Transition metal-nitrogen-doped carbon nanotube array self-supported electrode and preparation and application thereof

Abstract

The application belongs to the field of air electrode materials of zinc-air batteries, and discloses a kind of transition metal nitrogen-doped carbon nanotube array self-supporting electrode and preparation and application. First, the application dissolves poly-metallic sulfate in water according to the proportion, adjusts the acidic pH, and then reduces the metal to the working electrode under the voltage of-0.75V vs SCE. Then, the voltage of 0.3V vs SCE is applied to etch the copper metal, and a porous alloy thin film electrode is obtained. The product obtained above is subjected to chemical vapor deposition, and the target product, nitrogen-doped carbon nanotube-coated metal alloy array structure material, is obtained. The three-dimensional porous interconnected network structure promotes ion transmission and electrolyte diffusion, and combined with the metal alloy particles grown on the tip, there are more active site quantities. The active sites can better contact with the electrolyte, so that the electrode material has excellent oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance.

Description

Technical Field

[0001] This invention belongs to the field of air electrode materials for zinc-air batteries, and specifically relates to a class of transition metal@nitrogen-doped carbon nanotube array self-supporting electrodes and their preparation and application. Background Technology

[0002] Modern society continues to see a growing demand for energy from fossil fuels with limited reserves. Against this backdrop, global investment in the development of clean and renewable energy sources is increasing, but the effective utilization of these intermittent energy sources requires efficient and economical energy storage systems. The limited energy density, poor safety performance, and high cost of raw materials for lithium-ion batteries restrict their further development. Zinc-air batteries, due to their relatively high specific energy (1218 Wh / kg), offer a solution. -1 Zinc-air batteries are among the best choices due to their excellent safety, low cost, and environmental friendliness. Zinc is abundant in the Earth's crust, inexpensive, and recyclable; furthermore, the aqueous electrolyte is non-flammable in the event of a short circuit, ensuring the safety of zinc-air batteries.

[0003] However, zinc-air batteries have not yet achieved large-scale practical application, mainly due to several challenges they face. A major bottleneck hindering their development is the oxygen evolution / reduction reaction (OER / ORR), the primary reaction on the air electrode during charge and discharge. This reaction is typically limited by its slow kinetics, leading to high overpotential, suboptimal energy efficiency, low power density, and poor cycle stability. These problems severely restrict the commercialization of zinc-air batteries. Currently, precious metals such as platinum and ruthenium are commonly used, but their scarcity, high cost, limited functionality, and poor durability hinder their large-scale practical application.

[0004] In recent years, a large amount of research has been dedicated to improving the performance of zinc-air batteries for their practical applications. Among these efforts, the air cathode, as a crucial component of the zinc-air battery system, directly impacts the electrochemical performance of the battery, making it a key research focus. Currently, the initial fabrication of air cathodes is primarily based on traditional slurry coating methods. In this method, an electrocatalyst and binder additives are mixed to form a slurry, which is then loaded onto a conductive substrate via droplet casting. Due to the non-conductive nature of the binder additives, the internal resistance inevitably increases. Furthermore, electrocatalyst stripping caused by binder deactivation during operation leads to reduced performance and shortened lifespan of the zinc-air battery. Therefore, designing and fabricating binder-free air cathodes integrated with highly active materials to reduce discharge charge overpotential and achieve well-optimized open-pore structures to promote mass transfer is one research direction. Another research direction is the development of low-cost, non-precious metal-based bifunctional electrocatalysts. Transition metal-based electrocatalysts with different combinations (single-metal and bi-metal) have been identified as promising OER catalytic candidates due to their active sites, attractive conductivity and synergistic effects, affordability, and environmental friendliness. Adding transition metals (such as Fe, Co, and Mn) to carbon has been shown to further enhance ORR activity. Therefore, transition metal-doped carbon nanotubes (CNTs) are considered effective electrocatalysts for ORR / OER. However, metal CNTs are prone to aggregation during synthesis or degradation under extreme operating conditions. The challenge lies in dispersing high-density and well-defined catalyst particles on carbon nanotubes; increasing the amount of active sites is an effective way to achieve high-performance bifunctional catalysts. In summary, exploring self-supporting air cathodes, which are inexpensive, easy to prepare and scalable, possess excellent conductivity, and exhibit good bifunctional catalytic activity, is an effective way to improve the electrochemical performance of zinc-air batteries and realize their practical application. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a class of transition metal@nitrogen-doped carbon nanotube array self-supporting electrodes.

[0006] Another objective of this invention is to provide a transition metal@nitrogen-doped carbon nanotube array self-supporting electrode prepared by the above method. In this electrode, the nitrogen-doped carbon nanotube array grows neatly and orderly on the self-supporting electrode, and the top of the nitrogen-doped carbon nanotube array is enriched with transition metal.

[0007] Another objective of this invention is to provide the application of the aforementioned transition metal alloy@nitrogen-doped carbon nanotube array self-supporting electrode in zinc-air batteries and flexible wearable devices.

[0008] The objective of this invention is achieved through the following solution:

[0009] A method for fabricating a class of transition metal@nitrogen-doped carbon nanotube array self-supporting electrodes includes the following steps:

[0010] (1) Wet electrochemical preparation of copper-containing transition metal alloys: First, soluble copper salt and soluble transition metal salt are uniformly dissolved in water, then boric acid is added and stirred until completely dissolved, then the pH value is adjusted to acidity, a three-electrode system is used, a reverse voltage is applied, and copper-containing transition metal alloys are prepared on a conductive substrate.

[0011] (2) Electrochemical etching to prepare porous transition metal alloy: Apply a positive voltage to the copper-containing transition metal alloy obtained in step (1) to etch part or all of the copper metal to prepare a porous transition metal self-supporting sheet material. Wash it repeatedly with water until the washing solution is clear and then dry it.

[0012] (3) Preparation of nitrogen-doped carbon nanotube-coated transition metal by vapor deposition: The porous transition metal self-supporting sheet material obtained in step (2) is coated in a ceramic boat containing dicyandiamide, and then carbonized at high temperature under N2 atmosphere. After the reaction is completed, the transition material coated with nitrogen-doped carbon nanotubes is obtained, namely the transition metal@nitrogen-doped carbon nanotube array self-supporting electrode.

[0013] The transition metal in the transition metal@nitrogen-doped carbon nanotube array self-supporting electrode includes a single elemental transition metal and a transition metal alloy.

[0014] The soluble copper salt and soluble transition metal salt mentioned in step (1) are all relatively independent hydrochloride, sulfate or nitrate; the soluble transition metal is at least one of soluble nickel salt, soluble iron salt, soluble manganese salt and soluble cobalt salt.

[0015] The amounts of the soluble copper salt and soluble transition metal salt mentioned in step (1) satisfy the following:

[0016] When the soluble transition metal salt is a soluble nickel salt and a soluble iron salt, the soluble nickel salt, soluble iron salt and soluble copper salt are NiSO4·6H2O, FeSO4·7H2O and CuSO4·5H2O, respectively, and their molar ratio is 1:0.1-1:0.01-0.5, preferably 1:0.1:0.01.

[0017] When the soluble transition metal salt is a soluble nickel salt and a soluble cobalt salt, the soluble nickel salt, soluble cobalt salt and soluble copper salt are NiSO4·6H2O, CoSO4·7H2O and CuSO4·5H2O, respectively, and their molar ratio is 1:0.01-1:0.01-0.5, preferably 1:0.1:0.01.

[0018] When the soluble transition metal salt is a soluble nickel salt and a soluble manganese salt, the soluble nickel salt, soluble manganese salt and soluble copper salt are NiSO4·6H2O, MnSO4, and CuSO4·5H2O, respectively, and their molar ratio is 1:0.05-1:0.01-0.5, preferably 1:0.1:0.01.

[0019] When the soluble transition metal salt is a soluble nickel salt, the soluble nickel salt and soluble copper salt are NiSO4·6H2O and CuSO4·5H2O, respectively, and their molar ratio is 1:0.01-0.5, preferably 1:0.02.

[0020] The amount of boric acid used in step (1) satisfies the following: the molar ratio of soluble copper salt to boric acid is 1:20-100, preferably 1:50.

[0021] The amount of water used in step (1) satisfies the following condition: the concentration of soluble copper salt in the completely dissolved solution is 0.01-0.03 mol / L.

[0022] The wet electrochemical method described in step (1) refers to using a three-electrode system in a Chenhua 660E electrochemical workstation, using a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and a conductive substrate as the working electrode, and applying a constant voltage, preferably a constant potential of -0.75 to -1V, for 1 to 2 hours, with the preferred values ​​being -0.75V and 1 hour.

[0023] The conductive substrate mentioned in step (1) is one of the following: carbon substrate (such as carbon cloth), foam metal substrate, conductive sponge, and melamine sponge.

[0024] The etching of copper metal in step (2) refers to applying a constant potential of 0.1 to 0.4V, preferably 0.3V, to the three-electrode system of step (1) until the current is 0.1 to 1A or the current returns to zero. When the current returns to zero, all the copper metal is etched; when the current is 0.1 to 1A, preferably 0.5A, the copper is partially etched, and a good porous structure is formed.

[0025] The amount of dicyandiamide used in step (3) is 0.05–0.5 g / cm³. -2 The merit value is 0.13 g / cm³. -2 The area refers to the area of ​​the conductive substrate.

[0026] The high-temperature carbonization mentioned in step (3) refers to holding at 600-900℃ for 0.5-3h; preferably at 750℃ for 0.5-1h.

[0027] A transition metal alloy@nitrogen-doped carbon nanotube array self-supporting electrode, prepared by the above method, possesses both mechanical flexibility and electrocatalytic activity. It can be directly used as the air cathode in both liquid and all-solid-state zinc-air batteries, achieving zinc-air batteries with considerable charge-discharge specific capacity and high cycle stability. In liquid zinc-air batteries, it can provide an open-circuit voltage as high as 1.52V and can cycle stably for 350 hours. In all-solid-state zinc-air batteries, it can provide an open-circuit voltage as high as 1.53V and can cycle stably for 24 hours. It can normally provide power to LED panels under different bending conditions, and holds promise for providing power to emerging flexible wearable and portable electronic devices.

[0028] This invention first dissolves a polymetallic sulfate in water according to a certain ratio, adjusts the pH to acidic, and then reduces the metal to the working electrode under a voltage of -0.75V vsSCE. Next, a voltage of 0.3V vsSCE is applied to etch the copper metal, resulting in a porous alloy thin-film electrode. The obtained product is then subjected to chemical vapor deposition. During this process, dicyandiamide is carbonized to obtain N-doped carbon, providing a carbon-nitrogen source, while the electrodeposited metal provides the metal source. Its porous structure increases surface roughness, facilitating the growth of carbon nanotubes into a nanoarray. Furthermore, the growth of carbon nanotubes follows a "tip effect" mechanism, where metal particles are encapsulated at the tips of the carbon nanotubes. Therefore, after the reaction, the target product, a nitrogen-doped carbon nanotube-coated metal alloy array structure, is obtained. This three-dimensional porous interconnected network structure promotes ion transport and electrolyte diffusion, and the combination of tip-grown metal alloy particles results in a greater number of active sites. These active sites can better contact the electrolyte, giving the electrode material excellent oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] (1) The nitrogen-doped carbon nanotube-coated metal alloy array structure self-supporting material prepared by this invention can be directly grown on flexible materials without the need for binders and industrial ball milling coating, thus reducing industrial input. Moreover, the synthesis process adopts the electrodeposition process that is already ready for industrial production, the synthesis method is simple, highly reproducible, and can be rapidly scaled up for industrial production.

[0031] (2) The nitrogen-doped carbon nanotube-coated metal alloy array structure self-supporting material prepared by the present invention has high electrochemical activity, good cycle performance, and high mechanical flexibility. It can be used to prepare flexible zinc-air batteries, which have good flexibility and portability, and have good application and development prospects in the field of flexible wearable devices. Attached Figure Description

[0032] Figure 1Examples 1 and 2 show the OER performance of nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrodes prepared with different precursors in a three-electrode system.

[0033] Figure 2 Examples 1 and 2 show the ORR performance of nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrodes prepared with different precursors in a three-electrode system.

[0034] Figure 3 The X-ray diffraction (XRD) spectra of the NiFe-P alloy electrode, Ni-P electrode, NiCo-P alloy electrode, NiMn-P alloy electrode, and NiCu-P alloy electrode prepared in Examples 2, 3, 4, 5, and 6 are shown.

[0035] Figure 4 This is a scanning electron microscope (SEM) image of the NiFe-P porous metal alloy prepared in Example 2.

[0036] Figure 5 The image shows a scanning electron microscope (SEM) image of the NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy prepared in Example 2.

[0037] Figure 6 This is a transmission electron microscope (TEM) image of the NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy prepared in Example 2.

[0038] Figure 7 The OER performance diagrams for the nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrodes prepared in Examples 2, 3, 4, 5, and 6 are shown in a three-electrode system.

[0039] Figure 8 The ORR performance of the nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrodes prepared in Examples 2, 3, 4, 5, and 6 is shown in a three-electrode system.

[0040] Figure 9 The graph shows the cycle performance of the NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrode assembly example 8, a liquid zinc-air battery, under constant current charge-discharge testing.

[0041] Figure 10 The voltage-specific capacity curves of the NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrode assembly example 8, and the liquid zinc-air battery, are obtained from the constant current discharge test.

[0042] Figure 11This is a diagram illustrating the practical application of the NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrode assembly example 9, which is the air cathode of a flexible solid-state zinc-air battery. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0044] In the embodiments, porous metal elements or alloys are represented by P to indicate a porous structure and N to indicate a non-porous structure. For example, NiFe-N indicates a non-porous NiFe alloy, NiFe-P indicates a porous NiFe alloy, and similarly, NiFe@CNTs-P indicates a nickel-iron alloy@nitrogen-doped carbon nanotubes obtained by pyrolysis reduction of a NiFe-P alloy precursor.

[0045] In this embodiment, the area of ​​the conductive carbon cloth substrate is 3cm*5cm.

[0046] Example 1

[0047] This embodiment describes a method for preparing a flexible electrode material (precursor non-porous bimetallic alloy) coated with nitrogen-doped carbon nanotubes, named NiFe@CNTs-N. The specific preparation steps are as follows:

[0048] (1) Preparation of NiFe@CNTs-N flexible electrode: Dissolve 1M nickel sulfate, 0.1M ferrous sulfate, and 0.5M boric acid in 100ml of water. Adjust the pH to 4. Use a three-electrode method, with a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and carbon cloth as the working electrode, and perform electrodeposition for 3600s at -0.75V vs SCE voltage. Place the obtained NiFe-N alloy electrode in a ceramic boat containing dicyandiamide, with the amount of dicyandiamide being 0.13g / cm² of the NiFe-N alloy electrode area (3cm*5cm). -2 Calculations were performed, and then, under the protection of N2 atmosphere, the temperature was increased to 750℃ at a rate of 5℃ / min. After high-temperature carbonization for 1 hour, the NiFe@CNT-N flexible electrode was obtained.

[0049] Example 2

[0050] This embodiment describes a method for preparing a nitrogen-doped carbon nanotube-coated NiFe-P alloy flexible electrode material (precursor porous bimetallic alloy). The specific preparation steps are as follows:

[0051] (1) Preparation of NiFe@CNT-P flexible electrode: Dissolve 1M nickel sulfate, 0.1M ferrous sulfate, 0.01M copper sulfate, and 0.5M boric acid in 100ml of water. Adjust the pH to 4. Use a three-electrode method, with a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and carbon cloth as the working electrode, and perform electrodeposition for 3600s at -0.75V vs SCE voltage. Finally, etch copper metal at 0.3V vs SCE voltage until the current reaches zero. Wash repeatedly with water and dry in a vacuum drying oven at 50℃ to obtain the NiFe-P alloy electrode. Place the obtained NiFe-P alloy electrode in a ceramic boat containing dicyandiamide, with the amount of dicyandiamide being 0.13g / cm² of the NiFe-P alloy electrode area (3cm*5cm). -2 Calculations were performed, and then, under the protection of N2 atmosphere, the temperature was increased to 750℃ at a rate of 5℃ / min. After high-temperature carbonization for 1 hour, the NiFe@CNT-P flexible electrode was obtained.

[0052] Example 3

[0053] This embodiment describes a method for preparing a nitrogen-doped carbon nanotube-coated Ni-P metal flexible electrode material. The specific preparation steps are as follows:

[0054] (1) Preparation of Ni@CNT-P flexible electrode: Dissolve 1M nickel sulfate, 0.01M copper sulfate, and 0.5M boric acid in 100ml of water. Adjust the pH to 4. Use a three-electrode method, with a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and carbon cloth as the working electrode, and perform electrodeposition for 3600s at -0.75V vs SCE voltage. Finally, etch copper metal at 0.3V vs SCE voltage until the current reaches zero. Wash repeatedly with water and dry in a vacuum drying oven at 50℃ to obtain the Ni-P electrode. Place the obtained Ni-P electrode in a ceramic boat containing dicyandiamide, with the amount of dicyandiamide being 0.13g / cm² of the Ni-P electrode area (3cm*5cm). -2 Calculations were performed, and then, under the protection of N2 atmosphere, the temperature was increased to 750℃ at a rate of 5℃ / min. After high-temperature carbonization for 1 hour, the Ni@CNT-P flexible electrode was obtained.

[0055] Example 4

[0056] This embodiment describes a method for preparing a flexible electrode material of NiCo-P alloy coated with nitrogen-doped carbon nanotubes. The specific preparation steps are as follows:

[0057] (1) Preparation of NiCo@CNT-P flexible electrode: Dissolve 1M nickel sulfate, 0.1M cobalt sulfate, 0.01M copper sulfate, and 0.5M boric acid in 100ml of water. Adjust the pH to 4. Use a three-electrode method, with a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and carbon cloth as the working electrode, and perform electrodeposition for 3600s at -0.75V vs SCE voltage. Finally, etch copper metal at 0.3V vs SCE voltage until the current reaches zero. Wash repeatedly with water and dry in a vacuum drying oven at 50℃ to obtain the NiCo-P alloy electrode. Place the obtained NiCo-P alloy electrode in a ceramic boat containing dicyandiamide, with the amount of dicyandiamide being 0.13g / cm² of the NiCo-P alloy electrode area (3cm*5cm). -2 Calculations were performed, and then, under the protection of N2 atmosphere, the temperature was increased to 750℃ at a rate of 5℃ / min. After high-temperature carbonization for 1 hour, the NiCo@CNT-P flexible electrode was obtained.

[0058] Example 5

[0059] This embodiment describes a method for preparing a flexible electrode material of NiMn-P alloy coated with nitrogen-doped carbon nanotubes. The specific preparation steps are as follows:

[0060] (1) Preparation of NiMn@CNT-P flexible electrode: Dissolve 1M nickel sulfate, 0.1M manganese sulfate, 0.01M copper sulfate, and 0.5M boric acid in 100ml of water. Adjust the pH to 4. Use a three-electrode method, with a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and carbon cloth as the working electrode, and perform electrodeposition for 3600s at -0.75V vs SCE voltage. Finally, etch copper metal at 0.3V vs SCE voltage until the current reaches zero. Wash repeatedly with water and dry in a vacuum drying oven at 50℃ to obtain the NiMn-P alloy electrode. Place the obtained NiMn-P alloy electrode in a ceramic boat containing dicyandiamide, with the amount of dicyandiamide being 0.13g / cm² of the NiMn-P alloy electrode area (3cm*5cm). -2 Calculations were performed, and then, under the protection of N2 atmosphere, the temperature was increased to 750℃ at a rate of 5℃ / min. After high-temperature carbonization for 1 hour, the NiMn@CNT-P flexible electrode was obtained.

[0061] Example 6

[0062] This embodiment describes a method for preparing a flexible electrode material of NiCu-P alloy coated with nitrogen-doped carbon nanotubes. The specific preparation steps are as follows:

[0063] (1) Preparation of NiCu@CNT-P flexible electrode: Dissolve 1M nickel sulfate, 0.02M copper sulfate, and 0.5M boric acid in 100ml of water. Adjust the pH to 4. Use a three-electrode method, with a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and carbon cloth as the working electrode, and perform electrodeposition for 3600s at -0.75V vs SCE voltage. Finally, etch some copper metal at 0.3V vs SCE voltage. When the current reaches 0.5A, the porous structure is considered to be well formed. Wash repeatedly with water and dry in a vacuum drying oven at 50℃ to obtain the NiCu-P alloy electrode. Place the obtained NiCu-P alloy electrode in a ceramic boat containing dicyandiamide, with the amount of dicyandiamide being 0.13g / cm² of the NiCu-P alloy electrode area (3cm*5cm). -2 Calculations were performed, and then, under the protection of N2 atmosphere, the temperature was increased to 750℃ at a rate of 5℃ / min. After high-temperature carbonization for 1 hour, the NiCu@CNT-P flexible electrode was obtained.

[0064] Example 7

[0065] A three-electrode system was used, with a silver chloride electrode as the indicator electrode, a platinum sheet as the counter electrode, and a transition metal nickel / alloy@nitrogen-doped carbon nanotube self-supporting electrode as the working electrode. The OER and ORR performance of the pure carbon cloth CC electrode, NiFe-P electrode, NiFe@CNT-N electrode, NiFe@CNT-P electrode, Ni@CNT-P electrode, NiCo@CNT-P electrode, NiMn@CNT-P electrode, and NiCu@CNT-P electrode were tested using 1M KOH and oxygen-saturated 0.1M KOH, respectively.

[0066] Example 8

[0067] A zinc-air liquid battery was assembled using the obtained NiFe@CNT-P electrode. The NiFe@CNT-P electrode served as a self-supporting (no binder or conductive additive required) air cathode, and the zinc sheet served as the anode. A solution containing 0.2 mol L... -1 Potassium hydroxide with zinc acetate additive (concentration 6 mol / L) -1 It is used as an electrolyte to assemble a liquid zinc-air battery.

[0068] Example 9

[0069] A zinc-air solid-state battery was assembled using the obtained NiFe@CNT-P electrode. The NiFe@CNT-P electrode served as a self-supporting (no binder or conductive additive required) air cathode, and the zinc sheet served as the anode. A zinc-air solid-state battery containing 0.25 mol L... -1 Potassium hydroxide (concentration 11.25 mol L) as zinc oxide additive -15 mL of electrolyte was mixed with 0.5 g of acrylic acid and 0.075 g of methylenebisacrylamide and stirred for 5 min. After filtration, 75 μL of 0.3 M potassium persulfate was added as a traction agent to form a gel electrolyte. The above components were then assembled into a solid-state zinc-air battery.

[0070] Figure 1 The OER performance diagrams for the nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrodes prepared in Examples 1 and 2, the NiFe-P alloy electrode prepared in Example 2, and pure carbon cloth (CC) in the three-electrode system described in Example 7 are shown. (At a concentration of 1 mol L...) -1 In potassium hydroxide electrolyte, the OER onset potential of NiFe@CNTs-P (1.35V vs RHE) at a current density of 10 mA cm⁻¹ -2 The corresponding voltage is (1.450V vs RHE), and the OER onset potential of NiFe@CNTs-N is (1.35V vs RHE) at a current density of 10mA cm⁻¹. -2 The corresponding voltage is (1.47V vs RHE), and the OER limiting current density of NiFe@CNTs-P is also much greater than that of NiFe@CNTs-N, showing the necessity of porous transition metal alloys as precursors for improving OER performance.

[0071] Figure 2 The ORR performance diagrams for the nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrodes prepared in Examples 1 and 2, the NiFe-P alloy electrode prepared in Example 2, and pure carbon cloth CC are shown in the three-electrode system described in Example 7. The oxygen saturation concentration is 0.1 mol / L. -1 In potassium hydroxide electrolyte, the ORR limiting current density of NiFe@CNTs-P reaches 5 mA / cm². -2 The ORR limiting current density of NiFe@CNTs-N is only 3 mA / cm². -2 This demonstrates the good ORR performance of NiFe@CNTs-P.

[0072] Figure 3 The images show the X-ray diffraction (XRD) spectra of the porous NiFe-P alloy electrodes, Ni-P electrodes, NiCo-P alloy electrodes, NiMn-P alloy electrodes, and NiCu-P alloy electrodes prepared in Examples 2, 3, 4, 5, and 6. It can be seen that the porous metal alloy samples prepared in these examples exhibit obvious characteristic diffraction peaks of metal alloys. This demonstrates that the wet electrochemical method can successfully load metals or metal alloys onto flexible electrodes.

[0073] Figure 4This is a scanning electron microscope (SEM) image of the NiFe-P porous alloy prepared in Example 2. The image shows that the NiFe-P alloy grows uniformly in a porous, flower-like pattern on the carbon fiber substrate, possessing a highly porous structure.

[0074] Figure 5 This is a scanning electron microscope (SEM) image of the NiFe@CNTs-P nitrogen-doped carbon nanotubes coated with a transition metal alloy prepared in Example 2. It can be seen that the carbon nanotubes with NiFe alloy particles at their tips are neatly and uniformly loaded on the carbon fiber substrate, exhibiting an orderly, vertically growing array.

[0075] Figure 6 This is a transmission electron microscope (TEM) image of the NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy prepared in Example 2. It shows the synthesis of a carbon nanotube array structure with top structural domains encapsulating the NiFe alloy. The carbon nanotubes grow in a bamboo-like pattern, with NiFe metal alloy particles encapsulated and enriched only at the tips of the carbon nanotubes.

[0076] Figure 7 The OER performance graphs for the nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrodes prepared in Examples 2, 3, 4, 5, and 6 are shown in the three-electrode system described in Example 7. The OER performance was achieved at a concentration of 1 mol L⁻¹. -1 In potassium hydroxide electrolyte, the OER onset potential of Ni@CNTs-P (1.348 V vs RHE) at a current density of 10 mA cm⁻¹ -2 The corresponding voltage at this time is (1.458V vs RHE); the OER onset potential of NiCo@CNTs-P is (1.348V vs RHE), and the current density reaches 10 mA / cm². -2 The corresponding voltage at this time is (1.454V vs RHE); the OER onset potential of NiFe@CNTs-P is (1.348V vs RHE), and the current density reaches 10 mA / cm². -2 The corresponding voltage is (1.450V vs RHE), etc., which shows excellent OER activity compared with recently reported excellent bifunctional catalysts.

[0077] Figure 8 The ORR performance of the nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrodes prepared in Examples 2, 3, 4, 5, and 6 is shown in the three-electrode system described in Example 7. The oxygen saturation concentration is 0.1 mol / L. -1In potassium hydroxide electrolyte, the ORR onset potential of Ni@CNTs-P was 0.91V vs RHE, and the half-wave potential was 0.8V vs RHE; the ORR onset potential of NiCo@CNTs-P was 0.91V vs RHE, and the half-wave potential was 0.8V vs RHE; the ORR onset potential of NiFe@CNTs-P was 0.92V vs RHE, and the half-wave potential was 0.81V vs RHE, etc. These electrodes exhibited significant ORR activity.

[0078] Figure 9 Example 8: Assembling the NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrode prepared in Example 2, and performing a constant current test (current density of 10 mA cm⁻¹) on a liquid zinc-air battery. -2 The cycle performance graph of charge-discharge test. After 200 hours of cycling, the potential difference is only 0.79V, indicating that NiFe@CNTs-P can achieve excellent battery performance as the air cathode of zinc-air battery.

[0079] Figure 10 Example 8: Assembling the NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrode prepared in Example 2, and performing a constant current test (current density of 20 mA cm⁻¹) on a liquid zinc-air battery. -2 Voltage-specific capacity curves from discharge testing. The battery can achieve 799mAh g. Zn –1 Specific capacity.

[0080] Figure 11 Example 9 illustrates the assembly of a NiFe@CNTs-P nitrogen-doped carbon nanotube-coated transition metal alloy flexible electrode using a solid-state flexible zinc-air battery to power an LED light panel. Two flexible batteries can power an LED light panel with 42 small bulbs, and the batteries can be bent back to their original shape. Three batteries can charge a smartphone.

[0081] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for fabricating a class of transition metal@nitrogen-doped carbon nanotube array self-supporting electrodes, characterized in that... Includes the following steps: (1) Wet electrochemical preparation of copper-containing transition metal alloys: First, soluble copper salt and soluble transition metal salt are uniformly dissolved in water, then boric acid is added and stirred until completely dissolved, then the pH value is adjusted to acidity, a three-electrode system is used, a reverse voltage is applied, and copper-containing transition metal alloys are prepared on a conductive substrate. (2) Electrochemical etching to prepare porous transition metal alloy: Apply a positive voltage to the copper-containing transition metal alloy obtained in step (1) to etch part or all of the copper metal to prepare a porous transition metal self-supporting sheet material. Wash it repeatedly with water until the washing solution is clear and then dry it. (3) Preparation of nitrogen-doped carbon nanotubes coated with transition metal by vapor deposition: The porous transition metal self-supporting sheet material obtained in step (2) is coated in a ceramic boat containing dicyandiamide, and then carbonized in N2 atmosphere. After the reaction is completed, the transition material coated with nitrogen-doped carbon nanotubes is obtained, namely, the transition metal@nitrogen-doped carbon nanotube array self-supporting electrode; in this electrode, the nitrogen-doped carbon nanotube array grows neatly and orderly on the self-supporting electrode, and the top of the nitrogen-doped carbon nanotube array is enriched with transition metal; The soluble copper salt and soluble transition metal salt mentioned in step (1) are all relatively independent hydrochloride, sulfate or nitrate; the soluble transition metal salt is at least one of soluble nickel salt, soluble iron salt, soluble manganese salt and soluble cobalt salt.

2. The method for fabricating a transition metal@nitrogen-doped carbon nanotube array self-supporting electrode according to claim 1, characterized in that: The amounts of the soluble copper salt and soluble transition metal salt mentioned in step (1) satisfy the following: When the soluble transition metal salts are soluble nickel salts and soluble iron salts, the molar ratio of soluble nickel salts, soluble iron salts and soluble copper salts is 1:0.1-1:0.01-0.5; When the soluble transition metal salts are soluble nickel salts and soluble cobalt salts, the molar ratio of soluble nickel salts, soluble cobalt salts, and soluble copper salts is 1:0.01-1:0.01-0.5; When the soluble transition metal salts are soluble nickel salts and soluble manganese salts, the molar ratio of soluble nickel salts, soluble manganese salts and soluble copper salts is 1:0.05-1:0.01-0.5; When the soluble transition metal salt is a soluble nickel salt, the molar ratio of the soluble nickel salt to the soluble copper salt is 1:0.01-0.

5.

3. The method for fabricating a transition metal@nitrogen-doped carbon nanotube array self-supporting electrode according to claim 1, characterized in that: The amount of boric acid used in step (1) satisfies the following: the molar ratio of soluble copper salt to boric acid is 1:20-100; The amount of water used in step (1) satisfies the following condition: the concentration of soluble copper salt in the completely dissolved solution is 0.01-0.03 mol / L.

4. The method for fabricating a transition metal@nitrogen-doped carbon nanotube array self-supporting electrode according to claim 1, characterized in that: The wet electrochemical method described in step (1) refers to using a three-electrode system, with a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and a conductive substrate as the working electrode, applying a constant voltage, a constant potential of -0.75 to -1V, for 1 to 2 hours.

5. The method for fabricating a transition metal@nitrogen-doped carbon nanotube array self-supporting electrode according to claim 1, characterized in that: The wet electrochemical method described in step (1) refers to the use of a three-electrode system, with a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and a conductive substrate as the working electrode, applying a constant voltage, a constant potential of -0.75V, and a time of 1h.

6. The method for fabricating a transition metal@nitrogen-doped carbon nanotube array self-supporting electrode according to claim 1, characterized in that: The conductive substrate mentioned in step (1) is one of the following: carbon substrate, foam metal substrate, conductive sponge, and melamine sponge.

7. The method for fabricating a transition metal@nitrogen-doped carbon nanotube array self-supporting electrode according to claim 1, characterized in that: The etching of part or all of the copper metal mentioned in step (2) refers to using a calomel electrode as the indicator electrode, nickel foam as the counter electrode, and a conductive substrate as the working electrode in a three-electrode system, applying a constant potential of 0.1 to 0.4V until the current is 0.1 to 1A or the current returns to zero. When the current is zero, all the copper metal is etched; when the current is 0.1 to 1 A, the copper is partially etched.

8. The method for fabricating a transition metal@nitrogen-doped carbon nanotube array self-supporting electrode according to claim 1, characterized in that: The amount of dicyandiamide used in step (3) is 0.05–0.5 g / cm³. -2 ; The carbonization mentioned in step (3) refers to holding at 600-900℃ for 0.5-3 hours.

9. A transition metal@nitrogen-doped carbon nanotube array self-supporting electrode prepared by the method according to any one of claims 1-8.

10. The application of the transition metal@nitrogen-doped carbon nanotube array self-supporting electrode according to claim 9 in liquid zinc-air batteries, all-solid-state zinc-air batteries, flexible wearable electronic devices, and portable electronic devices.

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