Carbon nanotube / carbon fiber composite material loaded with ferrocobalt nanoparticles and preparation method of carbon nanotube / carbon fiber composite material

Abstract

The invention belongs to the technical field of catalysts, and relates to a cobalt-iron nanoparticle-loaded carbon nanotube / carbon fiber composite material and a preparation method thereof.The preparation method comprises the following steps that a potassium ferricyanide aqueous solution and ZIF-67 turbid liquid are stirred at the room temperature to react, and ZIF-coated PBA powder is obtained; dissolving the ZIF-coated PBA powder and polyacrylonitrile in an organic solvent, and performing electrostatic spinning to obtain a ZIF-coated PBA fiber membrane; and calcining the pre-oxidized ZIF-coated PBA fiber membrane and dicyandiamide in an inert atmosphere to prepare the composite material disclosed by the invention. According to the preparation method, the completeness of the ZIF-PBA hollow structure is ensured by regulating and controlling the relative dosage and the reaction time of potassium ferricyanide, the ZIF-PBA fiber membrane and dicyandiamide are further subjected to an in-situ vapor deposition reaction, and the carbon nano tubes are successfully loaded on the carbon nano fibers, so that CNT and CNF aggregation can be effectively prevented; the unique hierarchical structure is beneficial for obtaining a larger electrochemical active surface area, shows optimal initial potential, half-wave potential (0.88 V) and limiting current density in ORR reaction, has Tafel slope of less than or equal to 47.05 mV dec-1, and has excellent ORR electro-catalytic performance.

Description

Technical Field

[0001] This invention belongs to the field of oxygen reduction catalytic materials technology, specifically, it relates to a carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles and its preparation method. Background Technology

[0002] Zinc-air batteries (ZABs) convert chemical energy into electrical energy through a chemical reaction between oxygen in the air and metals. ZABs have attracted widespread attention due to their high theoretical energy density and safety. However, the slow oxygen reduction (ORR) reaction kinetics of zinc-air batteries has become a technological bottleneck restricting their application. Therefore, finding and designing highly active, highly stable, and low-cost electrocatalysts is of great significance for the large-scale application of ZABs.

[0003] To accelerate the slow ORR reaction kinetics of zinc-air batteries, it is essential to design high-performance electrocatalysts with multiple active sites. The synergistic effect between active sites on the catalyst surface can accelerate ORR kinetics by lowering the energy barrier of the rate-determining step.

[0004] Existing technology, such as CN 117552187 A, discloses a carbon nanofiber material assembled from CoS2 / CoO heterojunction nanosheets, its preparation method, and its application. The method includes the following steps: S1, preparing ZIF-67 nanoparticles; S2, preparing a ZIF-67 / PAN mixed sol, followed by electrospinning to obtain a solid carbon fiber film; S3, growing Co(OH)2 / PAN from a template in the presence of Co(NO3)2; S4, after pre-oxidation in air at 200–300℃, heat treatment is performed in a nitrogen atmosphere at 300–600℃ with a reaction product to sulfur source at a mass ratio of 1:(10–40), thus obtaining the carbon nanofiber material assembled from CoS2 / CoO heterojunction nanosheets. This method uniformly covers the surface of a one-dimensional carbon nanofiber material with CoS2 / CoO heterojunction nanosheets. The combination of CoS2 and CoO enhances the electrocatalytic activity of the catalyst. This material possesses a multi-level composite structure, numerous active sites, low overpotential, and good stability.

[0005] The carbon nanofiber materials assembled from the aforementioned CoS2 / CoO heterojunction nanosheets are mainly used for oxygen evolution reaction (OER) catalysis rather than ORR reaction catalysis. In addition, this prior art enhances the activity of single metal compounds by constructing heterojunctions, but its active center is singular and the support structure still has certain limitations. Furthermore, CoS2 / CoO heterojunction nanosheets cannot be directly exposed to alkaline electrolytes and are easily corroded, dissolved, and oxidized by the electrolyte, resulting in insufficient stability of the catalyst during use. Summary of the Invention

[0006] To address the problems of existing cobalt-based electrocatalysts, such as single active sites, insufficient stability, and the difficulty in synergistically improving catalytic activity through carbon support mass transfer, this invention aims to provide a carbon nanotube / carbon fiber composite material supported on cobalt-iron nanoparticles and its preparation method. This invention uses a ZIF@PBA fiber membrane as the growth substrate for one-dimensional carbon nanotubes. Under CoFe bimetallic catalysis, dicyandiamide is used to grow secondary one-dimensional carbon nanotubes in situ on the surface of the one-dimensional carbon nanotubes in a high-temperature inert environment, constructing a multi-level structure. The synergistic effect between the one-dimensional carbon nanotubes and the secondary one-dimensional carbon nanotubes facilitates electron transport and reactant diffusion, thereby improving electrocatalytic performance. In the ORR reaction, it exhibits optimal onset potential, half-wave potential (0.88 V), and limiting current density, with a Tafel slope not exceeding 47.05 mV dec. -1 It exhibits good ORR electrocatalytic performance and excellent long-cycle durability in alkaline media.

[0007] Based on the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles, comprising the following steps: S1: Potassium ferricyanide aqueous solution and ZIF-67 suspension were stirred and reacted at room temperature. The reaction product was washed and dried to obtain ZIF@PBA powder. S2: ZIF@PBA powder and polyacrylonitrile are dissolved in an organic solvent to form a spinning solution, and ZIF@PBA fiber membrane is obtained by electrospinning. S3: The ZIF@PBA fiber membrane is pre-oxidized, and the pre-oxidized ZIF@PBA fiber membrane is calcined with dicyandiamide under an inert atmosphere to obtain a carbon nanotube / carbon fiber composite material loaded with cobalt iron nanoparticles.

[0008] By introducing potassium ferricyanide, this invention can not only utilize the difference in interfacial ion exchange rates to form a hollow structure with a larger specific surface area through the Kirkendall effect, but also transform a single cobalt active center into a cobalt-iron bimetallic system with a stronger synergistic effect. This further regulates the d-band center of the active site, reduces the adsorption energy barrier of oxygen intermediates, and enhances ORR activity.

[0009] This invention, through co-calcination with dicyandiamide, not only introduces abundant nitrogen doping but also promotes the vertical or staggered growth of carbon nanotubes on the carbon fiber surface, forming a nitrogen-doped carbon nanotube / carbon fiber three-dimensional hierarchical conductive network. The unique hierarchical structure helps to obtain a larger electrochemically active surface area.

[0010] Compared to existing CoS2 / CoO heterojunction nanosheets which are directly exposed to the electrolyte during use, the cobalt-iron nanoparticles prepared in this invention are encapsulated by in-situ grown graphitized carbon nanoparticles, which can effectively protect the internal metal nanoparticles from corrosion, dissolution and oxidation by the electrolyte during catalysis, and also prevent the agglomeration of metal nanoparticles under high-temperature sintering, thus improving the stability of the catalyst.

[0011] Preferably, the mass ratio of ZIF-67 to potassium ferricyanide in step S1 is 1:1.5 to 2.5.

[0012] Preferably, in step S2, the mass ratio of ZIF@PBA powder to polyacrylonitrile is 2 to 4:3.

[0013] Preferably, the pre-oxidation treatment in step S3 includes heating the ZIF@PBA fiber membrane to 240°C to 260°C in air at a heating rate of 1 to 3°C / min and maintaining it for 1.5 to 2.5 hours.

[0014] Preferably, the calcination in step 3 includes heating the pre-oxidized ZIF@PBA fiber membrane to 500-600°C with dicyandiamide, holding it at that temperature for 2-4 hours, and then annealing it at 700-800°C for 1.5-2.5 hours.

[0015] Preferably, in step S3, the mass ratio of ZIF@PBA fiber membrane to dicyandiamide is 1:5 to 15.

[0016] Preferably, the stirring reaction in step S1 lasts for 2 to 4 hours.

[0017] Secondly, the present invention provides a carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles prepared by the above method.

[0018] Thirdly, the present invention provides the application of the above-mentioned carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles in oxygen reduction catalysts.

[0019] Preferably, the half-wave potential of the ORR electrocatalysis of the carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles is 0.88 V, and the Tafel slope does not exceed 47.05 mVdec. -1 .

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention ensures the integrity of the ZIF@PBA hollow structure by controlling the relative amount of potassium ferricyanide and the reaction time. The intact hollow structure provides sufficient space to mitigate the volume expansion during the cobalt-iron alloying reaction in the pyrolysis process. Furthermore, the intact hollow structure maximizes the exposure of the metal active sites, serving as seed sites for the catalytic growth of CNTs, avoiding the embedding of internal active sites, thus ensuring the accessibility of active sites and structural stability, thereby enhancing ORR activity.

[0021] This invention further involves in-situ vapor deposition of ZIF@PBA fiber membrane with dicyandiamide to successfully load carbon nanotubes onto carbon nanofibers. This not only effectively prevents the aggregation of CNTs and CNFs, but the unique hierarchical structure also helps to obtain a larger electrochemically active surface area. Through its excellent conductivity, specific surface area and chemical durability, it enhances the overall catalytic activity of the composite material.

[0022] The carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles prepared in this invention exhibits a superior half-wave potential (0.88 V) and a Tafel slope not exceeding 47.05 mV dec compared to Pt / C in the ORR reaction. -1 Furthermore, it exhibits excellent cycle stability in alkaline media, making the material of this invention a superior electrocatalyst for ORR. Attached Figure Description

[0023] Figure 1 SEM images of ZIF-67@PBA in Example 1: (a) ZIF@PBA (1:1 3 h), (b) ZIF@PBA (1:2 3 h), (c) ZIF@PBA (1:4 3 h), (d) ZIF@PBA (1:1 6 h), (e) ZIF@PBA (1:2 6 h), (f) ZIF@PBA (1:4 6 h); Figure 2 The XRD patterns of ZIF@PBA and ZIF-67 in Example 1 are shown below. Figure 3 Here is a SEM-EDS image of the CoFe / CNTF sample from Example 1; Figure 4 SEM images of Comparative Example 1 Co / CNTF before calcination (a); SEM images of Comparative Example 1 Co / CNTF after calcination (b, c); SEM images of Example 1 CoFe / CNTF before calcination (d); SEM images of Example 1 CoFe / CNTF after calcination (e, f); Figure 5 SEM images of Comparative Example 2 CoFe / CNT (a) and Comparative Example 3 CoFe / CNF (b) are shown. Figure 6 XRD patterns of Co / CNTF, CoFe / CNTF, and CoFe / CNT (a); Raman spectra of CoFe / CNF, CoFe / CNTF, and CoFe / CNT (b); Figure 7 ORR polarization curves (a) and Tafel curves (b) for CoFe / CNTF, CoFe / CNF, CoFe / CNT, Co / CNTF, and Pt / C; Figure 8 CV curves of CoFe / CNTF (a); polarization curves at different rotational speeds (b); KL curves of CoFe / CNTF (c); calculated electron transfer number (d). Figure 9 The stability test curves for CoFe / CNTF are shown. Detailed Implementation

[0024] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Unless otherwise specified, the experimental methods used in the embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available. Example 1

[0025] This embodiment provides a method for preparing carbon nanotube / carbon fiber composite materials loaded with cobalt-iron nanoparticles, including the following steps: (1) Preparation of ZIF@PBA 100 mg of ZIF-67 cubes were dispersed in 30 mL of ethanol and ultrasonically dispersed for 10 min to obtain an ethanol suspension of ZIF-67.

[0026] Dissolve 200 mg of potassium ferricyanide (K3[Fe(CN)6]) in 10 mL of deionized water to obtain a potassium ferricyanide solution.

[0027] Under magnetic stirring, potassium ferricyanide solution was rapidly poured into an ethanol suspension of ZIF-67, and stirring was continued for 3 h at room temperature. The product was collected by centrifugation and washed three times each with deionized water and ethanol, and dried overnight at 60 °C to obtain ZIF@PBA composite powder.

[0028] (2) Preparation of ZIF@PBA fiber membrane 0.3 g ZIF@PBA powder was dissolved in 3 mL DMF and sonicated for 30 min to form a homogeneous solution. Then, 0.3 g PAN was added to the solution and stirred overnight at room temperature. The resulting viscous liquid was injected into a 10 mL syringe, with the distance between the nozzle and the collector fixed at 18 cm. The DC high voltage was adjusted to 18 kV, and the solution was injected at a rate of 1 mL / h. -1 The liquid inlet speed was adjusted, and a spinning membrane was prepared by electrospinning to obtain a ZIF@PBA fiber membrane.

[0029] (3) Preparation of CoFe / CNTF The 0.1 g ZIF@PBA fiber membrane was placed in a tube furnace and heated to 250°C in air at a heating rate of 1°C / min, and held for 2 h for pre-oxidation to improve the thermal stability of the fiber membrane.

[0030] The pre-oxidized ZIF@PBA fiber membrane was placed at one end of a covered ceramic boat, and 1 g of dicyandiamide was placed at the other end of the ceramic boat. The mixture was heated to 550°C at a heating rate of 2°C / min under a nitrogen atmosphere and held for 3 h. Then it was annealed at 700°C for 2 h to obtain a carbon nanotube / carbon fiber composite material loaded with cobalt iron nanoparticles, abbreviated as CoFe / CNTF.

[0031] In the above reaction process, the mass ratio of ZIF@PBA fiber membrane to dicyandiamide was controlled between 1:5 and 15. This is because the high-temperature decomposition of dicyandiamide can generate abundant carbon and nitrogen sources, which are important reactive gases for catalyzing the growth of carbon nanotubes. Therefore, it is necessary to ensure a sufficient supply of carbon and nitrogen gases to effectively catalyze the in-situ growth of a continuous CNT network on the carbon fiber surface and achieve significant nitrogen doping. When the relative amount of dicyandiamide is low, it is difficult to promote the growth of CNTs, or the generated CNTs are sparse and short, unable to form a continuous three-dimensional network, and the N doping level is also low. If the relative amount of dicyandiamide is too high, it will lead to excessive amorphous carbon covering the surface of CNTs and carbon nanofibers, clogging micropores and mesopores. In summary, the mass ratio of ZIF@PBA fiber membrane to dicyandiamide should be controlled between 1:5 and 15. Too low or too high a relative amount of dicyandiamide will reduce the ORR catalytic activity of the final product.

[0032] During the 550℃ holding stage, the polymer components in the pre-oxidized ZIF@PBA fiber membrane undergo carbonization to form a one-dimensional carbon nanofiber substrate. Simultaneously, cobalt and iron in the ZIF@PBA are reduced and interdiffused to form cobalt-iron alloy nanoparticles, which are uniformly loaded onto the one-dimensional carbon nanofibers. Dicyandiamide, located at the other end of the tube furnace, sublimates and decomposes at high temperature, producing carbon and nitrogen-rich gaseous small molecules, which are transported to the one-dimensional carbon nanofiber substrate region by an inert gas stream. During the 700℃ annealing stage, the cobalt-iron alloy nanoparticles loaded on the one-dimensional carbon nanofibers are fully activated, forming metastable semi-liquid particles. Carbon and nitrogen in the gas phase are captured by the highly dynamic surface of the cobalt-iron alloy nanoparticles to form a Co-C alloy. When the carbon concentration exceeds its solubility limit, carbon atoms precipitate from the liquid phase and, guided by cobalt-iron catalysis, self-assemble and grow on the one-dimensional carbon nanofibers to form a one-dimensional carbon nanotube secondary structure, thus obtaining a carbon nanotube / carbon fiber composite material with a multi-level structure loaded with cobalt-iron nanoparticles.

[0033] By adjusting the amount of potassium ferricyanide and the reaction time during the preparation of ZIF@PBA in step (1), precise control of the hollow structure of the material can be achieved. SEM images of the ZIF@PBA products obtained when the reaction time is 3 hours and the mass ratio of ZIF-67 to potassium ferricyanide is 1:1, 1:2, and 1:4 are shown below. Figure 1 As shown in (a), (b), and (c), when the mass ratio of ZIF-67 to potassium ferricyanide is 1:1, the ZIF@PBA (1:1 3 h) cube does not fully achieve the expected etching degree, the etching depth is insufficient, and the material exhibits an uneven etching effect.

[0034] As the amount of potassium ferricyanide increases, the hollow structure of ZIF@PBA becomes more and more obvious. When the mass ratio of ZIF-67 to potassium ferricyanide is 1:2, the cubic ZIF@PBA (1:2 3 h) group has an ideal etching morphology, exhibiting an open hollow structure. The etching reaction at this ratio is just right, which not only achieves the formation of the hollow structure, but also maintains the basic morphology of the cube, providing an ideal precursor for subsequent material preparation.

[0035] When the relative dosage of potassium ferricyanide was 1:4, the cubic etching of the ZIF@PBA (1:4 3 h) group was excessive, and some cubic structures were incomplete and decomposed. This indicates that excessive potassium ferricyanide will destroy the cubic structure of ZIF-67, affecting the integrity and stability of the material.

[0036] Furthermore, the SEM images of the ZIF@PBA products obtained with ZIF-67 to potassium ferricyanide mass ratios of 1:1, 1:2, and 1:4, as the reaction time was extended to 6 h, are shown below. Figure 1As shown in (d), (e), and (f), the cubic structure is incomplete regardless of the amount of potassium ferricyanide added, indicating that excessively long reaction times can also lead to the destruction of the material structure.

[0037] The crystal structures of ZIF@PBA and ZIF-67 were analyzed by X-ray diffraction (XRD), such as... Figure 2 As shown, ZIF@PBA hardly alters the structure of ZIF-67. Although a hollow structure is formed and some interactions and surface modifications occur, the overall framework and main structural features of ZIF-67 are maintained.

[0038] The CoFe / CNTF sample prepared in this embodiment was subjected to EDS analysis using the built-in scanning electron microscope (SEM). Figure 3 As shown, by Figure 3 The uniform distribution of C, N, Fe, Co, and O elements in CoFe / CNTF indicates the successful synthesis of the carbon nanotube / carbon fiber composite structure and the achievement of abundant N doping. Comparative Example 1

[0039] Comparative Example 1 provides a preparation process for Co / CNTF material. The difference from Example 1 is that ZIF-67 in this comparative example did not react with potassium ferricyanide. Instead, the Co / CNTF material was synthesized by referring to steps (2) and (3) of Example 1. The specific synthesis method is as follows: (1) Dissolve 0.3 g ZIF-67 powder in 3 mL DMF and sonicate for 30 min to form a homogeneous solution. Then add 0.3 g PAN to the solution and stir overnight at room temperature. Inject the resulting viscous liquid into a 10 mL syringe, keeping the distance between the nozzle and the collector at 18 cm. Adjust the DC high voltage to 18 kV and inject at a rate of 1 mL / h. -1 The liquid inlet speed is adjusted, and a spinning membrane is produced by electrospinning to obtain a ZIF fiber membrane.

[0040] (2) Place the above 0.1 g ZIF fiber membrane in a tube furnace and heat it to 250°C in air at a heating rate of 1°C / min, and keep it for 2 h for pre-oxidation to improve the thermal stability of the fiber membrane.

[0041] The pre-oxidized ZIF fiber membrane was placed at one end of a covered ceramic boat, and 1 g of dicyandiamide was placed at the other end of the ceramic boat. The mixture was heated to 550°C at a heating rate of 2°C / min under a nitrogen atmosphere and held for 3 h. Then it was annealed at 700°C for 2 h to obtain the Co / CNTF material.

[0042] Comparative Example 1: SEM images of Co / CNTF before calcination (as shown in Figure 1) Figure 4As shown in (a), the SEM images of Comparative Example 1 Co / CNTF after calcination are as follows: Figure 4 As shown in (b) and (c); SEM images of CoFe / CNTF before calcination in Example 1 are shown in Figure 1. Figure 4 As shown in (d), the SEM image of CoFe / CNTF after calcination in Example 1 is as follows. Figure 4 As shown in (e) and (f).

[0043] Depend on Figure 4 It can be seen that the fibers in Co / CNTF and CoFe / CNTF are densely and tightly arranged, exhibiting good structural integrity and a high specific surface area. The carbon nanofibers are covered with coiled fibrous filaments, which are carbon nanotubes. This demonstrates the successful synthesis of multi-level CNTFs, proving that the structure not only improves the material's conductivity and specific surface area but also significantly enhances its stability in electrocatalytic reactions. Comparative Example 2

[0044] This comparative example provides a method for preparing CoFe / CNT material. The difference from Example 1 is that this comparative example does not perform electrospinning with PAN, but directly pyrolyzes ZIF@PBA powder according to step (3) of Example 1 to obtain CoFe / CNT material. The specific synthesis method is as follows: (1) 100 mg of ZIF-67 cubes were dispersed in 30 mL of ethanol and ultrasonically dispersed for 10 min to obtain an ethanol suspension of ZIF-67.

[0045] Dissolve 200 mg of potassium ferricyanide (K3[Fe(CN)6]) in 10 mL of deionized water to obtain a potassium ferricyanide solution.

[0046] Under magnetic stirring, potassium ferricyanide solution was rapidly poured into an ethanol suspension of ZIF-67, and stirring was continued for 3 h at room temperature. The product was collected by centrifugation and washed three times each with deionized water and ethanol, and dried overnight at 60 °C to obtain ZIF@PBA composite powder.

[0047] (2) Place the above 0.1 g ZIF@PBA powder in a tube furnace, heat it to 250°C in air at a heating rate of 1°C / min, and maintain it for 2 h for pre-oxidation.

[0048] The pre-oxidized ZIF@PBA powder was placed at one end of a covered ceramic boat, and 1 g of dicyandiamide was placed at the other end of the ceramic boat. The mixture was heated to 550°C at a heating rate of 2°C / min under a nitrogen atmosphere and held for 3 h. Then it was annealed at 700°C for 2 h to obtain CoFe / CNT material. Comparative Example 3

[0049] This comparative example provides a method for preparing CoFe / CNF materials, which involves direct pyrolysis of ZIF@PBA fiber membranes without reaction with dicyandiamide. The specific synthesis process is as follows: (1) Preparation of ZIF@PBA 100 mg of ZIF-67 cubes were dispersed in 30 mL of ethanol and ultrasonically dispersed for 10 min to obtain an ethanol suspension of ZIF-67.

[0050] Dissolve 200 mg of potassium ferricyanide (K3[Fe(CN)6]) in 10 mL of deionized water to obtain a potassium ferricyanide solution.

[0051] Under magnetic stirring, potassium ferricyanide solution was rapidly poured into an ethanol suspension of ZIF-67, and stirring was continued for 3 h at room temperature. The product was collected by centrifugation and washed three times each with deionized water and ethanol, and dried overnight at 60 °C to obtain ZIF@PBA composite powder.

[0052] (2) Preparation of ZIF@PBA fiber membrane 0.3 g of ZIF@PBA powder was dissolved in 3 mL of DMF and sonicated for 30 min to form a homogeneous solution. Then, 0.3 g of PAN was added to the solution and stirred overnight at room temperature. The resulting viscous liquid was injected into a 10 mL syringe, with the distance between the nozzle and the collector fixed at 18 cm. The DC high voltage was adjusted to 18 kV, and the liquid was fed at a rate of 1 mL / h. The solution was then electrospun to form a spun membrane, thus obtaining a ZIF@PBA fiber membrane.

[0053] (3) Preparation of CoFe / CNF The 0.1 g ZIF@PBA fiber membrane was placed in a tube furnace and heated to 250°C in air at a heating rate of 1°C / min, and held for 2 h for pre-oxidation to improve the thermal stability of the fiber membrane.

[0054] The pre-oxidized ZIF@PBA fiber membrane was placed in a covered ceramic boat and heated to 550°C at a heating rate of 2°C / min under a nitrogen atmosphere, held for 3 h, and then annealed at 700°C for 2 h to obtain CoFe / CNF. Performance Characterization

[0055] SEM images of Comparative Example 2 CoFe / CNT and Comparative Example 3 CoFe / CNF are shown below. Figure 5 As shown. Figure 5(a) is a SEM image of CoFe / CNT. It can be seen that although CNT structures were successfully formed under the action of dicyandiamide, significant entanglement and aggregation occurred between the CNTs, resulting in clustering. In contrast, the CoFe / CNTF sample with introduced carbon nanofibers (Example 1) showed better results. Figure 4 The ef exhibits less stacking and aggregation, which is more conducive to the exposure of active sites, thereby effectively increasing the electrochemical active area.

[0056] Comparative Example 3: SEM image of CoFe / CNF as shown Figure 5 As shown in (b), after calcination, the polymer decomposes and carbonizes to form a porous carbon fiber structure. However, because there is no dicyandiamide, no secondary carbon nanotubes are formed. In contrast, in Example 1, carbon nanotubes create numerous "nanobridges" between fibers, forming a three-dimensional interpenetrating network with multiple electron transport paths and low resistance. Simultaneously, carbon nanotubes can also push metal nanoparticles onto the carbon fiber surface, thereby significantly increasing the effective contact area with the electrolyte.

[0057] To determine the phase composition of the composite materials, XRD tests were performed on Example 1 (CoFe / CNTF), Comparative Example 1 (Co / CNTF), and Comparative Example 2 (CoFe / CNT). Figure 6 As shown in (a), after the introduction of potassium ferricyanide, CoFe / CNTF and CoFe / CNT form a Co7Fe3 alloy as the main component, containing a small amount of CoC. x The composite phase.

[0058] To characterize the types of carbon, Raman spectroscopy was performed on Example 1 (CoFe / CNTF), Comparative Example 1 (Co / CNTF), and Comparative Example 2 (CoFe / CNT). Figure 6 As shown in (b), in CoFe / CNF, CoFe / CNTF, and CoFe / CNT, I D / I G The ratios were 2.3, 3.5 and 1.7, respectively. CoFe / CNTF had the most defects in the C atom crystal and the highest degree of graphitization, which is beneficial to improving the electrical conductivity and catalytic activity of the material. Electrocatalytic performance test

[0059] ORR electrocatalytic performance tests were performed on Example 1 and Comparative Examples 1-3. The ORR polarization curves and Tafel curves of CoFe / CNTF, CoFe / CNF, CoFe / CNT, Co / CNTF, and Pt / C are shown below. Figure 7As shown in (a) and (b), the half-wave potentials of CoFe / CNTF, CoFe / CNF, CoFe / CNT, Co / CNTF, and Pt / C are 0.88 V, 0.86 V, 0.84 V, 0.80 V, and 0.87 V, respectively. Example 1 exhibits a much higher onset potential, half-wave potential, and limiting current density than the comparative example, indicating its superior ORR catalytic activity. This can be attributed to the synergistic effect of the CoFe bimetallic structure and multi-level stereostructure in the CoFe / CNTF sample.

[0060] The Tafel slopes of Co / CNTF, CoFe / CNT, Pt / C, CoFe / CNF, and CoFe / CNTF are 77.01 mVdec, respectively. -1 58.31 mV dec -1 56.02 mV dec -1 53.69 mV dec -1 47.05 mV dec -1 Among them, CoFe / CNTF exhibited the lowest Tafel slope (47.05 mV dec) compared to other samples. -1 The concentration of the CoFe / CNTF composite material prepared in this invention is 16% lower than that of Pt / C, indicating that the CoFe / CNTF composite material prepared in this invention exhibits relatively fast ORR reaction kinetics.

[0061] Example 1: CV curve of CoFe / CNTF sample (a); polarization curves at different rotational speeds (b); KL curve of CoFe / CNTF (c); calculated electron transfer number (d) Figure 8 As shown, within the potential range of 0.2–0.6 V, the electron transfer number of CoFe / CNTF is 3.78–4.0, indicating that CoFe / CNTF exhibits a more efficient four-electron pathway in the ORR process.

[0062] Example 1: Stability test results of CoFe / CNTF sample in 0.1M KOH are as follows. Figure 9 As shown, after CoFe / CNTF operated continuously at a constant potential of 0.85 V for 16 h, its current retention rate remained above 91%, indicating that it exhibits excellent long-cycle durability in alkaline media.

[0063] Based on the above embodiments and comparative examples 1-3, this invention prepares a multi-layered one-dimensional carbon nanotube / carbon nanofiber composite material (CoFe / CNTF) using electrospinning and heat treatment. In this structure, one-dimensional carbon nanofibers serve as the growth substrate, and one-dimensional carbon nanotube secondary structures are grown in situ on the surface of the carbon nanofibers through the catalytic effect of CoFe nanoparticles. This in-situ growth method ensures a tight connection between the carbon nanotubes and carbon nanofibers, which not only improves the overall structural stability but also facilitates rapid electron transport.

[0064] CoFe nanoparticles play a crucial role as catalysts in the growth of carbon nanotubes. They catalyze the decomposition of the carbon source in carbon nitride and form carbon atoms on the fiber surface. Guided by the catalyst, these carbon atoms self-organize and grow into one-dimensional carbon nanotube secondary structures, thus co-constructing a multi-level structure with one-dimensional carbon nanotubes. The multi-level structure of CoFe / CNTF not only increases the specific surface area of ​​the material but also provides abundant active sites. Simultaneously, the synergistic effect between one-dimensional carbon nanotubes and secondary one-dimensional carbon nanotubes facilitates electron transport and reactant diffusion, thereby improving electrocatalytic performance.

[0065] In the ORR reaction, the CoFe / CNTF composite material prepared in this invention exhibits the best onset potential, half-wave potential (0.88 V), and limiting current density, with a Tafel slope of 47.05 mV dec. -1 It exhibits good ORR electrocatalytic performance and excellent long-cycle durability in alkaline media.

Claims

1. A method for preparing carbon nanotube / carbon fiber composite materials loaded with cobalt-iron nanoparticles, characterized in that, Includes the following steps: S1: Potassium ferricyanide aqueous solution and ZIF-67 suspension were stirred and reacted at room temperature. The reaction product was washed and dried to obtain ZIF@PBA powder. S2: ZIF@PBA powder and polyacrylonitrile are dissolved in an organic solvent to form a spinning solution, and ZIF@PBA fiber membrane is obtained by electrospinning. S3: The ZIF@PBA fiber membrane is pre-oxidized, and the pre-oxidized ZIF@PBA fiber membrane is calcined with dicyandiamide under an inert atmosphere to obtain a carbon nanotube / carbon fiber composite material loaded with cobalt iron nanoparticles.

2. The method for preparing carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles as described in claim 1, characterized in that, The mass ratio of ZIF-67 to potassium ferricyanide in step S1 is 1:1.5 to 2.

5.

3. The method for preparing carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles as described in claim 1, characterized in that, In step S2, the mass ratio of ZIF@PBA powder to polyacrylonitrile is 2-4:

3.

4. The method for preparing carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles as described in claim 1, characterized in that, The pre-oxidation treatment in step S3 includes heating the ZIF@PBA fiber membrane to 240℃~260℃ in air at a heating rate of 1~3℃ / min and maintaining it for 1.5~2.5 h.

5. The method for preparing carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles as described in claim 1, characterized in that, The calcination in step 3 includes heating the pre-oxidized ZIF@PBA fiber membrane to 500-600°C with dicyandiamide, holding it at that temperature for 2-4 hours, and then annealing it at 700-800°C for 1.5-2.5 hours.

6. The method for preparing carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles as described in claim 1, characterized in that, In step S3, the mass ratio of ZIF@PBA fiber membrane to dicyandiamide is 1:5 to 15.

7. The method for preparing carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles as described in claim 1, characterized in that, The stirring reaction in step S1 lasts for 2 to 4 hours.

8. A carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles, characterized in that, The composite material is prepared by the preparation method described in claims 1 to 7.

9. The application of the carbon nanotube / carbon fiber composite material supported on cobalt-iron nanoparticles as described in claim 8 in oxygen reduction catalysts.

10. The application as described in claim 9, characterized in that, The half-wave potential of the ORR electrocatalysis of the carbon nanotube / carbon fiber composite material loaded with cobalt-iron nanoparticles was 0.88 V, and the Tafel slope did not exceed 47.05 mVdec. -1 .

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