 hours to obtain the FeCoNiMnCe-MOF precursor grown in situ on the surface of nickel foam.

[0031] 3. Preparation of FeCoNiMnCeOOH bifunctional electrode materials (electrochemical activation and reconstruction) A three-electrode electrochemical system was constructed using nickel foam loaded with FeCoNiMnCe-MOF precursor as the working electrode, a carbon rod as the counter electrode, and Hg / HgO as the reference electrode. The precursor was activated in 1 M KOH electrolyte using cyclic voltammetry at a scan rate of 100 mV / s. -1 The process was repeated 100 times. During activation, the FeCoNiMnCe-MOF precursor underwent in-situ electrochemical reconstruction on the nickel foam surface, forming a FeCoNiMnCeOOH nanosheet array bifunctional electrode material. After activation, the electrode was rinsed with deionized water and dried to obtain the FeCoNiMnCeOOH bifunctional electrode material.

[0032] Example 2: Changing electrochemical activation parameters The steps are basically the same as in Example 1, except that in step 3, the number of CV scan cycles is changed to 8, 12, 20, 30 and 50 times respectively to obtain the bifunctional electrode material.

[0033] Comparative Example 1: Preparation of FeCoNiOOH electrode material without Mn and Ce The steps are basically the same as in Example 1, except that in step 2, manganese nitrate tetrahydrate and cerium nitrate hexahydrate are not added; only equimolar amounts of iron, cobalt, and nickel salts (0.6 mmol each) are added. The remaining steps and conditions remain unchanged to prepare the FeCoNi-MOF precursor. Electrochemical activation is then performed according to the activation conditions in step 3 of Example 1 to obtain the FeCoNiOOH electrode material.

[0034] Comparative Example 2: Preparation of Ce-free FeCoNiMnOOH materials The steps are basically the same as in Example 1, except that in step 2, cerium nitrate hexahydrate is not added, while the other steps and conditions remain unchanged, to prepare the FeCoNiMn-MOF precursor. Electrochemical activation is then performed under the activation conditions of step 3 in Example 1 to obtain the FeCoNiMnOOH material.

[0035] Characterization and performance testing 1. Material structure characterization The structure and morphology of the FeCoNiMnCeOOH electrode material prepared in Example 1 were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and compared with the precursor material.

[0036] like Figure 1 The figures show the XRD and Raman spectra of the precursor and activated samples. It can be seen that the precursor sample exhibits obvious MOF characteristic diffraction peaks and organic framework vibrational peaks. However, after electrochemical activation, the original characteristic peaks are significantly weakened or disappear, and no clear crystalline diffraction peaks corresponding to the metal oxides are observed. This indicates that the material underwent significant structural reconstruction in an alkaline electrochemical environment, transforming from an ordered MOF framework into an amorphous or low-crystallinity multimetallic hydroxyl oxide active phase.

[0037] like Figure 2The figures show the TEM, HRTEM, SAED, and HAADF-STEM characterization results of the sample prepared in Example 1. It can be seen that the reconstructed sample exhibits a nanosheet morphology and a relatively loose and fragmented structural feature, which is beneficial for exposing more active sites. Only locally ordered short-range structures were observed in the high-resolution images, and the selected area electron diffraction pattern showed diffuse characteristics, further proving that the material has amorphous features. Elemental distribution results show that Fe, Co, Ni, Mn, and Ce elements are uniformly distributed in the material, indicating that the high-entropy multimetallic properties are preserved during the reconstruction process.

[0038] The surface chemical state and electronic structure of the FeCoNiMnCeOOH electrode material prepared in Example 1 and the comparative sample were analyzed by X-ray photoelectron spectroscopy (XPS).

[0039] like Figure 3 As shown, compared with Comparative Example 2 (which does not contain Ce), the binding energies of transition metals such as Fe, Co, and Ni in FeCoNiMnCeOOH show a significant shift, indicating that their local electronic structure is regulated and the metal oxidation states change. Further analysis reveals that the introduction of Ce promotes the formation of high-valence metal species, which is beneficial for improving the electrochemical activity of the material. Simultaneously, the coexistence of Ce in different valence states in the sample indicates that it can play a role in electronic compensation and defect regulation, thereby improving interfacial charge transport performance and enhancing the material's reactivity.

[0040] 2. Electrocatalytic performance test of oxygen evolution reaction To evaluate the oxygen evolution reaction activity of the prepared electrode materials under alkaline conditions, the electrochemical performance of Example 1, Comparative Example 1, and Comparative Example 2 was tested.

[0041] In a 1 M KOH electrolyte, a three-electrode system was used to perform linear sweep voltammetry tests, with a carbon rod as the counter electrode, Hg / HgO as the reference electrode, and the sample from Example 1 or the comparative example as the working electrode. The reaction kinetics and interfacial charge transport behavior of the materials were analyzed by combining Tafel curves, electrochemical double-layer capacitance, and electrochemical impedance spectroscopy.

[0042] like Figure 4 As shown, comparing the electrocatalytic performance of Example 1 and the comparative sample reveals that, at a speed of 10 mA cm⁻¹, [the electrocatalytic performance] is significantly improved. -2At the specified current density, the FeCoNiMnCeOOH catalyst in Example 3 required the lowest overpotential (210 mV), followed by Comparative Example 2 (FeCoNiMnOOH) (250 mV), and Comparative Example 1 (FeCoNiOOH) had the highest (260 mV). The FeCoNiMnCeOOH electrode material prepared in Example 1 exhibited superior oxygen evolution reaction (OER) activity and faster reaction kinetics, while also possessing a larger electrochemical active surface area and lower interfacial charge transport resistance. This indicates that the introduction of Mn and Ce, especially Ce doping, significantly enhances the OER catalytic activity of the material. Ce doping and the synergistic effect of high-entropy multimetals can effectively optimize the electronic structure and surface reaction behavior of the material, thereby significantly improving its OER performance.

[0043] 3. Supercapacitor Performance Testing To evaluate the energy storage performance of the prepared electrode materials, supercapacitor performance tests were conducted on Example 1, Comparative Example 1, and Comparative Example 2, and asymmetric supercapacitor devices were assembled and subjected to actual load tests.

[0044] In a 1 M KOH electrolyte, using a standard three-electrode system, with the sample from Example 1 or the comparative example as the working electrode, cyclic voltammetry, constant current charge-discharge, and electrochemical impedance spectroscopy were performed. Figure 5 As shown in the constant current charge-discharge curve, at 1 mA cm⁻¹ -2 At the specified current density, the FeCoNiMnCeOOH electrode material of Example 1 exhibited the longest discharge time, and its areal capacitance reached 6098 mF / cm². -2 The value was significantly higher than the 1828 mF / cm² of the FeCoNiMnOOH comparative example. -2 2224 mF cm compared with FeCoNiOOH -2 The values ​​are approximately 3.34 times and 2.74 times those of the two comparative examples mentioned above, respectively. These results demonstrate that Ce-doped high-entropy multimetallic systems can significantly improve the pseudocapacitive energy storage performance of electrode materials.

[0045] An asymmetric supercapacitor, FeCoNiMnCeOOH prepared in Example 1, was assembled using FeCoNiMnCeOOH as the positive electrode and activated carbon (AC) as the negative electrode, and its constant current charge-discharge performance was tested. Figure 6 The constant current charge-discharge curves shown indicate that the device maintains good symmetry under different current densities, demonstrating its excellent electrochemical reversibility and charge-discharge stability. Further calculations show that the device exhibits good symmetry under different current densities of 1, 2, 3, 4, 5, 6, 8, 10, and 20 mA cm⁻¹. -2At that time, the areal capacitance of the device was 849, 758, 694, 647, 609, 578, 532, 495 and 373 mFcm, respectively. -2 This indicates that the device can still maintain a certain charge storage capacity at high current densities, and has good rate performance.

[0046] In summary, this invention successfully prepared an amorphous multimetallic hydroxyl oxide nanosheet array electrode material grown on nickel foam by Ce doping, high-entropy design, and an electrochemical in-situ reconstruction strategy. This material has a simple preparation method, strong adhesion to the substrate, and simultaneously possesses excellent oxygen evolution reaction electrocatalytic activity and supercapacitor energy storage performance, showing broad application potential in integrated energy conversion and storage systems.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. 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 Ce-doped high-entropy metal-organic framework-derived multimetallic hydroxyl oxide bifunctional electrode material, characterized in that, It includes a conductive substrate and an active material layer grown in situ on the surface of the conductive substrate; the active material layer is a multi-metal hydroxyl oxide nanosheet array containing iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn) and cerium (Ce) elements; the active material layer is formed by electrochemical activation and in-situ reconstruction of a Ce-doped high-entropy metal-organic framework precursor containing the Fe, Co, Ni, Mn and Ce elements in an alkaline electrolyte.

2. The bifunctional electrode material according to claim 1, characterized in that, The conductive substrate is nickel foam.

3. The bifunctional electrode material according to claim 1, characterized in that, The Ce-doped high-entropy metal-organic framework precursor is FeCoNiMnCe-MOF with terephthalic acid as a ligand; the polymetallic hydroxyoxide is FeCoNiMnCeOOH, and the Fe, Co, Ni, Mn and Ce elements are uniformly distributed in the material.

4. The bifunctional electrode material according to claim 1 or 3, characterized in that, The polymetallic hydroxyoxides have an amorphous or low-crystallinity structure.

5. A method for preparing a bifunctional electrode material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Pre-treat the conductive substrate; S2. Dissolve the iron source, cobalt source, nickel source, manganese source, cerium source, organic ligand and surfactant in a mixed solvent to obtain a precursor solution; S3. The pretreated conductive substrate is placed in the precursor solution and subjected to a solvothermal reaction to obtain a Ce-doped high-entropy metal-organic framework precursor by in-situ growth on the surface of the conductive substrate. S4. The conductive substrate loaded with the Ce-doped high-entropy metal-organic framework precursor is placed in an alkaline electrolyte and electrochemically activated to reconstruct the precursor in situ into the bifunctional electrode material.

6. The method according to claim 5, characterized in that, In step S2, the iron source, cobalt source, nickel source, manganese source, and cerium source are their respective nitrates; the organic ligand is terephthalic acid; the surfactant is hexadecyltrimethylammonium bromide; the molar ratio of metal ions in the iron source, cobalt source, nickel source, manganese source, and cerium source is (0.2-2.3):(0.2-2.3):(0.2-2.3):(0.2-2.3); the mixed solvent includes N,N-dimethylformamide, ethanol, and water, with a volume ratio of 40-60:1-10:1-10.

7. The method according to claim 5, characterized in that, In step S3, the temperature of the solvothermal reaction is 105-170℃, and the time is 8-37 hours.

8. The method according to claim 5, characterized in that, In step S4, the electrochemical activation treatment is performed using cyclic voltammetry with a scan rate of 10-100 mV s⁻¹, a potential window of 0-0.4 V to 1-1.3 V (relative to the Hg / HgO reference electrode), and 10-180 cycles.

9. The application of a bifunctional electrode material as described in any one of claims 1-4 as a working electrode in the electrocatalytic oxygen evolution reaction.

10. The application of a bifunctional electrode material as described in any one of claims 1-4 as an electrode active material in a supercapacitor.

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