Method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste and application of nitrogen-oxygen co-doped hierarchical porous carbon in oxygen reduction of fuel cell

Abstract

The invention discloses a method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste and application of the nitrogen-oxygen co-doped hierarchical porous carbon in fuel cell oxygen reduction, and relates to the technical field of fuel cell catalysis, the preparation method comprises the following steps: pretreatment of a textile waste precursor: cutting the textile waste into fragments and drying to obtain a dried pretreated precursor; placing the dried precursor in a quartz tube, carrying out programmed heating to a target temperature under the protection of an inert atmosphere, and introducing carbon dioxide and ammonia gas to carry out synergistic activation treatment; the textile waste which is low in cost and easy to obtain serves as the raw material, the developed preparation process has the advantages of being simple, safe and controllable, the prepared graded porous carbon material has the high specific surface area, the optimized micropore size and the developed mesoporous system, the unique structure is beneficial to sufficient exposure and improvement of accessibility of catalytic active sites, and the preparation method is suitable for industrial production. And meanwhile, the mass transfer resistance of the electrolyte and oxygen is reduced, so that the electrolyte shows ORR catalytic activity comparable to that of commercial Pt / C and better long-term stability.

Description

Technical Field

[0001] This invention relates to the field of fuel cell catalysis technology, specifically to a method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste and its application in oxygen reduction in fuel cells. Background Technology

[0002] Fuel cells, due to their high energy density, high efficiency, and low environmental pollution, are considered an important technological direction for alleviating the energy crisis and solving environmental pollution problems. However, their commercialization is still limited by the core bottleneck of slow cathode ORR reaction kinetics. Currently, this reaction heavily relies on noble metal platinum (Pt)-based catalysts (such as commercial Pt / C) to accelerate the reaction rate, but this brings the following insurmountable limitations: (1) Resource constraints and cost pressures Platinum, a precious metal, is scarce in the Earth's crust, making it extremely expensive. In typical fuel cell stacks, platinum-based catalysts on the cathode side can account for more than 30% of the total cost, severely restricting their large-scale application in fields such as new energy vehicles.

[0003] (2) The preparation process is complicated: it involves multiple steps, high energy consumption and high cost. The preparation process of existing nitrogen-doped or nitrogen-oxygen co-doped porous carbon materials generally involves multiple steps such as pretreatment, carbonization, and activation. The process is cumbersome and energy-intensive, as shown in the following ways: Ma et al. (Journal of Materials Science, 2024, 59: 19825-19836) used commercial activated carbon as raw material, first treated it with ash removal, then pre-oxidized it with 2 mmol / L nitric acid at 90℃, the pre-oxidized product was washed with ultrapure water until neutral, and then modified by ammonia gas at high temperature, finally obtaining nitrogen-doped porous carbon. Invention patents CN201910375140.X and CN202311450781.X disclose that the former prepares nitrogen-doped carbon by multi-step processing of specific raw materials, while the latter mixes cellulose-like substances, magnesium salts, strong alkalis, nitrogen-containing organic compounds and water, freeze-dries them first and then carbonizes them at high temperature to obtain nitrogen-oxygen co-doped porous carbon.

[0004] (3) Insufficient durability and performance degradation Under harsh fuel cell operating conditions, Pt nanoparticles are prone to dissolution, migration, and aggregation, leading to a reduction in electrochemical active area and a continuous decline in catalytic performance, directly affecting the lifespan of the battery. For example: The optimal catalytic sample NOPC-700 prepared by Lu et al. (Applied Surface Science, 2023, 640: 158308) had a nitrogen content of only 8.45 at.% as determined by XPS. Xiang et al. (Separation and Purification Technology, 2024, 125761) dispersed activated carbon and melamine in a water-ethanol mixture (volume ratio 20:80), stirred at 25°C for 5 h, dried at 120°C, and then activated at high temperature for 40 min under a nitrogen atmosphere to obtain nitrogen-doped activated carbon. XPS analysis showed that the nitrogen content of their CAN-600 sample was only 7.69 at.% and the oxygen content was only 4.81 at.%. Compared with the raw activated carbon (specific surface area 998 m² / g), the specific surface area of ​​the modified CAN-600 decreased to 754 m² / g, and the total pore volume also showed a decreasing trend.

[0005] (4) Poor ability to resist poisoning Trace amounts of carbon monoxide, which may be present in the actual working environment of a fuel cell, or methanol molecules in a direct methanol fuel cell, can strongly adsorb onto the active sites of Pt, causing catalyst "poisoning" and resulting in permanent or temporary deactivation.

[0006] To reduce reliance on precious metals, researchers are working to develop non-precious metal or completely metal-free ORR catalysts. Among them, heteroatom-doped carbon materials (such as nitrogen, oxygen, sulfur, and phosphorus) are considered a highly promising alternative due to their tunable electronic structure and good stability.

[0007] Currently, some studies have attempted to use various biomass (such as fruit shells, straw, and lignin) or synthetic polymers as carbon precursors. However, these precursors are either expensive or require complex preparation processes. More importantly, the carbon materials derived from them often face challenges such as limited specific surface area and unreasonable pore structure, which not only limit the exposure and utilization efficiency of active sites but also hinder the transport efficiency of reactants and products, ultimately resulting in overall catalytic performance that still falls short of practical application requirements.

[0008] Therefore, developing a novel ORR catalyst that simultaneously meets the following requirements has become an urgent technical need in this field: (1) the raw materials are cheap and readily available, and waste resources can be utilized; (2) the preparation process is simple, safe and controllable; (3) the resulting material has an ideal structure with high specific surface area and hierarchical pores to ensure high catalytic activity and long cycle stability. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste and its application in oxygen reduction in fuel cells, aiming to overcome the technical defects of existing precious metal catalysts such as high cost and poor stability, as well as the poor pore structure of biomass carbon materials.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste includes the following steps: S1: Textile waste precursor pretreatment: Textile waste is cut into irregular pieces and then dried to remove free moisture and volatile impurities from the raw material to obtain a dried precursor. S2: High-temperature synergistic activation and doping: Filling and atmosphere replacement: The dried precursor is uniformly loaded into the quartz tube, ensuring that the height of the precursor does not exceed 2 / 3 of the length of the constant temperature zone of the quartz tube. Then the quartz tube is placed into the constant temperature zone of the tube furnace. Inert gas is introduced from the bottom of the quartz tube to replace the air inside the quartz tube. Programmed heating and atmosphere switching: After inert gas replacement is completed, the tube furnace is heated to a specified activation temperature T of 700-1000℃ under an inert atmosphere by programmed heating; after the temperature T stabilizes, the inert gas path is switched to a constant temperature bubbler containing ammonium salt solution, and the ammonium salt is hydrolyzed by bubbling to generate a gas flow containing NH3 and water vapor; after this gas flow is dried and dehydrated, it is mixed with CO2 to form a synergistic activation atmosphere, and the volume flow ratio of CO2 to NH3 is controlled to be 1:1 to 1:3; Thermal activation: At temperature T, keep warm in the synergistic activation atmosphere for 60~180 min; S3: Cooling and Sample Collection: After activation, stop the CO2 supply and switch the three-way valve on the inert gas pipeline to the passage directly connected to the quartz tube, and continue to supply inert gas to form an inert protective atmosphere; after the tube furnace cools naturally to room temperature, remove the quartz tube and collect the solid product inside the tube, which is the nitrogen-oxygen co-doped hierarchical porous carbon material.

[0011] Preferably, in step S1, the drying temperature is set to 80°C and the drying time is set to 12 hours; the side length of the irregular fragments is set to 0.5-1cm to ensure uniform heating in the subsequent process.

[0012] Preferably, in the filling and atmosphere replacement step of S2, the inert gas is nitrogen or argon, the gas flow rate is set to 50~200mL / min, and the replacement time is set to 30~60min.

[0013] Preferably, in the programmed heating and atmosphere switching step S2, the programmed heating rate is 3°C / min.

[0014] Preferably, in the programmed temperature rise and atmosphere switching step S2, the ammonium salt solution is an aqueous solution of ammonium nitrate, ammonium chloride, or ammonium citrate with a concentration of 0.5~2 mol / L, and the temperature of the constant temperature bubbling flask is controlled at 60~90℃.

[0015] Preferably, in the programmed heating and atmosphere switching step S2, the drying and dehydration is achieved by passing the gas mixture generated by bubbling through a dryer filled with 4Å molecular sieves. The dryer is 10-15 cm long and the molecular sieve filling amount is 50-100 g. The CO2 flow rate is 25-100 mL / min. During the heat preservation and activation period, the NH3 generation concentration is precisely controlled by adjusting the inert gas flow rate, ammonium salt solution concentration, and constant temperature bubbling flask temperature.

[0016] Preferably, in step S3, the flow rate of the inert gas maintaining the protective atmosphere is set to 100 mL / min, and cooling to room temperature means a temperature ≤30°C.

[0017] The present invention also provides an application of the nitrogen-oxygen co-doped hierarchical porous carbon material prepared by the above preparation method, wherein the nitrogen-oxygen co-doped hierarchical porous carbon material is used as a metal-free catalyst in the cathode ORR of a fuel cell.

[0018] Preferably, the specific steps of the application are as follows: Accurately weigh 5 mg of the nitrogen-oxygen co-doped hierarchical porous carbon material, add 0.2 mL of ultrapure water, 0.8 mL of isopropanol and 20 μL of 5 wt% Nafion solution, and place the mixture in an ultrasonic cleaner for ultrasonic dispersion for 1.5 hours to obtain a uniform and stable catalyst dispersion. 10 μL of the above dispersion was precisely transferred using a microsyringe and uniformly drop-coated onto the surface of the pretreated glassy carbon electrode. The electrode was first dried under an infrared lamp to quickly remove the solvent, and then transferred to a vacuum drying oven and dried at 30 °C for 12 hours to further remove residual solvent and enhance the adhesion between the catalyst film and the electrode substrate, thus obtaining the working electrode to be tested.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. Advantages of raw materials and processes: Using textile waste as a carbon precursor not only realizes the resource utilization of waste, but also has extremely low raw material costs. The CO2 and NH3 synergistic activation process adopted is simple, safe and highly controllable, providing favorable conditions for large-scale production.

[0020] 2. Material structural characteristics: The obtained nitrogen-oxygen co-doped hierarchical porous carbon material has a high specific surface area and an ideal pore system (developed mesopores and optimized micropores). This unique structure can effectively expose catalytic active sites and significantly reduce the mass transfer resistance of electrolyte and oxygen.

[0021] 3. Application performance advantages: Based on the synergistic effect of the above structure and composition, the material exhibits excellent ORR catalytic activity, outstanding cycle stability and excellent resistance to methanol poisoning. Attached Figure Description

[0022] Figure 1 The microscopic physical structure characterization results of textile waste-based porous carbon (corresponding to TW-C-900, TW-N-900, and TW-NC-900, respectively) prepared under different activation atmospheres (pure CO2, pure NH3, and a mixture of CO2 and NH3) are as follows: (a) nitrogen adsorption-desorption isotherm and (b) corresponding pore size distribution curve; (ce) are scanning electron microscope (SEM) images of TW-C-900, TW-N-900, and TW-NC-900 samples at 1000x magnification.

[0023] Figure 2 The surface chemical state analysis results of textile waste-based porous carbon prepared under different activation atmospheres are as follows: (a) XPS O 1s spectrum, (b) XPS N 1s spectrum, (c) atomic content of each oxygen configuration and (d) atomic content of each nitrogen configuration.

[0024] Figure 3 The pore structure evolution results of textile waste-based porous carbon prepared at different activation temperatures: (a) nitrogen adsorption-desorption isotherms and (b) corresponding pore size distribution diagrams.

[0025] Figure 4 The results of the surface chemical composition difference analysis of porous carbon based on textile waste prepared at different activation temperatures are as follows: (a) XPS O 1s spectrum and (b) XPS N 1s spectrum; and the corresponding (c) oxygen configuration and (d) nitrogen configuration atomic contents.

[0026] Figure 5 Comparison of electrochemical performance of TW-C-900, TW-N-900, TW-NC-900 and commercial Pt / C catalyst in 0.1 M KOH electrolyte: (a) Cyclic voltammetry (CV) curves under oxygen saturation (solid line) and nitrogen saturation (dashed line) conditions; (b) Linear sweep voltammetry (LSV) curves measured at 1600 rpm.

[0027] Figure 6 The electrocatalytic performance evaluation results of TW-NC series materials (TW-NC-700, TW-NC-800, TW-NC-900) and commercial Pt / C are as follows: (a) LSV curve at 1600 rpm; (b) corresponding Tafel slope plot.

[0028] Figure 7The oxygen reduction kinetics of the TW-NC-900 catalyst in an oxygen-saturated 0.1 M KOH electrolyte were studied. Specifically, this included: (a) LSV curves measured at different rotating disk electrode speeds; and (b) corresponding Koutecky-Levich equation curves plotted based on current densities at different potentials.

[0029] Figure 8 The results of the comparative evaluation of the stability and methanol tolerance of TW-NC-900 and commercial Pt / C catalysts are as follows: (a) Chronoamperometry curve at 0.5V (vs. RHE) (characterizing long-term operational durability); (b) Current density response curve after the introduction of methanol (verifying methanol poisoning resistance). Detailed Implementation

[0030] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0031] Please see Figure 1-8 The present invention provides the following technical solutions: Example 1: Preparation of nitrogen-oxygen co-doped hierarchical porous carbon material (TW-NC-900) derived from textile waste S1: Textile waste precursor pretreatment: The textile waste was cut into irregular pieces with sides of approximately 0.5 cm to ensure uniform heating during subsequent heat treatment and to avoid localized overheating or agglomeration caused by uneven material size. The cut textile waste was then placed in a vacuum drying oven and dried continuously at 80°C for 12 hours to remove adsorbed free moisture and volatile impurities from the raw material, obtaining a dried pretreated precursor.

[0032] S2: High-temperature synergistic activation and doping: (1) Loading and atmosphere replacement: The dried precursor is uniformly loaded into the quartz tube, ensuring that the height of the precursor does not exceed 2 / 3 of the length of the isothermal zone of the quartz tube. Then, the quartz tube is placed in the isothermal zone of the tube furnace. Inert gas, high-purity nitrogen, is introduced from the bottom of the quartz tube at a flow rate of 100 mL / min for 40 minutes to completely replace and remove the air in the tube, preventing the precursor from being oxidized by residual oxygen during subsequent heating. (2) Programmed heating and atmosphere switching: After the inert gas replacement is completed, the tube furnace control program is started, and the temperature is heated to the set target activation temperature of 900℃ at a heating rate of 3℃ / min. When the furnace temperature reaches and stabilizes at 900℃, the following operations are performed simultaneously to build a synergistic activation atmosphere: the nitrogen pipeline is switched to a constant temperature bubbling flask containing 1.5 mol / L ammonium nitrate solution (temperature controlled at 70℃). Nitrogen bubbling promotes the decomposition of ammonium salt, thereby generating NH3 gas. To precisely control the activation process, a mixed gas carrying NH3 is first passed through a desiccator (12 cm in length) filled with 80 g of 4 Å molecular sieve to remove excess water vapor from the reaction system. Simultaneously, the CO2 cylinder valve is opened, and its flow rate is precisely controlled at 75 mL / min using a volumetric flow meter. Key process parameters: In this step, the following core parameters need to be precisely controlled to regulate the final structure of the material: Activation temperature: 900℃; Activation time: 120 minutes; Gas ratio: The actual volumetric flow rate ratio of CO2 to NH3 is controlled at 1:2 (determined by the CO2 flow rate of 75 mL / min and the NH3 generation rate).

[0033] S3: Cooling and Sample Collection After activation, CO2 supply was stopped, and the three-way valve on the nitrogen line was switched to the direct connection to the quartz tube. Nitrogen was continuously supplied at a flow rate of 100 mL / min to create an inert protective atmosphere. After the tube furnace cooled naturally to room temperature (≤30℃), the quartz tube was removed, and the solid product inside was collected. The sample was labeled TW-NC-900, indicating that it was prepared by synergistic activation with CO2 and NH3 at 900℃.

[0034] Comparative Example 1: Porous carbon was prepared using only pure NH3 activation. Except for the absence of CO2 introduction, the preparation conditions were identical to those in Example 1. This sample was designated TW-N-900.

[0035] Comparative Example 2 serves as another comparison: porous carbon was prepared using only pure CO2 activation. Except for setting the CO2 flow rate to 100 mL / min and not introducing NH3, the preparation conditions were the same as in Example 1. This sample was designated TW-C-900.

[0036] according to Figure 1As can be seen from this, the nitrogen adsorption-desorption curves of both TW-C-900 activated with pure CO2 and TW-N-900 activated with pure NH3 belong to Type I isotherms. In the low-pressure region where the relative pressure (P / P0) is below 0.1, the nitrogen adsorption capacity of both increases rapidly with increasing relative pressure, and then tends to plateau. This characteristic indicates that both materials have well-developed microporous structures. Figure 1 Further analysis of the pore size distribution diagram (b) reveals that the pores of TW-C-900 and TW-N-900 are mainly concentrated in the range of 0.7-1.1 nm, with only a small number of mesopores of 3-4 nm present in TW-N-900. The data in Table 1 further confirms that the micropore volume accounts for as high as 88.47% and 82.39% of the total pore volume, respectively, which confirms the structural characteristic that single-gas activation mainly forms micropores.

[0037] In contrast, the isotherm of TW-NC-900, which is synergistically activated by CO2 and NH3, conforms to the characteristics of a Class IV curve and is accompanied by an H3-type hysteresis loop. Figure 1 a) This is a typical indicator that the material contains a large number of mesopores. Table 1 shows that its specific surface area reaches 1305 m². 2 / g, which are 1.63 times that of TW-N-900 and 1.54 times that of TW-C-900, respectively. Figure 1 b further demonstrates that the pore structure of TW-NC-900 is more developed: on the one hand, its micropore volume is as high as 0.4782 cm³. 3 The per-g of the catalyst is 1.46 times that of TW-C-900 and 1.54 times that of TW-N-900, respectively, and the micropore size is expanded to 1-2 nm. The larger micropore size and higher micropore volume help to improve the accessibility and utilization of catalytic active sites. On the other hand, its mesopore size distribution range is wider (2-24 nm), and the mesopore volume is as high as 0.4126 cm³. 3 / g, which is 9.6 times that of TW-C-900 and 6.4 times that of TW-N-900, respectively. This hierarchical porous structure of "micropore-mesopore" can effectively reduce the transport resistance of reactants and products, laying a structural foundation for the efficient conduct of oxygen reduction reaction.

[0038] Figure 1Images 'ce' represent SEM images of TW-C-900, TW-N-900, and TW-NC-900 at 1000x magnification. Microscopic morphology reveals well-developed pore structures on the surfaces of all three materials. TW-NC-900 exhibits larger pore sizes and a greater number of pores, demonstrating a denser and more interconnected porous structure compared to the two single-gas activated samples. This phenomenon further confirms the synergistic activation effect of CO2 and NH3: the initial etching of NH3 provides channels for deep pore formation by CO2, while the pore-expanding effect of CO2 enhances the pore-forming efficiency of NH3, with both working together to construct a more developed hierarchical pore structure.

[0039] The sample yield data directly corroborates the existence of this synergistic effect. As shown in Table 1, the yields of TW-C-900, TW-N-900, and TW-NC-900 are 55.24%, 49.71%, and 34.87%, respectively. The sample activated by the mixed gas has the lowest yield, indicating that its activation reaction is more vigorous, consuming more carbon skeleton and thus forming more developed pores. The above results fully demonstrate the technical advantages of synergistic activation by CO2 and NH3 in regulating pore structure.

[0040] Table 1. Effect of activation atmosphere on sample structural properties (activation temperature: 900℃)

[0041] Note: Pyridine nitrogen / graphite nitrogen content (at.%) = relative content of nitrogen configuration corresponding to Table 2 × nitrogen element content in Table 1; COOH content (at.%) = relative content of oxygen configuration corresponding to Table 2 × oxygen element content in Table 1; Yield (%) = (mass of activated carbon catalyst m) e () × 100 / mass of dried textile waste m0.

[0042] The catalytic performance of carbon materials depends not only on their pore structure but also significantly on their surface chemical properties. X-ray photoelectron spectroscopy (XPS) results (Table 1) show that the main constituent elements of the three types of porous carbon materials are C, N, and O, but their elemental contents differ significantly: TW-C-900 has a nitrogen content of only 0.86 at.%, TW-N-900 has a nitrogen content that increases to 4.17 at.%, while TW-NC-900 has the highest nitrogen content, reaching 9.01 at.%; the oxygen content shows a trend of "TW-C-900 > TW-NC-900 > TW-N-900".

[0043] Existing research indicates that the ORR activity of carbon-based catalysts is not only related to the total amount of heteroatoms but also closely related to their specific chemical configuration. For example, the nitrogen content in graphite affects the limiting current density of ORR, the nitrogen content in pyridine helps to increase the onset potential of the reaction, and carboxyl groups (-COOH) can enhance the adsorption capacity of oxygen molecules on the carbon surface through hydrogen bonding or electrostatic interactions, thereby lowering the activation energy of the ORR reaction and increasing the reaction kinetic rate. Therefore, this study further performed peak fitting on the O1s and N1s high-resolution spectra of XPS, and the results are as follows: Figure 2 As shown in Table 2.

[0044] As shown in Table 2, TW-C-900 has the highest -COOH content (3.87 at.%), but its pyridine N (0.25 at.%) and graphite N (0.27 at.%) contents are the lowest among the three. TW-N-900 has -COOH, pyridine N, and graphite N contents of 2.08 at.%, 1.24 at.%, and 1.66 at.%, respectively. TW-NC-900 not only has the second highest -COOH content (3.47 at.%) after TW-C-900, but also has the highest pyridine N (2.77 at.%) and graphite N (3.81 at.%) contents.

[0045] The above results indicate that, compared with single NH3 activation, synergistic activation by CO2 and NH3 is more conducive to the effective doping of nitrogen and oxygen elements, thereby introducing more potential ORR active sites. This is attributed to the synergistic effect of CO2 and NH3: the edge defects and dangling bonds generated by CO2 etching provide more doping sites for active nitrogen species generated by NH3 decomposition; at the same time, the oxygen-containing functional groups introduced by CO2 can also serve as anchoring sites for nitrogen species. Ultimately, this material successfully achieves the synergistic advantages of "high specific surface area + optimized microporous structure + hierarchical porous structure + high nitrogen and oxygen doping amount": the hierarchical porous structure effectively reduces the mass transfer resistance of O2 / electrolyte, the high doping amount provides abundant active sites, and the high specific surface area and optimized microporous structure significantly improve the exposure and accessibility of catalytic active sites. These factors jointly promote the efficient ORR process, fully demonstrating the significant advantages of CO2 and NH3 mixed activation technology.

[0046] Table 2. Relative nitrogen / oxygen configuration contents of TW-C-900, TW-N-900 and TW-NC-900 (based on XPS fitting analysis)

[0047] Example 2 The activation temperature T was adjusted to 700℃, and other preparation conditions were the same as in Example 1, denoted as TW-NC-700.

[0048] Example 3 The activation temperature T was adjusted to 800℃, and other preparation conditions were the same as in Example 1, denoted as TW-NC-800.

[0049] Example 4 The activation temperature T was adjusted to 1000℃, and other preparation conditions were the same as in Example 1, denoted as TW-NC-1000.

[0050] To investigate the effect of activation temperature on the synergistic activation effect of CO2 and NH3 mixed gas, the pore structure and elemental composition of the products obtained in the above examples and Example 1 were characterized.

[0051] Figure 3 The nitrogen adsorption-desorption isotherms and pore size distribution of porous carbon prepared at different temperatures (700℃, 800℃, 900℃, 1000℃) are shown in Table 3. The relevant quantitative parameters are listed in Table 3.

[0052] Pore ​​structure analysis shows that the development of the pore structure in porous carbon exhibits a significant temperature dependence. For example... Figure 3 As shown in Figure a, the isotherm of TW-NC-700 prepared at 700℃ conforms to a Type I curve, indicating that the material is predominantly microporous. When the temperature rises to 800℃ and above, the isotherms of TW-NC-800, TW-NC-900, and TW-NC-1000 all exhibit Type IV curves accompanied by H3-type hysteresis loops, confirming the formation of a large number of mesopores in the material. This conclusion is consistent with... Figure 3 The aperture distribution characteristics of b are consistent.

[0053] As shown in Table 3, the specific surface area (S) of the product BET ), micropore volume (V) mic ) and total pore volume (V t All values ​​showed a trend of first increasing and then decreasing with increasing temperature. At 700℃, the pore structure was poorly developed due to insufficient activation reaction. As the temperature increased to 900℃, the oxidation and etching reaction between CO2 and the carbon matrix intensified, promoting continuous expansion and improvement of the pores, resulting in TW-NC-900 achieving the maximum S BET (1395 m) 2 / g), V mic (0.4782 cm) 3 / g) and V t (0.8909 cm) 3 / g). When the temperature is further increased to 1000℃, excessive etching causes some pores to collapse and micropores to transform into mesopores, resulting in a significant decrease in the above parameters. In contrast to this trend, the mesopore volume (V mesThe proportion of the gas and its pore volume in the total pore volume (increasing from 20.76% to 49.84%) showed a continuous increase with increasing temperature. Furthermore, all the co-activated samples exhibited a wider micropore size distribution (0.7-2 nm) than the control samples activated by a single gas (TW-N-900 and TW-C-900, 0.7-1.1 nm). Among the series of samples, TW-NC-900 exhibited the most developed pore structure, with its S... BET V mic All key parameters are at their highest levels, except for V. mes Slightly lower than TW-NC-1000. The change in product yield further supports the above-mentioned evolution of pore structure. Table 3 shows that the yield decreased from 60.32% at 700℃ to 34.87% at 900℃ (the lowest value in the series of samples), reflecting that the activation reaction was most intense at 900℃. The yield did not decrease further at 1000℃, which may be related to the large loss of carbon skeleton due to excessive etching.

[0054] The nitrogen and oxygen content and their chemical configuration, which play a crucial role in the oxygen reduction reaction, are also significantly affected by the activation temperature (see Table 3 and...). Figure 4 XPS full-spectrum analysis (Table 3) showed that the nitrogen content of the four synergistically activated samples (8.21-9.33 at.%) was significantly higher than that of the single gas activation products (0.86-4.17 at.%), with the nitrogen content of TW-NC-800 (9.33 at.%) and TW-NC-900 (9.08 at.%) falling within the peak range. The oxygen content, however, decreased continuously from 5.28 at.% to 2.81 at.% with increasing temperature; this decreasing trend was mainly due to the difference in thermal stability of oxygen-containing functional groups, such as the preferential decomposition of weakly bonded groups like -COOH at high temperatures.

[0055] Fitting analysis of O1s and N1s high-resolution spectra ( Figure 4 Table 4 further reveals the temperature-dependent characteristics of active sites: (1) Oxygen-containing active sites: The content of -COOH, as a potential active site, continuously decreased from 4.12 at.% in TW-NC-700 to 1.93 at.% in TW-NC-1000 with increasing temperature; (2) Nitrogen-containing active sites: The contents of pyridine nitrogen and graphitic nitrogen both showed a trend of first increasing and then decreasing, reaching a maximum value at TW-NC-900 (2.77 at.% and 3.81 at.% respectively), while significantly decreasing in TW-NC-1000. This phenomenon is related to the transformation behavior of nitrogen species at high temperatures: In the range of 800-900℃, the increase of carbon skeleton defects provides more sites for nitrogen doping; while when the temperature exceeds 1000℃, the rearrangement of graphite microcrystals will reduce defects, and isolated graphitic nitrogen atoms are more likely to desorb and be lost.

[0056] Based on the combined characteristics of pore structure and active sites, it can be concluded that under the experimental conditions, 900℃ is the optimal temperature for the synergistic activation of CO2 and NH3. TW-NC-900 prepared at this temperature possesses the following characteristics: (1) Structural characteristics: It has the largest specific surface area and micropore volume among the series of samples, as well as a well-developed hierarchical porous structure (mesoporosis accounts for 46.32%), forming a synergistic mass transfer pathway of micropores and mesopores. The larger micropore size is beneficial to the utilization rate of catalytic sites, while the well-developed mesoporous structure can effectively reduce the mass transfer resistance of reactants and electrolytes. (2) Active site characteristics: It possesses both a high total nitrogen content and a relatively optimal combination of heteroatoms, namely, a high content of pyridine nitrogen, graphitic nitrogen, and a relatively high COOH content. These functional groups are widely considered to be able to work synergistically to jointly improve ORR performance.

[0057] The above results indicate that the technical solution of "co-activation of textile waste by CO2 and NH3 to prepare hierarchical porous carbon catalyst" provided by the present invention can achieve effective synergy of high specific surface area, optimized microporous structure, hierarchical pore structure and high-density heteroatom active configuration by controlling the activation temperature, especially around 900℃, thereby obtaining carbon materials with excellent ORR catalytic performance potential.

[0058] Table 3. Structural and compositional parameters of carbon catalysts prepared by synergistic activation of CO2 and NH3 at different activation temperatures.

[0059] Table 4. Relative nitrogen / oxygen configuration contents of TW-NC-700, TW-NC-800, TW-NC-900 and TW-NC-1000 (based on XPS fitting analysis)

[0060] The present invention evaluates the ORR catalytic activity, stability and methanol resistance of the prepared hierarchical porous carbon catalyst through the following test methods.

[0061] (1) Preparation of working electrode The fabrication of the working electrode follows a standardized procedure to ensure the reliability and comparability of the test results: (1.1) Pretreatment of glassy carbon electrode: The electrode was polished on chamois leather with 0.25 μm and 0.05 μm alumina polishing powder in sequence. After each polishing step, it was rinsed with ultrapure water and ultrasonically cleaned in ethanol and ultrapure water for 5 minutes each to finally obtain a clean surface with mirror gloss.

[0062] (1.2) Preparation of catalyst slurry: 5.0 mg of catalyst was accurately weighed and mixed with 0.2 mL of ultrapure water, 0.8 mL of isopropanol and 20 μL of 5 wt% Nafion solution. The mixture was ultrasonically dispersed for 1.5 hours to form a uniform dispersion.

[0063] (1.3) Catalyst loading: 10.0 μL of dispersion was dropped onto the surface of the pretreated glassy carbon electrode (5 mm in diameter), pre-dried with an infrared lamp, and then treated in a vacuum drying oven at 30 °C for 12 hours to obtain the working electrode.

[0064] (1.4) Comparative electrode: The working electrode of a commercial 20 wt% Pt / C catalyst was prepared using the same method and used as a performance benchmark.

[0065] (2) Testing system and conditions All electrochemical tests were conducted at room temperature using an electrochemical workstation, a rotating disk electrode apparatus, and a conventional three-electrode electrolytic cell. In the electrolytic cell, the working electrode was a self-made catalyst-supported electrode, the counter electrode was a platinum wire electrode, and the reference electrode was a saturated Ag / AgCl electrode. The electrolyte was a 0.1 mol / L KOH solution, which was saturated with high-purity O2 or N2 for at least 30 minutes before testing.

[0066] During the testing process, all measured potentials relative to the Ag / AgCl reference electrode (EAg / AgCl) were converted to potentials relative to the reversible hydrogen electrode (RHE) (ERHE) using the following formula for performance comparison and analysis: E RHE = E Ag / AgCl +0.0591 × pH + 0.197, where E Ag / AgCl For the measurement potential, 0.197 V is the standard potential of the saturated Ag / AgCl reference electrode used at 25 °C.

[0067] (3) Performance evaluation methods The ORR performance of the catalyst was systematically evaluated through the following tests: (3.1) Cyclic voltammetry (CV) test: In O2-saturated 0.1 M KOH electrolyte, the test was performed at a scan rate of 100 mV / s in a potential range of 0 V to 1.0 V (vs. RHE). Twenty cycles were performed before the test to stabilize the electrode performance.

[0068] (3.2) Linear scanning voltammetry (LSV) test: In 0.1 M KOH electrolyte saturated with O2, the test was performed at a scan rate of 10 mV / s in the potential range of 0~1.1 V (vs. RHE) and a rotation speed of 400 rpm to 2000 rpm.

[0069] (3.3) Electron transfer number analysis: The electron transfer number (n) of the ORR process was calculated by using the LSV curves of the sample at different electrode rotation speeds (400~2000 rpm) and the Koutecky-Levich equation was adopted: J -1 =J L -1 + J K -1 =B -1 ω 0.5 + J K -1 (1-1) B=0.2nF(D O2 ) 2 / 3 ν -1 / 6C O2 (1-2) In the formula, J is the measured current density; J K ω is the kinetic limiting current density; B is the Levich constant; ω is the electrode rotation speed; n is the number of electrons transferred per oxygen molecule during electrocatalysis; F is the Faraday constant (96485 C·mol⁻¹). -1 ); D O2 and C O2 These are the diffusion constants of oxygen (1.9 × 10⁻⁶). -5 cm 2 ·s -1 ) and concentration (1.2×10 -3 mol·cm -3 ); ν is the kinematic viscosity of the solution (0.01 cm⁻¹). 2 ·s -1 ).

[0070] (3.4) Stability and methanol resistance: The chronoamperometry method was used to test the stability and methanol resistance of the electrolyte after the current stabilized at a potential of 0.5 V (vs. RHE) and a rotation speed of 600 rpm.

[0071] (4) Test result example (4.1) Effect of different activation atmospheres on the catalytic performance of porous carbon ORR To visually compare the ORR catalytic performance of textile waste-based porous carbon prepared by three methods—pure CO2 activation (TW-C-900), pure NH3 activation (TW-N-900), and synergistic activation of CO2 and NH3 (TW-NC-900)—the three were fabricated as working electrodes, and their ORR catalytic performance was tested in a 0.1 mol / L KOH electrolyte. The results are as follows: Figure 5 As shown.

[0072] Figure 5(a) shows the CV curves of the three materials in 0.1 mol / L KOH electrolytes with saturated N2 and saturated O2: Under saturated N2 atmosphere, none of the three materials showed obvious reduction peaks (no ORR reaction occurred); under saturated O2 atmosphere, TW-C-900, TW-N-900, and TW-NC-900 showed typical ORR cathode reduction peaks near 0.707 V, 0.752 V, and 0.819 V (vs. RHE), respectively, and the reduction peak current density increased sequentially. Among them, TW-NC-900 had the most positive reduction peak potential and the sharpest peak shape, indicating that it had the best adsorption and activation ability for O2 and the best initial ORR catalytic activity.

[0073] Figure 5 (b) The LSV curve at 1600 rpm under saturated O2 conditions. Key performance parameters are as follows: TW-C-900 (initial potential E0 = 0.883 V, half-wave potential E 1 / 2 =0.754 V, limiting current density J L = -4.186 mA·cm -2 ), TW-N-900 (E0=0.902 V, E 1 / 2 =0.805 V, J L = -5.009 mA·cm -2 ), TW-NC-900 (E0=0.962 V, E 1 / 2 =0.861V, J L = -6.014 mA·cm -2 The performance parameters of TW-NC-900 all surpass those of commercial Pt / C catalysts (E0=0.958 V, E...). 1 / 2 =0.854 V, J L = -5.672 mA·cm -2 This advantage stems from the synergistic optimization of "structure-composition": ① Pore structure optimization: TW-NC-900 has the highest specific surface area, the largest micropore volume, large-sized micropores (1~2 nm) and abundant mesopores (2~24 nm). Among them, micropores can provide sufficient active sites, and mesopores can accelerate mass transfer efficiency; ② Doping configuration optimization: TW-NC-900 has the second highest COOH content (3.47 at.%) after TW-C-900, and the highest pyridine nitrogen (2.77 at.%) and graphitic nitrogen (3.81 at.%) among the three. The asymmetric electronic structure of the material caused by heteroatom doping can enhance the O2 adsorption capacity, increase the selective adsorption sites and reduce the reaction activation energy.

[0074] Comparing TW-N-900 and TW-C-900 further clarifies the role of heteroatom doping: both have similar pore structures, S BET 802 m respectively 2 / g and 845 m 2 The values ​​are similar, and both are mainly composed of micropores of 0.7~1.5 nm, but the ORR catalytic performance of TW-N-900 (E0, E) is different. 1 / 2 J L The results show that nitrogen doping is significantly better than oxygen doping in ORR catalysis, which further confirms the key role of pyridine nitrogen and graphitic nitrogen as core active sites.

[0075] In summary, the synergistic activation of CO2 and NH3 endows the material with excellent ORR catalytic performance through "dual regulation": on the one hand, synergistic pore-forming constructs a "micropore-mesopore" hierarchical structure, realizing full exposure of active sites and improving mass transfer efficiency; on the other hand, synergistic doping optimizes the N and O configuration distribution, introducing abundant highly active sites, ultimately enabling TW-NC-900 to exhibit ORR catalytic performance that surpasses other comparative examples.

[0076] Table 5. Comparison of ORR performance parameters of different catalysts in O2-saturated 0.1 M KOH solution

[0077] (4.2) Regulation of ORR performance of porous carbon materials by activation temperature To investigate the regulatory effect of different activation temperatures on the ORR performance of textile waste-based porous carbon under a mixed atmosphere of CO2 and NH3, this study prepared a series of N and O co-doped hierarchical porous carbon materials at 700℃, 800℃, 900℃ and 1000℃, and analyzed their ORR catalytic behavior by electrochemical testing. Figure 6 (a) Shows the linear sweep voltammetric curves of catalysts prepared at different temperatures in 0.1 M KOH solution saturated with O2 at 1600 rpm, with E0 and E2 values. 1 / 2 J L Key performance parameters are summarized in Table 6.

[0078] As shown in Table 6, the ORR performance of the catalyst continuously improves as the activation temperature increases from 700℃ to 900℃. Specifically, this is manifested in a positive shift in E0 and an increase in E... 1 / 2 Improve and J L The TW-NC-900 sample prepared at 900℃ exhibited relatively optimal ORR catalytic activity, with E0 and E2 increasing. 1 / 2 The highest, J LThis also reached the maximum value among the series of samples. When the temperature was further increased to 1000℃, all of the above parameters decreased.

[0079] The Tafel slope is a key parameter for evaluating the dynamics of ORR. For example... Figure 6 As shown in (b), the Tafel slopes of TW-NC-700, TW-NC-800, TW-NC-900, and TW-NC-1000 are 71.8 mV / dec, 67.3 mV / dec, 58.6 mV / dec, and 97.4 mV / dec, respectively. Among them, TW-NC-900 has the lowest Tafel slope, indicating that it possesses the optimal reaction kinetics in this series of catalysts, namely a faster electron transfer rate and lower charge transfer resistance. This result further confirms from a kinetic perspective that 900 °C is the optimal temperature for achieving synergistic activation of CO2 and NH3 within the investigated temperature range. The significantly increased Tafel slope of TW-NC-1000 may be related to changes in pore structure or alterations in the properties of active sites caused by high temperature.

[0080] Table 6 Key ORR performance parameters of TW-NC series catalysts and commercial Pt / C

[0081] To clarify the ORR electron transfer pathway of TW-NC-900, this study tested its LSV curves at different rotation speeds (400~2000 rpm) in 0.1 mol / L KOH electrolyte and saturated O2 atmosphere, and quantitatively analyzed the number of electrons transferred using the Koutecky-Levich equation. The results are shown in Figure 7. Figure 7 (a) shows the LSV curves of TW-NC-900 at rotational speeds of 400, 650, 900, 1225, 1600, and 2000 rpm. As the electrode rotational speed increases, the ORR limiting current density (absolute value) increases significantly. This is because the increased rotational speed accelerates the diffusion rate of O2 in the electrolyte, reducing the mass transfer resistance of O2 on the electrode surface. This conforms to the basic law that "the diffusion control current increases with increasing rotational speed" in ORR, providing reliable basic data for subsequent Koutecky-Levich equation analysis. Figure 7(b) shows the Koutecky-Levich curves of TW-NC-900 at 0.2 V, 0.3 V, 0.4 V, and 0.5 V (vs. RHE). The kinetic current (J / L) can be seen... -1 ) and electrode rotation speed (ω) -1 / 2The data showed a good linear relationship, with linear correlation coefficients all greater than 0.99, indicating that the ORR process of this material conforms to the Koutecky-Levich equation assumptions, and the data has high reliability. Based on the correlation formula between the Koutecky-Levich slope B and the number of electrons transferred n (Formula 1-2), the number of electrons transferred at different potentials was calculated as follows: 3.81 at 0.5 V, 3.88 at 0.4 V, 3.90 at 0.3 V, and 3.91 at 0.2 V, all slightly lower than the theoretical value of four-electron transfer (4.00). This result indicates that the ORR process catalyzed by TW-NC-900 mainly follows a near-ideal four-electron transfer path, with water as the main reaction product (rather than hydrogen peroxide via the two-electron path), which avoids the corrosion of the electrode by hydrogen peroxide and demonstrates highly efficient electrocatalytic kinetics. This is directly related to the synergistic advantage of the material's "hierarchical porous structure promoting mass transfer + highly active nitrogen and oxygen sites accelerating electron transfer," further confirming the effectiveness of the CO2 and NH3 synergistic activation strategy at 900℃.

[0082] (4.3) Cyclic stability and resistance to methanol interference test In practical applications such as fuel cells, the cycle stability and anti-interference ability (e.g., resistance to methanol cross-interference) of electrocatalysts are core indicators for evaluating their practical value, and are as important as catalytic activity. To systematically evaluate the long-term performance of TW-NC-900, this study tested its cycle stability using the chronoamperometry (It) method under a 0.1 mol / L KOH electrolyte and a saturated O2 atmosphere, and examined its tolerance to methanol cross-interference. The results are shown in Figure 8.

[0083] Cyclic stability testing was conducted for 5000 seconds at a potential of 0.5 V (vs. RHE) and a rotational speed of 600 rpm. Figure 8 The chronoamperometry curve in (a) shows that the relative current retention of TW-NC-900 reaches 89.54%, which is significantly higher than that of commercial Pt / C catalysts (87.92%). This excellent stability is attributed to its hierarchical porous structure—the well-developed mesopores effectively mitigate the erosion of the carbon skeleton by the electrolyte during the reaction, and the stable chemical bonds formed by N and O co-doping enhance the binding force between the active sites and the carbon matrix, reducing the loss of active components.

[0084] The methanol interference resistance test was conducted under the same potential and rotation speed conditions, and the test was started in 100 mL of electrolyte. Figure 8(b) The results showed that when 10 mL of methanol solution was added to the electrolyte at 450 s, the current density of TW-NC-900 only fluctuated slightly and quickly recovered to more than 98% of the initial current within 100 s; while the current density of commercial Pt / C catalysts dropped sharply by more than 15% after the addition of methanol and could not recover to the initial level. This is because Pt-based catalysts readily catalyze the methanol oxidation reaction, and the resulting oxidation intermediates cover the active sites, leading to irreversible decay of ORR activity; while TW-NC-900 exhibits excellent resistance to methanol interference due to the weak adsorption capacity of the electronic structure formed by N and O co-doping and the hierarchical channels inhibiting the enrichment of methanol near the active sites.

[0085] In summary, TW-NC-900 surpasses commercial Pt / C in both cycle stability and resistance to methanol interference. Combined with its excellent ORR catalytic activity and four-electron transfer characteristics, it fully demonstrates that the textile waste-based porous carbon prepared by synergistic activation of CO2 and NH3 at 900℃ has the practical potential to become a high-efficiency ORR catalyst for fuel cells.

[0086] (5) Material characterization and analysis methods To systematically evaluate the physicochemical properties of the prepared catalysts, the following characterization techniques were used: (5.1) Characterization of specific surface area and pore structure The specific surface area, pore structure, and pore size distribution of carbon catalysts were determined using the N2 adsorption-desorption isotherm method. The instrument used was the Autosorb iQ2 physical adsorption instrument from Quantachrome, USA.

[0087] The testing procedure is as follows: Approximately 0.1 g of sample was accurately weighed and placed in a specially designed quartz tube. Using liquid nitrogen as the adsorption medium, the adsorption volume of N2 by the sample within the relative pressure range (0.0~1.0) was measured at 77 K, and adsorption isotherms were obtained. Based on the isotherm data, the specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method; the total pore volume was determined by the adsorption amount at a relative pressure of 0.99; the micropore volume was calculated using the Dubinin-Radushkevich equation; the mesopore volume was obtained by subtracting the micropore volume from the total pore volume; and the pore size distribution was analyzed using the quenched solid density functional theory model.

[0088] (5.2) Characterization of surface chemical properties The elemental composition, content and surface functional groups of the samples of this invention were determined by X-ray photoelectron spectroscopy (XPS). The test depth was within 10 nm of the sample surface. The instrument used was an ESCALAB 250Xi X-ray photoelectron spectrometer from Thermo Fisher Scientific, USA.

[0089] The test parameters are as follows: Al Kα rays (hν=1486.6 eV) were used as the excitation source; the full-spectrum scan beam size was 400 μm, the operating voltage was 12 kV, the lens mode was standard mode, the analyzer mode was CAE, the pass energy was 100 eV, and the step size was 1 eV; the narrow-spectrum scan parameters were the same as the full-spectrum scan except for the pass energy of 50 eV and the step size of 0.05 eV, and the number of scans for each element was no less than 5 cycles of signal accumulation. Peak fitting was performed using XPSPEAK 4.1 peak-splitting software, and graphs were plotted using Origin2021 software.

[0090] (5.3) Microscopic morphological characterization The surface morphology and microstructure of the material were observed using scanning electron microscopy (SEM). The instrument used was a Carl Zeiss Gemini 300 field emission scanning electron microscope from Germany. The specific test conditions are as follows: Sample preparation: TW-NC-900 was thoroughly ground and uniformly dispersed on the surface of the conductive adhesive. Platinum target coating was performed using a magnetron sputtering instrument with a coating thickness of 3~5 nm to enhance the conductivity of the sample and avoid charge accumulation during imaging.

[0091] Vacuum mode: High vacuum mode (vacuum degree ≤ 10) is adopted. -3 Pa) reduces the scattering of the electron beam by gas molecules, thereby improving image resolution.

[0092] Acceleration voltage: 5 kV is used for low-magnification morphology observation, and 10~15 kV is used for high-magnification pore structure detail characterization, balancing imaging clarity and sample damage control.

[0093] Working distance: Set to 8~12 mm. This range can balance depth of field and resolution, and is suitable for the 3D structural imaging needs of porous carbon materials.

[0094] Imaging mode: Employs the Inlens secondary electron detector (SEI mode), utilizing Zeiss's exclusive cross-path-free optical design to capture the surface porosity distribution, morphological features, and micro-texture details of the material.

[0095] Imaging magnification: The scanned photo was taken at a magnification of 1000x.

[0096] Based on the foregoing embodiments, comparative examples, and systematic test results, the nitrogen-oxygen co-doped porous carbon catalyst based on textile waste disclosed in this invention exhibits the following advantages: (1) The preparation process combines economy, safety and high controllability. Raw material cost advantage: Using widely available and inexpensive textile waste as a carbon precursor realizes the resource utilization of solid waste; selecting industrial-grade ammonium salt aqueous solution with a unit cost far lower than high-purity ammonia gas as a nitrogen source further significantly reduces raw material costs.

[0097] Process efficiency and simplification: An innovative one-step synergistic activation strategy using a CO2 and NH3 mixed gas is employed, enabling simultaneous hierarchical pore formation of the carbon framework and co-doping with nitrogen and oxygen elements in a single step, directly producing porous carbon materials that meet ORR requirements. This process route is significantly shorter than the multi-step methods commonly used in existing technologies, resulting in a substantial improvement in production efficiency.

[0098] The process is safe and controllable: the reaction is carried out under mild conditions of low or normal pressure, effectively avoiding the equipment requirements and safety risks associated with high pressure or highly corrosive reagents. Crucially, this invention employs a "bubbling release of ammonia from ammonium salt aqueous solution + dilution with inert gas" method to generate ammonia in situ, fundamentally solving the high-pressure leakage risk and strong irritant problem of ammonia cylinders during storage and transportation.

[0099] Flexible parameter control: By precisely controlling key parameters such as the mixed gas ratio, ammonium salt concentration, and bubbling rate, it is possible to accurately design the material's pore structure (such as the micropore / mesopore ratio) and surface chemical properties (such as the type and content of nitrogen and oxygen doping), providing a wide range of control options for adapting to different application scenarios.

[0100] (2) Unique hierarchical porous structure optimizes mass transfer efficiency The prepared nitrogen-oxygen co-doped porous carbon material has a high specific surface area and a well-developed hierarchical pore structure.

[0101] Microporous structure: The material possesses a rich microporous structure, with pore sizes mainly concentrated in the range of 1-2 nm. Larger micropore sizes and higher micropore volumes significantly improve the accessibility and contact efficiency of active sites and reactant molecules.

[0102] Mesoporous structure: The material possesses large-volume mesopores with a wide pore size distribution range (2-24 nm) and a high proportion of the total pore volume. This hierarchical structure, in which micropores and mesopores coexist synergistically, can fully expose catalytic active sites and greatly reduce the transport resistance of electrolyte and O2, thus providing an ideal structural basis for the efficient ORR reaction.

[0103] (3) High-efficiency nitrogen and oxygen atom doping Leveraging the synergistic effect of CO2 and NH3 during the activation process, efficient co-doping of nitrogen and oxygen heteroatoms in a porous carbon framework was successfully achieved. This not only significantly increased the absolute number of catalytically active sites but also effectively modulated the electronic structure of the carbon material, thus providing a solid material and electronic structural foundation for improving ORR catalytic performance.

[0104] (4) Excellent ORR catalytic performance Under optimized conditions at 900℃, the sample (TW-NC-900) prepared through synergistic activation by CO2 and NH3 exhibited the best ORR catalytic activity. In 0.1 mol / L KOH electrolyte, its onset potential reached 0.958 V (vs. RHE), its half-wave potential reached 0.854 V (vs. RHE), and its limiting current density was 5.672 mA·cm⁻¹. -2 Key performance parameters comprehensively surpass commercial Pt / C catalyst benchmarks. (5) Excellent stability and resistance to methanol poisoning The TW-NC-900 catalyst exhibited excellent performance in long-term cycling stability tests, with activity degradation significantly lower than that of commercial Pt / C. Furthermore, it maintained high activity even in the presence of methanol molecules, demonstrating superior resistance to methanol poisoning compared to Pt / C. This provides a significant advantage for its application in practical devices such as direct methanol fuel cells.

[0105] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste, characterized in that, Includes the following steps: S1: Textile waste precursor pretreatment: Textile waste is cut into irregular pieces and then dried to remove free moisture and volatile impurities from the raw material to obtain a dried precursor. S2: High-temperature synergistic activation and doping: Filling and atmosphere replacement: The dried precursor is uniformly loaded into the quartz tube, ensuring that the height of the precursor does not exceed 2 / 3 of the length of the constant temperature zone of the quartz tube. Then the quartz tube is placed into the constant temperature zone of the tube furnace. Inert gas is introduced from the bottom of the quartz tube to replace the air inside the quartz tube. Programmed heating and atmosphere switching: After inert gas replacement is completed, the tube furnace is heated to a specified activation temperature T of 700-1000℃ under an inert atmosphere by programmed heating; after the temperature T stabilizes, the inert gas path is switched to a constant temperature bubbler containing ammonium salt solution, and the ammonium salt is hydrolyzed by bubbling to generate a gas flow containing NH3 and water vapor; after this gas flow is dried and dehydrated, it is mixed with CO2 to form a synergistic activation atmosphere, and the volume flow ratio of CO2 to NH3 is controlled to be 1:1 to 1:3; Thermal activation: At temperature T, keep warm in the synergistic activation atmosphere for 60~180 min; S3: Cooling and Sample Collection: After activation, stop the CO2 supply and switch the three-way valve on the inert gas pipeline to the passage directly connected to the quartz tube, and continue to supply inert gas to form an inert protective atmosphere; after the tube furnace cools naturally to room temperature, remove the quartz tube and collect the solid product inside the tube, which is the nitrogen-oxygen co-doped hierarchical porous carbon material.

2. The method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste according to claim 1, characterized in that, In step S1, the drying temperature is set to 80℃ and the drying time is set to 12 hours; the side length of the irregular fragments is set to 0.5-1cm to ensure uniform heating in the subsequent process.

3. The method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste according to claim 1, characterized in that, In the loading and atmosphere replacement step S2, the inert gas is nitrogen or argon, the gas flow rate is set to 50~200mL / min, and the replacement time is set to 30~60min.

4. The method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste according to claim 3, characterized in that, In the programmed heating and atmosphere switching step S2, the programmed heating rate is 3℃ / min.

5. The method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste according to claim 1, characterized in that, In the programmed temperature rise and atmosphere switching step S2, the ammonium salt solution is an aqueous solution of ammonium nitrate, ammonium chloride, or ammonium citrate with a concentration of 0.5~2 mol / L, and the temperature of the constant temperature bubbling flask is controlled at 60~90℃.

6. A method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste according to claim 5, characterized in that, In the S2 process of programmed heating and atmosphere switching, the drying and dehydration is achieved by passing the gas mixture generated by bubbling through a dryer filled with 4Å molecular sieves. The dryer is 10-15 cm long and the molecular sieve filling amount is 50-100 g. The CO2 flow rate is 25-100 mL / min. During the heat preservation and activation period, the concentration of NH3 generated is precisely controlled by adjusting the inert gas flow rate, the concentration of ammonium salt solution, and the temperature of the constant temperature bubbling flask.

7. A method for preparing nitrogen-oxygen co-doped hierarchical porous carbon from textile waste according to claim 1, characterized in that, In step S3, the flow rate of the inert gas used to maintain the protective atmosphere is set to 100 mL / min, and cooling to room temperature means a temperature ≤ 30°C.

8. An application of a nitrogen-oxygen co-doped hierarchical porous carbon material prepared by any one of the preparation methods described in claims 1-7, characterized in that, The nitrogen-oxygen co-doped hierarchical porous carbon material is used as a metal-free catalyst in the cathode ORR of a fuel cell.

9. The application of the hierarchical porous carbon material prepared by the nitrogen-oxygen co-doping method according to claim 8, characterized in that, The specific steps are as follows: Accurately weigh 5 mg of the nitrogen-oxygen co-doped hierarchical porous carbon material, add 0.2 mL of ultrapure water, 0.8 mL of isopropanol and 20 μL of 5 wt% Nafion solution, and place the mixture in an ultrasonic cleaner for ultrasonic dispersion for 1.5 hours to obtain a uniform and stable catalyst dispersion. 10 μL of the above dispersion was precisely transferred using a microsyringe and uniformly drop-coated onto the surface of the pretreated glassy carbon electrode. The electrode was first dried under an infrared lamp to quickly remove the solvent, and then transferred to a vacuum drying oven and dried at 30 °C for 12 hours to further remove residual solvent and enhance the adhesion between the catalyst film and the electrode substrate, thus obtaining the working electrode to be tested.

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