An orr-oer bifunctional electrocatalyst for zinc-air battery and a preparation method thereof

Abstract

The application discloses an ORR-OER bifunctional electrocatalyst for a zinc-air battery and a preparation method thereof, and belongs to the technical field of porous carbon catalyst material preparation.The preparation process of the nitrogen-doped porous carbon coated carbon nanotube catalyst is as follows: taking medium-temperature coal pitch as a carbon matrix, providing nitrogen source by using melamine, uniformly mixing the melamine with the carbon nanotube, and adopting one-step catalytic activation process to realize the preparation of the nitrogen-doped porous carbon coated carbon nanotube catalyst which has developed pores and nitrogen atom doping.In specific, the medium-temperature coal pitch is fully mixed with the melamine and the carbon nanotube, carbon dioxide is introduced during the activation process, and the nitrogen-doped porous carbon coated carbon nanotube catalyst is prepared through one-step catalytic activation.The porous carbon pore and the mixed structure of the carbon nanotube can be synergistically controlled by changing the carbon nanotube, the activation temperature, the heating rate and the activation time, and then the porous carbon catalyst material with developed pores and high nitrogen doping content can be obtained.

Description

Technical Field

[0001] This invention belongs to the technical field of catalysts for preparing battery electrodes from porous carbon materials, specifically relating to an ORR-OER bifunctional electrocatalyst for zinc-air batteries and its preparation method. Background Technology

[0002] With the shortage of traditional energy sources, global warming, and increasingly severe air pollution, the world is facing an energy crisis. To alleviate these problems, the development of renewable energy conversion and storage technologies has attracted significant attention. Zinc-air batteries are a new type of green energy storage technology with advantages primarily in the following aspects: High energy density: Zinc-air batteries have a high energy density, exceeding that of traditional lead-acid batteries by more than 50%. This means they can store more energy, providing a longer operating time for energy storage systems. Environmental friendliness: Zinc-air batteries use zinc and air as raw materials and do not contain harmful chemicals, making them more environmentally friendly. Compared to traditional batteries, zinc-air batteries generate significantly less waste and emissions during manufacturing, use, and disposal. Long lifespan: Zinc-air batteries have a very long lifespan, reaching over 5 years under normal use. This is mainly due to the stable nature of zinc, the positive electrode material, which does not exhibit significant corrosion or failure during long-term use. Rechargeability: Zinc-air batteries are also rechargeable, as a reverse electrochemical reaction can reduce oxygen at the anode to water and reform zinc particles. This rechargeability makes zinc-air batteries more flexible and adaptable to various energy storage needs. From the perspectives of ORR and OER, zinc-air batteries also offer certain advantages. Regarding ORR, since zinc-air batteries use air as an oxygen source, the ORR reaction can be carried out directly in air without the need for additional oxidants. This reduces catalyst costs and avoids environmental pollution caused by toxic oxidants. In terms of OER, the anode material of zinc-air batteries is zinc, rather than traditional heavy metals such as lead oxide or cadmium oxide. This means that zinc-air batteries have a much smaller environmental impact. At the same time, zinc also has good corrosion resistance, effectively preventing anode corrosion during the OER process, thus extending the lifespan of the zinc-air battery. In summary, zinc-air batteries offer high energy density, good environmental performance, long lifespan, and strong rechargeability, and possess certain advantages from both ORR and OER perspectives, thus showing broad application prospects.

[0003] With the development of new energy technologies, zinc-air batteries are expected to become an important energy storage technology and contribute to the realization of sustainable development. The high energy density and theoretical capacity, low cost, high safety and stability of zinc-air batteries make them have great development potential in the field of energy storage and energy conversion. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a decisive role in the energy conversion efficiency of zinc-air batteries. Both ORR and OER involve complex multi-electron transfer processes. The inherently slow kinetics of ORR and OER lead to relatively high overpotentials, resulting in low energy efficiency, low power density and short cycle life of zinc-air batteries in actual use. In alkaline solution, ORR follows the four-electron reaction rule: (1) O2(g) + * → *O2; (2) *O2 + H2O(l) + e– → *OOH + OH–; (3) *OOH + e– → *O + OH–; (4) *O + H2O(l) + e– → *OH + OH–; (5) *OH + e– → OH– + *, where * represents the active site. Both steps two and four involve the coupling process of reactive oxygen species (*O2 and *O) with protons dissociated from water; therefore, the efficiency of proton production from water dissociation largely determines the ORR reaction rate. In the ORR process, O2 adsorption and activation are another key factor determining the reaction rate. Traditional platinum-carbon battery catalysts have the following drawbacks from the perspectives of ORR (Oxygen Reduction Reaction) and OER (Oxygen Evolution Reaction): Regarding ORR: While platinum-carbon battery catalysts exhibit good catalytic performance in ORR, their drawbacks are also significant. Platinum metal resources are scarce and expensive, and its catalytic activity decreases due to surface oxidation, limiting their widespread use in practical applications. Regarding OER: Traditional platinum-carbon battery catalysts show relatively poor catalytic performance in OER, requiring a large electrical energy input to initiate the reaction and exhibiting low catalytic activity and stability. Furthermore, the OER activity of platinum-carbon battery catalysts is easily affected by impurities or contaminants, further reducing their catalytic performance. Therefore, to overcome the shortcomings of traditional platinum-carbon battery catalysts, it is necessary to find novel catalysts. Developing highly active water dissociation and O2 activation catalysts is key to improving ORR kinetics. Noble metal-based electrocatalysts exhibit high oxygen electrocatalytic activity, but their high cost and poor stability hinder the large-scale commercial development of rechargeable zinc-air batteries. Developing low-cost, highly active, stable, and durable non-noble metal-based ORR / OER bifunctional electrocatalysts for energy conversion has far-reaching significance. With the continuous development of science and technology, people are paying increasing attention to environmental protection and resource utilization, seeking more efficient, environmentally friendly, and sustainable energy and materials. Among these new energy and materials, carbon materials, due to their excellent physicochemical properties, are widely used in batteries, catalysis, adsorption, and other fields. At the same time, carbon materials with porous structures and large specific surface areas also have significant advantages in these fields.Therefore, the preparation of porous carbon materials has become one of the current research hotspots.

[0004] In recent years, coal tar pitch has been widely used in the preparation of carbon materials due to its abundant resources and low cost. Previous studies have reported methods for preparing porous carbon materials using raw materials such as coal tar pitch. However, coal tar pitch varies in composition and properties, thus requiring further improvements to its preparation process to enhance its performance. Summary of the Invention

[0005] The purpose of this invention is to address the following problems: ① poor ORR reaction activity due to proton shortage under alkaline conditions; ② poor power density and cycle stability of zinc-air batteries due to insufficient activity and stability of noble metal catalysts in ORR / OER bifunctional applications; ③ high OER overpotential (E) of catalysts prepared using high-cost noble metals. This invention provides an ORR-OER bifunctional electrocatalyst for zinc-air battery electrodes and its preparation method.

[0006] This invention addresses the preparation of nitrogen-doped porous carbon-coated carbon nanotube catalysts. Using medium-temperature coal tar pitch as the carbon matrix and melamine as the nitrogen source, these materials are uniformly mixed with carbon nanotubes. A one-step catalytic activation process is employed to prepare a nitrogen-doped porous carbon-coated carbon nanotube catalyst with both well-developed porosity and nitrogen atom doping. Specifically, medium-temperature coal tar pitch is used as the carbon matrix, thoroughly mixed with melamine and carbon nanotubes. Carbon dioxide is introduced during activation, and a nitrogen-doped porous carbon-coated carbon nanotube catalyst is prepared through a one-step catalytic activation process. By changing the carbon nanotubes, activation temperature, heating rate, and activation time, the porosity of the porous carbon and the mixed structure of the carbon nanotubes can be synergistically controlled, thereby obtaining a porous carbon catalyst material with well-developed porosity and high nitrogen doping content. The resulting nitrogen-doped porous carbon-coated carbon nanotube catalyst has a specific surface area of ​​up to 382.58 m². 2 / g, with a total pore volume of up to 0.1927cm³. 3 It contains a high nitrogen-doped structure with a nitrogen content of 1 / g. This invention has broad application prospects in porous carbon catalysts and other fields.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] An ORR-OER bifunctional electrocatalyst for zinc-air batteries, wherein the catalyst has the molecular formula NPC@CNTs (nitrogen-doped porous carbon-coated carbon nanotubes) and the structure is carbon nanotubes uniformly mixed in medium-temperature coal tar pitch uniformly dispersed in nitrogen-doped melamine.

[0009] A method for preparing the above-mentioned ORR-OER catalyst for zinc-air batteries, wherein the method comprises:

[0010] Step 1: Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence, and then mixed evenly to obtain the precursor;

[0011] Step 2: Mixing nanomaterials with precursors: Thoroughly mix the precursors and nanomaterials obtained in Step 1 and dissolve them in an ethanol solution. Sonicate for 5-300 min (preferably 30 min) to obtain a homogeneous mixture. Place the mixture in an oven at 30-100℃ and dry for 0.1-30 h to obtain a homogeneous mixture.

[0012] Step 3: High-temperature activation: Transfer the mixture obtained in Step 2 to a tube furnace, place it in an inert atmosphere, raise the temperature to 600-1200℃, and activate it with carbon dioxide for 0.5-30h. Then, allow the tube furnace to cool naturally to room temperature to obtain the ORR-OER bifunctional electrocatalyst for zinc-air batteries.

[0013] Furthermore, in step one, the mass ratio of the medium-temperature coal tar pitch to melamine (precursor) is 3:0.1-10.

[0014] Further, in step one, the medium-temperature coal tar pitch is obtained through the following process: coal tar is left to stand and dehydrate → desalted with sodium carbonate → coal tar is pumped into the convection section of a tubular heater → during this stage, the coal tar is heated to 120-130 degrees Celsius → it enters an evaporator for dehydration → light oil vapor is distilled off at the top of the tower and enters an oil-water separator for oil-water separation via a condenser → the dehydrated coal tar at the bottom of the tower flows into an anhydrous tar tank → the coal tar is pumped into the radiant section of the tubular heater for heating → it enters a secondary evaporator → the light fractions in the coal tar are immediately evaporated and collected in a fractionation tower for graded processing, successively obtaining light oil, phenolic oil, naphthalene oil, wash oil, and anthracene oil → medium-temperature pitch is discharged from the bottom of the tower at a temperature of about 370 degrees Celsius → it is cooled to 220-240 degrees Celsius by a vaporization cooler → it enters an asphalt high-level tank for natural cooling for several hours to obtain medium-temperature pitch. The coal tar pitch and melamine are mixed evenly in a mass ratio of 3:2.

[0015] Furthermore, in step two, the nanomaterial is carbon nanotubes.

[0016] Furthermore, in step two, the mass ratio of medium-temperature coal tar pitch: melamine: carbon nanotubes is 15:10:0.5-20.

[0017] Furthermore, in step two, the drying method is vacuum drying, hot air drying, or natural evaporation drying; the drying temperature is 60℃, and the drying time is 60 minutes.

[0018] Furthermore, step two is replaced by: thoroughly mixing the precursor obtained in step one with carbon nanotubes to obtain a homogeneous mixture.

[0019] Furthermore, in step three, the inert atmosphere is high-purity nitrogen and high-purity carbon dioxide, the volume of carbon dioxide is 5%-60% of the total gas volume, and the gas flow rate is 50mL / min to 500mL / min.

[0020] Furthermore, in step three, the heating rate of the tubular furnace is 1℃ / min to 20℃ / min, and the carbon dioxide activation treatment time is 0.1-10h.

[0021] The advantages of this invention over the prior art are as follows:

[0022] 1. This invention uses medium-temperature coal tar pitch as the main raw material for porous carbon precursors. The carbon source is widely available, naturally derived, and inexpensive. It has a high fixed carbon content and low impurity content, and does not require additional pretreatment (such as carbonization). By effectively utilizing the natural structure of medium-temperature coal tar pitch, precursors with high microcrystalline content can be obtained, providing a platform for in-depth control of the microcrystalline structure of porous carbon carbon nanotubes. It is suitable for mass production. At the same time, medium-temperature coal tar pitch can act as a fluid to disperse carbon nanotubes, greatly maximizing the superior performance of carbon nanotubes.

[0023] 2. Compared to the template method, which requires the precursor to be in a fluid state, this invention adopts a one-step high-temperature activation method, which does not require complex processes such as melting, nor does it require the addition of additional catalysts. Through the mixing, co-heating and activation process of carbon nanotubes with the precursor, pores can be formed by the diffusion between carbon nanotubes and solid materials and the etching effect of CO2. The operation is simple and eliminates the cumbersome and complicated process route. At the same time, the activation and pore-forming process of carbon dioxide will make the pore structure of coal tar pitch more developed, thereby making the carbon nanotubes more uniformly dispersed.

[0024] 3. The introduction of carbon nanotubes provides essential protons for the nitrogen-doped porous carbon@carbon nanotubes (NPC@CNTs) catalyst in ORR catalysis, lowering the water dissociation energy barrier, optimizing the four-electron reaction pathway of ORR, and enhancing the ORR reactivity. The redox peak in the CV of ORR is 0.837V, which is superior to the commercial catalyst Pt / C-20% (0.803V) prepared with noble metals. The half-wave potential and onset potential are 0.879V and 0.985V, respectively, both higher than those of Pt / C-20% (0.81V and 0.928V).

[0025] 4. An innovative nitrogen-doped porous carbon-coated carbon nanotube catalyst based on intermediate-temperature coal tar pitch was synthesized. The catalyst has a monolithic porous carbon structure, with multi-walled carbon nanotubes uniformly doped into the channels of the intermediate-temperature coal tar pitch. The confinement effect of the intermediate-temperature coal tar pitch channels results in uniform size and distribution of carbon nanotubes. Further processing yields fine and uniformly distributed NPC@CNT nanoparticles, which can be used for highly efficient OER catalysis.

[0026] 5. The extremely high ORR and OER catalytic activity and stability of NPC@CNTs enable liquid and quasi-solid-state zinc-air batteries assembled using them as electrode catalysts to exhibit superior peak power density and cycle stability. The power density of NPC@CNTs is 170 mW / cm³. 2 Superior to Pt / C-20% (66mW / cm) 2 The open-circuit voltage of NPC@CNTs reaches 1.53V, which is 0.2V higher than that of Pt / C-20%.

[0027] 6. Low cost and high performance. The NPC@CNTs catalyst prepared using medium-temperature coal tar pitch, melamine, and carbon nanotubes exhibits extremely high ORR / OER catalytic activity, with an overpotential (E) in OER as low as 381 mV, which is superior to the commercial catalyst Pt / C-20% (E = 424 mV) prepared using precious metals.

[0028] In summary, this invention is applicable to the rapid preparation of a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries. Based on the precursor and carbon nanotubes undergoing a one-step CO2 activation at high temperature, porous carbon materials with higher carbon nanotube crystal quality and more developed pore structure can be obtained. This material has broad application prospects in the field of energy storage zinc-air battery technology. Attached Figure Description

[0029] Figure 1 The image shows a TEM image of the 5 nm NPC@CNTs catalyst prepared in Example 1.

[0030] Figure 2 A scanning electron microscope image of the 100 nm NPC@CNTs catalyst prepared in Example 1;

[0031] Figure 3 The nitrogen adsorption isotherm of the NPC@CNTs catalyst prepared in Example 1 is shown below.

[0032] Figure 4 The XRD pattern of the NPC@CNTs catalyst prepared in Example 1 is shown below.

[0033] Figure 5 The Raman spectrum of the NPC@CNTs catalyst prepared in Example 1 is shown below.

[0034] Figure 6 XPS image of the NPC@CNTs catalyst prepared in Example 1;

[0035] Figure 7 A scanning electron microscope image of the 100 nm NPC@CNTs catalyst prepared in Example 2;

[0036] Figure 8 The XRD pattern of the NPC@CNTs catalyst prepared in Example 2 is shown below.

[0037] Figure 9 A scanning electron microscope image of the 100 nm NPC@CNTs catalyst prepared in Example 3;

[0038] Figure 10 The XRD pattern of the NPC@CNTs catalyst prepared in Example 3 is shown below.

[0039] Figure 11 A scanning electron microscope image of the 100 nm NPC@CNTs catalyst prepared in Example 4;

[0040] Figure 12 The XRD pattern of the NPC@CNTs catalyst prepared in Example 4 is shown below.

[0041] Figure 13 A scanning electron microscope image of the 100 nm pure multi-walled carbon nanotube catalyst prepared in Example 9;

[0042] Figure 14 The ORR performance graphs of the catalysts prepared in Examples 1, 2, 3, and 4 are shown.

[0043] Figure 15 The OER performance graphs of the catalysts prepared in Examples 1, 2, 3, and 4 are shown.

[0044] Figure 16 The ORR performance graphs of the catalysts prepared in Examples 5, 6, 7, 8, and 9 are shown.

[0045] Figure 17 The OER performance graphs of the catalysts prepared in Examples 5, 6, 7, 8, and 9 are shown.

[0046] Figure 18 The graph shows the power density analysis of the zinc-air battery assembled with the NPC@CNTs catalyst prepared in Example 1.

[0047] Figure 19 The graph shows the stability analysis of the zinc-air battery assembled with the NPC@CNTs catalyst prepared in Example 1. Detailed Implementation

[0048] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0049] Based on the analysis of high-temperature activation methods and porous carbon precursor structures, this invention uses medium-temperature coal tar pitch as a carbon source to prepare porous carbon materials with a large number of stable carbon nanotube microcrystals and well-developed pores through a one-step high-temperature 5-60% CO2 activation method. This achieves the one-step synergistic development of carbon nanotube microcrystals and pores. Specifically, using medium-temperature coal tar pitch and melamine as porous carbon precursors, carbon nanotubes and precursors are co-heat-treated at high temperature. The relatively regular structure of medium-temperature coal tar pitch itself, as well as the CO2 activation pore-forming process during high-temperature activation, provide an opportunity for the microcrystalline fragment structure to reassemble, thereby obtaining high-quality porous carbon materials with well-developed pores and carbon nanotube microcrystals.

[0050] Intermediate-temperature coal tar pitch is a volatile polymer material, primarily composed of carbon, hydrogen, and oxygen, and typically also contains small amounts of sulfur and nitrogen. As a battery catalyst, intermediate-temperature coal tar pitch offers the following advantages: Rich chemical composition: It contains various organic substances, such as aromatic compounds, aliphatic compounds, and phenols, which can undergo different chemical reactions at different temperatures, allowing for adjustment of its catalytic performance as needed. High catalytic activity: Intermediate-temperature coal tar pitch exhibits high catalytic activity and stability, effectively promoting battery reactions and improving energy output and cycle life. Low cost: Compared to other commonly used catalysts, intermediate-temperature coal tar pitch is inexpensive and readily available, effectively reducing battery costs. Among them, the medium-temperature coal tar pitch resin (MLPR) prepared by chemical cross-linking modification of the molecular structure of medium-temperature coal tar pitch showed that: the aromaticity of the modified medium-temperature coal tar pitch resin was enhanced; the functional groups, various types of hydrogen, substitution and aromaticity of the medium-temperature coal tar pitch resin were changed, and the average molecular structure was a hexacyclic fused ring structure with predominantly planar arrangement; the pyrolysis reaction mechanism of medium-temperature coal tar pitch resin conformed to the random nucleation and subsequent growth model, and the model function was G(α)=[-ln(1-α)]3 / 4.

[0051] Using intermediate-temperature coal tar pitch as the carbon matrix, a co-firing process was conducted with a certain amount of melamine and carbon nanotubes at 600-1200℃. Activation and pore-forming were then performed at 600-1200℃ with 5-60% carbon dioxide, ultimately yielding a nitrogen-doped porous carbon-coated carbon nanotube catalyst with high nitrogen doping and excellent performance. Melamine provided the nitrogen source, allowing the carbon nanotubes to be uniformly mixed in the intermediate-temperature coal tar pitch, resulting in superior thermal and electrical conductivity. The uniform mixing of carbon nanotubes in intermediate-temperature coal tar pitch breaks through relatively fixed application limitations, opening up more possibilities. The carbon atoms in the carbon nanotubes are bonded by sp2 hybridization, giving the carbon nanotubes a high Young's modulus. Coal tar pitch is a chemical substance with an exceptionally complex structure and composition, but its advantages lie in its good fluidity and high carbon content, making it an excellent carbon matrix. Simultaneously, the nitrogen-doped porous carbon-coated carbon nanotube catalyst enhances the oxygen reduction (ORR) performance during discharge and the oxygen efficiency (OER) performance during charging in zinc-air batteries, significantly improving the battery's performance.

[0052] Melamine can be used as a conductive matrix. Its structure was characterized using elemental analysis, and the degree of crosslinking of the polymer was theoretically calculated using the elemental analysis data. Using melamine as a conductive matrix, its room temperature conductivity was significantly improved after doping. Using medium-temperature coal tar pitch as a carbon matrix, a certain amount of melamine and carbon nanotubes were co-fired at 600-1200℃ with 5-60% CO2 for heat treatment, ultimately obtaining nitrogen-doped porous carbon-coated carbon nanotube catalysts with high doping degree and excellent performance. Studies show that the treated carbon nanotubes are uniformly mixed on the carbon fiber surface, forming a complex porous three-dimensional honeycomb structure that enhances the oxygen reduction (ORR) performance during discharge and the oxygen return (OER) performance during charging.

[0053] Carbon nanotubes, as a battery catalyst, offer the following advantages: High specific surface area: Carbon nanotubes possess an extremely high specific surface area, meaning they can provide more catalytic active sites, thereby promoting battery reactions. Excellent electrical conductivity: Carbon nanotubes are highly conductive, effectively transferring electrons and ions, improving battery efficiency and energy output. Good chemical stability: Carbon nanotubes exhibit good chemical stability and corrosion resistance, maintaining stable catalytic performance even in complex battery environments. High tunability: The size, morphology, and structure of carbon nanotubes can be controlled through different preparation methods and subsequent processing techniques, enabling fine-tuning of their catalytic performance. Environmental friendliness: Compared to some traditional catalysts, carbon nanotubes offer advantages such as environmental friendliness and low resource consumption, aligning with the requirements of sustainable development.

[0054] In summary, the carbon nanotube battery catalyst prepared using intermediate-temperature coal tar pitch as the carbon source has the following advantages from the perspectives of ORR (Oxygen Reduction Reaction) and OER (Oxygen Evolution Reaction): Advantages in ORR: Intermediate-temperature coal tar pitch as a carbon source can produce carbon nanotubes with good electrochemical activity. Compared with traditional platinum-carbon battery catalysts, carbon nanotubes prepared using intermediate-temperature coal tar pitch exhibit higher catalytic activity and longer lifespan, effectively promoting the ORR reaction. Advantages in OER: Carbon nanotubes prepared using intermediate-temperature coal tar pitch as a carbon source also show good catalytic performance in OER. Their high catalytic activity, stability, and low cost make them a strong candidate to replace traditional platinum-carbon battery catalysts. This invention creatively establishes a combination of carbon nanotubes, melamine, and intermediate-temperature coal tar pitch to enhance the ORR performance during discharge and the OER performance during charging, and it also possesses high safety, environmental friendliness, high energy and power output, and ultra-long cycle life, solving the shortcomings of current zinc-air batteries.

[0055] In summary, carbon nanotube battery catalysts prepared using medium-temperature coal tar pitch as the carbon base have significant advantages in both ORR and OER, effectively improving battery energy output and cycle life while reducing costs, and have broad application prospects.

[0056] Example 1:

[0057] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0058] I. Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence to obtain a uniformly mixed medium-temperature coal tar pitch and melamine (the mixture is a precursor) with a mass ratio of 3:2;

[0059] II. Mixing of Carbon Nanotubes and Precursor: The precursor obtained in step one is thoroughly mixed with carbon nanotubes and dissolved in an ethanol solution. The mixture is then sonicated for 30 minutes to obtain a homogeneous solution. This solution is then dried in a 60°C oven for 2 hours to obtain a homogeneous mixture. The mass ratio of the medium-temperature coal tar pitch, melamine, and carbon nanotubes is 15:10:1.

[0060] III. High-temperature activation: The mixture obtained in step II was transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature was increased to 1000℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1 hour. The gas volume flow rate was 200mL / min. Then the tube furnace was naturally cooled to room temperature to obtain a nitrogen-doped porous carbon-coated carbon nanotube catalyst.

[0061] To test the microcrystalline and carbon nanotube structures of the catalyst, TEM characterization, scanning electron microscopy, Raman analysis, and nitrogen adsorption detection were performed. Figure 1 The image shows a TEM image of the NPC@CNTs prepared in Example 1. Figure 1 The structure exhibits distinct carbon nanotube stripes composed of similarly oriented carbon nanotube crystals. The carbon nanotube crystals are numerous and highly ordered, exhibiting a three-dimensional layered structure composed of porous amorphous carbon and uniformly dispersed carbon nanotube crystals. This structure is conducive to exposing active sites, and the close contact between amorphous carbon and crystalline carbon facilitates rapid electron transport. Figure 2 Here are scanning electron microscope (SEM) images of the NPC@CNTs catalyst prepared in Example 1. Figure 2 It can be seen that carbon dioxide activates at 1000℃ and exhibits a honeycomb structure, which is beneficial for the doping of carbon nanotube crystals. Exposing active sites is conducive to electron transport. Figure 3 The low-temperature nitrogen adsorption isotherm of NPC@CNTs obtained in Example 1 shows a typical type I-IV binding curve, with a hysteresis loop appearing in the relative pressure range of 0.4–1.0 MPa, indicating the presence of micropores and mesopores / macropores within the pores. Calculations show that the specific surface area of ​​the nitrogen-doped porous carbon-coated carbon nanotube catalyst is 382.58 m². 2 The total pore volume is 0.1927 cm3 / g, with micropores accounting for 86.14%, indicating a well-developed pore structure. Figure 4 The image shows the XRD pattern of the NPC@CNTs catalyst prepared in Example 1. The figure shows a relatively broad peak at 25.2°, which is roughly the same as the characteristic peak exhibited by carbon nanotubes and carbon crystals. Figure 8 , 10 The smaller degree of peaks 1 and 2 compared to peak 1 indicates that the degree of disorder inside the catalyst is smaller under this operating condition, and that the carbon nanotube microcrystalline structure of the nitrogen-doped porous carbon-coated carbon nanotube catalyst is more uniform. Figure 5 The Raman spectrum of the NPC@CNTs catalyst prepared in Example 1 shows that, in the NPC@CNTs catalyst, the concentrations at 1337 and 1590 cm⁻¹ are... -1 Two Raman peaks appeared, corresponding to the D band (disordered sp3 carbon) and the G band (sp2 carbon), respectively, indicating the presence of sp3 hybridized carbon structures (σ bonds) in the porous carbon activated at 1000℃, and a strong excitation signal in the ~1600cm⁻¹ region. Activation at 1000℃ yields structures with a certain degree of microcrystalline order. Furthermore, for D3-D4 (1440cm⁻¹, 1200cm⁻¹, respectively),... -1Further Raman spectroscopy deconvolution was performed, corresponding to heteroatom-containing oxygen-containing amorphous sp3 carbon bonds and disordered lattice carbon bonds, respectively. This indicates that the pore-forming effect of carbon dioxide on NPC@CNTs catalysts at higher temperatures can still successfully obtain porous carbon materials with a large number of pores and demonstrate their high electrocatalytic performance. The above analysis shows that the porous carbon materials prepared by this method can achieve uniform dispersion of carbon nanotubes for the preparation of highly efficient electrocatalysts, indicating that the porous carbon materials prepared by this method have good crystallite quality. Figure 1 The conclusions are consistent. Figure 6 The XPS plot of the NPC@CNTs catalyst prepared in Example 1 shows three peaks at 284.0 eV, 447.0 eV, and 530.6 eV, corresponding to the C, N, and O elemental compositions, respectively. The above analysis indicates that this material possesses both high-quality microcrystals and a well-developed pore structure.

[0062] The oxygen reduction performance of the nitrogen-doped porous carbon-coated carbon nanotube catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst prepared in the above steps, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was dropped onto the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific test parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 14 We can obtain that the oxygen reduction half-wave potential is 0.879V and the initiation potential is 0.985V.

[0063] Example 2:

[0064] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0065] I. Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence to obtain a uniformly mixed medium-temperature coal tar pitch and melamine (the mixture is a precursor) with a mass ratio of 3:2;

[0066] II. Mixing of Carbon Nanotubes and Precursor: The precursor obtained in step one is thoroughly mixed with carbon nanotubes and dissolved in an ethanol solution. The mixture is then sonicated for 30 minutes to obtain a homogeneous solution. This solution is then dried in a 60°C oven for 2 hours to obtain a homogeneous mixture. The mass ratio of the medium-temperature coal tar pitch, melamine, and carbon nanotubes is 15:10:1.

[0067] III. High-temperature activation: The mixture obtained in step II was transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature was increased to 800℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1h. The volumetric flow rate of the gas was 200mL / min. Then the tube furnace was naturally cooled to room temperature to obtain a nitrogen-doped porous carbon-coated carbon nanotube catalyst.

[0068] Figure 7 The image shows a scanning electron microscope image of the NPC@CNTs catalyst prepared in Example 2. It can be seen that the carbon nanotubes in the NPC@CNTs catalyst also have a certain carbon nanotube microcrystalline structure after activation by carbon dioxide at 800℃. This indicates that the carbon nanotube microcrystalline structure of nitrogen-doped porous carbon-coated carbon nanotube catalyst can also be developed at a lower activation temperature, but the microcrystalline size is smaller. Figure 8 The image shows the XRD pattern of the NPC@CNTs catalyst prepared in Example 2. The figure shows a relatively broad peak at 25.8°, which is roughly the same as the characteristic peak exhibited by carbon nanotubes and carbon crystals. This indicates that at a lower activation temperature, nitrogen-doped porous carbon-coated carbon nanotubes can also develop a microcrystalline structure, but the degree of disorder is less than that of nitrogen-doped porous carbon-coated carbon nanotubes. Figure 4 It is relatively large.

[0069] The oxygen reduction performance of the nitrogen-doped porous carbon-coated carbon nanotube catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst prepared in the above steps, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was dropped onto the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific test parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 14 We can obtain that the oxygen reduction half-wave potential is 0.66V and the initial potential is 0.832V.

[0070] Example 3:

[0071] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0072] I. Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence to obtain a uniformly mixed medium-temperature coal tar pitch and melamine (precursor) in a mass ratio of 3:2;

[0073] II. Mixing of Carbon Nanotubes and Precursor: The precursor obtained in step one is thoroughly mixed with carbon nanotubes and dissolved in an ethanol solution. The mixture is then sonicated for 30 minutes to obtain a homogeneous solution. This solution is then dried in a 60°C oven for 2 hours to obtain a homogeneous mixture. The mass ratio of the medium-temperature coal tar pitch, melamine, and carbon nanotubes is 15:10:1.

[0074] III. High-temperature activation: The mixture obtained in step II was transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature was increased to 900℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1h. The volumetric flow rate of the gas was 200mL / min. Then the tube furnace was naturally cooled to room temperature to obtain a nitrogen-doped porous carbon-coated carbon nanotube catalyst.

[0075] Figure 9 The image shows a scanning electron microscope (SEM) image of the NPC@CNTs catalyst prepared in Example 3, and... Figure 2 In comparison, the carbon nanotubes in the NPC@CNTs catalyst activated with carbon dioxide at 900℃ are thicker and the crystallite size is slightly smaller; the carbon nanotube crystallites and pores in the NPC@CNTs catalyst prepared according to the method of this embodiment still have high quality. Figure 10 The image shows the XRD pattern of the NPC@CNTs catalyst prepared in Example 3. The figure shows a relatively broad peak at 25.6°, which is roughly the same as the characteristic peak exhibited by carbon nanotubes and carbon crystals. This indicates that at an activation temperature of 900°C, nitrogen-doped porous carbon-coated carbon nanotubes can also develop a microcrystalline structure, but the degree of disorder is similar to that of carbon nanotubes. Figure 4 It is relatively large.

[0076] The oxygen reduction performance of the nitrogen-doped porous carbon-coated carbon nanotube catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst prepared in the above steps, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was dropped onto the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific test parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 14 We can obtain that the oxygen reduction half-wave potential is 0.7V and the initiation potential is 0.87V.

[0077] Example 4:

[0078] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0079] I. Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence to obtain a uniformly mixed medium-temperature coal tar pitch and melamine (precursor) in a mass ratio of 3:2;

[0080] II. Mixing of Carbon Nanotubes and Precursor: The precursor obtained in step one is thoroughly mixed with carbon nanotubes and dissolved in an ethanol solution. The mixture is then sonicated for 30 minutes to obtain a homogeneous solution. This solution is then dried in a 60°C oven for 2 hours to obtain a homogeneous mixture. The mass ratio of the medium-temperature coal tar pitch, melamine, and carbon nanotubes is 15:10:1.

[0081] 3. High-temperature activation: The mixture obtained in step 2 is transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature is increased to 1100℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1h. The volume flow rate of the gas is 200mL / min. Then the tube furnace is naturally cooled to room temperature to obtain nitrogen-doped porous carbon-coated carbon nanotubes.

[0082] Figure 11 The image shows a scanning electron microscope image of the NPC@CNTs catalyst prepared in Example 4. It can be seen that the NPC@CNTs catalyst also has a certain carbon nanotube microcrystalline structure after activation with carbon dioxide at 1100℃. This indicates that the carbon nanotube microcrystalline structure of the NPC@CNTs catalyst can also be developed at a higher activation temperature, but the microcrystalline size is small. Figure 12 The XRD pattern of the NPC@CNTs catalyst prepared in Example 4 shows a relatively broad peak at 25.5°, which is roughly the same as the characteristic peak exhibited by carbon nanotubes and carbon crystals. This indicates that at higher activation temperatures, nitrogen-doped porous carbon-coated carbon nanotubes can also develop a microcrystalline structure, although the degree of disorder is similar to that of carbon nanotubes. Figure 4 It is relatively large.

[0083] The oxygen reduction performance of the nitrogen-doped porous carbon-coated carbon nanotube catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst prepared in the above steps, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was dropped onto the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific test parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 14 We can obtain that the oxygen reduction half-wave potential is 0.737V and the initial potential is 0.901V.

[0084] Example 5:

[0085] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0086] I. Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence to obtain a uniformly mixed medium-temperature coal tar pitch and melamine (precursor) in a mass ratio of 3:2;

[0087] 2. Dissolve the precursor obtained in step 1 in an ethanol solution and sonicate for 30 minutes to obtain a homogeneous mixture. Place the mixture in an oven at 60°C and dry for 2 hours to obtain a homogeneous mixture.

[0088] III. High-temperature activation: The mixture obtained in step II was transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature was increased by 1000℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1h. The volumetric flow rate of the gas was 200mL / min. Then the tube furnace was naturally cooled to room temperature to obtain a nitrogen-doped porous carbon-coated carbon nanotube catalyst.

[0089] The oxygen reduction performance of the nitrogen-doped porous carbon catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was added to the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 16 We can obtain that the oxygen reduction half-wave potential is 0.641V and the initial potential is 0.839V.

[0090] Example 6:

[0091] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0092] I. Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence to obtain a uniformly mixed medium-temperature coal tar pitch and melamine (precursor) in a mass ratio of 3:2;

[0093] II. Mixing of Nanomaterials and Precursors: The precursor obtained in step one is thoroughly mixed with carbon nanotubes and dissolved in an ethanol solution. The mixture is then sonicated for 30 minutes to obtain a homogeneous solution. This solution is then dried in a 60°C oven for 2 hours to obtain a homogeneous mixture. The mass ratio of the medium-temperature coal tar pitch, melamine, and carbon nanotubes is 15:10:0.5.

[0094] 3. High-temperature activation: The mixture obtained in step 2 is transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature is increased by 1000℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1h. The volume flow rate of the gas is 200mL / min. Then the tube furnace is naturally cooled to room temperature to obtain nitrogen-doped porous carbon material.

[0095] The oxygen reduction performance of the nitrogen-doped porous carbon catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was added to the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 16 We can obtain that the oxygen reduction half-wave potential is 0.824V and the initiation potential is 0.98V.

[0096] Example 7:

[0097] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0098] I. Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence to obtain a uniformly mixed medium-temperature coal tar pitch and melamine (precursor) in a mass ratio of 3:2;

[0099] II. Mixing of Carbon Nanotubes and Precursor: The precursor obtained in step one is thoroughly mixed with carbon nanotubes and dissolved in an ethanol solution. The mixture is then sonicated for 30 minutes to obtain a homogeneous solution. This solution is then dried in a 60°C oven for 2 hours to obtain a homogeneous mixture. The mass ratio of the medium-temperature coal tar pitch, melamine, and carbon nanotubes is 15:10:2.

[0100] III. High-temperature activation: The mixture obtained in step II was transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature was increased by 1000℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1h. The volumetric flow rate of the gas was 200mL / min. Then the tube furnace was naturally cooled to room temperature to obtain a nitrogen-doped porous carbon-coated carbon nanotube catalyst.

[0101] The oxygen reduction performance of the nitrogen-doped porous carbon-coated carbon nanotube catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst prepared in the above steps, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was dropped onto the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific test parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 16 We can obtain that the oxygen reduction half-wave potential is 0.817V and the initial potential is 0.984V.

[0102] Example 8:

[0103] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0104] I. Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence to obtain a uniformly mixed medium-temperature coal tar pitch and melamine (precursor) in a mass ratio of 3:2;

[0105] II. Mixing of Carbon Nanotubes and Precursor: The precursor obtained in step one is thoroughly mixed with carbon nanotubes and dissolved in an ethanol solution. The mixture is then sonicated for 30 minutes to obtain a homogeneous solution. This solution is then dried in a 60°C oven for 2 hours to obtain a homogeneous mixture. The mass ratio of the medium-temperature coal tar pitch, melamine, and carbon nanotubes is 15:10:5.

[0106] III. High-temperature activation: The mixture obtained in step II was transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature was increased by 1000℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1h. The volumetric flow rate of the gas was 200mL / min. Then the tube furnace was naturally cooled to room temperature to obtain a nitrogen-doped porous carbon-coated carbon nanotube catalyst.

[0107] The oxygen reduction performance of the nitrogen-doped porous carbon-coated carbon nanotube catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst prepared in the above steps, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was dropped onto the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific test parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 16 We can obtain that the oxygen reduction half-wave potential is 0.824V and the initiation potential is 0.974V.

[0108] Example 9:

[0109] A rapid preparation method for a highly active and stable ORR-OER bifunctional electrocatalyst for zinc-air batteries, the method comprising:

[0110] 1. Carbon nanotubes: Dissolve carbon nanotubes in an ethanol solution and sonicate for 30 minutes to obtain a homogeneous mixture. Place the mixture in an oven at 60°C and dry for 2 hours to obtain a homogeneous mixture.

[0111] II. High-temperature activation: The mixture obtained in step one is transferred to a tube furnace and placed in a nitrogen atmosphere. The temperature is increased by 1000℃ at a rate of 10℃ / min and maintained at 20% CO2 for 1h. The volumetric flow rate of the gas is 200mL / min. Then the tube furnace is naturally cooled to room temperature to obtain the carbon nanotube catalyst.

[0112] Figure 13 The image shows a scanning electron microscope (SEM) image of the pure carbon nanotube catalyst prepared in Example 9. The image reveals that the carbon nanotubes agglomerate due to strong van der Waals forces, making them prone to entanglement or clustering. In practical applications, this agglomeration often disrupts the excellent mechanical and electrical properties of individual carbon nanotubes. Therefore, without the addition of medium-temperature coal tar pitch, carbon nanotubes will agglomerate, affecting their performance. However, medium-temperature coal tar pitch acts as a fluid, dispersing the carbon nanotubes and greatly enhancing their superior performance. Simultaneously, the activation and pore-forming effect of carbon dioxide further develops the pore structure of the coal tar pitch, resulting in more uniform dispersion of the carbon nanotubes.

[0113] The oxygen reduction performance of the carbon nanotube catalyst prepared in the above steps was tested using a rotating disk electrode. 5 mg of the catalyst, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion were placed in a centrifuge tube and sonicated for more than 30 min. During testing, 10 μL of ink was added to the working electrode. A Pt wire electrode was used as the counter electrode, and a saturated mercuric oxide electrode was used as the reference electrode. Electrochemical tests were conducted at room temperature in an oxygen-saturated 0.1 mol / L KOH solution. The specific parameters for the linear sweep voltammetry (LSV) curve were: scan voltage -1 to 0 V (vs SCE, 0 to 1 V vs RHE), scan rate 5 mV / s, and disk electrode rotation speed 1600 rpm. Figure 16 We can obtain that the oxygen reduction half-wave potential is 0.435V and the initial potential is 0.824V.

[0114] Catalyst ORR / OER catalytic performance test

[0115] The catalysts prepared in Examples 1-9 were subjected to ORR / OER electrochemical tests. Electrochemical tests were performed on an electrochemical workstation. A sample slurry was coated onto a rotating disk electrode (RDE) or rotating disk electrode (RRDE) as the working electrode, a platinum wire electrode as the counter electrode, and a mercuric oxide electrode (HgCl) as the reference electrode. A 0.1M KOH solution was used as the electrolyte. The voltage data were converted to vs. RHE using the following formula: Evs, RHE = Evs, Ag / AgCl + 0.059pH + 0.197

[0116] Preparation of catalyst ink for ORR / OER testing: Place 5 mg of catalyst, 480 μL of ethanol, 480 μL of deionized water, and 50 μL of Nafion in a centrifuge tube and sonicate for more than 30 min. During testing, add 10 μL of ink to the working electrode. Figure 14 , 15 Experimental characterization of the catalyst ORR / OER at different temperatures in Examples 1-4, from Figure 14 As can be seen, the catalyst treated at 1000 degrees Celsius in Example 1 exhibited the highest half-wave potential (0.879 V) during the ORR reaction compared to catalysts treated at other temperatures; from Figure 15 It can be seen that during OER catalysis, the catalyst treated at 1000 degrees Celsius, compared to those treated at other temperatures, reaches 10 mA cm⁻¹. -2 The required overpotential is relatively low (391 mV) at the circuit density. This indicates that the construction of activated water molecule sites greatly enhances the ORR / OER bifunctional catalytic activity of the catalyst.

[0117] Figure 16 , 17For the experimental characterization of the ORR / OER of the catalysts in Examples 5-9 with different carbon nanotube ratios, from Figure 16 , 17 As can be seen, the addition of carbon nanotubes improves the catalytic performance of the catalyst. However, as the proportion of carbon nanotubes increases, the catalytic performance first increases and then decreases. Under the conditions of 15:10:1, i.e., Example 1, the catalyst exhibits the best catalytic performance, with a half-wave potential (0.879V) that is higher than that of the traditional Pt / C (20%) catalyst (0.802V), reaching 10 mA / cm². -2 The catalyst exhibits good catalytic performance with a low overpotential (391 mV) at a certain circuit density. This indicates that carbon nanotubes enhance the ORR / OER bifunctional catalytic activity of the catalyst at a certain ratio.

[0118] Catalyst Zinc-Air Battery Performance Testing

[0119] The optimal catalyst prepared in Example 1 was used in zinc-air battery testing with Pt / C (20%) + RuO2 (mass ratio 1:1). For the liquid zinc-air battery test, a 99.9% pure zinc sheet (10*3*0.02cm) was used as the negative electrode, a 6M KOH aqueous solution was used as the electrolyte, and an ion exchange membrane, nickel foam, catalyst-coated carbon paper, a gas diffusion layer, potassium hydroxide solution as the electrolyte, and zinc foil as the electrode. The prepared monolithic catalyst was directly used as the air electrode. Figure 18 The image shows the power density analysis of the liquid zinc-air battery assembled with the catalyst prepared under the conditions of Example 1 and Pt / C (20%) + RuO2. Figure 18 It can be seen that the liquid zinc-air battery assembled based on Example 1 has a higher peak power density (174 mW / cm²). -2 The commercial noble metal catalyst Pt / C(20%) + RuO2 has a peak power density of 66 mW / cm². -2 Superior to traditional platinum-carbon catalysts Figure 19 The figure shows the stability analysis of the zinc-air battery assembled with the NPC@CNTs catalyst prepared in Example 1. It can be seen from the figure that the zinc-air battery assembled with the nitrogen-doped porous carbon-coated carbon nanotube catalyst exhibits superior stability after 229.8 h (1280 cycles) compared to the traditional platinum-carbon catalyst. Figure 18 , 19 It can be concluded that the catalyst of this invention improves the power density and stability of zinc-air batteries.

[0120] The nitrogen-doped porous carbon-coated carbon nanotube catalyst prepared by the method described in this invention can achieve controllable preparation of catalyst morphology and structure by adjusting the carbon nanotube ratio and preparation process, such as activation temperature, doping temperature, and doping time. The optimal specific surface area of ​​the catalyst is 382.58 m² when the doping temperature is controlled. 2 / g.

[0121] The above analysis shows that using medium-temperature coal tar pitch as the carbon source for porous carbon catalysts, melamine as the nitrogen source, and the optimal carbon nanotube ratio, activation with carbon dioxide not only creates a rich and accessible pore structure, achieving a high specific surface area, but also allows for the full development of carbon nanotube microcrystals in the carbon material, greatly improving the conductivity of the carbon material. When used as an electrode material in zinc-air batteries, it exhibits high capacity and excellent rate performance. This method successfully realizes the superior catalytic performance of nitrogen-doped porous carbon-coated carbon nanotube catalysts.

[0122] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the claims. All equivalent changes or modifications made according to the spirit and essence of the present invention should be included within the protection scope of this invention.

Claims

1. A method for preparing an ORR-OER bifunctional electrocatalyst for zinc-air batteries, characterized in that: The catalyst is NPC@CNTs, nitrogen-doped porous carbon-coated carbon nanotubes; the method is as follows: Step 1: Raw material refinement: Medium-temperature coal tar pitch and melamine are ground and sieved in sequence, and then mixed evenly to obtain the precursor; Step 2: Mixing nanomaterials with precursors: Thoroughly mix the precursors obtained in Step 1 with carbon nanotubes and dissolve them in an ethanol solution. Sonicate for 5-300 min to obtain a homogeneous mixture. Place the mixture in an oven at 30-100℃ and dry for 0.1-30 h to obtain a homogeneous mixture. The mass ratio of medium-temperature coal tar pitch: melamine: carbon nanotubes is 15:10:0.5-20. Step 3: High-temperature activation: Transfer the mixture obtained in Step 2 to a tube furnace, place it in an inert atmosphere, raise the temperature to 600~1200℃, and activate it with carbon dioxide for 0.5~30h. Then, let the tube furnace cool naturally to room temperature to obtain the ORR-OER bifunctional electrocatalyst for zinc-air batteries.

2. The method for preparing an ORR-OER bifunctional electrocatalyst for zinc-air batteries according to claim 1, characterized in that: In step one, the medium-temperature coal tar pitch is obtained through the following process: coal tar is left to stand and dehydrate → desalted with sodium carbonate → coal tar is pumped into the convection section of a tubular heater → during this stage, the coal tar is heated to 120-130 degrees Celsius → it enters the evaporator for dehydration → light oil vapor is distilled off at the top of the tower and enters the oil-water separator for oil-water separation via a condenser → the dehydrated coal tar at the bottom of the tower flows into an anhydrous tar tank → the coal tar is pumped into the radiant section of the tubular heater for heating → it enters the secondary evaporator → the light fractions in the coal tar are immediately evaporated and collected in a fractionation tower for graded processing, yielding light oil, phenolic oil, naphthalene oil, wash oil, and anthracene oil in sequence → medium-temperature pitch is discharged from the bottom of the tower at a temperature of about 370 degrees Celsius → it is cooled to 220-240 degrees Celsius by a vaporization cooler → it enters the high-level pitch tank and is naturally cooled for several hours to obtain medium-temperature pitch. The coal tar pitch and melamine are mixed evenly in a mass ratio of 3:

2.

3. The method for preparing an ORR-OER bifunctional electrocatalyst for zinc-air batteries according to claim 1, characterized in that: In step two, the drying method is vacuum drying, hot air drying, or natural evaporation drying; the drying temperature is 60℃, and the drying time is 60 minutes.

4. The method for preparing an ORR-OER bifunctional electrocatalyst for zinc-air batteries according to claim 1, characterized in that: In step three, the inert atmosphere is high-purity nitrogen and high-purity carbon dioxide, the volume of carbon dioxide is 5% to 60% of the total gas volume, and the gas volume flow rate is 50 mL / min to 500 mL / min.

5. The method for preparing an ORR-OER bifunctional electrocatalyst for zinc-air batteries according to claim 1, characterized in that: In step three, the heating rate of the tubular furnace is 1℃ / min to 20℃ / min, and the carbon dioxide activation treatment time is 0.1 to 10h.

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