Preparation of hollow sulfydryl MOF-ON-MOF composite material and application of supercapacitor

Abstract

The invention discloses preparation of a hollow sulfydryl MOF-ON-MOF composite material and application of a supercapacitor, and belongs to the technical field of battery materials. The preparation method of the hollow sulfydryl MOF-ON-MOF composite material comprises the following steps: mixing a substrate material, a first cobalt source, 2, 5-dihydroxyterephthalic acid and a solvent, and carrying out first heating reaction to obtain a substrate loaded with a metal organic framework; and mixing the substrate loaded with the metal organic framework with a second cobalt source, 2, 5-dimercapto terephthalic acid and a solvent, and carrying out a second heating reaction to obtain the hollow mercapto MOF-ON-MOF composite material. The hollow sulfydryl MOF-ON-MOF composite material prepared by the invention shows excellent electrochemical performance, has high area capacitance, good rate capability, excellent conductivity and good cycle performance, and solves the problem of low capacitance activity of the MOF material in the prior art.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to the preparation of a hollow mercapto MOF-ON-MOF composite material and its application in supercapacitors. Background Technology

[0002] In the global energy mix, traditional fossil fuels (such as coal, oil, and natural gas) still account for a large proportion of total energy consumption. Therefore, promoting the development of renewable energy and energy storage technologies has become a key research hotspot. Currently, rechargeable batteries, as a promising energy storage device, dominate the market. However, their drawbacks include low power density and limited charge-discharge cycles. Supercapacitors, as an energy storage device that bridges the performance gap between traditional capacitors and batteries, offer advantages such as fast charge-discharge speeds and long cycle life, making them a widely studied energy storage option. However, existing electrode materials are generally limited by poor conductivity, low specific capacitance, and insufficient stability, restricting their practical application effectiveness. Therefore, improving the capacitance, conductivity, rate performance, and energy / power density of electrode materials is currently a core challenge.

[0003] After years of research, various electrode materials for supercapacitors have been explored, such as conductive polymers, carbon nanotubes, metal oxides, organic electrolytes, two-dimensional materials, and metal-organic frameworks (MOFs). Among them, MOF materials have shown significant potential in the field of supercapacitors due to their tunable pore structure, high specific surface area, and ease of functionalization. In particular, the MOF-ON-MOF hierarchical structure, by constructing a conductive MOF thin layer on a relatively thick supporting MOF substrate, can synergistically improve ionic conductivity, alleviate diffusion limitations, and enhance the electrochemically active interface. MOF-ON-MOF frameworks possess functionalized pore surfaces, good conductivity, controllable geometry, and pore size, showing potential applications in oxygen evolution reaction, photoelectric sensors, biosensors, electrocatalysts, photoreduction, and Hg(II) detection. However, to date, research on MOF-ON-MOF materials for energy storage applications is still in its early stages, and their structure-property relationships and performance optimization mechanisms urgently need systematic exploration. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing hollow thiol-based MOF-ON-MOF composite materials and their application in supercapacitors, thereby addressing the aforementioned problems in the prior art. The hollow thiol-based MOF-ON-MOF composite materials prepared by this invention exhibit excellent electrochemical performance, possessing high areal capacitance, good rate capability, excellent conductivity, and good cycle performance, thus solving the problem of low capacitive activity in existing MOF materials.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of this invention is to provide a method for preparing hollow mercapto MOF-ON-MOF composite materials, comprising the following steps:

[0007] The substrate material, the first cobalt source, 2,5-dihydroxyterephthalic acid and solvent were mixed and heated for the first reaction to obtain a substrate loaded with a metal-organic framework;

[0008] The substrate with the supported metal-organic framework is mixed with a second cobalt source, 2,5-dimercaptoterephthalic acid and a solvent, and then heated for a second reaction to obtain the hollow mercapto MOF-ON-MOF composite material.

[0009] Preferably, the first cobalt source is Co(NO3)2, and the molar ratio of the first cobalt source to 2,5-dihydroxyterephthalic acid is 3:1.

[0010] Preferably, the substrate material is nickel foam; the mass ratio of the substrate material to the first cobalt source is 1.506:1.

[0011] Preferably, the temperature of the first heating reaction is 120°C and the time is 24 hours.

[0012] Preferably, the molar ratio of the second cobalt source to 2,5-dimercaptoterephthalic acid is 3:1.

[0013] Preferably, the mass ratio of the substrate supporting the metal-organic framework to the second cobalt source is 1.506:1.

[0014] Preferably, the temperature of the second heating reaction is 120°C and the time is 24 hours.

[0015] Preferably, the solvent contains N,N-dimethylformamide, ethanol, and water.

[0016] The second technical solution of the present invention provides a hollow mercapto MOF-ON-MOF composite material obtained according to the above preparation method.

[0017] The third technical solution of the present invention provides an application of the above-mentioned hollow mercapto MOF-ON-MOF composite material in the field of supercapacitors.

[0018] The beneficial technical effects of the present invention are as follows:

[0019] The hollow thiol-based MOF-ON-MOF heterojunction material Co2(L1)@Co2(L2) / NF prepared in this invention exhibits excellent electrochemical performance, possessing a high areal capacitance (at 1 mA / cm²). 2 The maximum strength can reach 4677mF / cm 2It exhibits good rate performance, excellent conductivity, and good cycling performance. The prepared Co2(L1)@Co2(L2) / / ACACS device retains 73.27% capacitance after 10,000 cycles and achieves a maximum energy density of 58.6 Wh / kg at a power density of 221.2 W / kg, making it suitable for high-energy-density supercapacitors.

[0020] The MOF-ON-MOF heterostructure material synthesized in this invention exhibits unique structural advantages and excellent electrochemical performance, solving the problem of low capacitive activity in existing MOF materials. This material employs a two-component composite structure design. The outer Co2(L2) nanosheets significantly improve conductivity by shortening the charge transport path, while the inner Co2(L1) rod-like structure effectively addresses structural stability issues that may arise during electrochemical redox processes. Notably, the inner rod-like structure not only provides a stable support framework for the outer nanosheets but also achieves uniform dispersion of the nanosheets, effectively preventing the aggregation of Co2(L2) nanosheets. This unique structural design enables the material to exhibit outstanding performance in electrochemical energy storage, specifically in high specific capacitance and excellent rate capability. Based on its outstanding energy storage performance, this MOF-ON-MOF heterostructure material has broad application potential in energy storage devices such as supercapacitors.

[0021] The MOF-ON-MOF heterojunction material Co2(L1)@Co2(L2) / NF prepared by this invention has the characteristics of simple process, easy operation and low equipment requirements. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the preparation process of Co2(L1)@Co2(L2) in Example 1 of the present invention.

[0024] Figure 2 These are scanning electron microscope (SEM) images of Co2(L1), Co2(L1)@Co2(L2) from Example 1 of the present invention, and Co2(L2) from Comparative Example 1. In the images, (a) and (b) represent Co2(L2) at different magnifications, (c) and (d) represent Co2(L1) at different magnifications, and (e) and (f) represent Co2(L1)@Co2(L2) at different magnifications.

[0025] Figure 3 The infrared spectra of Co2(L1), Co2(L1)@Co2(L2) in Example 1 and Co2(L2) in Comparative Example 1 are shown.

[0026] Figure 4 The crystal structure analysis diagrams are of Co2(L1), Co2(L1)@Co2(L2) in Example 1 of the present invention and Co2(L2) in Comparative Example 1.

[0027] Figure 5 The Co2(L1), Co2(L1)@Co2(L2) of Example 1 and the Co2(L2) of Comparative Example 1 are at 1 mA / cm 2 The constant current charge-discharge diagram (GCD) at the current density.

[0028] Figure 6 The Co2(L1)@Co2(L2) of Example 1 of this invention is used at a current density of 1-30 mA / cm². 2 The constant current charge-discharge diagram (GCD) is shown below.

[0029] Figure 7 The image shows the cyclic voltammetry (CV) curves of Co2(L1)@Co2(L2) in Embodiment 1 of the present invention at scan rates of 5-100mV / s within a voltage range of 0 to 0.6V.

[0030] Figure 8 This is a pseudocapacitance diagram of Co2(L1)@Co2(L2) in Embodiment 1 of the present invention. Among them, (a) is a graph showing the relationship between scan rate and current density, (b) is a graph showing the separation of capacitance / diffusion contribution, and (c) is a statistical graph showing the capacitance control contribution rate at different scan rates.

[0031] Figure 9 This is a comparison diagram of the surface capacitance of Co2(L1), Co2(L1)@Co2(L2) in Embodiment 1 of the present invention and Co2(L2) in Comparative Example 1.

[0032] Figure 10 Impedance comparison diagram of Co2(L1)@Co2(L2) before and after cycling in Embodiment 1 of the present invention.

[0033] Figure 11 Cyclic performance diagram of Co2(L1)@Co2(L2) in Example 1 of this invention.

[0034] Figure 12 The impedance comparison diagram (EIS) is shown for Co2(L1), Co2(L1)@Co2(L2) in Embodiment 1 of the present invention and Co2(L2) in Comparative Example 1.

[0035] Figure 13 This is the cyclic voltammetry (CV) curve of Co2(L1)@Co2(L2) / / AC in Embodiment 2 of the present invention.

[0036] Figure 14 For Example 2 of this invention, Co2(L1)@Co2(L2) / / AC is used at a current density of 1-20 mA / cm². 2 The constant current charge-discharge curve (GCD) at that time.

[0037] Figure 15 This is the energy density / power density diagram of Co2(L1)@Co2(L2) / / AC in Embodiment 2 of the present invention.

[0038] Figure 16 In Embodiment 2 of the present invention, Co2(L1)@Co2(L2) / / AC is used at a current density of 10 mA / cm². 2 The following is a graph showing the cyclic stability of the circuit. Detailed Implementation

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0040] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0042] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0043] This invention discloses a method for preparing a hollow thiol-based MOF-ON-MOF heterojunction material Co2(L1)@Co2(L2) / NF, comprising the following steps:

[0044] I. Preparation of Co2(L1) / NF

[0045] Co(NO3)2·6H2O, 2,5-dihydroxyterephthalic acid (H4DOBDC), N,N-dimethylformamide, ethanol and water were mixed and added to a high-pressure reactor, and sonicated. Nickel foam (NF) was added to the high-pressure reactor after sonication, and the mixture was heated at 120°C for 24 hours in a constant temperature oven. After cooling, the sample was washed with ultrapure water and anhydrous ethanol, and dried at 60°C for 4 hours to obtain Co2(L1) / NF.

[0046] II. Preparation of Co2(L1)@Co2(L2) / NF

[0047] Co(NO3)2·6H2O, 2,5-dimercaptoterephthalic acid, N,N-dimethylformamide, ethanol and water were mixed and added to a high-pressure reactor, and sonicated to obtain a mixture.

[0048] The Co2(L1) / NF was placed in a high-pressure reactor containing the mixture and heated at 120°C for 24 hours. After cooling, the sample was washed with ultrapure water and anhydrous ethanol, and then dried at 60°C for 4 hours to obtain the Co2(L1)@Co2(L2) / NF.

[0049] This invention also discloses a method for preparing an asymmetric supercapacitor (ASC) using the above-mentioned hollow thiol MOF-ON-MOF heterojunction material Co2(L1)@Co2(L2) / NF, comprising the following steps:

[0050] In a two-electrode system, using 1M KOH solution as the electrolyte, the aforementioned Co2(L1)@Co2(L2) / NF as the positive electrode, and the material containing activated carbon (AC) as the negative electrode, an asymmetric supercapacitor is assembled.

[0051] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0052] Example 1

[0053] A method for preparing a hollow thiol MOF-ON-MOF heterojunction material Co2(L1)@Co2(L2) / NF includes the following steps:

[0054] I. Preparation of Co2(L1) / NF

[0055] Take a piece of material measuring 2.0 x 2.0 cm. 2161.1 mg of nickel foam (NF) was sequentially ultrasonicated for 10 minutes each with 10 wt% hydrochloric acid solution, acetone, deionized water, and anhydrous ethanol, and then dried at 60 °C for 4 hours to obtain pretreated nickel foam (NF), which was then set aside for later use. Co(NO3)2·6H2O (107 mg, 0.36 mmol), 2,5-dihydroxyterephthalic acid (H4DOBDC, 24 mg, 0.12 mmol), 3 ml of N,N-dimethylformamide, 3 ml of ethanol, and 3 ml of ultrapure water were added to a 25 ml high-pressure reactor and ultrasonicated for 15 minutes. The pretreated nickel foam was then placed into the reactor using tweezers. The mixture was heated at 120 °C for 24 hours in a constant-temperature oven. After cooling, the surface of the nickel foam turned reddish-brown, indicating that a Co2(L1) nanoarray was successfully formed on the nickel foam through in-situ interfacial growth. The mixture was washed with ultrapure water and ethanol respectively, and then dried at 60°C for 4 hours to obtain Co2(L1) / NF (denoted as Co2(L1)).

[0056] II. Preparation of Co2(L1)@Co2(L2) / NF

[0057] Co(NO3)2·6H2O (107 mg, 0.36 mmol), 2,5-dimercaptoterephthalic acid (H4DSBDC, 28 mg, 0.12 mmol), 3 ml of N,N-dimethylformamide, 3 ml of ethanol, and 3 ml of ultrapure water were added to a 25 ml high-pressure reactor and sonicated for 15 min. Then, the Co2(L1) / NF mixture was placed into the 25 ml high-pressure reactor using tweezers. The mixture was heated at 120 °C for 24 h in a constant-temperature oven. After cooling, the NF surface turned black, indicating that a Co2(L1)@Co2(L2) / NF nanoarray was successfully formed on Ni foam. The nanoarray was washed with ultrapure water and ethanol, and then dried at 60 °C for 4 h to obtain Co2(L1)@Co2(L2) / NF (denoted as Co2(L1)@Co2(L2)).

[0058] Figure 1 This is a schematic diagram of the preparation process of Co2(L1)@Co2(L2) in Example 1 of the present invention.

[0059] Comparative Example 1

[0060] Preparation of Co2(L2) / NF electrode materials:

[0061] Take a piece of material measuring 2.0 x 2.0 cm. 2161.1 mg of nickel foam (NF) was sequentially sonicated for 10 minutes each with 10 wt% hydrochloric acid solution, acetone, deionized water, and anhydrous ethanol, and then dried at 60 °C for 4 hours to obtain pretreated nickel foam (NF), which was then set aside for later use. 107 mg (0.36 mmol) of Co(NO3)2·6H2O, 28 mg (0.12 mmol) of 2,5-dimercaptoterephthalic acid (H4DSBDC, 28 mg, 0.12 mmol), 3 ml of N,N-dimethylformamide, 3 ml of ethanol, and 3 ml of ultrapure water were added to a 25 ml high-pressure reactor and sonicated for 15 minutes. The pretreated nickel foam was then placed into the reactor using tweezers. The mixture was heated at 120 °C for 24 hours in a constant-temperature oven. After cooling, the mixture was washed with ultrapure water and ethanol, and then dried at 60 °C for 4 hours to obtain Co2(L2) / NF (denoted as Co2(L2)).

[0062] Figure 2 These are scanning electron microscope (SEM) images of Co2(L1), Co2(L1)@Co2(L2) from Example 1 of the present invention, and Co2(L2) from Comparative Example 1. In the images, (a) and (b) represent Co2(L2) at different magnifications, (c) and (d) represent Co2(L1) at different magnifications, and (e) and (f) represent Co2(L1)@Co2(L2) at different magnifications.

[0063] Figure 2 In the images, (a) and (b) show nanosheet-like Co2(L2) clusters, (c) and (d) demonstrate the successful synthesis of rod-shaped Co2(L1), and (e) and (f) clearly show that the originally smooth surface of the rod-shaped Co2(L1) becomes rough, revealing the presence of uniformly deposited sheet-like Co2(L2) on the surface of Co2(L1) and clearly demonstrating the hollow configuration of the material, thus confirming the successful synthesis of hollow Co2(L1)@Co2(L2).

[0064] Example 2

[0065] Fabrication of asymmetric supercapacitors (ASCs):

[0066] Activated carbon (AC), acetylene black, and polyvinylidene fluoride (PVDF) were blended in a mass ratio of 8:1:1, and then 3-5 drops of N-methyl-2-pyrrolidone (NMP) were added dropwise using a dropper to prepare the negative electrode. The Co2(L1)@Co2(L2) / NF, Co2(L1) / NF prepared in Example 1, or Co2(L2) / NF in Comparative Example 1 were used as the positive electrode. In a two-electrode system, using 1M KOH solution as the electrolyte, the above positive and negative electrodes were assembled into asymmetric supercapacitors (referred to as Co2(L1)@Co2(L2) / / AC, Co2(L1) / / AC, and Co2(L2) / / AC, respectively, according to the type of positive electrode material), and electrochemical tests were performed.

[0067] Effect verification

[0068] Figure 3 The infrared spectra of Co2(L1), Co2(L1)@Co2(L2) in Example 1 and Co2(L2) in Comparative Example 1 are shown.

[0069] In the range of 400-4000cm -1 FT-IR spectra were recorded within the frequency range. From Figure 3 It can be seen that this invention successfully prepared Co2(L1), Co2(L2), and Co2(L1)@Co2(L2) on nickel foam. The original Co2(L1) and Co2(L2) have similar structures, and their characteristic peaks are at 800 cm⁻¹. -1 The above corresponds to the vibrations of organic ligands. At 1576 cm⁻¹ -1 and 1375cm -1 The characteristic peaks observed are attributed to the CC vibration in the organic ligand and the in-plane deformation vibration of CH, respectively. The synthesized Co2(L1)@Co2(L2) material exhibits characteristic peaks similar to those of the original MOF, confirming the successful synthesis of Co2(L1)@Co2(L2).

[0070] Figure 4 The crystal structure analysis diagrams are of Co2(L1), Co2(L1)@Co2(L2) in Example 1 of the present invention and Co2(L2) in Comparative Example 1.

[0071] Detection was performed using X-ray powder diffraction (XRD). Figure 4 It can be seen that the powder X-ray diffraction (PXRD) pattern of Co2(L2) is in 2 θTwo main peaks were observed at 8.35° and 11.52°, indicating a good match between the experimental PXRD spectrum and the simulated peaks of Co2(L2), confirming the successful synthesis of Co2(L2), CCDC reference number 1430630. Furthermore, the powder X-ray diffraction (PXRD) spectrum of Co2(L1) showed two prominent peaks at 6.78° and 11.73°, corresponding to (210) and (300) respectively (CCDC No. 288477), proving the successful preparation of Co2(L1). In the case of Co2(L1)@Co2(L2), the peaks at 6.89° and 11.85° confirmed the presence of Co2(L1), while the peaks at 8.27° and 11.27° indicated the presence of Co2(L2).

[0072] The electrochemical performance of the electrode materials in Example 1 and Comparative Example 1 was tested using a three-electrode system. The specific test method was as follows: a platinum electrode was used as the counter electrode, a calomel electrode as the reference electrode, and a 1.0 × 1.0 cm electrode was used. 2 Co2(L1) / NF, Co2(L2) / NF, and Co2(L1)@Co2(L2) / NF are the working electrodes.

[0073] Figure 5 The Co2(L1), Co2(L1)@Co2(L2) of Example 1 and the Co2(L2) of Comparative Example 1 are at 1 mA / cm 2 The constant current charge-discharge diagram (GCD) at the current density.

[0074] from Figure 5 It can be seen that the Co2(L1)@Co2(L2) / NF electrode has the longest discharge time.

[0075] Figure 6 The Co2(L1)@Co2(L2) of Example 1 of this invention is used at a current density of 1-30 mA / cm². 2 The constant current charge-discharge diagram (GCD) is shown below.

[0076] from Figure 6 It can be seen that the Co2(L1)@Co2(L2) electrode has a clear discharge plateau, the curve has good symmetry under different current densities, and it has excellent rate performance.

[0077] Figure 7 The image shows the cyclic voltammetry (CV) curves of Co2(L1)@Co2(L2) in Embodiment 1 of the present invention at scan rates of 5-100mV / s within a voltage range of 0 to 0.6V.

[0078] from Figure 7It can be seen that the peak current of the Co2(L1)@Co2(L2) electrode material increases with the increase of the scan rate. Although the potentials of the oxidation peak and the reduction peak are slightly shifted, the shape of the curve remains basically unchanged, which fully demonstrates that it has a fast current response.

[0079] Figure 8 This is a pseudocapacitance diagram of Co2(L1)@Co2(L2) in Embodiment 1 of the present invention. Among them, (a) is a graph showing the relationship between scan rate and current density, (b) is a graph showing the separation of capacitance / diffusion contribution, and (c) is a statistical graph showing the capacitance control contribution rate at different scan rates.

[0080] from Figure 8 From 'a', we know that the calculated value of 'b' is 0.72, close to 0.5, indicating that diffusion control is dominant. For example... Figure 8 As shown in b, at a scan rate of 1 mV / s, the capacitance control contribution of the Co2(L1)@Co2(L2) / NF electrode is as high as 62%. Furthermore, from... Figure 8 As shown by c, at scan rates of 1, 2, 4, 6, 8, and 10 mV / s, the capacitive control contribution rates of the Co2(L1)@Co2(L2) electrode are 52%, 56%, 62%, 67%, 72%, and 78%, respectively, further indicating that capacitive control is dominant. Therefore, the charge storage capacity of the Co2(L1)@Co2(L2) electrode is mainly achieved through a capacitive control mechanism.

[0081] Figure 9 This is a comparison diagram of the surface capacitance of Co2(L1), Co2(L1)@Co2(L2) in Embodiment 1 of the present invention and Co2(L2) in Comparative Example 1.

[0082] from Figure 9 It can be seen that the Co2(L1)@Co2(L2) electrode of Example 1 has the highest specific capacitance, reaching 4677 mF / cm. 2 .

[0083] Figure 10 Impedance comparison diagram of Co2(L1)@Co2(L2) before and after cycling in Embodiment 1 of the present invention.

[0084] from Figure 10 It can be seen that the inherent impedance in the high-frequency region did not change significantly before and after cycling, the charge transfer impedance in the mid-frequency region remained basically unchanged, and the impedance in the low-frequency region changed slightly. This is because the diffusion behavior is greater after cycling, and charge transfer is more easily controlled by the diffusion behavior. Therefore, the Co2(L1)@Co2(L2) electrode prepared by this invention has good stability.

[0085] Figure 11 Cyclic performance diagram of Co2(L1)@Co2(L2) in Example 1 of this invention.

[0086] from Figure 11 It can be seen that the Co2(L1)@Co2(L2) has a density of 40 mA / cm³. 2 The material still maintains a cycle efficiency of 56.09% after 5000 cycles, indicating that it has good cycle stability.

[0087] Figure 12 The impedance comparison diagram (EIS) is shown for Co2(L1), Co2(L1)@Co2(L2) in Embodiment 1 of the present invention and Co2(L2) in Comparative Example 1.

[0088] from Figure 12 It can be seen that the Co2(L1)@Co2(L2) electrode of Example 1 has excellent conductivity.

[0089] Figure 13 This is the cyclic voltammetry (CV) curve of Co2(L1)@Co2(L2) / / AC in Embodiment 2 of the present invention.

[0090] Cyclic voltammetry curves of Co2(L1)@Co2(L2) / / AC in Example 2 were tested at scan rates of 5-100 mV / s within a voltage range of 0-1.6V. From... Figure 13 It can be seen that the entire CV curve exhibits the mixed characteristics of the two electrodes. With the increase of the scan rate, the peak currents of oxidation and reduction both increase accordingly, and the CV curve remains closed with no change in shape. These characteristics prove that Co2(L1)@Co2(L2) / NF has good reversibility as a cathode material.

[0091] Figure 14 For Example 2 of this invention, Co2(L1)@Co2(L2) / / AC is used at a current density of 1-20 mA / cm². 2 The constant current charge-discharge curve (GCD) at that time.

[0092] from Figure 14 It can be seen that Co2(L1)@Co2(L2) has a clear discharge plateau, the curve has good symmetry under different current densities, and it has excellent rate performance.

[0093] Figure 15 This is the energy density / power density diagram of Co2(L1)@Co2(L2) / / AC in Embodiment 2 of the present invention.

[0094] from Figure 15 It can be seen that the Ragone plot of energy density versus power density shows an energy density of 221.09 W / kg at a power density of 58.61 Wh / kg.

[0095] Figure 16 In Embodiment 2 of the present invention, Co2(L1)@Co2(L2) / / AC is used at a current density of 10 mA / cm². 2 The following is a graph showing the cyclic stability of the circuit.

[0096] Figure 16 In this context, Co2(L1)@Co2(L2) represents the asymmetric supercapacitor prepared using Co2(L1)@Co2(L2) from Example 1 (i.e., Co2(L1)@Co2(L2) / / AC from Example 2).

[0097] from Figure 16 It can be seen that at 10mA / cm 2 After 10,000 cycles at a current density, the capacitance retention of Co2(L1)@Co2(L2) / / AC is 73.27%, which indicates that it has excellent cycle stability.

[0098] In summary, the hollow mercapto-MOF-ON-MOF heterojunction material Co2(L1)@Co2(L2) prepared by this invention has good capacitance performance and excellent stability, and can be used as an active material for supercapacitors.

[0099] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a hollow mercapto MOF-ON-MOF composite material, characterized in that, Includes the following steps: The substrate material, the first cobalt source, 2,5-dihydroxyterephthalic acid and solvent were mixed and heated for the first reaction to obtain a substrate loaded with a metal-organic framework; The substrate with the supported metal-organic framework is mixed with a second cobalt source, 2,5-dimercaptoterephthalic acid and a solvent, and then heated for a second reaction to obtain the hollow mercapto MOF-ON-MOF composite material.

2. The preparation method according to claim 1, characterized in that, The first cobalt source is Co(NO3)2, and the molar ratio of the first cobalt source to 2,5-dihydroxyterephthalic acid is 3:

1.

3. The preparation method according to claim 1, characterized in that, The substrate material is nickel foam; the mass ratio of the substrate material to the first cobalt source is 1.506:

1.

4. The preparation method according to claim 1, characterized in that, The temperature of the first heating reaction was 120°C, and the time was 24 hours.

5. The preparation method according to claim 1, characterized in that, The molar ratio of the second cobalt source to 2,5-dimercaptoterephthalic acid is 3:

1.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the substrate supporting the metal-organic framework to the second cobalt source is 1.506:

1.

7. The preparation method according to claim 1, characterized in that, The second heating reaction was carried out at a temperature of 120°C for 24 hours.

8. The preparation method according to claim 1, characterized in that, The solvent contains N,N-dimethylformamide, ethanol and water.

9. A hollow mercapto MOF-ON-MOF composite material obtained by the preparation method according to any one of claims 1-8.

10. The application of the hollow mercapto MOF-ON-MOF composite material according to claim 9 in the field of supercapacitors.

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