Preparation method of bimetallic oxide loaded carbon-based nano composite fiber membrane

Abstract

The invention belongs to the field of new materials, and particularly relates to a preparation method of a bimetallic oxide loaded carbon-based nano composite fiber membrane. The preparation method comprises the following steps: dissolving polyacrylonitrile and a phenolic resin aqueous solution in different proportions in N, N-dimethylformamide, uniformly stirring to obtain a spinning solution, obtaining a polymer nanofiber membrane through an electrostatic spinning method, heating the fiber membrane in air for pre-oxidation, and then performing high-temperature carbonization in a nitrogen atmosphere to obtain the polymer nanofiber membrane. And finally, growing a layer of NiCo2O4 with a nanosheet structure on the surface of the porous carbon nanofiber membrane by adopting a hydrothermal method, so as to obtain the bimetallic oxide loaded carbon-based nano composite fiber membrane. The bimetallic oxide loaded porous carbon nanofiber membrane prepared by the invention has the advantages of high stability, large specific surface area, good electrolyte infiltration, large specific capacity and the like, and has potential application prospects in the fields of catalysis, energy storage and the like.

Description

Technical Field

[0001] The invention belongs to the field of new materials, and in particular relates to a method for preparing a bimetallic oxide-loaded carbon-based nanocomposite fiber membrane. Background Art

[0002] With the development of renewable energy and the increasing popularity of electronic products, the demand for energy storage devices is increasing. Among various energy devices, supercapacitors have the advantages of good stability, fast charging and discharging speed, low heat generation, and long life. They have broad application prospects in battery replacement, power management, energy harvesting and other fields. In the field of electrochemical energy storage and conversion technology, supercapacitors are known for their practicality and versatility. The difference between supercapacitors and other electrochemical energy storage systems is that they provide a unique high-power balancing capability that exceeds that of batteries; compared with traditional capacitors, their energy density is also improved. Due to the miniaturization and portability of fiber supercapacitors, they show considerable potential in the field of smart electronic devices.

[0003] Carbon nanofibers have attracted widespread attention due to their unique one-dimensional structure, good conductivity and self-supporting properties. Carbon nanofibers can not only load active materials, but also improve the electrochemical performance of materials. Among various porous nanomaterials, porous carbon nanomaterials have attracted much attention because they combine the advantages of carbon nanostructures and nanoscale materials. They have broad application prospects in many application fields such as catalyst supports, adsorbents, drug delivery / release systems, electrochemical energy storage, etc. Porous nanomaterials have a large specific surface area and a stable pore structure. Therefore, depending on their use and application, their surface can be functionalized for a variety of purposes because they have a high aspect ratio and sufficient surface area, which is ideal in many practical applications. The production of precursor nanofibers is relatively easy due to the convenient electrospinning method.

[0004] Metal compounds are very suitable for the preparation of electrode materials due to their excellent properties such as high theoretical capacity, wide voltage range, good electrochemical stability, simple preparation method and low cost. However, in actual applications, the problem of low conductivity has arisen. At the same time, since only the surface and near-surface materials can contact the electrolyte, the internal compounds cannot participate in the redox reaction, resulting in low utilization of active materials, making the actual specific capacitance lower than the theoretical specific capacitance. Composite porous carbon nanomaterial films with high pseudocapacitance materials is a feasible strategy for preparing high-performance flexible electrode materials. Since the composite does not use adhesives, it can effectively reduce the "dead volume" and production cost of the electrode material, and the gaps between adjacent nanostructures can provide sufficient space to withstand the volume changes of the active material during charging and discharging, thereby enhancing the cycle stability of the electrode material. Summary of the Invention

[0005] To address the above problems, the present invention provides a method for preparing a bimetallic oxide-loaded carbon-based nanocomposite fiber membrane, which solves the following problems: ① Polymer fibers prepared from phenolic resin (PR) and polyacrylonitrile (PAN) can produce pores of varying sizes within the carbon fibers due to phase separation and varying residual carbon content during pre-oxidation and carbonization, thereby increasing the specific surface area of the material and enhancing the utilization rate of the active material. ② PAN and PR can be doped with nitrogen and oxygen atoms during the carbonization process, enhancing the wettability between the electrolyte and the electrode material. ③ During the pre-oxidation and carbonization processes, the PAN molecular chains can transform from chain to trapezoidal, and the migration of PR within and outside the fibers can achieve sufficient cross-linking of the fiber membrane, all of which improve the mechanical stability of the fiber membrane. ④ The prepared carbon nanofiber membrane is a partially graphitized carbon material with good electrical conductivity. ⑤ The flake-like bimetallic oxide is tightly coated on the carbon fiber surface, which not only increases the specific capacity of the electrode material, but also provides a buffer space for the volume change of the active material during charge and discharge, thereby enhancing the cycling stability of the electrode material.

[0006] A method for preparing a bimetallic oxide-loaded carbon-based nanocomposite fiber membrane, characterized in that the composite fiber membrane has a porous core-shell structure, the inner layer of the fiber membrane is carbon nanofibers co-doped with O and N elements, and the outer layer of the fiber membrane is a lamellar structure formed by bimetallic oxides. The preparation process comprises the following steps: 1) Preparation of polymer nanofiber membranes: 6-9.6 wt% polyacrylonitrile and 2.4-6 wt% phenolic resin aqueous solution were dissolved in N,N-dimethylformamide and stirred to form a uniform electrospinning solution, from which polymer nanofiber membranes were obtained by electrospinning. 2) Preparation of carbon nanofiber membrane: The polymer nanofiber membrane prepared in step 1) was heated in air at 2°C min -1 The temperature was heated to 260-280℃ and kept at this temperature for 2h for pre-oxidation, and then transferred to a nitrogen atmosphere at a rate of 5℃min -1 The temperature is raised to 800-1000°C at a rate of 1000°C and kept at this temperature for 2 hours for high-temperature carbonization to obtain a porous carbon nanofiber membrane with high conductivity; 3) Preparation of bimetallic oxide-supported carbon-based nanocomposite fiber membrane: Ni(NO3)2·6H2O, Co(NO3)2·6H2O and urea at a molar ratio of 1:2:8 were completely dissolved in ethanol to prepare a hydrothermal solution, which was then transferred to a high-pressure reactor. The carbon nanofiber membrane prepared in step 2) was immersed in the above solution. After the high-pressure reactor was sealed, it was kept at 120°C for 2-12 hours, cooled to room temperature, and then taken out and washed with deionized water and ethanol. After drying, it was evaporating at 2°C min in a nitrogen atmosphere. -1The carbon-based nanocomposite fiber membrane loaded with bimetallic oxides was obtained by heating the mixture to 350°C at a heating rate of 10000 ℃ and keeping the temperature for 2 hours for annealing treatment.

[0007] The present invention has the following beneficial technical effects: ① PAN and PR are selected as carbon nanofiber precursors. While introducing N and O atom doping, the specific surface area of the material can be increased and the pore distribution can be optimized, thereby improving the material's conductivity and wettability with the electrolyte; ② During the oxidation and carbonization process, the transformation of the PAN chain configuration and the cross-linking of PR inside and outside the fiber can improve the mechanical properties of the membrane layer and enhance the cycle stability; ③ The sheet-like bimetallic oxide is tightly coated on the carbon fiber surface, which not only increases the specific capacity of the electrode material, but also the gaps between the sheets and between the fibers provide a buffer space for the volume changes of the active material during the charge and discharge process, thereby enhancing the cycle stability of the electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a scanning electron microscope photograph of the bimetallic oxide-loaded carbon-based nanocomposite fiber membrane obtained in Example 1.

[0009] Figure 2 This is a scanning electron microscope photograph of the bimetallic oxide-loaded carbon-based nanocomposite fiber membrane obtained in Example 2.

[0010] Figure 3 This is a scanning electron microscope photograph of the porous carbon nanofiber membrane obtained in Comparative Example 1.

[0011] Figure 4 This is a scanning electron microscope photograph of the bimetallic oxide-loaded carbon-based nanocomposite fiber membrane obtained in Comparative Example 2. DETAILED DESCRIPTION

[0012] The principles and features of the present invention are described below in conjunction with embodiments. The examples listed are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0013] Example 1: 1) Preparation of polymer nanofiber membrane: Dissolve 1.5g of polyacrylonitrile and 1.5ml of a 70wt% aqueous phenolic resin solution in 19ml of N,N-dimethylformamide solvent and stir at room temperature for 10 hours to obtain a uniform spinning solution. The solution was drawn into a dry, clean syringe and placed in the injection device of a spinning machine for electrospinning. After spinning, the solution was dried in a 60°C oven. 2) Preparation of carbon nanofiber membrane: The nanofiber membrane prepared in step 1) was cut into 2 cm × 2 cm fiber membrane pieces and incubated in air at 2 ° C min -1The temperature was raised to 260℃ and kept at this temperature for 2h for pre-oxidation, then the sample was taken out after cooling to room temperature. Then the sample was put into a tube furnace and heated at 5℃ min-1 under nitrogen atmosphere. -1 The heating rate was raised to 1000 °C and kept at this temperature for 2 h for high temperature carbonization, and finally a porous carbon nanofiber membrane was obtained; 3) Preparation of bimetallic oxide-supported carbon-based nanocomposite fiber membrane: 0.29 g nickel nitrate hexahydrate, 0.58 g cobalt nitrate hexahydrate, 0.48 g urea and 35 mL ethanol were mixed and transferred to an autoclave. The porous carbon nanofiber membrane prepared in step 2) was immersed in the autoclave. After the autoclave was sealed, it was kept at 120 ° C for 8 h, cooled to room temperature, and then taken out and washed with deionized water and ethanol. After drying, it was heated in a nitrogen atmosphere at 2 ° C min -1 The carbon-based nanocomposite fiber membrane loaded with bimetallic oxides was obtained by heating the mixture to 350°C at a heating rate of 10000 ℃ and keeping the temperature for 2 hours for annealing treatment.

[0014] Example 2: 1) Preparation of polymer nanofiber membrane: proceed as in Example 1; 2) Preparation of carbon nanofiber membrane: proceed as in Example 1; 3) Preparation of bimetallic oxide-supported carbon-based nanocomposite fiber membrane: 0.58 g nickel nitrate hexahydrate, 1.16 g cobalt nitrate hexahydrate, 0.96 g urea and 35 mL ethanol were mixed and transferred to an autoclave. The carbon nanofiber membrane prepared in step 2) was immersed in the above solution. After the autoclave was sealed, it was kept at 120 ° C for 8 h, cooled to room temperature and then taken out, washed with deionized water and ethanol, dried and heated in a nitrogen atmosphere at 2 ° C min -1 The carbon-based nanocomposite fiber membrane loaded with bimetallic oxides was obtained by heating the mixture to 350°C at a heating rate of 10000 ℃ and keeping the temperature for 2 hours for annealing treatment.

[0015] Comparative Example 1: 1) Preparation of polymer nanofiber membrane: proceed as in Example 1; 2) Preparation of carbon nanofiber membrane: proceed as in Example 1.

[0016] Comparative Example 2: 1) Preparation of polymer nanofiber membrane: Dissolve 1.8g of polyacrylonitrile in 13.2ml of N,N-dimethylformamide and stir at room temperature for 10 hours to obtain a uniform spinning solution. The solution was then drawn into a clean, dry syringe and placed in the injection device of a spinning machine for electrospinning. After spinning, the solution was dried in a 60°C oven. 2) Preparation of carbon nanofiber membrane: proceed as in Example 2; 3) Preparation of bimetallic oxide-supported carbon-based nanocomposite fiber membrane: proceed as in Example 2.

[0017] Performance testing: 1) Preparation of the working electrode: The bimetallic oxide-loaded carbon-based nanocomposite fiber membrane was cut into discs of the same diameter using a 9 mm punching die, and the mass of the discs was weighed using a balance. A nickel foam with a diameter of 10 mm was cut using a punching machine to serve as the current collector of the electrode material. Subsequently, a 30 mm long and 6 mm wide nickel foam strip was cut using scissors. The nickel foam was ultrasonically treated with acetone, anhydrous ethanol, and deionized water for 30 minutes to wash the oxide layer on the surface of the nickel foam, and finally dried in an oven at 60°C for 3 hours. The weighed carbon fiber disc was taken out and placed between two pieces of nickel foam. The two nickel foam discs were clamped with the notch of the long strip of nickel foam. The assembled nickel foam was pressed at a pressure of 10 MPa for 30 seconds using a tablet press to prepare the working electrode, and then soaked in 6 M KOH solution for more than 8 hours before use; 2) Electrochemical Performance Test: Electrochemical performance tests were conducted using a three-electrode system on an electrochemical workstation. The reference electrode was a saturated calomel electrode, and the counter electrode was a platinum mesh electrode. The constant current charge-discharge (GCD) method was used, and the mass specific capacitance of the electrode material was calculated based on the GCD curve. The calculation formula is as follows: ; Where, C: specific capacitance (F g -1 ); I: discharge current of active material (A); m: mass of active material (mg); Δt: discharge time (s); ΔV (V): voltage window. The specific surface area of the nanofibers prepared in the examples and comparative examples and the corresponding electrodes at 1 A g -1 The specific capacity values measured at current density are listed below.

[0018]

[0019] The above examples show that the carbon fibers prepared with PAN and PR dual polymers have a larger specific surface area, and at the same time, due to the introduction of diatomic doping, they are given a higher specific capacity. In the specific capacity of electrode materials, the contribution of bimetallic oxides is the most obvious, and the specific capacity of composite carbon fiber electrodes containing bimetallic oxides is much greater than that of pure composite carbon fibers. When the conditions for coating bimetallic oxides are the same, the carbon fiber base sample electrodes prepared with dual polymers not only have a large specific surface area, but also a high specific capacity. This shows that the bimetallic oxide-loaded carbon-based nanocomposite fiber membrane prepared by the present invention has a higher specific surface area and a larger specific capacity when used as a supercapacitor electrode material.

[0020] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a bimetallic oxide-supported carbon-based nanocomposite fiber membrane, characterized in that: The composite fiber membrane has a porous core-shell structure, the inner layer of the fiber membrane is carbon nanofibers co-doped with O and N elements, and the outer layer of the fiber membrane is a lamellar structure formed by bimetallic oxides. The preparation process includes the following steps: ① Preparation of polymer nanofiber membrane: 6-9.6 wt% polyacrylonitrile and 2.4-6 wt% phenolic resin aqueous solution were dissolved in N,N-dimethylformamide and stirred to form a uniform electrospinning solution, and polymer nanofiber membrane was obtained by electrospinning; ② Preparation of carbon nanofiber membrane: The polymer nanofiber membrane prepared in step ① was placed in air at 2°C min -1 The temperature was heated to 260-280℃ and kept at this temperature for 2h for pre-oxidation, and then transferred to a nitrogen atmosphere and heated at 5℃ min -1 The carbon nanofiber membrane was heated to 800-1000℃ at a heating rate of 1000℃ and kept warm for 2h for high-temperature carbonization to obtain a porous carbon nanofiber membrane with high conductivity; ③ Preparation of bimetallic oxide-loaded carbon-based nanocomposite fiber membrane: Ni(NO3)2·6H2O, Co(NO3)2·6H2O and urea with a molar ratio of 1:2:8 were completely dissolved in ethanol to prepare a hydrothermal solution, which was then transferred to a high-pressure reactor. The carbon nanofiber membrane prepared in step ② was immersed in the above solution. After the high-pressure reactor was sealed, it was kept at 120℃ for 2-12h, cooled to room temperature, taken out, washed with deionized water and ethanol, dried, and condensed in a nitrogen atmosphere at 2℃ min -1 The carbon-based nanocomposite fiber membrane loaded with bimetallic oxides was obtained by heating the mixture to 350°C at a heating rate of 10000 ℃ and keeping the temperature for 2 hours for annealing treatment.

2. The method for preparing a bimetallic oxide-supported carbon-based nanocomposite fiber membrane according to claim 1, wherein: The prepared polymer fiber membrane has a smooth surface layer and a core layer that is an inhomogeneous dispersed phase.

3. The method for preparing a bimetallic oxide-supported carbon-based nanocomposite fiber membrane according to claim 1, wherein: The prepared carbon nanofiber membrane has a porous structure with a pore size distribution between 1.5-10nm and a specific surface area distribution between 185-367m 2 g -1 The carbon nanofiber membrane is doped with N and O atoms, the nitrogen atom doping amount is between 3.62-2.36at%, and the oxygen atom doping amount is between 5.51-6.64at%. The carbon nanofiber membrane has a certain degree of graphitization.

4. The method for preparing a bimetallic oxide-supported carbon-based nanocomposite fiber membrane according to claim 1, wherein: The bimetallic oxide-loaded carbon-based nanocomposite fiber membrane has a porous structure with a pore size distribution of 1.8 nm to 130.2 nm, an adjustable Ni content of 2.62 to 9.31 at%, and an adjustable Co content of 4.56 to 16.21 at%.

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