Preparation method of nitrogen-doped carbon quantum dot modified CoS / CoFe (CN) 5NO composite material for positive electrode of hybrid supercapacitor and application of nitrogen-doped carbon quantum dot modified CoS / CoFe (CN) 5NO composite material

Abstract

The invention belongs to the technical field of nano composite materials, and relates to a preparation method and application of a nitrogen-doped carbon quantum dot modified CoS / CoFe (CN) 5NO composite material for a hybrid supercapacitor positive electrode, and the preparation method comprises the steps: firstly dispersing nitrogen-doped carbon quantum dots in ethylene glycol, then adding a cobalt source and a sulfur source, and carrying out solvothermal reaction to prepare a CoS precursor; and reacting the precursor with sodium nitroferricyanide under a hydrothermal condition to finally obtain the composite material. The method is simple in process and mild in condition. In the prepared composite material, the nitrogen-doped carbon quantum dots and the CoFe (CN) 5NO are uniformly attached to the surfaces of the CoS nanosheets, and the nitrogen-doped carbon quantum dots, the CoFe (CN) 5NO and the CoS nanosheets generate a synergistic effect, so that the electrical conductivity, the structural stability and the electrochemical activity of the material are remarkably improved. When the material is used as a positive electrode of a hybrid supercapacitor, the specific capacity under the current density of 1A / g reaches up to 609C / g, the capacity retention rate under the high rate of 20A / g reaches 76.2%, and the material shows excellent energy storage performance and rate capability and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of nanocomposite materials technology, and relates to composite electrode materials, particularly to a method for preparing a nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor and its application. Technical Background

[0002] The continued consumption of fossil fuels and the escalating environmental problems have made the development of efficient energy storage technologies particularly urgent. Meanwhile, renewable energy sources such as wind and hydropower, due to their abundant reserves and environmental friendliness, are considered important ways to alleviate the energy crisis; their inherent intermittency and instability further drive the demand for new energy storage technologies. Supercapacitors, with their advantages of rapid charging and discharging capabilities, superior power density, and ultra-long cycle life, demonstrate unique value in the energy storage field. Based on differences in electrode materials, supercapacitors can be divided into two categories: symmetrical and hybrid. Hybrid supercapacitors combine the characteristics of capacitive negative electrode materials and battery-type positive electrode materials, while widening the device's operating voltage window, thereby effectively improving energy storage performance and optimizing energy density.

[0003] The selection and composition of electrode materials directly determine the electrochemical performance of hybrid supercapacitors. In recent years, transition metal sulfides have attracted widespread attention due to their multiple advantages, including high electronic conductivity, multi-electron reaction characteristics, low electronegativity, and excellent electrochemical activity. However, their poor cycle stability and insufficient rate performance still limit their application in high-performance energy storage devices. Metal-organic frameworks (MOFs), with their large specific surface area, controllable structure, extremely high crystallinity, and abundant active sites, have been proven to be suitable as electrode materials for supercapacitors. Therefore, these materials can simultaneously meet several key requirements for supercapacitor electrode materials, thereby synergistically achieving high power density and energy density. On the other hand, carbon-based materials, due to their good conductivity and stable double-layer energy storage behavior, are often used as capacitive anodes or carrier materials. Among them, nitrogen-doped carbon quantum dots exhibit unique advantages in the energy storage field due to their high specific surface area, nanoscale effect, and abundant surface functional groups. As an auxiliary electrode material, the unique structure and physicochemical properties of nitrogen-doped carbon quantum dots can effectively expand the contact area between the electrolyte and the electrode, promote ion migration and electron transport, and thus improve the energy storage performance of the device. Hybridizing nitrogen-doped carbon quantum dots with cobalt-based sulfides can effectively improve the conductivity and structural stability of electrodes. However, performance improvements achieved solely through simple composite strategies remain limited, and further breakthroughs are needed to optimize their effectiveness.

[0004] Therefore, developing a simple method for preparing composite electrode materials that can significantly improve the conductivity, structural stability, and overall electrochemical performance of transition metal sulfides is of great research significance and application value. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the present invention aims to propose a method for preparing a nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor.

[0006] Technical solution

[0007] A method for preparing a nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor includes the following steps:

[0008] S1. Take nitrogen-doped carbon quantum dots and ethylene glycol at a material ratio of 4-12 mg: 35 mL, add nitrogen-doped carbon quantum dots to ethylene glycol and disperse them by ultrasonication to obtain a uniform dispersion.

[0009] S2. Cobalt chloride hexahydrate and thiourea were added to the above dispersion at a material ratio of 1 mmol: 2 mmol. After being ultrasonically treated to ensure full dispersion, the mixture was transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 180–220 °C for 8–12 h. After the reaction was completed, the precipitate was centrifuged, washed, and dried to obtain a black powder precursor.

[0010] S3. Take sodium nitrosoferricyanide powder and distilled water at a material ratio of 5-15 mg: 20 mL. Add the sodium nitrosoferricyanide powder to the distilled water and stir to form a mixed solution. Add the above black powder precursor to the mixed solution at a material ratio of 50 mg: 20 mL. After ultrasonic treatment to make it uniformly dispersed, transfer it to a polytetrafluoroethylene-lined reactor and carry out a solvothermal reaction at 100-140℃ for 8-12 h. After the reaction is completed, the precipitate is separated by centrifugation, washed and dried to obtain nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material.

[0011] In a preferred embodiment of the present invention, in step S1, the material ratio is 8 mg:35 mL.

[0012] In a preferred embodiment of the present invention, in step S2, the solvothermal reaction conditions are 200°C for 10 h.

[0013] In a preferred embodiment of the present invention, in step S3, the material ratio of sodium nitrosoferricyanide to distilled water is 10 mg: 20 mL.

[0014] The nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material prepared by the method disclosed in this invention has a morphology in which nitrogen-doped carbon quantum dots and CoFe(CN)5NO are uniformly attached to the surface of CoS nanosheets.

[0015] The second objective of this invention is to disclose a hybrid supercapacitor comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material.

[0016] Application Experiment Steps:

[0017] The electrochemical performance of nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material was tested using a three-electrode system in 6M KOH electrolyte.

[0018] The reference electrode was a standard mercury / mercury oxide electrode, the counter electrode was a platinum sheet, and the working electrode was prepared as follows: nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material, polytetrafluoroethylene binder and acetylene black conductive agent were mixed in a mass ratio of 8:1:1 and dispersed in ethanol; after thorough stirring to form a uniform slurry, it was directly coated on the surface of nickel foam, compacted under a pressure of 10 MPa, and then dried at 60°C for 8 h to obtain the working electrode.

[0019] The nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material prepared in this invention has the following advantages:

[0020] (1) Nitrogen-doped carbon quantum dots can increase surface active sites and enhance electrochemical activity due to their high specific surface area and nano-size effect.

[0021] (2) Nitrogen-doped carbon quantum dot nanoparticles can improve the conductivity and electrochemical stability of CoS / CoFe(CN)5NO nanosheets.

[0022] (3) CoFe(CN)5NO has a high specific surface area, tunable pore size and structure, and can provide specific active sites for Faraday reactions. These active sites help to realize electrochemically driven ion transport and exchange within the pores, thereby synergistically improving the overall electrochemical performance of the composite material.

[0023] These advantages enable the composite material to exhibit excellent electrochemical performance, showing high specific capacity (test data from Example 1, specific capacity of 609 C / g at a current density of 1 A / g) and excellent rate performance (specific capacity of 464 C / g at a current density of 20 A / g) when used as a cathode material for hybrid supercapacitors.

[0024] Beneficial effects

[0025] This invention successfully constructs a multi-component composite material by effectively combining nitrogen-doped carbon quantum dots with CoS and CoFe(CN)5NO. The preparation process is simple, the conditions are mild, and it has good potential for industrial implementation. Thanks to the synergistic effect between the components, when used as the positive electrode of a hybrid supercapacitor, it achieves a specific capacitance of 609 C / g at a current density of 1 A / g, and maintains a specific capacitance of 464 C / g even at a high current density of 20 A / g, with a capacity retention rate of 76.2% (464 / 609≈76.2%). It shows potential application prospects in hybrid supercapacitor positive electrode materials. Attached Figure Description

[0026] Figure 1 X-ray diffraction (XRD) pattern of the nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material prepared in Example 1;

[0027] Figure 2 X-ray photoelectron spectroscopy (XPS) of the nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material prepared in Example 1;

[0028] Figure 3 Transmission electron microscopy (TEM) image of the nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material prepared in Example 1;

[0029] Figure 4 Charge-discharge curves of the nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material prepared in Example 1 in 6M KOH. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments to enable those skilled in the art to better understand the present invention, but the present invention is not limited to the following embodiments.

[0031] Example 1

[0032] A method for preparing a nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor includes: ultrasonically dispersing 8 mg of nitrogen-doped carbon quantum dots in 35 mL of ethylene glycol to obtain a uniform dispersion; subsequently, adding 1 mmol of cobalt chloride hexahydrate and 2 mmol of thiourea to the dispersion, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 200 °C for 10 h; after centrifugation, washing, and drying, a black powder precursor is obtained. Adding 10 mg of sodium nitrosoferricyanide powder to 20 mL of distilled water and stirring to form a mixed solution; adding 50 mg of the black powder precursor to this solution, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 120 °C for 10 h; after centrifugation, washing, and drying, the resulting precipitate is obtained to obtain the nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material.

[0033] The nitrogen-doped carbon quantum dots were prepared by hydrothermal method using citric acid and ethylenediamine as raw materials, and their average particle size was 3 nm.

[0034] Figure 1 The image shows the XRD pattern of the composite material prepared in this embodiment. All diffraction peaks in the image correspond to hexagonal CoS (standard card: 03-065-8977) and cubic CoFe(CN)5NO (standard card: 97-041-7544), indicating that the CoS / CoFe(CN)5NO composite material was successfully prepared.

[0035] Figure 2 The XPS image of the composite material prepared in this embodiment clearly shows that the composite material is composed of Fe, Co, S, C, N and O elements, indicating that CoS, CoFe(CN)5NO and nitrogen-doped carbon quantum dots were successfully composited together.

[0036] Figure 3 The TEM image of the composite material prepared in this embodiment shows that CoFe(CN)5NO nanoparticles with a diameter of about 50 nm are uniformly attached to the surface of CoS nanosheets. In the high-resolution TEM image, the lattice stripes of 0.22 nm, 0.19 nm and 0.25 nm correspond to the (100), (102) and (400) crystal planes of nitrogen-doped carbon quantum dots, CoS and CoFe(CN)5NO, respectively.

[0037] Figure 4 The charge-discharge curves of the composite material prepared in this embodiment are shown in 6M KOH. The specific capacity of the composite material is 609 C / g at a current density of 1 A / g and 464 C / g at a current density of 20 A / g.

[0038] Example 2

[0039] A method for preparing a nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor includes: ultrasonically dispersing 8 mg of nitrogen-doped carbon quantum dots in 35 mL of ethylene glycol to obtain a uniform dispersion; subsequently, adding 1 mmol of cobalt chloride hexahydrate and 2 mmol of thiourea to the dispersion, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 200 °C for 10 h; after centrifugation, washing, and drying, a black powder precursor is obtained. Adding 5 mg of sodium nitrosoferricyanide powder to 20 mL of distilled water and stirring to form a mixed solution; adding 50 mg of the black powder precursor to this solution, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 120 °C for 10 h; after centrifugation, washing, and drying, the resulting precipitate is obtained to obtain the nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material.

[0040] Its specific capacity is 506 C / g at a current density of 1 A / g and 400 C / g at a current density of 20 A / g.

[0041] Example 3

[0042] A method for preparing a nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor includes: ultrasonically dispersing 8 mg of nitrogen-doped carbon quantum dots in 35 mL of ethylene glycol to obtain a uniform dispersion; subsequently, adding 1 mmol of cobalt chloride hexahydrate and 2 mmol of thiourea to the dispersion, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 200 °C for 10 h; after centrifugation, washing, and drying, a black powder precursor is obtained. Adding 15 mg of sodium nitrosoferricyanide powder to 20 mL of distilled water and stirring to form a mixed solution; adding 50 mg of the black powder precursor to this solution, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 120 °C for 10 h; after centrifugation, washing, and drying, the resulting precipitate is obtained to obtain the nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material.

[0043] Its specific capacity is 469 C / g at a current density of 1 A / g and 364 C / g at a current density of 20 A / g.

[0044] Example 4

[0045] A method for preparing a nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor includes: ultrasonically dispersing 4 mg of nitrogen-doped carbon quantum dots in 35 mL of ethylene glycol to obtain a uniform dispersion; subsequently, adding 1 mmol of cobalt chloride hexahydrate and 2 mmol of thiourea to the dispersion, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 200 °C for 10 h; after centrifugation, washing, and drying, a black powder precursor is obtained. Adding 10 mg of sodium nitrosoferricyanide powder to 20 mL of distilled water and stirring to form a mixed solution; adding 50 mg of the black powder precursor to this solution, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 120 °C for 10 h; after centrifugation, washing, and drying, the resulting precipitate is obtained as the nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material.

[0046] Its specific capacity is 551 C / g at a current density of 1 A / g and 413 C / g at a current density of 20 A / g.

[0047] Example 5

[0048] A method for preparing a nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor includes: ultrasonically dispersing 12 mg of nitrogen-doped carbon quantum dots in 35 mL of ethylene glycol to obtain a uniform dispersion; subsequently, adding 1 mmol of cobalt chloride hexahydrate and 2 mmol of thiourea to the dispersion, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 200 °C for 10 h; after centrifugation, washing, and drying, a black powder precursor is obtained. Adding 10 mg of sodium nitrosoferricyanide powder to 20 mL of distilled water and stirring to form a mixed solution; adding 50 mg of the black powder precursor to this solution, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 120 °C for 10 h; after centrifugation, washing, and drying, the resulting precipitate is obtained as the nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material.

[0049] Its specific capacity is 478 C / g at a current density of 1 A / g and 382 C / g at a current density of 20 A / g.

[0050] Example 6

[0051] A method for preparing a nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor includes: ultrasonically dispersing 8 mg of nitrogen-doped carbon quantum dots in 35 mL of ethylene glycol to obtain a uniform dispersion; subsequently, adding 1 mmol of cobalt chloride hexahydrate and 2 mmol of thiourea to the dispersion, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 180 °C for 10 h; after centrifugation, washing, and drying, a black powder precursor is obtained. Adding 10 mg of sodium nitrosoferricyanide powder to 20 mL of distilled water and stirring to form a mixed solution; adding 50 mg of the black powder precursor to this solution, ultrasonically dispersing the mixture, and then transferring it to a polytetrafluoroethylene-lined reactor for a solvothermal reaction at 120 °C for 10 h; after centrifugation, washing, and drying, the resulting precipitate is obtained as the nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material.

[0052] Its specific capacity is 576 C / g at a current density of 1 A / g and 442 C / g at a current density of 20 A / g.

[0053] The above description is an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon quantum dot-modified CoS / CoFe(CN)5NO composite material for the positive electrode of a hybrid supercapacitor, characterized in that, Includes the following steps: S1. Take nitrogen-doped carbon quantum dots and ethylene glycol at a material ratio of 4-12 mg: 35 mL, add nitrogen-doped carbon quantum dots to ethylene glycol and disperse them by ultrasonication to obtain a uniform dispersion. S2. Cobalt chloride hexahydrate and thiourea were added to the above dispersion at a material ratio of 1 mmol: 2 mmol. After being ultrasonically treated to ensure full dispersion, the mixture was transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 180–220 °C for 8–12 h. After the reaction was completed, the precipitate was centrifuged, washed, and dried to obtain a black powder precursor. S3. Take sodium nitrosoferricyanide powder and distilled water at a material ratio of 5-15 mg: 20 mL. Add the sodium nitrosoferricyanide powder to the distilled water and stir to form a mixed solution. Add the above black powder precursor to the mixed solution at a material ratio of 50 mg: 20 mL. After ultrasonic treatment to make it uniformly dispersed, transfer it to a polytetrafluoroethylene-lined reactor and carry out a solvothermal reaction at 100-140℃ for 8-12 h. After the reaction is completed, the precipitate is separated by centrifugation, washed and dried to obtain nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material.

2. The method for preparing the nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material for the positive electrode of the hybrid supercapacitor according to claim 1, characterized in that: In step S1, the material ratio is 8 mg: 35 mL.

3. The method for preparing the nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material for the positive electrode of the hybrid supercapacitor according to claim 1, characterized in that: In step S2, the solvothermal reaction conditions are 200°C for 10 hours.

4. The method for preparing the nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material for the positive electrode of the hybrid supercapacitor according to claim 1, characterized in that: In step S3, the material ratio of sodium nitrosoferricyanide to distilled water is 10 mg: 20 mL.

5. A nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material, characterized in that: The composite material is prepared by any one of the preparation methods described in claims 1-4.

6. The composite material according to claim 5, characterized in that: The nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material has a morphology in which nitrogen-doped carbon quantum dots and CoFe(CN)5NO are uniformly attached to the surface of CoS nanosheets.

7. A hybrid supercapacitor, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that: The positive electrode comprises the nitrogen-doped carbon quantum dot modified CoS / CoFe(CN)5NO composite material as described in claim 5 or 6.

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