Nickel-cobalt alloy loaded bamboo-shaped carbon nanofiber, method for preparing same, and use thereof

Abstract

The application discloses a bamboo-shaped carbon nanofiber loaded with a nickel-cobalt alloy and a preparation method and application thereof. The method comprises the following steps: firstly, using a hydrothermal method to synthesize spherical nickel-cobalt metal organic frameworks (NiCo-MOFs) from nickel salt and cobalt salt; then, adding the NiCo-MOFs and nickel nitrate into a polyacrylonitrile solution to mix uniformly; using an electrostatic spinning method to prepare a metal organic fiber membrane; and finally, through calcination and carbonization reactions, the bamboo-shaped carbon nanofiber loaded with the nickel-cobalt alloy is prepared. The catalytic synergy of the nickel-cobalt alloy, the excellent electrical conductivity, large specific surface area and structural stability of the carbon nanofiber, and the unique bamboo-shaped structure of the carbon nanofiber enable the formation of an efficient catalytic network inside the bamboo-shaped carbon nanofiber loaded with the nickel-cobalt alloy. The preparation process is easy to control, raw materials are cheap and easy to obtain, and the method is suitable for large-scale production. The bamboo-shaped carbon nanofiber loaded with the nickel-cobalt alloy prepared by the method exhibits excellent water electrolysis oxygen evolution performance, low overpotential, high catalytic activity and durability.

Description

TECHNICAL FIELD

[0001] The present application relates to a nickel-cobalt alloy loaded bamboo-shaped carbon nanofiber and a preparation method and application thereof, and belongs to the technical field of electrochemical catalyst preparation. BACKGROUND

[0002] Fossil energy has long supported the rapid development of the global economy, but its negative impact on the environment is becoming increasingly serious. The burning of fossil fuels has led to environmental problems such as climate change, air pollution, resource depletion, and ecological destruction. Therefore, the increasing demand for energy and environmental pollution has stimulated the research of clean energy such as hydrogen energy. Hydrogen is one of the most promising alternatives to fossil fuels. As a clean energy, hydrogen has the advantages of zero emissions, energy storage, and convenient transportation, which can effectively reduce carbon emissions and air pollution and support the transformation of energy structure. It is widely used in transportation, industry and other fields, providing an important solution for the global sustainable development goals and green low-carbon transformation.

[0003] The methods of water decomposition for hydrogen production include photolysis of water, electrolysis of water, thermal decomposition of water, and biomass catalytic hydrolysis. Photolysis of water uses sunlight to irradiate catalysts to decompose water, but the efficiency is low and is limited by material performance. Thermal decomposition of water decomposes water at high temperature, which consumes a lot of energy and relies on fossil fuels, which may cause carbon emissions. Biomass catalytic hydrolysis decomposes water through biological catalysts, but the efficiency and stability of the catalysts are low, making it difficult to be applied on a large scale. In contrast, electrolysis of water has significant advantages. It decomposes water molecules by electric current, has high efficiency and can be combined with renewable energy to support green hydrogen production. Electrolysis of water can be used as an energy storage means when renewable power is surplus, providing flexible hydrogen supply, and can achieve zero carbon emissions under the drive of renewable energy.

[0004] Although electrolysis of water has advantages that other methods cannot match, electrolysis of water technology also faces a series of challenges. Electrolysis of water is divided into two reaction steps: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The OER reaction is a four-electron transfer process of oxidation reaction, so the reaction kinetics of OER reaction is more difficult than that of HER reaction. Therefore, in recent years, OER reaction has become the focus of researchers.

[0005] Among various materials, noble metal catalysts have achieved excellent electrocatalytic performance in OER, such as platinum, iridium and ruthenium. Although these catalysts have good catalytic performance, there are several obvious problems: 1) high cost, limiting large-scale application; 2) resource scarcity, especially iridium and ruthenium, difficult to sustain supply; 3) poor stability, may cause catalyst dissolution or deactivation in long-term use, reducing catalytic efficiency; 4) low selectivity, may cause side reactions to occur, increasing energy consumption. Therefore, the development of new, low-cost, high-stability catalysts (such as transition metal oxides and carbon-based materials) has become the key to breaking this bottleneck.

[0006] Non-noble metal catalysts such as iron, cobalt, nickel-based catalysts are low in cost, rich in resources, and good in catalytic activity, but due to the lack of support materials, they are easy to agglomerate, fall off, and poor in stability. Among them, metal support materials such as foam nickel have the disadvantages of low surface activity, poor corrosion resistance in acidic and alkaline environments, weak bonding force between the catalyst and the support material, and poor structural stability. Carbon-based support materials such as carbon nanotubes, carbon cloth, graphene and the like have good electrical conductivity and strong chemical stability, and can enhance stability, but the surface area of these materials is small, and they are prone to deformation under high current density, and lack mechanical strength, which may lead to catalyst failure during long-term operation. These deficiencies limit the long-term application effect of carbon-based materials in water electrolysis, so further optimization of material design has become the current research focus. SUMMARY

[0007] The purpose of the present application is to provide a nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber and its preparation method and application in view of the deficiencies in the prior art. The method first uses a hydrothermal method to prepare a nickel-cobalt organic framework derivative, and then adds it and nickel nitrate to a polyacrylonitrile solution and stirs thoroughly to prepare carbon nanofibers. The preparation process of the method is easy to control, and the raw materials are cheap and easy to obtain, suitable for large-scale production. The catalytic synergy of the nickel-cobalt alloy, the excellent electrical conductivity, large specific surface area and structural stability of the carbon nanofiber. At the same time, the NiCo alloy obtained by calcining NiCo-MOFs at high temperature is loaded on the carbon nanofiber to successfully prepare a bamboo-shaped morphology. It is precisely due to the unique bamboo-shaped structure that an efficient catalytic network is formed inside the nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber. The bamboo-shaped nickel-cobalt alloy carbon nanofiber material prepared by this method not only enhances its structural stability, but also exposes a large number of active sites, enhances its electrical conductivity, reduces the overpotential in the catalytic process, and improves the ion diffusion and electron transfer rate. The preparation method is simple, has excellent catalytic activity and durability, and thus obtains better OER performance.

[0008] One of the technical solutions of the present application provides a preparation method of a nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber, and the steps are as follows:

[0009] a. Dissolve polyvinylpyrrolidone (PVP), nickel nitrate hexahydrate and cobalt nitrate hexahydrate in N,N-dimethylformamide (DMF) respectively and stir uniformly to obtain PVP solution, nickel nitrate solution and cobalt nitrate solution respectively; add the prepared cobalt nitrate solution, nickel nitrate solution and trimesic acid to the PVP solution at the same time, stir uniformly to obtain a mixed solution;

[0010] b. Transfer the mixed solution prepared in step a to a high-pressure kettle, place it in an oven and heat for reaction;

[0011] c. After the reaction is completed, the reactor is taken out and naturally cooled, and the solid reaction product is collected by centrifugation, washed and dried to obtain purple spherical nickel-cobalt metal organic framework (NiCo-MOFs) powder;

[0012] d. Polyacrylonitrile (PAN) is added to DMF and heated and stirred to fully mix and dissolve, then nickel nitrate hexahydrate is added and heated and stirred to fully dissolve; then the NiCo-MOFs prepared in step c is added and heated and stirred to ensure uniform dispersion of the NiCo-MOFs in the solution;

[0013] e. The mixed solution obtained in step d is placed on an electrospinning machine and electrospun on aluminum foil to obtain a uniform purple fiber film;

[0014] f. The fiber film obtained in step e is peeled off and dried on aluminum foil, then placed in a muffle furnace for reaction to obtain a black-brown fiber film;

[0015] g. The black-brown fiber film obtained in step f is placed in a tube furnace for heating and reaction to finally obtain black nickel-cobalt alloy-loaded bamboo-shaped carbon nanofibers (NiCo@Ni-CNF).

[0016] Further, in step a, the concentration of the polyvinylpyrrolidone (PVP) solution is 0.0167-0.0333 g / mL; the concentration of the nickel nitrate solution is 0.1-0.2 mM; the concentration of the cobalt nitrate solution is 0.1-0.133 mM; the amount of the cobalt nitrate solution, the nickel nitrate solution, and the PVP solution is 15 mL: 15 mL: 0.1-0.2 g: 30 mL; and the stirring time is 30-40 min;

[0017] Further, in step b, the autoclave is preferably a stainless steel autoclave with a polytetrafluoroethylene liner; the heating reaction temperature is 130-160 ℃, and the time is 6-10 h;

[0018] In some specific embodiments, the volume of the polytetrafluoroethylene liner stainless steel autoclave in step b is 100 mL;

[0019] Further, in step c, the washing and drying is washing with anhydrous ethanol 3-5 times to remove impurities; the washed solid product is dried in an oven; the drying temperature is 60-80 ℃, and the time is 8-12 h; in some specific embodiments, the oven in step c is a vacuum oven;

[0020] Further, the amount of the polyacrylonitrile (PAN), DMF, nickel nitrate hexahydrate and NiCo-MOFs in step d is 0.5-1.5 g: 10 mL: 0.1-0.5 g: 0.1-0.5 g; the temperature of the heating and stirring is 60-90℃; the time of the first two heating and stirring is 2-4 h, and the time of the stirring after adding the NiCo-MOFs is 20-24 h.

[0021] Further, in step e, the mixed solution is first moved into a syringe with a stainless steel needle, and then placed on an electrospinning machine during electrospinning; the voltage of the electrospinning is 0.1-0.5 V, and the pushing speed of the syringe pump is 0.05-0.1 mm / min.

[0022] Further, the drying in step f is preferably performed in a vacuum oven; the temperature of the drying is 50-70℃, and the time is 8 h; the temperature of the reaction in the muffle furnace is 200-300℃, and the time is 1-3 h.

[0023] Further, the heating reaction in step g is performed in an inert gas environment, and the inert gas is preferably nitrogen; the temperature of the heating reaction is 700-900℃, and the time is 1-3 h.

[0024] The second technical solution of the present application provides a nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber prepared by the above technical solution.

[0025] The third technical solution of the present application provides an application of the above nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber in electrolytic water oxygen evolution, wherein the nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber is used as a catalyst in electrolytic water oxygen evolution.

[0026] Compared with the prior art, the method has the following obvious and substantial characteristics and advantages:

[0027] (1) The process of the present application is simple, and the reaction conditions are mild. The transition metal-based NiCo-MOFs are generated by hydrothermal reaction, and then mixed into a nickel-doped electrospinning solution for spinning to prepare the nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber (NiCo@Ni-CNF).

[0028] (2) The synthesis method is green and environmentally friendly, and the raw materials are cheap and easy to obtain, which is suitable for large-scale production needs.

[0029] (3) The bamboo-shaped nickel-cobalt alloy carbon nanofiber material prepared by the present application has good electrolytic water hydrogen evolution performance, exhibits low overpotential, high catalytic activity and durability. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A scanning electron microscope (SEM) photo of the bamboo-shaped nickel-cobalt alloy carbon nanofiber prepared in the embodiment of the present application;

[0031] Figure 2 An X-ray diffraction (XRD) spectrum of the bamboo-shaped nickel-cobalt alloy carbon nanofiber prepared in the embodiment of the present application;

[0032] Figure 3 A linear sweep voltammetry (LSV) curve of the bamboo-shaped nickel-cobalt alloy carbon nanofiber prepared in the embodiment of the present application;

[0033] Figure 4 A current-time (i-t) curve of the bamboo-shaped nickel-cobalt alloy carbon nanofiber prepared in the embodiment of the present application in the constant potential test in the OER performance test. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solutions of the present application, the present application will be described in detail below in conjunction with specific embodiments. It should be pointed out that the following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These all belong to the protection scope of the present application.

[0035] All raw materials of the present application are not particularly limited in source, and can be purchased on the market or prepared according to the conventional method well known to those skilled in the art.

[0036] Example 1: A bamboo-shaped carbon nanofiber loaded with nickel-cobalt alloy

[0037] The process and steps of the preparation method of the bamboo-shaped carbon nanofiber loaded with nickel-cobalt alloy provided in the present embodiment are as follows:

[0038] a. First, 0.8 g of polyvinylpyrrolidone (PVP) was dissolved in 30 mL of N,N-dimethylformamide (DMF) and stirred for 30 min to prepare a polyvinylpyrrolidone solution (PVP solution). 1.5 mmol of nickel nitrate hexahydrate and 1.5 mmol of cobalt nitrate hexahydrate were respectively dissolved in 15 mL of DMF and stirred for 30 min to obtain a nickel nitrate solution and a cobalt nitrate solution, respectively. The prepared 15 mL of cobalt nitrate solution, 15 mL of nickel nitrate solution, and 0.15 g of trimesic acid were simultaneously added to the PVP solution, stirred for 30 min, and mixed uniformly to obtain a mixed solution.

[0039] b. The mixed solution prepared in step a was transferred to a 100 mL polytetrafluoroethylene inner liner stainless steel autoclave, placed in an oven, and heated at 150°C for 6 h.

[0040] c. After the reaction was completed, the reaction kettle was removed and allowed to cool naturally, and the solid reaction product was collected by centrifugation and washed with anhydrous ethanol three times to remove impurities. The washed solid product was placed in a 60°C vacuum oven overnight to dry, obtaining a purple powder of nickel-cobalt metal organic framework (NiCo-MOFs).

[0041] d. 1.0 g of polyacrylonitrile (PAN) was added to 10 mL of DMF and heated and stirred at 80°C for 2 h to fully mix and dissolve, and then 0.15 g of nickel nitrate hexahydrate was added and continued to be heated and stirred at 80°C for 2 h to completely dissolve. 0.5 g of NiCo-MOFs obtained in step c was added to the above obtained solution and heated and stirred at 80°C for 20 h to ensure uniform dispersion of NiCo-MOFs in the solution.

[0042] e. The mixed solution obtained in step d was moved into a syringe with a stainless steel needle and placed on an electrospinning machine to perform electrospinning on aluminum foil paper, obtaining a uniform purple fiber membrane; the voltage of the electrospinning was 0.22 kV, and the pushing speed of the syringe pump was 0.09 mm / min.

[0043] f. The fiber membrane obtained in step e was peeled off from the aluminum foil paper and placed in a vacuum oven to dry at 60°C for 8 h, and then placed in a muffle furnace to react at 260°C for 2 h, obtaining a black-brown fiber membrane.

[0044] g. The black-brown fiber membrane obtained in step f was placed in a tube furnace and heated and reacted at 800°C under nitrogen for 2 h, finally obtaining a black nickel-cobalt alloy-loaded bamboo-like carbon nanofiber.

[0045] Example 2 Test of the electrocatalytic oxygen evolution reaction (OER) of a nickel-cobalt alloy-loaded bamboo-like carbon nanofiber

[0046] This example is to verify the OER performance of the nickel-cobalt alloy-loaded bamboo-like carbon nanofiber of the present application. An electrochemical workstation (Metrohm Autolab, M204) was used to systematically study the OER performance of the electrode material in a three-electrode system with 1 M KOH as the electrolyte. Hydrogen production performance test: 6 mg of nickel-cobalt alloy carbon nanofiber catalyst, 10 microliters of Nafion, and 300 microliters of water alcohol were placed in a 1 mL reagent bottle, ultrasonic for 1 h, and then dropped onto a nickel foam (NF) and ensured that the drop-coating area was 1*1 cm 2After drying, the prepared foam is clamped on the working electrode, and the electrochemical performance test is carried out in a three-electrode system, and the electrolyte is 1M potassium hydroxide. The counter electrode used in this embodiment is a stone mill stick electrode, and the reference electrode is a mercury / mercury oxide electrode with the model number R501-A, which are both purchased from Shanghai Yueci Electronics Company. The specific steps include the following steps:

[0047] All electrodes are immersed in 1M KOH electrolyte for more than 8h before electrochemical test, and CV scanning is performed at a potential interval of 0-0.8V (vs. Hg / HgO) at a scanning speed of 100mV s -1 for 50 cycles to ensure that the surface active material has reached an electrochemically stable state during subsequent testing. At the same time, the stability test is carried out at a current density of 20 mA cm -2 , and the current is timed for potential testing. All potentials in this patent are converted into reversible hydrogen electrode potential (RHE) according to the formula E RHE = E Hg / HgO +0.059×pH +0.098.

[0048] Figure 1 The scanning electron microscope (SEM) photo of the bamboo-shaped nickel-cobalt alloy carbon nanofiber prepared in the embodiment of the application can be seen that the material forms a bamboo-shaped morphology, and the NiCo-MOfs derivative is uniformly distributed therein.

[0049] Figure 2 The X-ray diffraction (XRD) spectrum of the bamboo-shaped nickel-cobalt alloy carbon nanofiber prepared in the embodiment of the application is shown, and by comparing with the NiCo alloy standard PDF card (PDF#04-004-8490), it can be seen that the NiCo-MOFs derivative is successfully synthesized and successfully loaded in the nickel-doped carbon nanofiber.

[0050] Figure 3 The linear sweep voltammetry curve (LSV) of the bamboo-shaped nickel-cobalt alloy carbon nanofiber prepared in this embodiment is shown, and the experiment is carried out at a scanning speed of 5mV s -1 in a potential interval of 0.8-0V (vs. Hg / HgO) by negative scanning. It can be seen that the starting overpotential of the material is small, close to 0mV. And at a current density of 10mA cm -2 , the overpotential is only 248mV, which has a lower overpotential and exhibits excellent OER performance, exceeding most OER electrocatalysts.

[0051] Figure 4The current-time (i-t) curve of the OER potentiostatic test of the bamboo-shaped nickel-cobalt alloy carbon nanofiber still has a nearly 90% initial current retention rate after 200 h of continuous catalysis, and has excellent cycle stability.

[0052] The foregoing description of the embodiments is for the purpose of enabling a person with ordinary skill in the art to understand and use the invention. It is apparent to a person skilled in the art that various modifications can be made to the embodiments and the general principles described herein can be applied to other embodiments without departing from the scope of the invention. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of the present invention.

Claims

1. A method for preparing bamboo-like carbon nanofibers supported on a nickel-cobalt alloy, characterized in that, The preparation method is as follows: a. Dissolve polyvinylpyrrolidone, nickel nitrate hexahydrate and cobalt nitrate hexahydrate in N,N-dimethylformamide respectively, and stir until uniform, to obtain a polyvinylpyrrolidone solution, a nickel nitrate solution and a cobalt nitrate solution respectively; add the prepared cobalt nitrate solution, nickel nitrate solution and trimesic acid into the polyvinylpyrrolidone solution simultaneously, and stir until uniform to obtain a mixed solution; b. Transfer the mixed solution prepared in step a into an autoclave, and place it in an oven for heating reaction; c. After the reaction is completed, take out the reaction kettle, and after it is naturally cooled, centrifugally collect the solid reaction product, wash and dry it to obtain purple spherical NiCo-MOFs powder; d. Add polyacrylonitrile into N,N-dimethylformamide, heat and stir to fully mix and dissolve, then add nickel nitrate hexahydrate into it, continue to heat and stir to completely dissolve; then add the NiCo-MOFs prepared in step c into it, heat and stir to ensure that the NiCo-MOFs are uniformly dispersed in the solution; e. Place the mixed solution obtained in step d on an electrostatic spinning machine, and perform electrostatic spinning on aluminum foil to obtain a uniform purple fiber membrane; f. After the fiber membrane obtained in step e is peeled off from the aluminum foil and dried, then place it in a muffle furnace for reaction to obtain a black brown fiber membrane; g. Place the black brown fiber membrane obtained in step f in a tube furnace for heating reaction, and finally obtain a black nickel and cobalt alloy loaded bamboo joint carbon nanofiber.

2. The method according to claim 1, wherein the nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber is prepared by the steps of: (a) preparing a bamboo-shaped carbon nanofiber; (b) preparing a nickel-cobalt alloy precursor; and (c) loading the nickel-cobalt alloy precursor onto the bamboo-shaped carbon nanofiber. In step a, the concentration of the polyvinylpyrrolidone solution is 0.0167-0.0333 mM; the stirring time is 30-40 min.

3. The method according to claim 1, wherein the nickel-cobalt alloy-loaded bamboo-shaped carbon nanofiber is prepared by the steps of: (a) preparing a nickel-cobalt alloy precursor solution; (b) preparing a bamboo-shaped carbon nanofiber; (c) mixing the nickel-cobalt alloy precursor solution and the bamboo-shaped carbon nanofiber; and (d) drying the mixture. In step b, the heating reaction temperature is 130-160℃, and the time is 6-10 h.

4. The method for preparing bamboo-like carbon nanofibers supported on nickel-cobalt alloy according to claim 1, characterized in that, In step c, the drying temperature is 60-80℃, and the time is 8-12 h.

5. The method for preparing bamboo-like carbon nanofibers supported on nickel-cobalt alloy according to claim 1, characterized in that, In step d, the amount of polyacrylonitrile, N,N-dimethylformamide, nickel nitrate hexahydrate and NiCo-MOFs is 0.5-1.5 g: 10 mL: 0.1-0.5 g: 0.1-0.5 g; the heating and stirring temperature is 60-90℃; the heating and stirring time is 2-4 h for the first two times, and the stirring time after adding NiCo-MOFs is 20-24 h.

6. The method for preparing bamboo-like carbon nanofibers supported on nickel-cobalt alloy according to claim 1, characterized in that, In step e, the pushing speed of the syringe pump is 0.05-0.1 mm / min.

7. The method for preparing bamboo-like carbon nanofibers supported on nickel-cobalt alloy according to claim 1, characterized in that, In step f, the drying temperature is 50-70℃, and the time is 8 h; the reaction temperature in the muffle furnace is 200-300℃, and the time is 1-3 h.

8. The method for preparing bamboo-like carbon nanofibers supported on nickel-cobalt alloy according to claim 1, characterized in that, In step g, the heating reaction is carried out in an inert gas environment; the heating reaction temperature is 700-900℃, and the time is 1-3 h.

9. A nickel-cobalt alloy-loaded bamboo-like carbon nanofiber, characterized by, The nickel and cobalt alloy loaded bamboo joint carbon nanofiber is prepared by the method of any one of items 1-8.

10. Use of the nickel-cobalt alloy-loaded bamboo-like carbon nanofiber according to claim 9 in the oxygen evolution of electrolysis water, characterized by, The nickel and cobalt alloy loaded bamboo joint carbon nanofiber is used as a catalyst in water electrolysis oxygen evolution.

Images