Short-branched carbon nanotube / alloy / carbon fiber self-supporting catalytic electrode material, preparation method and application thereof

Abstract

This invention belongs to the field of catalysis technology, specifically relating to a self-supporting catalytic electrode material made of short-branched carbon nanotubes / alloys / carbon fibers, its preparation method, and applications. A three-dimensional framework of fabric-like carbon fibers is used, with short-branched carbon nanotubes covalently bonded to the surface of the framework. Bimetallic alloy nanoparticles are embedded within the short-branched carbon nanotubes, which have a length of 0.1–2.5 μm. The bimetallic alloy nanoparticles are Co3Fe7 nanoparticles and Fe... 0.64 Ni 0.36 Nanoparticles or CoNi nanoparticles. The catalytic electrode material provided by this invention can operate efficiently and stably under strongly alkaline conditions, while also possessing dual ORR and OER activity. Experiments show that this catalytic electrode material can operate stably for a long time when used as an anode catalyst for anion exchange membrane water electrolysis; when used as a cathode catalyst for flexible zinc-air batteries, its cycle life is superior to commercial platinum-carbon and ruthenium dioxide catalysts.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, and relates to self-supporting catalytic electrode materials of short-branched carbon nanotubes / alloys / carbon fibers, their preparation methods and applications. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] The oxygen evolution reaction (OER) is a key anodic reaction in electrochemical energy conversion technologies, such as zinc-air batteries and water electrolysis for hydrogen production. OER involves a multi-step proton-coupled electron transfer process with slow kinetics, typically requiring highly efficient catalysts to reduce overpotential and improve energy conversion efficiency. An ideal OER catalyst should possess high intrinsic catalytic activity, excellent electron transport capabilities, and long-term chemical and structural stability under specific environments. Simultaneously, to meet the demands of large-scale applications, the catalyst must also be cost-effective and resource-rich. Furthermore, in addition to the above requirements, OER catalysts have specific needs in different application areas. For example, water electrolysis for hydrogen production (especially AEM water electrolysis) is usually carried out under strongly alkaline conditions with a pH of 10–14, requiring the OER catalyst to have excellent resistance to alkali corrosion; while the slow oxygen reduction (ORR) reaction kinetics at the air cathode of a zinc-air battery (ZAB) can severely affect battery performance, requiring the OER catalyst to possess both ORR and OER bifunctional activities. Currently, inexpensive non-precious metal-based OER catalysts are only studied for a single field and cannot meet the specific requirements of different fields, making it difficult for existing inexpensive non-precious metal-based OER catalysts to be universally applicable in multiple fields. Therefore, there is an urgent need to develop non-precious metal-based OER catalysts that can operate efficiently and stably under strongly alkaline conditions at a low cost, while also possessing bifunctional activity of ORR and OER.

[0004] Studies have shown that integrated self-supporting electrodes (such as nanostructures grown in situ on carbon substrates) exhibit significant potential by eliminating binders, strengthening interfacial bonding (MOC bonds), and constructing open mass transfer channels. However, existing fabrication techniques face common challenges: while high-temperature pyrolysis methods (such as pyrolysis of ferrocene / melamine) can grow carbon nanotubes (CNTs) on carbon substrates, their length has a double-edged sword effect on electrode performance—excessive growth or longitudinal extension (>3 μm) will significantly prolong the mass / electron transport path, leading to increased impedance and kinetic degradation. More seriously, it may damage the structural integrity of the carbon fiber skeleton, ultimately limiting the mechanical stability and electrochemical durability of the device. Therefore, there is an urgent need to develop an in-situ synthesis technique for precisely controlling the longitudinal scale of CNTs to synergistically enhance the catalytic activity, mass transfer efficiency, and mechanical robustness of the electrode. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a self-supporting catalytic electrode material made of short-branched carbon nanotubes / alloys / carbon fibers, along with its preparation method and applications. The catalytic electrode material provided by this invention can operate efficiently and stably under strongly alkaline conditions, while also exhibiting dual-functionality of ORR and OER. Furthermore, the preparation method provided by this invention avoids excessive CNT elongation. Experiments show that this catalytic electrode material, when used as an anode catalyst in anion exchange membrane water electrolysis, can operate stably for extended periods; and when directly used as a cathode catalyst in flexible zinc-air batteries, its cycle life is superior to commercial platinum-carbon and ruthenium dioxide catalysts.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, a self-supporting catalytic electrode material consisting of short-branched carbon nanotubes / alloys / carbon fibers is disclosed. The material uses a fabric-like carbon fiber as a three-dimensional framework, with short-branched carbon nanotubes covalently bonded to the surface of the framework. Bimetallic alloy nanoparticles are embedded within the bodies of the short-branched carbon nanotubes. The length of the short-branched carbon nanotubes is 0.1-2.5 μm, and the bimetallic alloy nanoparticles are Co3Fe7 nanoparticles and Fe... 0.64 Ni 0.36 Nanoparticles or CoNi nanoparticles.

[0007] This invention employs a fabric-like carbon fiber as a three-dimensional framework. The fabric-like carbon fiber has a uniformly interwoven three-dimensional network, exhibiting excellent bending properties and providing a foundation for the self-supporting characteristics of the catalytic electrode material. The carbon nanotubes of this invention are embedded with bimetallic alloy nanoparticles, which can form highly efficient MNC active sites to optimize oxygen adsorption energy. Simultaneously, the carbon nanotubes covalently bridge carbon fibers to construct a "point-line-surface" electron transport network, and the three-dimensional pores ensure rapid mass transfer. This invention utilizes Co3Fe7 nanoparticles and Fe... 0.64 Ni 0.36 The embedding of nanoparticles or CoNi nanoparticles can not only avoid excessive growth or longitudinal extension of carbon nanotubes and control the length of carbon nanotubes to 0.1-2.5 μm, but also help maintain the high thermal stability and deformation adaptability of the catalytic electrode material.

[0008] On the other hand, a method for preparing a self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers includes the following steps: The fiber cloth is pyrolyzed and carbonized to produce cloth-like carbon fibers; Add two of the iron salt, cobalt salt, and nickel salt to water and mix them thoroughly to make a mixed solution; The fabric-like carbon fibers are added to the mixed solution for impregnation; The impregnated fabric-like carbon fibers are dried and coated onto melamine powder. Under an inert atmosphere, the temperature is programmed to rise to 850-950 ℃ and calcined at that temperature to obtain the final product.

[0009] The fiber cloth possesses a three-dimensional network structure. After being pyrolyzed and carbonized into cloth-like carbon fibers, it maintains this three-dimensional network structure, resulting in excellent bending properties and the ability to serve as a three-dimensional framework. Two salts are impregnated onto the cloth-like carbon fibers, which are then coated with melamine powder and calcined. This causes the melamine to decompose and deposit on the cloth-like carbon fibers, forming covalently bonded carbon nanotubes, thus constructing a "point-line-surface" electron transport network. The three-dimensional porosity ensures rapid mass transfer. Simultaneously, the loaded salts pyrolyze and, under the reduction of the pyrolyzed carbon, form Co3Fe7 nanoparticles and Fe... 0.64 Ni 0.36 The carbon nanotubes are embedded with nanoparticles or CoNi nanoparticles, thereby avoiding excessive growth or longitudinal extension of the carbon nanotubes and controlling the length of the carbon nanotubes to 0.1-2.5 μm. At the same time, it is beneficial to maintain the high thermal stability and deformation adaptability of the catalytic electrode material.

[0010] Thirdly, the application of a self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers as described in the first aspect of the present invention or a self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers obtained by the preparation method described in the second aspect of the present invention in flexible zinc-air batteries or water electrolysis for hydrogen production.

[0011] The beneficial effects of this invention are as follows: 1. This invention uses flexible, fabric-like carbon fibers as a three-dimensional framework, bridging short-branch carbon nanotubes with covalent bonds to construct a stable "point-line-surface" hierarchical conductive network. This network structure not only enhances electron transport capabilities, but its open three-dimensional pores also greatly promote mass transfer of reactants. This invention embeds bimetallic alloy nanoparticles into the carbon nanotube walls to form highly active MNC sites; simultaneously, it effectively suppresses excessive longitudinal growth of carbon nanotubes, precisely controlling their length within the "short branch" range of 0.1-2.5 μm. This invention solves the problems of extended transport paths, increased impedance, and compromised carbon fiber framework structural integrity caused by long carbon nanotubes (>3 μm), thereby synergistically achieving high catalytic activity, excellent mass transfer efficiency, and good mechanical flexibility / stability in the electrode material.

[0012] 2. The catalytic electrode material provided by this invention, through the synergistic effect of short-branched carbon nanotubes and alloy particles, not only exhibits excellent intrinsic electrocatalytic activity under strongly alkaline conditions, but also has dual ORR / OER functions, enabling it to simultaneously meet the stringent requirements of different application scenarios such as water electrolysis for hydrogen production and flexible zinc-air batteries.

[0013] 3. The preparation method provided by this invention utilizes a simple impregnation-programmed temperature calcination process, taking advantage of the differences in catalytic activity of different bimetallic salt precursors (Fe / Co, Fe / Ni, Co / Ni) during the carbon deposition process of melamine pyrolysis, to achieve precise customization of the longitudinal growth scale of carbon nanotubes. In particular, the Co3Fe7 alloy can significantly suppress the carbon deposition rate, locking the carbon nanotube length at the submicron level, thus solving the common technical problem of difficulty in controlling the length of carbon nanotubes and the tendency for them to over-elongate. This method is simple, highly controllable, and provides a reliable route for the large-scale preparation of self-supporting electrode materials with uniform structure and optimized performance.

[0014] 4. Experiments show that the catalytic electrode material provided by this invention exhibits excellent comprehensive performance and long-term stability. Firstly, in anion exchange membrane (AEM) water electrolysis, an electrolyzer using this material as the anode was used at 0.5 A·cm⁻¹. -2 It operated stably for over 1000 hours at high current densities without significant degradation, demonstrating excellent resistance to alkali corrosion and catalytic stability. Furthermore, in flexible zinc-air batteries, the specific capacity of batteries assembled using it directly as the flexible zinc-air cathode reached as high as 663 mAh·g. -1 Zn Superior to commercial Pt / C+RuO2 mixed catalyst systems (574 mAh·g) -1 Zn It can cycle stably for more than 200 times. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0016] Figure 1 The following are (a) a synthesis flowchart and (bd) photographs of Comparative Example 1 and Example 1 of the present invention; a is a synthesis flowchart, b is a photograph of BF, c is a photograph of CF, and d is a photograph of CoFe / NCNT / CF.

[0017] Figure 2 These are photographs of actual objects used in the bending tests of Embodiments 1-3 of the present invention; a is Embodiment 1, b is Embodiment 2, and c is Embodiment 3.

[0018] Figure 3 The images shown are scanning electron microscope (SEM) images and particle size distribution diagrams for Example 1; a is 100 µm, b is 2 µm, c is 500 nm, and d is the particle size distribution diagram.

[0019] Figure 4The images shown are SEM images and particle size distribution diagrams for Example 2; a is 100 µm, b is 2 µm, c is 500 nm, and d is the particle size distribution diagram.

[0020] Figure 5 The images shown are SEM images and particle size distribution diagrams for Example 3; a is 100 µm, b is 2 µm, c is 500 nm, and d is the particle size distribution diagram.

[0021] Figure 6 The following are transmission electron microscope (TEM) images of Embodiment 1 of the present invention; a is 100 nm, b is 50 nm, c is 5 nm, d is 5 nm, e is 2 nm, f is 2 nm, g is Fourier transform (FFT), h is selected electron diffraction (SAEM), i is high-angle annular dark field (HAADF) and elemental distribution map.

[0022] Figure 7 The X-ray diffraction (XRD) and Raman spectra of Examples 1-3 and Comparative Examples 1-2 of this invention are shown; a is the XRD pattern, b is the Raman pattern, and c is the I-ray diffraction pattern. D / I G A bar chart of values.

[0023] Figure 8 The following are X-ray diffraction (XPS) data for Examples 1-3 of this invention: a is the full spectrum, b is the N 1s spectrum, c is the N element content, d is the Fe 2p spectrum, e is the Co 2p spectrum, and f is the Ni 2p spectrum.

[0024] Figure 9 The OER performance of Examples 1-3 and Comparative Examples 1-2 of the present invention is shown; a is the polarization curve, b is the overpotential, c is the Tafel slope, and d is the stability.

[0025] Figure 10 The ORR performance of Examples 1-3 and Comparative Examples 1-2 of the present invention is shown; a is the polarization curve, b is the half-wave potential, c is the Tafel slope, and d is the stability.

[0026] Figure 11 Examples of the present invention (Example 1) and commercial Pt / C+RuO2 are shown in the AEM performance test; a) shows the comparison of initial activation voltage, and b) shows the long-term stability test.

[0027] Figure 12 Examples 1-3 of this invention and the performance of commercial Pt / C+RuO2 flexible zinc-air batteries are shown; a is a schematic diagram, b is an open-circuit voltage curve and a physical diagram of the power supply application, c is the discharge capacity, and d is the charge-discharge cycle. Detailed Implementation

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0030] Given that existing inexpensive non-precious metal-based OER catalysts are difficult to operate efficiently and stably under strongly alkaline conditions, and cannot achieve both ORR and OER dual-functionality, this invention proposes a self-supporting catalytic electrode material made of short-branched carbon nanotubes / alloys / carbon fibers, its preparation method, and its application.

[0031] A typical embodiment of the present invention provides a self-supporting catalytic electrode material of short-branch carbon nanotubes / alloys / carbon fibers. The material uses a three-dimensional framework of cloth-like carbon fibers, with short-branch carbon nanotubes covalently bonded to the surface of the framework. Bimetallic alloy nanoparticles are embedded in the bodies of the short-branch carbon nanotubes. The length of the short-branch carbon nanotubes is 0.1-2.5 μm, and the bimetallic alloy nanoparticles are Co3Fe7 nanoparticles and Fe... 0.64 Ni 0.36 Nanoparticles or CoNi nanoparticles.

[0032] In some embodiments, the length of the short-branched carbon nanotubes is 0.1-1 μm. Studies have shown that the length of carbon nanotubes is strongly negatively correlated with electrochemical performance: when the length of carbon nanotubes exceeds 1 μm (such as in the CoNi system), the ORR activity loss reaches 60 mV, and fiber structure breakage is induced, with flexibility and catalytic performance deteriorating simultaneously. When the length of carbon nanotubes is 0.1-0.4 μm, the catalytic electrode material exhibits better flexibility and catalytic performance. Among these, the carbon nanotubes catalyzed by Co3Fe7 nanoparticles are even shorter, allowing the carbon nanotube length to be ≤0.4 μm.

[0033] In some embodiments, the Co3Fe7 nanoparticles have a metal interface.

[0034] In some embodiments, the fabric-like carbon fiber is fabric-like bamboo carbon fiber. Bamboo carbon fiber has better porosity and self-supporting properties.

[0035] Another embodiment of the present invention provides a method for preparing a self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers, comprising the following steps: The fiber cloth is pyrolyzed and carbonized to produce cloth-like carbon fibers; Add two of the iron salt, cobalt salt, and nickel salt to water and mix them thoroughly to make a mixed solution; The fabric-like carbon fibers are added to the mixed solution for impregnation; The impregnated fabric-like carbon fibers are dried and coated onto melamine powder. Under an inert atmosphere, the temperature is programmed to rise to 850-950 ℃ and calcined at that temperature to obtain the final product.

[0036] In some embodiments, bamboo fiber cloth is pyrolyzed and carbonized to produce cloth-like carbon fibers.

[0037] In some embodiments, the pyrolysis carbonization temperature is 950-1050 °C. Specifically, the pyrolysis carbonization time is 1.8-2.2 h.

[0038] The iron salts mentioned in this invention refer to compounds whose cations are iron ions (especially ferric ions), such as ferric nitrate, ferric chloride, and ferric sulfate.

[0039] The cobalt salts mentioned in this invention refer to compounds whose cations are divalent cobalt ions, such as cobalt nitrate, cobalt dichloride, and cobalt sulfate.

[0040] The nickel salts mentioned in this invention refer to compounds whose cations are divalent nickel ions, such as nickel nitrate, nickel dichloride, and nickel sulfate.

[0041] In some embodiments, the concentration of the mixed salt in the mixed solution is 0.27-0.33 mol·L⁻¹. -1 .

[0042] In some embodiments, iron salts, cobalt salts, or iron salts and nickel salts are added to water and mixed thoroughly to prepare a mixed solution. Studies have shown that Co3Fe7 nanoparticles formed by the pyrolysis and reduction of iron and cobalt salts, or Fe nanoparticles formed by the pyrolysis and reduction of iron and nickel salts, can be produced. 0.64 Ni 0.36 Nanoparticles can better suppress the excessive growth or longitudinal extension of carbon nanotubes, thereby controlling the length of carbon nanotubes to 0.1-1 μm. Among them, Co3Fe7 nanoparticles formed by the pyrolysis reduction of iron salts and cobalt salts can control the length of carbon nanotubes to 0.1-0.4 μm.

[0043] In some embodiments, the impregnation process involves ultrasonic treatment followed by a settling process. Specifically, the ultrasonic treatment time is 1.8-2.2 hours. Specifically, the settling time is 4.5-5.5 hours.

[0044] In some embodiments, the programmed temperature rise rate is 4.5-5.5 °C·min. -1 .

[0045] In some embodiments, the calcination time is 1.8-2.2 h.

[0046] A third embodiment of the present invention provides an application of the self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers described in the first aspect of the present invention or the self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers obtained by the preparation method described in the second aspect of the present invention in flexible zinc-air batteries or water electrolysis for hydrogen production.

[0047] In some embodiments, the short-branched carbon nanotube / alloy / carbon fiber self-supporting catalytic electrode material is directly used as the air cathode of a flexible zinc-air battery.

[0048] In some embodiments, the short-branched carbon nanotube / alloy / carbon fiber self-supporting catalytic electrode material is used as an anode catalyst for water electrolysis to produce hydrogen.

[0049] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0050] Comparative Example 1 Cut the bamboo fiber cloth (BF) into 5*5 cm pieces. 2 The sample was then transferred to a tube furnace and heated at 5 °C / min under a N2 atmosphere. -1 The temperature was increased to 1000 °C and calcined for 2 h. The resulting flexible material was named bamboo fiber (CF).

[0051] Comparative Example 2 The two CF sheets were then placed in a ceramic boat containing 1.5g of melamine powder and transferred into a tube furnace, where they were heated at 5 °C / min under a N2 atmosphere. -1 The temperature was increased to 900 °C and calcined for 2 h to obtain the final product, which was named N-CF.

[0052] Example 1 Dissolve 3 mmol Fe2(NO)3·9H2O and 3 mmol Co(NO)2·6H2O in 20 mL of deionized water to prepare a 0.3 mol·L⁻¹ solution. -1 The two CF tablets were then completely immersed in the mixed solution and sonicated at room temperature for 2 hours, followed by standing for 5 hours. The CF tablets containing Co / Fe ions were then removed and dried at 60 °C. They were then placed in a ceramic boat containing 1.5 g of melamine powder and transferred to a tube furnace, where they were heated at 5 °C / min under a N2 atmosphere. -1The temperature was increased to 900 °C and calcined for 2 h to obtain the final product, which was named CoFe / NCNT / CF.

[0053] Example 2 Dissolve 3 mmol Fe2(NO)3·9H2O and 3 mmol Ni(NO)2·6H2O in 20 mL of deionized water to prepare a 0.3 mol·L⁻¹ solution. -1 The two CF tablets were then completely immersed in the mixed solution and sonicated at room temperature for 2 hours, followed by standing for 5 hours. The CF tablets containing Co / Fe ions were then removed and dried at 60 °C. They were then placed in a ceramic boat containing 1.5 g of melamine powder and transferred to a tube furnace, where they were heated at 5 °C / min under a N2 atmosphere. -1 The temperature was increased to 900 °C and calcined for 2 h to obtain the final product, which was named FeNi / NCNT / CF.

[0054] Example 3 Dissolve 3 mmol Co(NO3)2·6H2O and 3 mmol Ni(NO3)2·6H2O in 20 mL of deionized water to prepare a 0.3 mol·L⁻¹ solution. -1 The two CF tablets were then completely immersed in the mixed solution and sonicated at room temperature for 2 hours, followed by standing for 5 hours. The CF tablets containing Co / Fe ions were then removed and dried at 60 °C. They were then placed in a ceramic boat containing 1.5 g of melamine powder and transferred to a tube furnace, where they were heated at 5 °C / min under a N2 atmosphere. -1 The temperature was increased to 900 °C and calcined for 2 h to obtain the final product, which was named CoNi / NCNT / CF.

[0055] The parameters in the above embodiments can fluctuate by 10%.

[0056] Figure 1 Figure a illustrates the fabrication process of a flexible CoFe / NCNT / CF self-supporting electrode based on bamboo fabric (Example 1): the flexible BF is carbonized at high temperature to form a CF (Comparative Example 1) substrate, which then adsorbs Fe. 3+ / Co 2+ The final product was obtained through secondary calcination of melamine. The photograph shows a sample size of 5 × 5 cm. 2 BF ( Figure 1 (b) After carbonization, it shrinks to 3×3 cm. 2 CF (Example 1) fiber cloth ( Figure 1 (c) maintains excellent bending properties; the electrode dimensions are stable after in-situ CNT growth. Figure 1In example d), CoFe / NCNT / CF (Example 1) still has high flexibility and can be used as a self-supporting electrode, which confirms the high thermal stability and deformation adaptability of the CF skeleton structure.

[0057] Different metal combinations significantly affect the mechanical properties of the electrode. The CoFe / NCNT / CF (Example 1) electrode sheet structure remained intact and unbroken after 500 repeated folding and bending cycles. Figure 2 As shown in a. However, after 500 repeated folding and bending, the unfolded electrode sheet structure of FeNi / NCNT / CF (Example 2) showed partial damage, as shown in Figure a. Figure 2 As shown in b. However, CoNi / NCNT / CF (Example 3) completely shattered and lost its flexibility after 500 repeated folding and bending, as... Figure 2 As shown in c in the figure. The above results clearly point to the flexibility sequence: CoFe / NCNT / CF (Example 1) > FeNi / NCNT / CF (Example 2) > CoNi / NCNT / CF (Example 3).

[0058] To reveal the root cause of the flexibility difference, the microstructure was first analyzed using a SEM system. CoFe / NCNT / CF (Example 1) exhibited a uniformly interwoven three-dimensional network, and its high mechanical flexibility was attributed to the unbroken integrity of its intact fiber network structure. Figure 3 As shown in a, its fiber surface is uniformly covered with a thin active layer, such as... Figure 3 As shown in b, the active layer is a short-branch type CNT with relatively large pores, and the substrate is visible, as shown in Figure 2. Figure 3 As shown in 'c', this is beneficial for material transport. Statistical analysis of particle size distribution revealed that the length and particle size of the short-branched CNTs in Example 1 were all less than 0.4 μm. Figure 3 As shown in d in the figure. For FeNi / NCNT / CF (Example 2), the fibers are significantly thicker and some fibers have poor continuity and breakage, as shown in the figure. Figure 4 As shown in a, this fracture originates from the disruption of the fiber structure by a large number of long CNTs catalyzed by FeNi, such as... Figure 4 As shown in b, this long CNT completely covers the fiber substrate, such as Figure 4 As shown in c in the figure. Statistical analysis of particle size distribution revealed that the CNT length in Example 2 was relatively long, increasing to 0.5-1 μm, as shown in the figure. Figure 4 As shown in d. The fibers of CoNi / NCNT / CF (Example 3) also thickened and exhibited large-area fiber breakage, as shown in... Figure 5 As shown in a, its CNTs are more dense and further elongated, as... Figure 5 As shown in b, it also completely covers the carbon fiber substrate, such as Figure 5As shown in c in the figure. Statistical analysis of particle size distribution revealed that the CNT length in Example 3 was further increased, with almost all being greater than 1 μm, as shown in c. Figure 5 As shown in d, excessive CNT growth can damage the flexibility of the underlying fibers; therefore, short-branched thin-layer CNTs are the main reason for maintaining flexibility.

[0059] The CoFe / NCNT / CF prepared in Example 1 was subjected to fine TEM analysis, such as... Figure 6 As shown in figure a, the carbon nanotubes are embedded with metal nanoparticles and exhibit a bamboo-like multi-cavity structure, as shown in figure a. Figure 6 As shown in b in the figure. HRTEM revealed that the metal particles were encapsulated by approximately 10 layers of dense graphitic carbon, as... Figure 6 As shown in c, local magnification confirms the existence of adjacent grain boundaries between adjacent particles, such as... Figure 6 As shown in d. Although the lattice orientations on both sides of the grain boundary are different, the characteristic lattice spacing remains at 0.21 nm, as shown in d. Figure 6 As shown in 'e', ​​phase separation is ruled out and the single-metal phase characteristic is confirmed. (See figure 'e'.) Figure 6 As shown in f and g, FFT analysis of the graphite coating layer shows that a 0.34 nm interlayer spacing corresponds to the graphite (002) crystal plane; FFT and electron diffraction of the metal core jointly confirm that the diffraction rings match the (110) / (200) crystal plane of the Co3Fe7 alloy, as shown in f and g. Figure 6 As shown in h in the figure. HAADF-STEM elemental distribution shows that the Co / Fe signals overlap at the nodular protrusions of carbon nanotubes, precisely locking the spatially confined distribution of alloy particles in the bamboo-like multi-chamber structure, as shown in h. Figure 6 As shown in i in the figure. This bamboo-like structure has a dual advantage: the multi-chamber space inhibits the high-temperature migration and agglomeration of alloy particles through the geometric confinement effect, while the continuous graphite carbon layer constructs an efficient electron channel, effectively blocking electrolyte corrosion and reducing the risk of metal dissolution.

[0060] like Figure 7 As shown in a, the XRD patterns reveal the evolution of the material's crystal structure. CF (Comparative Example 1) and N-CF (Comparative Example 2) only show broadened carbon peaks at 26° (002) and 44° (100), confirming the absence of a metallic crystal phase in the amorphous carbon framework. A comparison reveals that the C(002) peak is significantly sharpened after the introduction of metal, attributed to the metal catalytic generation of a large number of highly crystalline carbon nanotubes. All three self-supporting electrodes exhibit sharp alloy diffraction peaks: the three diffraction peaks in CoFe / NCNT / CF (Example 1) match the (110) / (200) / (211) crystal planes of Co3Fe7 (PDF#48-1816); while the three diffraction peaks in FeNi / NCNT / CF (Example 2) correspond to Fe... 0.64 Ni 0.36The (111) / (200) / (220) crystal plane of (PDF#47-1405); the three diffraction peaks of CoNi / NCNT / CF (Example 3) match the (111) / (200) / (220) of the CoNi phase (PDF#74-5694). The above results confirm that the metal in the three examples exists in the form of an alloy, and none of them have other metal impurity phase peaks, which together confirm that the heat treatment process achieves the directional crystallization of high-purity alloys in carbon nanotubes. Raman spectra are obtained by adjusting the ID / IG value (1350 cm⁻¹). -1 D belt and 1597 cm -1 (G-band intensity ratio) quantifies the degree of order in carbon structure, such as Figure 7 As shown in b in the diagram. CF(I) D / I G =1.35) and N-CF(I D / I G =1.34) reflects the dominance of highly defective amorphous carbon. The Ig of the three metal-based catalysts in Examples 1-3 D / I G The values ​​all decreased significantly, such as Figure 7 As shown in c, CNTs formed by metal catalysis are long-range ordered sp... 2 The carbon network enhances the graphitization of the material. The ID / IG sequence shows CoFe / NCNT / CF (1.18) > FeNi / NCNT / CF (1.09) > CoNi / NCNT / CF (0.88), which is completely consistent with the carbon nanotube density gradient and metal catalytic activity order observed by SEM.

[0061] XPS full spectrum analysis confirms that Examples 1-3 all contain C / O / N elements, such as Figure 8 As shown in a, in addition, corresponding metal signals were also detected in each embodiment (CoFe / NCNT / CF: Fe, Co; FeNi / NCNT / CF: Fe, Ni; CoNi / NCNT / CF: Co, Ni), matching the elemental distribution of SEM-EDS. The N 1s spectrum fitted revealed pyridine N (398.3 eV), pyrrole N (399.4 eV), graphite N (401.2 eV), and N oxide (404.2 eV), as shown in Figure a. Figure 8 As shown in b, the first three types of nitrogen synergistically optimize charge distribution and improve the density of ORR / OER active sites. It is noteworthy that the nitrogen content in the shallow surface layer of the material obtained based on XPS and the bulk nitrogen content obtained based on SEM-EDS both exceed 6 at%, such as... Figure 8 As shown in c in the figure. Among them, FeNi / NCNT / CF (Example 2) reaches as high as 10 at%, this nitrogen-rich carbon material provides abundant active sites for electrocatalytic reactions. Fine analysis of the metal valence state shows that, as... Figure 8As shown in d, e, and f, the Fe 2p, Co 2p, and Ni 2p spectra can all be fitted to the zero-valence state (metal alloy), two high-valence oxidation state peaks, and a satellite peak. The zero-valence peak belongs to the alloy core, while the oxidation state originates from the surface passivation layer. A key phenomenon revealed is that as the carbon nanotube density increases, the intensity of the zero-valence peak of the same metal significantly increases, attributed to the enhanced alloy signal within the XPS detection depth due to the thinning of the carbon capping layer. More importantly, differences in alloy composition induce binding energy shifts: compared to CoFe / NCNT / CF (Example 1), the Co 2p of CoNi / NCNT / CF (Example 3) shifts negatively by 0.75 eV; compared to CoFe / NCNT / CF (Example 1), the Fe 2p of FeNi / NCNT / CF (Example 2) shifts positively by 0.50 eV; and compared to FeNi / NCNT / CF (Example 2), the Ni 2p of CoNi / NCNT / CF (Example 3) shifts positively by 0.62 eV, clearly reflecting the valence band shift caused by electronic structure reconstruction in different alloys.

[0062] Electrocatalytic performance testing process: A three-electrode system (RRDE-3A, Japan) and an electrochemical workstation (CHI760E, Shanghai Chenhua) were used. Hg / HgO was used as the reference electrode, a glassy carbon electrode as the working electrode, and a carbon rod as the counter electrode. Potentials were all corrected to the reversible hydrogen electrode (RHE). The electrocatalytic performance was tested using linear sweep voltammetry (LSV, 10 mV·s). -1 The activity was determined at 1 mol·L⁻¹. -1 OER was tested in KOH solution, and the LSV scan rate of OER was 10 mV·s. -1 In O2-saturated 0.1 mol·L⁻¹ -1 ORR was tested in KOH with an LSV scan rate of 10 mV·s. -1 The rotating disk electrode rotates at 1600 rpm. At a rate of 10 mV·s... -1 The stability of ORR and OER LSV curves was remeasured after 5000 consecutive CV scans.

[0063] Figure 9 The OER performance of Examples 1-3 and Comparative Examples 1-2 of this invention is shown below. The polarization curves for OER performance analysis are as follows: Figure 9 As shown in a. CoFe / NCNT / CF (Example 1) at 10 mA·cm -2 While the overpotential at current density is as low as 380 mV, it is not optimal. However, CoFe / NCNT / CF (Example 1) at 20 mA·cm⁻¹... -2It exhibits outstanding advantages at high current densities (overpotential η = 410 mV), significantly outperforming N-CF (η = 450 mV), FeNi / NCNT / CF (η = 510 mV), and CoNi / NCNT / CF (η = 420 mV), and even surpassing commercial RuO2 (η = 450 mV), such as Figure 9 As shown in b. Notably, its high-current performance surpasses that of the CoNi alloy (which has high intrinsic activity), which is attributed to the unique short-cluster CNT structure of CoFe / NCNT / CF (Example 1), which effectively balances the utilization of active sites with electron transport impedance. Tafel slope analysis (138 mV·dec) -1 This further confirms its highly efficient oxygen evolution kinetics, such as Figure 9 As shown in c in the figure. During the 200-hour constant voltage test, the current density decay rate was only 9.4%, demonstrating significantly better durability than RuO2. Figure 9 As shown in d in the figure. In summary, the bifunctional activity (ORR / OER) of CoFe / NCNT / CF (Example 1) not only surpasses other self-made catalysts in all aspects, but also rivals the commercial benchmark of Pt / C+RuO2.

[0064] Figure 10 The ORR performance of Examples 1-3 and Comparative Examples 1-2 of this invention is shown. Figure 10 As shown in a, the ORR performance of CoFe / NCNT / CF, FeNi / NCNT / CF, and CoNi / NCNT / CF prepared in Examples 1-3 significantly surpasses that of the comparative CF and N-CF preparations. Among them, CoFe / NCNT / CF (Example 1) exhibits the best ORR activity: half-wave potential (E 1 / 2 =0.85 V) and limiting current density (|J L | = 6.1 mA·cm -2 It is approaching the commercial Pt / C (0.86 V; 5.2 mA·cm⁻¹) value. -2 ),like Figure 10 As shown in b, it outperforms most reported metal / carbon-based catalysts. Notably, the ORR performance systematically decreases with increasing CNT content: CoFe / NCNT / CF (0.85 V; 6.1 mA·cm⁻¹). -2 )>FeNi / NCNT / CF (0.81 V; 5.8mA·cm -2 )>CoNi / NCNT / CF (0.79 V; 5.6 mA·cm -2 This pattern suggests that excessive CNTs may hinder active site exposure and mass transfer efficiency. (Kinetic analysis) Figure 10c) further reveals that the lowest Tafel slope (57 mV·dec) of CoFe / NCNT / CF (Example 1) -1 59 mV·dec lower than Pt / C -1 This demonstrates that it possesses optimal charge transfer kinetics and oxygen adsorption / dissociation capabilities. After 5000 cycles of accelerated aging, the half-wave potential of CoFe / NCNT / CF (Example 1) shifted negatively by only 1 mV, exhibiting significantly higher stability than Pt / C (15 mV). Figure 10 As shown in d.

[0065] AEM Process: The anode diffusion layer of the anion exchange membrane water electrolyzer (AEM-WE) consists of a nickel mesh, a sintered nickel mesh, and a nickel felt (porosity ~80%). The cathode diffusion layer consists of a nickel felt (porosity ~80%) and a sintered nickel mesh. The cathode catalyst is Pt / C, and the anode catalyst is CoFe / NCNT / CF. The preparation method of the catalyst ink for the cathode and anode is as follows: 0.4 g of catalyst and 0.8 mL of FAA-3-SOLUTE-10 ionomer solution are homogenized in a 1:1 (v / v) ethanol-isopropanol mixed solvent by ultrasonication (ice-water bath, 40 kHz) combined with ball milling. With the aid of high-frequency ultrasound, argon-protected atomization, and substrate gradient temperature control, the resulting slurry is sprayed onto a PTFE plate through a continuous liquid supply platform and a high-precision peristaltic pump fluid control system, achieving continuous feeding with suppressed pulsation. The catalyst coating membrane (CCM) method was used, and the catalyst layer was embedded into a 100 μm thick AMVN anion exchange membrane via hot pressing (110 °C, 8 MPa, 240 s), followed by a stepped pressure release and pressure holding cooling process. Electrochemical performance was evaluated at 1 mol L⁻¹. -1 The process was carried out in KOH electrolyte (25 °C, 24 h) using an AEM-WE system (with anode circulation).

[0066] Figure 11 Performance testing of CoFe / NCNT / CF as an anode catalyst in AEM water electrolysis (with Pt / C catalyst as the cathode) was conducted. Figure 11 As can be seen from 'a', CoFe / NCNT / CF, as the anode catalyst for AEM water electrolysis, after 600 min of activation, had a voltage of 1.71 V, slightly lower than that of Pt / C+RuO2; subsequently, at 0.5 A / cm... 2 In a 1000-hour long-term stability test at current density, Pt / C+CoFe / NCNT / CF exhibited high stability and showed no degradation phenomenon. Figure 11 As shown in b in the figure. The above demonstrates that CoFe / NCNT / CF exhibits high activity and long-term stability in AEM water electrolysis.

[0067] Flexible zinc-air battery assembly process: Zinc foil is used as the anode, Examples 1-3 are directly used as self-supporting air cathodes, gel polymer electrolyte (GPE) is used, and nickel foam is used as the cathode conductive current collector layer for encapsulation.

[0068] The control group used a powdered Pt / C+RuO2 slurry coated with carbon cloth to prepare a flexible cathode sheet: 1 mg of catalyst, 1 mg of acetylene black, and 5% Nafion / ethanol solution (10 μL Nafion + 260 μL ethanol) were ultrasonically mixed to form a slurry, which was then uniformly coated onto the carbon cloth (loading 1 mg·cm⁻¹). -2 After drying at 60 ℃, it is used as an air cathode.

[0069] Preparation of gel electrolyte: 7.2 mL of acrylic acid was added dropwise to 10 mL of deionized water, followed by the addition of 4 g NaOH, 0.02 g of crosslinking agent N,N′-methylenebisacrylamide (MBA), and 0.22 g of initiator ammonium persulfate. After thorough stirring, the mixture was transferred to a petri dish and cured at 80 ℃ for 70 min. The resulting gel was then immersed in 6 mol·L⁻¹ ethylene glycol solution. -1 KOH solution, frozen at -30 ℃ for 30 min, promotes cross-linking.

[0070] Battery performance was measured on an electrochemical workstation (CHI 760E) and a battery testing system (LAND CT3001A).

[0071] Figure 12 This refers to the performance of zinc-air batteries in Examples 1-3 of the present invention and commercial Pt / C+RuO2. For example... Figure 12 As shown in a, based on the excellent ORR / OER bifunctional activity of CoFe / NCNT / CF (Example 1), it was used as an air cathode catalyst to assemble a flexible ZAB. Figure 12 As shown in b, CoFe / NCNT / CF-catalyzed FZAB successfully drove the small light bulb, and its open-circuit voltage remained stable at around 1.44 V for 800 seconds, which is superior to the Pt / C+RuO2 system (1.32 V), confirming the rapid activation capability and excellent stability of the electrode / electrolyte interface. Figure 12 As shown in c in the figure. In the constant current discharge test, its specific capacity reached 663 mAh g. -1 Zn It is significantly superior to the Pt / C+RuO2 system (574 mAh g). -1 Zn The most outstanding feature is its 200-cycle long-term performance, such as... Figure 12As shown in d, Example 1 can be stably cycled for more than 200 cycles, and its voltage difference from the 50th cycle to the 150th cycle increases (0.19 V), which is much better than the systems of Example 2 (0.22 V) and Example 3 (0.36 V). This difference is due to the shorter carbon nanotube integrated electrode structure effectively suppressing the shedding of active material and maintaining the integrity of the interface contact.

[0072] In summary, the self-supporting catalytic electrode material of the short-branched carbon nanotubes / alloys / carbon fibers of the present invention has high active sites and a stable metal composite structure, and exhibits excellent catalytic performance and device application performance as an electrocatalyst: (1) the OER overpotential of CoFe / NCNT / CF is 20 mA·cm -2 The limiting current density is only 410 mV, significantly lower than RuO2 (450 mV); at the same time, the oxygen reduction half-wave potential reaches 0.85 V, close to that of commercial Pt / C (0.86 V), but the limiting current density is increased by 17% (6.1 vs 5.2 mA·cm). -2 (2) Regarding the performance of AEM water electrolysis, CoFe / NCNT / CF was used as the anode catalyst for AEM water electrolysis. After 600 min of activation, the voltage was 1.71 V, which is slightly lower than that of Pt / C+RuO2. Subsequently, at 0.5 A / cm 2 After operating at the current density for 1000 h, the electrolyzer exhibited high stability and no degradation phenomenon. (3) The catalyst showed excellent performance in the flexible zinc-air battery, achieving 663 mAh·g in constant current discharge. -1 Zn Ultra-high specific capacity (574 mAh·g in commercial systems) -1 Zn It can be stably cycled for more than 100 cycles, and the polarization gap only increases by 0.19 V after 100 charge-discharge cycles.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-supporting catalytic electrode material made of short-branched carbon nanotubes / alloys / carbon fibers, characterized in that, The three-dimensional framework is composed of fabric-like carbon fiber, and the surface of the three-dimensional framework is connected to short-branch carbon nanotubes by covalent bonds. Bimetallic alloy nanoparticles are embedded in the tube body of the short-branch carbon nanotubes. The length of the short-branch carbon nanotubes is 0.1-0.4 μm. The bimetallic alloy nanoparticles are Co3Fe7 nanoparticles. The fabric-like carbon fiber is fabric-like bamboo carbon fiber. The preparation method of the short-branched carbon nanotube / alloy / carbon fiber self-supporting catalytic electrode material includes the following steps: The fiber cloth is pyrolyzed and carbonized to produce cloth-like carbon fibers; Add iron salts and cobalt salts to water and mix thoroughly to prepare a mixed solution; The fabric-like carbon fibers are added to the mixed solution for impregnation; The impregnated fabric-like carbon fibers are dried and coated onto melamine powder. Under an inert atmosphere, the temperature is programmed to rise to 850-950 ℃ and calcined at that temperature to obtain the final product.

2. The self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers as described in claim 1, characterized in that, The Co3Fe7 nanoparticles have a metal interface.

3. The self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers as described in claim 1, characterized in that, The temperature for pyrolysis carbonization is 950-1050 ℃.

4. The self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers as described in claim 1, characterized in that, The concentration of the mixed salt in the mixed solution is 0.27-0.33 mol·L⁻¹. -1 .

5. The self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers as described in claim 1, characterized in that, During the impregnation process, the sample is first ultrasonically treated, and then left to stand.

6. The self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers as described in claim 1, characterized in that, The programmed temperature rise rate is 4.5-5.5 ℃·min. -1 .

7. The self-supporting catalytic electrode material of short-branched carbon nanotubes / alloys / carbon fibers as described in claim 1, characterized in that, The calcination time is 1.8-2.2 h.

8. The application of the short-branch carbon nanotube / alloy / carbon fiber self-supporting catalytic electrode material according to any one of claims 1 to 7 in flexible zinc-air batteries or water electrolysis for hydrogen production.

9. The application as described in claim 8, characterized in that, The short-branched carbon nanotube / alloy / carbon fiber self-supporting catalytic electrode material is directly used as the air cathode of the zinc-air battery.

10. The application as described in claim 8, characterized in that, The short-branched carbon nanotube / alloy / carbon fiber self-supporting catalytic electrode material is used as the anode catalyst for hydrogen production by water electrolysis.

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