A co s2 / coo heterojunction nanosheet three-dimensional assembled carbon nanofiber material and a preparation method and application thereof

Abstract

The application discloses a CoS2 / CoO heterojunction nanosheet three-dimensional assembled carbon nanofiber material and a preparation method and application thereof, and the preparation method comprises the following steps: S1, preparing ZIF-67 nanoparticles; S2, preparing ZIF-67 / PAN mixed sol, and obtaining a solid carbon fiber film through electrostatic spinning; S3, growing Co(OH)2 / PAN from a template in the presence of Co(NO3)2; and S4, pre-oxidizing in an air atmosphere at 200-300 DEG C, and then performing heat treatment on a reaction product and a sulfur source in a nitrogen atmosphere at a mass ratio of 1:(10-40) at 300-600 DEG C, so that the CoS2 / CoO heterojunction nanosheet three-dimensional assembled carbon nanofiber material is obtained. The PAN used in the method is cheap and easy to obtain, and compared with a traditional method for preparing an electrocatalyst material of a zinc-air battery, the method has the advantages of simple process, low cost, simple operation and large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oxygen evolution catalysts, and particularly relates to a CoS2 / CoO heterojunction nanosheet stereoscopic assembly carbon nanofiber material and a preparation method and application thereof. BACKGROUND

[0002] At present, due to the serious consumption of earth resources and the aggravation of environmental pollution problems, it is imperative to develop sustainable clean energy. The storage and conversion technology of sustainable energy is particularly important. Among them, the rechargeable zinc-air battery has attracted widespread attention due to its high energy density, good safety, environmental friendliness and relatively low preparation cost. However, because OER has the characteristics of slow kinetics and high reaction energy barrier, in order to make substantial progress in this technology, it is necessary to develop a low-cost, high-efficiency and durable electrocatalyst to accelerate the kinetics of the anode oxygen evolution reaction (OER). So far, noble metal oxides (Ir / Ru-based oxides) have been recognized as the most advanced OER catalysts in commercial applications. However, due to the problems of high price, poor stability and easy poisoning, its large-scale application is limited. Therefore, the development of OER catalysts with low cost, high activity and good stability is the key to realize its practical application in zinc-air batteries.

[0003] Transition metal-based nanomaterials, such as cobalt-based catalysts, have become a good substitute for noble metal catalysts due to their abundant reserves, low price and adjustable electronic structure. Transition metal sulfides, in which S atoms are doped into the metal lattice, cause an increase in metal atomic spacing and a decrease in d-band gap, have good catalytic activity for OER, especially CoS2 as an electrocatalyst material for OER shows unique metal catalytic efficiency. However, the insufficient exposure of active sites and poor intrinsic activity of CoS2 still make its overall OER performance far inferior to commercial noble metal catalysts, so it is difficult to meet the actual requirements. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a CoS2 / CoO heterojunction nanosheet stereoscopic assembly carbon nanofiber material and a preparation method and application thereof. The method is simple and universal, and the cost is low. The obtained CoS2 / CoO heterojunction nanosheet stereoscopic assembly carbon nanofiber material exhibits excellent activity and stability as an oxygen evolution catalyst material.

[0005] To solve the problems of the prior art, the technical scheme adopted by the present application is as follows:

[0006] A preparation method of a CoS2 / CoO heterojunction nanosheet stereoscopic assembly carbon nanofiber material, comprising the following steps:

[0007] Step 1, preparing ZIF-67 nanoparticles;

[0008] Step 2: Prepare ZIF-67 / PAN mixed sol by combining ZIF-67 nanoparticles from Step 1 with PAN, and obtain solid carbon fiber film by electrospinning.

[0009] Step 3: In the presence of Co(NO3)2, ZIF-67 / PAN grows from the template to Co(OH)2 / PAN;

[0010] Step 4: After pre-oxidation in air at 200~300℃, the reaction product and sulfur source are heat-treated in nitrogen atmosphere at 300~600℃ with a mass ratio of 1:10~1:40 to obtain the carbon nanofiber material of three-dimensional assembly of CoS2 / CoO heterojunction nanosheets.

[0011] As an improvement, the preparation method of the ZIF-67 / PAN mixed sol is as follows: ZIF-67 is dissolved in DMF solution to obtain ZIF-67 solution; PAN is added to the ZIF-67 solution and stirred evenly to obtain the ZIF-67 / PAN mixed sol.

[0012] A further improvement is that the mass ratio of ZIF-67 to PAN in the PAN solution is 1:5 to 1:10.

[0013] As an improvement, the electrospinning conditions in step 2 are: temperature 15-35℃, syringe injection speed 0.5-1.0 mL / h. -1 Voltage 10-30kV.

[0014] As an improvement, in step 4, the sulfur source is sublimed sulfur, the mass ratio of the reaction product to sublimed sulfur is 1:10 to 1:40, and the heating rate is 1 to 20 °C / min.

[0015] A carbon nanofiber material with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets prepared by the above preparation method.

[0016] As an improvement, the carbon nanofiber material assembled from the CoS2 / CoO heterojunction nanosheets exhibits a regular and uniform morphology. The heterojunction nanosheets are ultrathin and uniformly cover the surface of the carbon nanofibers. This hierarchical structure of the ultrathin nanosheets and carbon nanofibers effectively promotes mass and charge transfer, exposes more active sites, and enhances the intrinsic activity of the catalyst.

[0017] The application of a carbon nanofiber material, which is a three-dimensionally assembled CoS2 / CoO heterojunction nanosheet as described above, as a catalyst in the alkaline oxygen evolution reaction.

[0018] The reaction principle of this invention is as follows: using ZIF-67 as the metal source and polyacrylonitrile as the carbon and nitrogen source, ZIF-67 / PAN composite fiber material is pre-prepared via electrospinning. In the presence of Co(NO3)2, a mild etching process occurs on the surface of ZIF-67. After pre-oxidation stabilization, low-temperature phosphating is performed to prepare a carbon nanofiber material with three-dimensionally assembled CoS2 / CoO heterojunction nanosheets. Furthermore, the heterojunction nanosheets are composed of CoS2 and CoO forming a heterojunction interface, resulting in a material with high oxygen evolution reaction catalytic activity and excellent stability.

[0019] The carbon nanofiber material with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets prepared in this invention has the following advantages:

[0020] CoS2 / CoO heterojunction nanosheets are ultrathin, and two-dimensional nanomaterials have extremely high specific surface area and expose the most surface atoms.

[0021] The carbon nanofiber material assembled from CoS2 / CoO heterojunction nanosheets has a one-dimensional carbon nanofiber structure, which gives the catalyst material a large specific surface area, inhibits the aggregation of metal particles, provides more active sites, and is conducive to the occurrence of the reaction. The one-dimensional carbon nanofiber structure can directionally promote the rapid transport of electrons and ions, improve the catalytic reaction rate, and promote the reaction of reactants and the rapid production of products.

[0022] The carbon nanofiber material, which is a three-dimensional assembly of CoS2 / CoO heterostructure nanosheets, assembles heterostructured nanosheets on nanofibers. The synergistic effect between the two Co-based species can easily reduce the energy barrier required for intermediate adsorption / desorption during the OER process. The fiber structure provides sufficient channels for charge transport and mass diffusion, and exhibits structural integrity to resist phase transition, thus endowing the material with activity and stability.

[0023] Beneficial effects:

[0024] Compared with existing technologies, the preparation method and application of carbon nanofiber materials based on the three-dimensional assembly of CoS2 / CoO heterojunction nanosheets of this invention have the following advantages:

[0025] Carbon nanofiber materials with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets were prepared by electrospinning technology that is simple and can be mass-produced, combined with low-temperature vulcanization technology. The selected PAN is inexpensive and readily available. Compared with the traditional method for preparing oxygen evolution electrocatalyst materials, this method is easy to operate, low in cost, and has a large output, which can realize large-scale production.

[0026] The prepared product has a regular morphology, with CoS2 / CoO heterojunction nanosheets uniformly covering the surface of one-dimensional carbon nanofiber material. As a result, the prepared material has the characteristics of multi-level composite structure, multiple active sites, low overpotential and good stability. Compared with conventional cobalt-based materials, the carbon nanofiber material with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets has superior structural characteristics and compositional advantages. It is a highly promising oxygen evolution electrocatalyst material with broad prospects for future applications in the energy industry.

[0027] Metal oxide species exhibit better hydrophilicity and good OH- oxidase activity in alkaline media. - The binding energy is beneficial to the dissociation and adsorption of water. The combination of CoS2 and CoO in this invention can enhance the electrocatalytic activity of the catalyst. The carbon nanofiber material obtained by three-dimensional assembly of CoS2 / CoO heterojunction nanosheets has good application prospects. Attached Figure Description

[0028] Figure 1 This is a low-magnification SEM image of the carbon nanofiber material assembled from CoS2 / CoO heterojunction nanosheets prepared in Example 1.

[0029] Figure 2 The magnified SEM image of the carbon nanofiber material assembled from negative CoS2 / CoO heterojunction nanosheets prepared in Example 1;

[0030] Figure 3 The magnified TEM image of the carbon nanofiber material assembled from CoS2 / CoO heterojunction nanosheets prepared in Example 1;

[0031] Figure 4 XRD patterns of carbon nanofiber materials stereoscopically assembled from CoS2 / CoO heterojunction nanosheets prepared in Example 1 and Comparative Examples 1 and 2.

[0032] Figure 5 Comparison of the basic oxygen evolution LSV of carbon nanofiber material assembled from CoS2 / CoO heterostructure nanosheets prepared in Example 1 and RuO2.

[0033] Figure 6 The image shows a comparison of the Tafel curves of the carbon nanofiber material assembled from CoS2 / CoO heterostructure nanosheets prepared in Example 1 and RuO2 under alkaline oxygen evolution conditions.

[0034] Figure 7 This is the chronoamperometry spectrum of the carbon nanofiber material assembled from CoS2 / CoO heterojunction nanosheets prepared by the method in Example 1;

[0035] Figure 8The electrochemical active area (ECSA) spectra of carbon nanofiber materials stereo-assembled from CoS2 / CoO heterojunction nanosheets prepared by the method of Example 1 and Comparative Examples 1 and 2 are shown.

[0036] Figure 9 These are the electrochemical impedance spectroscopy (EIS) spectra of carbon nanofiber materials stereo-assembled from CoS2 / CoO heterostructure nanosheets prepared by the method in Example 1 and Comparative Examples 1 and 2.

[0037] Figure 10 The graphs show the alkaline oxygen evolution performance test results of Example 1 and Comparative Examples 1 and 2. Detailed Implementation

[0038] The present invention will now be described in detail with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0039] Unless otherwise specified, the experimental methods described in the embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available. Example 1

[0040] A method for preparing a carbon nanofiber material with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets includes the following steps:

[0041] Preparation of ZIF-67 nanoparticles:

[0042] Solution A was obtained by dissolving 2.37 g cobalt nitrate and 2 g PVP in 200 mL methanol solution. Solution B was obtained by dissolving 2.65 g dimethylimidazole and 200 μL triethylamine in 200 mL methanol solution. Solution A and solution B were then mixed and stirred, and allowed to stand. The precipitate was collected by centrifugation, washed with methanol, and dried.

[0043] Preparation of ZIF-67 / PAN mixed sol:

[0044] Weigh 0.5g of ZIF-67 and add it to 5mL of DMF solution to obtain ZIF-67 solution, and sonicate for 1h. Then add 0.42g of PAN and mechanically stir at room temperature for 12h to mix it evenly, thus obtaining purple ZIF-67 / PAN mixed sol;

[0045] Preparation of carbon nanofibers with three-dimensional assembly of CoS2 / CoO heterostructure nanosheets by electrospinning:

[0046] The purple ZIF-67 / PAN mixed sol obtained in step 2) was electrospinned (the mixed solution was placed in a 5mL plastic syringe. The electrospinning voltage was 20kV, the distance between the nozzle and the collector was 15cm, and the injection speed was set to 0.15mm / min). -1 ), to obtain solid carbon fiber thin film material;

[0047] The solid carbon fiber film material was immersed in 0.1 mol / L cobalt nitrate ethanol solution for 2 hours, dried, and pre-oxidized in air at 200°C for 2 hours to obtain the precursor.

[0048] The precursor and sulfur source were placed downstream and upstream of the same ceramic state at a mass ratio of 1:20. Under N2 atmosphere, the temperature was increased to 300℃ at a heating rate of 2℃ / min and held at this temperature for 1h. Then, it was naturally cooled to room temperature to obtain carbon nanofiber material with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets, named CoS2 / CoO@CNFs.

[0049] The carbon nanofiber materials assembled from CoS2 / CoO heterojunction nanosheets prepared in the above examples were physically characterized by TEM, SEM, and XRD.

[0050] From low-magnification SEM (e.g.) Figure 1 As can be seen, the synthesized material is a hierarchical carbon fiber structure covered with heterogeneous nanosheets. Further magnified SEM images (such as...) Figure 2 It can be seen that the CoS2 / CoO heterojunction nanosheets are uniformly distributed on the carbon nanofibers.

[0051] TEM images (e.g.) Figure 3 This further confirmed the ultrathin nature of the nanosheets, and the structure was consistent with the SEM results. Figure 4 The XRD patterns show that when the precursor-to-sulfur source mass ratio is 1:20, the diffraction peaks of the material perfectly match the standard cards for CoS2 and CoO (PDF#41-1471, PDF#43-1004), proving the successful preparation of the CoS2 / CoO heterojunction. When the precursor-to-sulfur source mass ratio is 1:35, the material is CoS2 (PDF#41-1471). Without a sulfur source, the material is a pure-phase oxide, Co3O4.

[0052] Figure 5 This is a comparison chart of LSV (Laser Vapor Variable Value) obtained from alkaline oxygen evolution performance tests of the material and RuO2. The chart shows that at 10 mAcm⁻¹... -2 The overpotential of this material at the current density is only 304 mV. (Tafel curve) Figure 6 This indicates that the Tafel slope of this material is only 69.9 mV dec.-1 . Figure 7 The chronoamperometry results of the carbon nanofiber catalyst, which is a three-dimensionally assembled CoS2 / CoO heterojunction nanosheet, show that the catalyst performance essentially did not decline after 55 hours of chronoamperometry testing. Example 1 exhibits the smallest electrochemical active area, at 12.11 mF·cm⁻¹. -2 ,like Figure 8 As shown. Figure 9 Electrochemical impedance spectroscopy (EIS) tests confirmed that the material prepared in Example 1 had the lowest charge transfer resistance. Figure 10 The LSV comparison chart obtained by testing the alkaline oxygen evolution performance of the material with Comparative Examples 1 and 2 proves that the construction of heterostructure helps to improve oxygen evolution performance. Example 2

[0053] Except for step 2), where the amount of ZIF-67 added is 0.3g, the rest is the same as in Example 1. Example 3

[0054] Except for step 2), where the amount of ZIF-67 added is 0.8g, the rest is the same as in Example 1. Example 4

[0055] Except for the soaking time of 1 hour in step 4), the rest is the same as in Example 1. Example 5

[0056] Except for the soaking time of 3 hours in step 4), the rest is the same as in Example 1. Example 6

[0057] Except for step 4), where the temperature is increased to 250°C, the rest is the same as in Example 1. Example 7

[0058] Except for step 4), where the temperature is increased to 300°C, the rest is the same as in Example 1. Example 8

[0059] Except for step 5), where the mass ratio of the precursor to the sulfur source is 1:15, the rest is the same as in Example 1. Example 9

[0060] Except for step 5), where the mass ratio of the precursor to the sulfur source is 1:30, the rest is the same as in Example 1. Example 10

[0061] Except for step 5), where the programmed heating rate is changed to 5℃ / min, the rest is the same as in Example 1. Example 11

[0062] Except for step 2), where the temperature is increased to 300°C, the rest is the same as in Example 1.

[0063] Comparative Example 1

[0064] The only difference from Example 1 is that in step 5), the mass ratio of the precursor to the sulfur source is 1:35, while the other implementation conditions remain unchanged. It is named CoS2@CNFs.

[0065] Comparative Example 2

[0066] The only difference from Example 1 is that a sulfur source is not used in step 5), while the other implementation conditions remain the same, and it is named Co3O4@CNFs.

[0067] In summary, the present invention provides a simple and mass-producible electrospinning method for preparing an electrocatalyst with excellent OER performance. The selected reactants are inexpensive and readily available, and the process is simple and easy to implement. The sample is a one-dimensional carbon nanofiber material covered by heterojunction nanosheets. The heterostructure and hierarchical structure enhance the activity and stability of the catalyst, resulting in excellent oxygen evolution performance and broad application prospects.

[0068] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any simple changes or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing carbon nanofiber materials with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets, characterized in that, Includes the following steps: Step 1: Prepare ZIF-67 nanoparticles; Cobalt nitrate and PVP were dissolved in methanol to obtain solution A, and dimethylimidazole and triethylamine were dissolved in methanol to obtain solution B. Solution A and solution B were then mixed and stirred, and allowed to stand. The precipitate was collected by centrifugation, washed with methanol, and dried. Step 2: Dissolve ZIF-67 in DMF solution to obtain ZIF-67 solution, then add PAN and stir until homogeneous to obtain ZIF-67 / PAN mixed sol. Electrospinning is then performed to obtain a solid carbon fiber film. The mass ratio of ZIF-67 to PAN is 1:5 to 1:

10. The electrospinning conditions are: temperature 15-35℃, syringe injection speed 0.5-1.0 mL / h. -1 Voltage 10-30kV; Step 3: In the presence of Co(NO3)2, ZIF-67 / PAN grows from the template to Co(OH)2 / PAN; Step 4: After pre-oxidation in air at 200~300℃, the reaction product and sulfur source are heat-treated in nitrogen atmosphere at 300~600℃ with a mass ratio of 1:10~1:40 to obtain carbon nanofiber material with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets. The sulfur source is sublimed sulfur, the mass ratio of reaction product to sublimed sulfur is 1:10~1:40, and the heating rate is 1~20℃ / min.

2. A carbon nanofiber material based on the three-dimensional assembly of CoS2 / CoO heterojunction nanosheets prepared according to claim 1, characterized in that, The carbon nanofiber material assembled from the CoS2 / CoO heterojunction nanosheets has a regular and uniform morphology. The heterojunction nanosheets are ultrathin and uniformly cover the surface of the carbon nanofibers.

3. Application of carbon nanofiber materials with three-dimensional assembly of CoS2 / CoO heterojunction nanosheets prepared by the preparation method described in claim 1 in oxygen evolution catalysts.

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