An amplification synthesis preparation method of a transition metal single-atom catalyst based on nitrogen-sulfur doped carbon quantum dots

Abstract

The application relates to the technical field of electrocatalysts, and particularly discloses an amplification synthesis method for preparing a nitrogen and sulfur doped carbon-based transition metal monatomic catalyst from carbon quantum dots. The method comprises the following steps: (1) uniformly mixing sodium lignosulfonate and urea into an ethylene glycol aqueous solution, and obtaining nitrogen and sulfur doped carbon quantum dots through hydrothermal treatment; (2) carbonizing a biomass cellulose raw material at 800 DEG C to obtain a cellulose-based porous carbon material; (3) mixing and drying the cellulose-based porous carbon material, the nitrogen and sulfur doped carbon quantum dots and a transition metal salt solution, grinding the mixture with a nitrogen-containing compound, and then performing secondary carbonization at 800-1000 DEG C in an inert atmosphere, so as to finally obtain a biomass-derived nitrogen and sulfur doped monatomic carbon-based catalyst. The catalyst has a high specific surface area and rich active sites, and exhibits excellent catalytic activity. The biomass raw material used in the application is rich in source and cheap and easy to obtain, the preparation process is simple, and the application provides an effective way for high-value utilization of waste resources.

Description

Technical Field

[0001] This invention belongs to the field of transition metal single-atom catalyst preparation technology, specifically relating to a scale-up synthesis preparation method for a nitrogen-sulfur-doped carbon quantum dot transition metal single-atom catalyst. Background Technology

[0002] The purpose of disclosing the background section is to enhance the overall understanding of the technical field to which this invention pertains. The description of the literature, technology and market status contained therein does not imply an admission that such content was known or commonly used by those skilled in the art prior to the filing date of this invention, nor does it constitute any limitation or confirmation of the scope of the prior art.

[0003] Currently, the large-scale exploitation and consumption of oil resources globally has triggered a severe energy crisis and ecological environmental problems, posing a serious challenge to sustainable development. Promoting the innovation and application of green and clean energy technologies is a key path to address these challenges. Among these, electrocatalysis technology, as a core means of achieving efficient energy conversion and storage, plays a crucial role in clean energy systems such as fuel cells, metal-air batteries, and water electrolysis for hydrogen production, and is gradually becoming an important frontier direction for future energy technology development. However, many current electrocatalytic processes are still limited by slow reaction kinetics, severely restricting the improvement of energy conversion efficiency. Noble metal-based catalysts have long been regarded as "benchmark" materials in the field of electrocatalysis; however, they face challenges such as high cost, insufficient stability, and insufficient durability in practical applications, prompting researchers to continuously explore new catalytic materials that can replace precious metals. Therefore, developing high-performance catalytic materials is a key link in promoting the practical application of electrocatalysis technology.

[0004] Transition metal single-atom catalysts (SACs) have shown great potential in the field of electrocatalysis due to their high atom utilization, well-defined active centers, and nanoscale confinement. Currently, the preparation of SACs mainly employs methods such as atomic layer deposition and wet impregnation-high-temperature pyrolysis. These methods generally suffer from problems such as complex processes, expensive equipment, low metal loading, easy agglomeration, and difficulty in large-scale production. Furthermore, the catalytic function of traditional catalysts is often relatively singular, making it difficult to meet the practical requirements of integrated devices (such as urea-assisted energy-saving hydrogen production systems or direct urea fuel cells) for multifunctional synergistic catalysis. Summary of the Invention

[0005] To address the limitations of traditional single-atom catalyst preparation processes, such as complexity, high cost, and strong equipment dependence, this invention proposes a method for the large-scale synthesis of transition metal single-atom catalysts based on nitrogen-sulfur-doped carbon quantum dots. This process is simple and easy to implement, aligns with the concept of green and sustainable development, and not only realizes the utilization of biomass resources but also allows for the conversion of biomass into high-performance electrocatalysts for application in various reactions, demonstrating promising catalytic prospects. This invention also provides applications of the aforementioned transition metal single-atom catalysts, which are used as cathode oxygen reduction catalysts, particularly as anode catalysts in metal-air batteries, hydrogen-oxygen fuel cells, and methanol fuel cells. Addressing the problems of complex, high-cost, single-function, and difficult-to-scale preparation of single-atom catalysts in existing technologies, this invention provides a simple, inexpensive, and easily scalable method for preparing nitrogen- and sulfur-doped single-atom carbon-based catalysts from biomass carbon quantum dots. This method involves a stepwise design. First, nitrogen-sulfur-doped carbon quantum dots (N,S-CDs) with abundant heteroatoms and surface functional groups and excellent dispersion, and a porous carbon support with high specific surface area are prepared separately. Then, the two are combined with a metal precursor. By utilizing the strong coordination ability and nanoscale effect of carbon quantum dots, metal atoms are confined and anchored in the carbon matrix during the secondary carbonization process, ultimately obtaining a multifunctional single-atom catalyst that can achieve multiple functions and high performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of this invention provides a scaled-up synthesis method for preparing nitrogen- and sulfur-doped single-atom carbon-based catalysts from biomass carbon quantum dots, comprising the following steps:

[0008] (1) Preparation of nitrogen and sulfur doped carbon quantum dots (N,S-CDs): Sodium lignosulfonate from biomass was uniformly mixed with urea, ethylene glycol and aqueous solution, and subjected to hydrothermal treatment. After the reaction was completed, the mixture was cooled, dialyzed and dried to obtain solid N,S-CDs.

[0009] (2) Preparation of biomass cellulose-based porous carbon precursor: After mixing and drying the biomass cellulose raw material with the template agent solution, carbonization is carried out once under an inert atmosphere. After carbonization, the material is cooled to room temperature to obtain cellulose-based porous carbon material.

[0010] (3) Preparation of single-atom catalyst precursor: The porous carbon material obtained in step (2), the N,S-CDs obtained in step (1) are mixed with an appropriate transition metal salt solution, ultrasonically dispersed and dried to obtain a mixed precursor.

[0011] (4) Preparation of nitrogen and sulfur doped single-atom carbon-based catalyst: The mixed precursor obtained in step (3) is ground with a nitrogen-containing compound and then carbonized in an inert atmosphere. After carbonization, it is cooled to room temperature and then acid-washed, washed and dried to obtain the target catalyst.

[0012] This invention mainly utilizes the excellent dispersibility and abundant functional groups of nitrogen and sulfur-doped carbon quantum dots to coordinate metals. Through mixed pyrolysis, after removing the salt template, it is doped and pyrolyzed with nitrogen-containing compounds to synthesize a highly dispersed single-atom catalyst with a transition metal-nitrogen-sulfur structure.

[0013] In some embodiments, the metal salt is at least one of a transition metal chloride salt, acetate, nitrate, and sulfate.

[0014] In some embodiments, the transition metal is at least one selected from iron, cobalt, nickel, copper, zinc, and manganese.

[0015] In some embodiments, the template agent is at least one of sodium chloride, zinc chloride, potassium chloride, sodium carbonate, sodium bicarbonate, and sodium sulfate.

[0016] In some embodiments, the mixing time is 15-45 min, the freeze-drying conditions are -40 to -60°C, 0.1 mPa, and the freeze-drying time is 24 to 48 h; in some embodiments, the washing temperature is 50-60°C, the washing solution is 0.5-2 mol / L hydrochloric acid, sulfuric acid, or nitric acid, and the washing time is 8-24 h.

[0017] In some implementations, the drying temperature after washing is 50-90°C, and the drying time is 8-16 hours.

[0018] In some embodiments, the nitrogen-containing compound in the secondary pyrolysis is at least one of ammonium chloride, ammonium bromide, ammonium phosphate, urea, thiourea, ammonium dihydrogen phosphate, and melamine; in some embodiments, the mass ratio of the nitrogen-sulfur-doped carbon quantum dot-based single-atom catalyst precursor to the nitrogen-containing compound is 1:1-25.

[0019] In some embodiments, the conditions for secondary carbonization are as follows: under an inert atmosphere, the carbonization temperature is 800~1100℃, the carbonization time is 1-5 h, and the heating rate is 2~10℃ / min.

[0020] In some embodiments, the inert atmosphere is one of nitrogen, argon, carbon dioxide, or an argon-hydrogen mixture.

[0021] A second aspect of this invention provides the application of the nitrogen- and sulfur-doped single-atom carbon-based catalyst prepared by the above method in the field of electrocatalysis. The catalyst exhibits excellent catalytic activity and stability in the oxygen reduction reaction (ORR), urea oxidation reaction (UOR), and hydrogen evolution reaction (HER). Specifically, it can be applied to energy conversion and storage devices such as fuel cell cathodes, air electrodes in metal-air batteries (e.g., zinc-air batteries), and electrodes in urea-assisted water electrolysis or total water splitting devices.

[0022] When biomass-based carbon-based transition metal single-atom catalysts are used as oxygen electrode catalytic materials in zinc-air batteries, 6 M potassium hydroxide and 0.2 M zinc acetate solutions are prepared as electrolyte solutions for electrochemical performance testing; when used as cathode and anode catalytic materials for water electrolysis to produce hydrogen, 1 M potassium hydroxide solution is prepared as electrolyte solutions for electrochemical performance testing.

[0023] This invention utilizes biomass as a carbon source and nitrogen- and sulfur-doped carbon quantum dots as metal chelating agents to prepare a multifunctional carbon-based single-atom catalyst with atomically dispersed metal sites and high loading properties through specific conversion processes (metal coordination, controlled carbonization, and single-atom microenvironment regulation). This catalyst exhibits excellent synergistic catalytic activity and stability in electrocatalytic ORR, OER, and HER. This preparation method not only fully utilizes natural, renewable, and biocompatible biomass resources, achieving a green upgrade from low-value materials to high-performance multifunctional catalytic materials, but also features a green and simple preparation process with low energy consumption, reflecting environmentally friendly principles and conforming to the concept of sustainable green chemistry.

[0024] A third aspect of this invention provides that the biomass feedstock has advantages in preparing carbon-based single-atom catalysts with high catalytic activity for ORR, UOR, and HER applications. More specifically, different transition metal-based single-atom catalysts exhibit excellent selectivity for specific reaction pathways due to their unique electronic structures: Fe-based catalysts show excellent activity in the oxygen reduction reaction (ORR), Ni-based catalysts are highly efficient active centers in the urea oxidation reaction (UOR), and Co-based catalysts exhibit outstanding performance in the hydrogen evolution reaction (HER).

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. Green and inexpensive raw materials for high-value utilization of waste: This invention selects sodium lignosulfonate and cellulose as core precursors, both of which are widely available and inexpensive biomass-based or industrial by-product raw materials. Sodium lignosulfonate is a by-product generated in large quantities in the papermaking industry and is often used as an inexpensive chemical raw material; cellulose is the most abundant natural polymer in nature and can be extracted from renewable resources such as agricultural and forestry waste and herbaceous plants. These two raw materials are not only inexpensive and have a stable supply, but also contain abundant carbon, oxygen, sulfur, and other elements, possessing both structural tunability and chemical activity. By converting them into high-performance single-atom catalysts, this invention achieves structural and value upgrades from low-value waste to high-value functional materials, fully conforming to the core principles of green chemistry and providing a demonstrative technical path for the efficient and high-value utilization of biomass resources.

[0027] 2. Simple and controllable process, easy to scale up for production: The synthesis route adopted in this invention is based on mature hydrothermal reaction and high-temperature carbonization technology, without relying on sophisticated and expensive equipment such as atomic layer deposition. The process conditions are mild, the steps are clear, and key parameters (such as temperature, time, and material ratio) are easy to control precisely. The entire process has good repeatability and high batch stability. There are no significant technical barriers between gram-level preparation in the laboratory and large-scale production, laying a solid technological foundation for the low-cost, large-scale preparation of catalysts.

[0028] 3. Unique structural design and abundant active sites: The innovation of this method lies in the introduction of nitrogen-sulfur co-doped carbon quantum dots (NSCDs) as a multifunctional chelating agent. Their nanoscale size, high surface energy, and abundant oxygen-, nitrogen-, and sulfur-containing functional groups not only efficiently complex metal ions but also effectively inhibit the migration and aggregation of metal atoms during pyrolysis through spatial confinement and chemical anchoring, thereby guiding the formation of high-density, atomically dispersed metal-nitrogen-sulfur (MN) quantum dots. x S y Active sites. At the same time, the cellulose-derived defective porous carbon framework not only provides a high specific surface area to load a large number of active sites, but its open pore structure also greatly promotes electron conduction and mass diffusion during the reaction process, achieving synergistic optimization of activity, stability and mass transfer efficiency.

[0029] 4. Multifunctional and High-Performance Catalyst: Thanks to the unique structural design described above, the prepared catalyst simultaneously exhibits excellent electrocatalytic activities for oxygen reduction (ORR), urea oxidation (UOR), and hydrogen evolution reaction (HER). This characteristic of integrating three key reaction functions into a single material significantly broadens its application scenarios.

[0030] 5. Broad Application Prospects: Thanks to the unique structural design described above, the prepared catalyst simultaneously exhibits excellent electrocatalytic activities for oxygen reduction (ORR), urea oxidation (UOR), and hydrogen evolution reaction (HER). This characteristic of integrating three key reaction functions into a single material significantly broadens its application scenarios. For example, it can be directly used as a highly efficient bifunctional (ORR / OER) air electrode material for rechargeable zinc-air batteries, and can also be used to construct integrated devices for "urea-assisted energy-saving hydrogen production" systems, achieving the dual goals of low-energy hydrogen production and urea-containing wastewater purification, demonstrating the material's strong adaptability in complex energy chemical systems. Attached Figure Description

[0031] Figure 1 The images are scanning electron microscope (SEM) images of nitrogen-sulfur-carbon quantum dot-based transition metal single-atom catalysts prepared by the method described in Example 1 of this invention, showing typical sheet-like wrinkles and stacking morphology of two-dimensional layered materials.

[0032] Figure 2 These are transmission electron microscope (TEM) images and corresponding elemental mapping diagrams of the biomass nitrogen-sulfur co-doped carbon quantum dots prepared in this invention, reflecting the excellent dispersion of carbon quantum dots and the uniform distribution of their C, N, and S elements.

[0033] Figure 3 Figure 1 shows the ORR / HER / UOR reaction performance of the nitrogen-sulfur-carbon quantum dot-based transition metal single-atom catalysts prepared in Examples 1, 2, and 3 of this invention. Figure 2a is the ORR linear sweep voltammetric curve of the catalysts prepared in Example 1 and the comparative example in O2-saturated 0.1 M KOH solution; Figure 3b is the HER linear sweep voltammetric curve of the catalysts prepared in Example 2 and the comparative example in 1 M KOH solution; Figure 4c is the UOR linear sweep voltammetric curve of the catalysts prepared in Example 3 and the comparative example in 1 M KOH and 0.33 M Urea solution.

[0034] Figure 4 The constant current density (10 mA cm⁻¹) of the zinc-air battery assembled with the catalyst prepared in Example 1 of this invention is... -2 Charging and discharging cycle stability test diagram.

[0035] Figure 5 These are linear sweep voltammetric curves of ORR / HER / UOR of the catalysts prepared in Examples 1, 2, and 3 of this invention before and after 10,000 cyclic voltammetric cycles.

[0036] Figure 6 The current-time curves of the catalyst prepared in Example 1 of this invention and its comparative example in O2-saturated 0.1 M KOH solution are shown. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] As described in the background section, due to the high surface energy of a single atom, metal ions are prone to migration and aggregation during pyrolysis, making the development of highly stable and highly dispersed single-atom catalysts extremely challenging. At the same time, many published single-atom catalysts are limited by their pore structure or support characteristics, resulting in insufficient exposure of active sites or single catalytic function, which greatly limits their potential for multi-scenario applications.

[0039] To this end, this invention proposes the use of hydrothermal carbonization of biomass sodium lignin sulfonate to generate carbon quantum dots rich in N and S functional groups. These carbon quantum dots can serve as effective metal chelating agents and doping sources. Simultaneously, high-temperature carbonization of cellulose forms a three-dimensional porous conductive framework. After combining these two with a metal salt, during a secondary carbonization process, the functional groups on the carbon quantum dots strongly interact with metal ions, forming a stable MNSC coordination structure during pyrolysis. Metal atoms are confined within the carbon layers derived from the carbon quantum dots, thereby achieving single-atom-level dispersion.

[0040] Nitrogen- and sulfur-doped carbon quantum dots are rich in various active functional groups, including carboxyl, hydroxyl, sulfate, and amino groups. These functional groups exhibit strong coordination and complexation capabilities for metal cations, enabling effective anchoring of metal atoms in the early stages of material synthesis. This strong interaction helps suppress the migration and aggregation of metal atoms during subsequent high-temperature pyrolysis, thus ensuring that the metal is highly dispersed at the atomic level in the final product, while significantly enhancing the overall thermal stability of the catalyst.

[0041] The catalyst obtained in this invention can simultaneously and efficiently catalyze three key reactions: oxygen reduction (ORR), urea oxidation (UOR), and hydrogen evolution reaction (HER), achieving integrated multifunctional catalytic performance. This characteristic stems from the precisely customized single-atom metal active centers (such as Fe, Co, Ni, Cu, Zn, Mn, etc.) and the synergistic doping of nitrogen, sulfur, and other heteroatoms in the carbon substrate. The nitrogen-sulfur co-doped carbon quantum dot precursor not only provides abundant doping sources but also induces a unique atomic-scale coordination structure (M–N–S–C configuration) during pyrolysis, effectively controlling the electronic state and reaction pathway of the metal center. This synergistic effect between heteroatoms and the carbon framework lays the structural foundation for achieving efficient, stable, and multifunctional integrated applications with a single material.

[0042] Therefore, by using sodium lignosulfonate and cellulose as the core carbon precursor and heteroatom dopant source, the method described in this invention can not only effectively suppress the migration and aggregation of metal atoms during pyrolysis through the strong coordination of nitrogen and sulfur co-doped carbon quantum dots, significantly improving the stability and accessibility of active sites of the catalyst, but also, by leveraging their rich natural heteroatom composition and tunable carbon framework structure, construct a trifunctional single-atom catalyst that simultaneously possesses highly efficient oxygen reduction (ORR), urea oxidation (UOR), and hydrogen evolution reaction (HER) catalytic performance. This method fully utilizes the advantages of sodium lignosulfonate and cellulose, such as their wide availability, low cost, tunable structure, and diverse composition, providing a promising technical path for the low-cost, scalable, and environmentally friendly preparation of high-performance integrated electrocatalysts.

[0043] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof. Example 1

[0044] (1) Weigh 1.0 g of sodium lignosulfonate and 1.0 g of urea, dissolve them in 25 mL of ethylene glycol and 5 mL of deionized water, and stir magnetically for 30 minutes until completely dissolved. Transfer the solution to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and hydrothermally react at 200 °C for 24 hours. After natural cooling, dialyze the resulting brownish-black liquid through a dialysis bag (molecular weight cutoff 1000 Da) for 3 days to remove small molecule impurities, and then freeze-dry to obtain a brownish-black solid powder, which is N,S-CQDs.

[0045] (2) Weigh 2.0 g of microcrystalline cellulose powder and dissolve it in 50 ml of deionized water. Add 20 g of potassium chloride and zinc chloride (mass ratio 1:1) as template agents. Stir magnetically for 6 h and then dry. Then, under an argon atmosphere, heat the material to 800 °C at 5 °C / min and keep it at that temperature for 1 hour for carbonization. After natural cooling, black porous carbon material is obtained, which is denoted as PC-800.

[0046] (3) Weigh 200 mg of N,S-CQDs obtained in step (1), disperse them in 10 mL of deionized water, and then add 20 mL of 0.288 mmol of ferric chloride hexahydrate aqueous solution (containing about 16 mg of Fe) for chelation. Sonicate for 30 minutes. Then add 100 mg of PC-800 obtained in step (2) and continue sonicating for 1 hour. After freeze-drying the mixed suspension for 48 h, grind it evenly to obtain the mixed precursor.

[0047] (4) Place the mixed precursor in a tube furnace, weigh ammonium chloride at a mass ratio of 1:10, mix and grind evenly, heat to 900℃ at 5℃ / min under argon atmosphere, hold for 2 hours for secondary carbonization, and after natural cooling, acid wash with 2 M hydrochloric acid overnight and wash with deionized water to obtain the final nitrogen-sulfur doped carbon quantum dot-based transition metal single atom catalyst, denoted as NSCD Fe-SACs. Example 2

[0048] (1) Weigh 1.0 g of sodium lignosulfonate and 1.0 g of urea, dissolve them in 25 mL of ethylene glycol and 5 mL of deionized water, and stir magnetically for 30 minutes until completely dissolved. Transfer the solution to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and hydrothermally react at 200 °C for 24 hours. After natural cooling, dialyze the resulting brownish-black liquid through a dialysis bag (molecular weight cutoff 1000 Da) for 3 days to remove small molecule impurities, and then freeze-dry to obtain a brownish-black solid powder, which is N,S-CQDs.

[0049] (2) Weigh 2.0 g of microcrystalline cellulose powder and dissolve it in 50 ml of deionized water. Add 20 g of potassium chloride and zinc chloride (mass ratio 1:1) as template agents. Stir magnetically for 6 h and then dry. Then, under an argon atmosphere, heat the material to 800 ℃ at 5 ℃ / min and keep it at that temperature for 1 hour for carbonization. After natural cooling, black porous carbon material is obtained, which is denoted as PC-800.

[0050] (3) Weigh 200 mg of the NSCDs obtained in step (1), disperse them in 10 mL of deionized water, and then add 20 mL of 1.09 mmol of nickel chloride hexahydrate aqueous solution (containing about 64 mg of Ni) for chelation. Sonicate for 30 minutes. Then add 100 mg of PC-800 obtained in step (2) and continue sonicating for 1 hour. After freeze-drying the mixed suspension for 48 h, grind it evenly to obtain the mixed precursor.

[0051] (4) Place the mixed precursor in a tube furnace, weigh ammonium chloride at a mass ratio of 1:10, mix and grind evenly, heat to 900 ℃ at 5 ℃ / min under argon atmosphere, hold for 2 hours for secondary carbonization, and after natural cooling, acid wash with 2 M hydrochloric acid overnight and wash with deionized water to obtain the final nitrogen-sulfur doped carbon quantum dot-based transition metal single atom catalyst, denoted as NSCD Ni-SACs. Example 3

[0052] (1) Weigh 1.0 g of sodium lignosulfonate and 1.0 g of urea, dissolve them in 25 mL of ethylene glycol and 5 mL of deionized water, and stir magnetically for 30 minutes until completely dissolved. Transfer the solution to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and hydrothermally react at 200 °C for 24 hours. After natural cooling, dialyze the resulting brownish-black liquid through a dialysis bag (molecular weight cutoff 1000 Da) for 3 days to remove small molecule impurities, and then freeze-dry to obtain a brownish-black solid powder, which is NSCDs.

[0053] (2) Weigh 2.0 g of microcrystalline cellulose powder and dissolve it in 50 ml of deionized water. Add 20 g of potassium chloride and zinc chloride (mass ratio 1:1) as template agents. Stir magnetically for 6 h and then dry. Then, under an argon atmosphere, heat the material to 800℃ at 5 ℃ / min and keep it at that temperature for 1 hour for carbonization. After natural cooling, black porous carbon material is obtained, which is denoted as PC-800.

[0054] (3) Weigh 200 mg of NSCDs obtained in step (1), disperse them in 10 mL of deionized water, and then add 20 mL of 0.18 mmol of nickel chloride hexahydrate aqueous solution (containing about 16 mg of Co) for chelation. Sonicate for 30 minutes. Then add 100 mg of PC-800 obtained in step (2) and continue sonicating for 1 hour. After freeze-drying the mixed suspension for 48 h, grind it evenly to obtain the mixed precursor.

[0055] (4) Place the mixed precursor in a tube furnace, weigh ammonium chloride at a mass ratio of 1:10, mix and grind evenly, heat to 900 ℃ at 5 ℃ / min under argon atmosphere, hold for 2 hours for secondary carbonization, and after natural cooling, acid wash with 2 M hydrochloric acid overnight and wash with deionized water to obtain the final nitrogen-sulfur doped carbon quantum dot-based transition metal single atom catalyst, denoted as NSCD Co-SACs.

[0056] The remaining nitrogen-sulfur-doped carbon quantum dot-based transition metal single-atom catalysts all contain a uniform amount of 16 mg of transition metal. Comparative Example 1

[0057] The difference from Example 1 is that in step (1), the N-doped carbon quantum dots prepared by replacing sodium lignin sulfonate with an equal mass of lignin (alkaline) are used instead of the nitrogen-sulfur-doped carbon quantum dots synthesized in step (3). All other steps and parameters are exactly the same. The resulting catalyst is denoted as NCD M-SACs. Comparative Example 2

[0058] The difference from Example 1 is that step (1) is skipped, and in step (3) the nitrogen-sulfur-doped carbon quantum dots are replaced with an equal mass of glucose monohydrate. All other steps and parameters are identical. The resulting catalyst is denoted as M-SACs (glucose). Comparative Example 3

[0059] The difference from Example 1 is that step (1) is skipped, and in step (3) nitrogen-sulfur doped carbon quantum dots are not added; only PC-800 prepared by the cellulose template method in step (2) is added. All other steps and parameters are exactly the same. The resulting catalyst is denoted as NC.

[0060] These comparative examples are designed to reveal the importance of key components or process parameters in Example 1:

[0061] Comparative Example 1 (lignin instead of sodium lignin sulfonate): The effect of coordination mode on the formation of Fe single-atom coordination structure was investigated, and the difference in catalytic performance between symmetric and asymmetric structures was compared.

[0062] Comparative Example 2 (glucose instead of nitrogen-sulfur doped quantum dots): highlights the confinement effect of the abundant functional groups contained in nitrogen-sulfur doped quantum dots at the nanoscale, demonstrating the key role of regulating the coordination environment / achieving atomic-level dispersion. Removing nitrogen-sulfur doped quantum dots is expected to lead to a significant decrease in ORR, HER, and UOR performance.

[0063] Comparative Example 3 (without chelates): This demonstrates the effectiveness of chelates in forming atomic-level iron atom dispersion and coordination fixation, as well as the formation of stable and efficient Fe-N alloys. x S y The necessity of active centers. In the absence of chelates, during pyrolysis, iron ions, lacking coordination bonds for fixation, migrate freely and aggregate at lower temperatures, forming highly crystalline iron oxide (Fe2O3 / Fe3O4) nanoparticles.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. Structural characterization and performance testing

[0065] Morphological and structural characterization: such as Figure 1As shown, the examples of nitrogen-sulfur-doped carbon quantum dot-based transition metal single-atom catalysts prepared by the present invention exhibit a cross-linked porous layered structure. Figure 2 TEM and elemental mapping of NSCDs show that C, N, and S elements are uniformly distributed in the material. Electrochemical performance testing:

[0066] ORR performance: tested in 0.1 M KOH solution at 1600 rpm. Figure 3 As shown in Figure a, the half-wave potential (E) of the catalyst in Example 1 (NSCD Fe-SACs) is... 1 / 2 The voltage reached 0.90 V (vs. RHE), which is better than the 0.87 V of commercial 20% Pt / C and also significantly higher than comparative examples 1, 2 and 3.

[0067] HER performance: tested in 1 M KOH solution. Figure 3 As shown in Figure b, the NSCD Co-SACs catalyst at a current density of 100 mA cm⁻¹ -2 The overpotential is only 253 mV, which is superior to other comparative examples.

[0068] UOR performance: tested in 1 M KOH and 0.33 M Urea solution. (For example...) Figure 3 As shown in Figure c, the NSCD Ni-SACs catalyst at 100 mA cm⁻¹ -2 The overpotential is 1.36 V, which is superior to other comparative examples.

[0069] Figure 5 Linear scanning voltammetric data of ORR / HER / UOR performance after 10,000 cycles of cyclic voltammetry demonstrate the structural stability of the active sites of the catalyst material.

[0070] Zinc-air battery performance: A zinc-air battery was assembled using NSCD Fe-SACs as the air cathode catalyst. For example... Figure 4 As shown, and at 10 mA cm -2 It can cycle stably for more than 1000 hours at a current density, outperforming the Pt / C benchmark catalyst. Figure 6 The it curve further demonstrates its long-term cyclic stability.

[0071] The above results demonstrate that this invention successfully prepared a single-atom catalyst with high-density Fe-NxSy active sites through a composite strategy of sodium lignosulfonate-derived carbon quantum dots and cellulose-derived porous carbon. Benefiting from abundant heteroatom doping, atomically dispersed metal centers, and a well-developed porous structure, this catalyst exhibits superior performance in trifunctional electrocatalysis. Comparative results show that nitrogen-sulfur co-doped carbon quantum dots (N,S-CQDs) are crucial for achieving single-atom metal dispersion and enhancing catalytic activity.

Claims

1. A scaled-up synthesis method for preparing nitrogen- and sulfur-doped transition metal carbon single-atom catalysts based on carbon quantum dots, characterized in that, Includes the following steps: (1) Sodium lignosulfonate from biomass and urea were added to ethylene glycol and aqueous solution in proportion and mixed evenly. Hydrothermal treatment was then carried out to obtain nitrogen and sulfur doped carbon quantum dots. (2) The biomass cellulose raw material is carbonized once at 800°C under an inert atmosphere by template method (the cellulose solution is mixed with excess zinc chloride and potassium chloride and then dried) to obtain a biomass cellulose-based porous carbon material precursor. (3) The biomass cellulose-based porous carbon material precursor, the nitrogen and sulfur doped carbon quantum dots and the transition metal salt solution are mixed evenly and dried to obtain a mixed precursor. (4) The mixed precursor is subjected to secondary carbonization at 900°C under an inert atmosphere to obtain a nitrogen- and sulfur-doped carbon-based transition metal single-atom catalyst.

2. The scale-up synthesis method for preparing nitrogen- and sulfur-doped carbon-based transition metal single-atom catalysts from biomass carbon quantum dots as described in claim 1, characterized in that, The mass ratio of the biomass sodium lignin sulfonate to urea is 1:1, and the volume ratio of ethylene glycol to water is 1:

5.

3. The scale-up synthesis method for preparing nitrogen and sulfur-doped carbon-based single-atom transition metal catalysts from biomass carbon quantum dots as described in claim 1, wherein the transition metal salt is at least one of the nitrate, chloride, acetate, or sulfate of iron, cobalt, or nickel.

4. The scale-up synthesis method for preparing nitrogen and sulfur-doped single-atom carbon-based catalysts from biomass carbon quantum dots as described in claim 1, wherein the hydrothermal treatment in step (1) is performed at a temperature of 200-250°C for 12-24 h.

5. The scale-up synthesis method for preparing nitrogen and sulfur-doped single-atom carbon-based catalysts from biomass carbon quantum dots as described in claim 1, wherein the temperature of the first carbonization in step (2) is 800℃, the time is 1–2 h, and the heating rate is 5℃ / min.

6. The method for preparing nitrogen and sulfur-doped carbon-based transition metal single-atom catalysts from biomass carbon quantum dots as described in claim 1, wherein considering the different metal loading levels, the mass ratio of the biomass cellulose-based porous carbon material precursor, nitrogen and sulfur-doped carbon quantum dots to transition metal salt in step (3) is 1:2:0.8-1.

4.

7. The scale-up synthesis method for preparing nitrogen and sulfur-doped single-atom carbon-based catalysts from biomass carbon quantum dots as described in claim 1, wherein the secondary carbonization temperature in step (4) is 900℃, the time is 2–3 h, and the heating rate is 5℃ / min.

8. The application of nitrogen- and sulfur-doped carbon-based transition metal single-atom catalysts prepared by the method of any one of claims 1–8 in electrocatalytic oxygen reduction reaction, urea oxidation reaction, and hydrogen evolution reaction.

9. The application of nitrogen- and sulfur-doped carbon-based transition metal single-atom catalysts prepared by the method of any one of claims 1–8 in fuel cells, metal-air batteries, or water electrolysis devices.

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