Sulfur-nitrogen co-doped porous carbon nanosheet electrode material and preparation method thereof

Abstract

The invention provides a sulfur-nitrogen co-doped porous carbon nanosheet electrode material and a preparation method thereof. The sulfur-nitrogen co-doped porous carbon nanosheet electrode material is prepared by taking a waste mushroom stick as a carbon source and combining in-situ doping and a template method; the sulfur-nitrogen co-doped porous carbon nanosheet electrode material is 3-8 wt%, the sulfur content is 1-5 wt%, the specific surface area is not less than 1800 m < 2 > / g, the pore volume is not less than 1.2 cm < 3 > / g, the nitrogen element exists in the forms of pyridine nitrogen, pyrrole nitrogen and graphite nitrogen, and the sulfur element exists in the forms of C-S-C covalent bonds and-SOx-functional groups. According to the invention, the carbon nanosheet material with high specific surface area, hierarchical porous structure and uniform sulfur and nitrogen co-doping is prepared by a simple and green method, and the preparation method has important significance for promoting the development of high-performance electrode materials.

Description

Technical Field

[0001] This invention relates to the field of electrode fabrication technology, and in particular to a sulfur-nitrogen co-doped porous carbon nanosheet electrode material and its preparation method. Background Technology

[0002] With the rapid development of sustainable energy storage and conversion technologies, the demand for high-performance, low-cost electrode materials is becoming increasingly urgent. Carbon-based materials, due to their excellent conductivity, stable chemical properties, and tunable physical structure, exhibit enormous application potential in the field of electrochemical energy. Heteroatom doping is an important means of effectively controlling the electronic structure and surface chemical properties of carbon materials. Nitrogen doping has been extensively studied, while sulfur-nitrogen co-doping, due to its synergistic effect, can further optimize the charge distribution and catalytic activity of materials, and has received increasing attention in recent years.

[0003] Currently, the preparation of sulfur-nitrogen co-doped carbon materials mainly employs methods such as chemical vapor deposition and high-temperature pyrolysis. These methods typically suffer from problems such as complex processes, high costs, and high energy consumption. The carbon precursors used are mostly graphene oxides, carbon nanotubes, and organic polymers, which are expensive raw materials and may involve toxic chemicals in the preparation process. Furthermore, sulfur-nitrogen co-doped carbon materials prepared by existing methods often suffer from uneven doping, simple pore structures, and limited specific surface areas, resulting in limited improvements in their electrochemical performance. Especially in emerging fields such as sodium-ion batteries and zinc-air batteries, higher requirements are placed on the pore structure and surface chemistry of electrode materials, requiring materials to simultaneously possess abundant active sites, efficient ion / electron transport channels, and good structural stability.

[0004] Waste biomass, as a cheap, renewable, and widely available carbon source, is increasingly being explored for its application in carbon material preparation. However, direct carbonization of biomass typically yields carbon materials with underdeveloped pore structures and low doping levels, which are insufficient to meet the requirements of high-performance electrode materials. Summary of the Invention

[0005] The purpose of this invention is to provide a sulfur-nitrogen co-doped porous carbon nanosheet electrode material and its preparation method. The aim is to develop a simple and green method for preparing carbon nanosheet materials with high specific surface area, hierarchical porous structure and uniform sulfur-nitrogen co-doping using waste biomass as raw material. This is of great significance for promoting the development of high-performance electrode materials.

[0006] In a first aspect, the present invention provides a sulfur-nitrogen co-doped porous carbon nanosheet electrode material, characterized in that it is prepared by using waste shiitake mushroom sticks as a carbon source and combining in-situ doping and template method; The sulfur-nitrogen co-doped porous carbon nanosheet electrode material has a nitrogen content of 3-8 wt%, a sulfur content of 1-5 wt%, and a specific surface area of ​​not less than 1800 m². 2 / g, pore volume not less than 1.2 cm³ 3 / g, and nitrogen exists in the form of pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen, while sulfur exists in the form of CSC covalent bonds and -SOx- functional groups.

[0007] In some embodiments, it has a two-dimensional nanosheet morphology with a sheet thickness of 20-30 nanometers, and a three-dimensional interconnected hierarchical pore structure is formed between the sheets. The hierarchical pore structure includes: micropores (0.5-2 nm) accounting for 40-60%, mesopores (2-50 nm) accounting for 30-50%, and macropores (50-200 nm) accounting for 5-15%.

[0008] In some embodiments, the ratio of pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen in the material is (30-50):(25-40):(20-35), and the molar ratio of CSC to -SOx- is (1.5-3):1.

[0009] Secondly, the present invention provides a method for preparing the sulfur-nitrogen co-doped porous carbon nanosheet electrode material as described above, characterized by comprising the following steps: S01. Raw material pretreatment: Wash, crush, and sieve the waste shiitake mushroom logs to obtain raw material powder of 80-200 mesh; S02. Mixing and impregnation: Mix the raw material powder with thiourea and zinc chloride at a mass ratio of 1:0.5-2:1-3, add deionized water and stir to form a slurry, and impregnate for 6-24 hours; S03, freeze-drying: Freeze-dry the impregnated mixture at -50 to -80°C for 12-36 hours; S04, Two-step carbonization: The dried precursor is subjected to two-step heat treatment in a tube furnace: the first step is to hold at 300-500°C for 0.5-2 hours, and the second step is to hold at 700-900°C for 1-3 hours, with a heating rate of 2-10°C / min. S05. Post-treatment: After cooling, the product is acid-washed and water-washed until neutral, and finally vacuum-dried at 60-100°C for 6-12 hours.

[0010] In some embodiments, step S02 further includes adding a transition metal salt accounting for 2-5% of the raw material mass, wherein the transition metal salt is at least one of ferric chloride, nickel nitrate, or ammonium molybdate.

[0011] In some embodiments, both carbonization processes in step S04 are carried out under nitrogen / argon atmosphere protection, with a gas flow rate of 50-200 mL / min.

[0012] In some embodiments, the acid washing in step S05 uses a 0.5-2 mol / L sulfuric acid or nitric acid solution, and the washing is performed 2-4 times.

[0013] In some embodiments, the preparation method further includes: Step S06: The dried material is reactivated at 300-500°C in a carbon dioxide or water vapor atmosphere for 0.5-2 hours.

[0014] Thirdly, the present invention also provides an electrode comprising the sulfur-nitrogen co-doped porous carbon nanosheet electrode material as described above.

[0015] Fourthly, the present invention also provides an application of an electrode in a sodium-ion battery, a zinc-air battery, or a carbon dioxide electroreduction reaction.

[0016] Compared with the prior art, the present invention has the following advantages: 1. The sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared by this invention has a high specific surface area (≥1800 m²). 2 The material possesses a rich hierarchical pore structure ( / g), providing ample contact interfaces and rapid transport channels for electrolyte ions. Sulfur-nitrogen co-doping introduces abundant active sites, significantly enhancing the material's capacitance and catalytic activity. Experiments show that this material exhibits high specific capacity and excellent rate performance in sodium-ion batteries, high oxygen reduction catalytic activity in zinc-air batteries, and high selectivity and stability in the carbon dioxide electroreduction reaction.

[0017] 2. By combining two-dimensional nanosheet morphology with three-dimensional interconnected hierarchical pore structure, both abundant edge active sites are ensured and continuous electron conduction paths are provided; the sheet thickness is controlled at 20-30 nanometers, which effectively shortens the ion diffusion distance and improves the material's kinetic properties.

[0018] 3. By optimizing the preparation process, uniform co-doping of sulfur and nitrogen elements was achieved, and the ratio of different nitrogen species (pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen) and sulfur species (CSC, -SOx-) was precisely controlled. This allows for the regulation of the electronic structure and surface properties of the material to meet the needs of different application scenarios. Furthermore, using waste shiitake mushroom substrate as a carbon source achieves high-value utilization of waste resources. The preparation process employs a water-based system and low-temperature freeze-drying, avoiding the use of organic solvents and reducing energy consumption and environmental pollution. The overall process is simple and easy to scale up for production.

[0019] 4. The sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared by this invention is not only suitable for traditional supercapacitors and lithium-ion batteries, but also exhibits excellent performance in emerging fields such as sodium-ion batteries, zinc-air batteries and carbon dioxide electroreduction, and has broad application prospects. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, but does not exclude other elements or objects.

[0021] Example 1 S01. Raw material pretreatment: Wash, crush, and sieve the waste shiitake mushroom logs to obtain 100-mesh raw material powder. S02. Mixing and Impregnation: Mix the raw material powder with thiourea and zinc chloride in a mass ratio of 1:1:2, add deionized water and stir to form a slurry, and impregnate for 15 hours. S03, freeze-drying: Freeze-dry the impregnated mixture at -65°C for 24 hours; S04, Two-step carbonization: The dried precursor is subjected to two-step heat treatment in a tube furnace: the first step is to hold at 400°C for 1 hour, and the second step is to hold at 800°C for 2 hours. The heating rate is 6°C / min for both steps. Both carbonization processes are carried out under nitrogen / argon atmosphere protection with a gas flow rate of 125mL / min. S05. Post-treatment: The cooled product is acid-washed and water-washed until neutral, and finally vacuum-dried at 80°C for 9 hours. The acid washing is performed using a 1 mol / L sulfuric acid or nitric acid solution, and the washing is performed 3 times.

[0022] The test results of the sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared in Example 1 are as follows: Material characterization data: Specific surface area (BET): 1950 m² 2 / g; Pore volume: 1.35 cm³ 3 / g; Pore size distribution: micropores (55%), mesopores (38%); Elemental content: N: 5.8 wt%, S: 3.2 wt%; N species ratio (XPS): pyridine nitrogen (42%) : pyrrole nitrogen (33%) : graphitic nitrogen (25%); S species molar ratio (XPS): CSC : -SOx- ≈ 2.1 : 1; Morphology (SEM / TEM): Clear porous nanosheet structure with a sheet thickness of approximately 25 nm.

[0023] Electrochemical performance data: Sodium-ion battery (SIB): Reversible specific capacity of 420 mAh / g at a current density of 0.1 A / g; capacity retention of 78% (approximately 328 mAh / g) at a high current density of 1 A / g; capacity retention of 91% after 500 cycles. Zinc-air battery (ZAB): Oxygen reduction reaction (ORR) half-wave potential (E1 / 2) of 0.83 V (vs. RHE), limiting diffusion current density of 5.6 mA / cm². 2 CO2 electroreduction (CO2RR): At a potential of -0.6 V (vs. RHE), the CO Faraday efficiency (FE_CO) is 92%, and the total current density is 15 mA / cm². 2 .

[0024] Example 2 This embodiment is basically the same as Embodiment 1, except that 3 wt% FeCl3 (based on the mass of the mushroom sticks) is added in step S02.

[0025] The test results of the sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared in Example 2 are as follows: Material characterization data: Specific surface area (BET): 1900 m² 2 / g; Pore volume: 1.32 cm³ 3 / g; Elemental content: N: 5.5 wt%, S: 3.0 wt%. Trace Fe-Nx active sites were detected by XPS.

[0026] Electrochemical performance data: SIB: Capacity is the same as in Example 1, but rate performance is improved, with 82% capacity retention at 1 A / g. ZAB: ORR performance is significantly improved, E1 / 2 = 0.85 V, current density 5.9 mA / cm². 2 (Fe-Nx sites exhibit high catalytic activity). CO2RR: FE_CO remains stable at 90%, but H2 yield is effectively suppressed, resulting in enhanced stability.

[0027] Example 3 This embodiment is basically the same as embodiment 1, except that step S06 is added: secondary activation at 400°C in a CO2 atmosphere for 1 h.

[0028] The test results of the sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared in Example 3 are as follows: Material characterization data: Specific surface area (BET): 2350 m² 2 / g (significantly improved); pore volume: 1.65 cm³ 3 / g; Pore size distribution: Micropores increased to 65%, mesopores decreased to 30%. Elemental content decreased slightly: N: 5.0 wt%, S: 2.7 wt%.

[0029] Electrochemical performance data: SIB: At 0.1 A / g, the specific capacity is significantly increased to 480 mAh / g (thanks to the ultra-high specific surface area and abundant microporous sodium storage). However, the rate performance is slightly reduced to 75%. ZAB: E1 / 2 = 0.82 V, performance comparable to Example 1. CO2RR: Total current density increased to 18 mA / cm². 2 (Large specific surface area, large total number of active sites), FE_CO = 88%.

[0030] Comparative Example 1 This comparative example is basically the same as Example 1, except that only shiitake mushroom sticks and ZnCl2 (mass ratio 1:2) are used, and thiourea is not added.

[0031] The test results of the sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared in Comparative Example 1 are as follows: Material characterization data: Specific surface area: 1800 m² 2 / g. Pore volume: 1.20 cm³ 3 / g. Elemental content: N: <1.0 wt% (from biomass itself only), S: <0.5 wt%.

[0032] Electrochemical performance data: SIB: 0.1 A / g, with a capacity of only 210 mAh / g (lacking active sites).

[0033] ZAB: E1 / 2 = 0.75 V, extremely poor performance (no ORR active center). CO2RR: The main product is H2 (FE_H2>70%), FE_CO < 20% (cannot effectively activate CO2).

[0034] Comparative Example 2 This comparative example is basically the same as Example 1, except that shiitake mushroom sticks and thiourea (mass ratio 1:1) are used, and ZnCl2 is not added.

[0035] The test results of the sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared in Comparative Example 2 are as follows: Material characterization data: Specific surface area: 650 m² 2 / g (extremely low); pore volume: 0.45 cm³ 3 / g; The material has a block structure and no porous nanosheet morphology; Elemental content: N: 4.5 wt%, S: 2.5 wt% (the doping amount is not low, but cannot be effectively utilized).

[0036] Electrochemical performance data: SiB capacity <100 mAh / g, ORR and CO2RR activities are negligible. This demonstrates that the ZnCl2 template agent is crucial for constructing high specific surface area and porous structures; without channels, dopant atom and ion transport are blocked. This indicates severe performance degradation in all applications.

[0037] Comparative Example 3 This comparative example is basically the same as Example 1, except that after the raw materials are mixed, they are directly subjected to high-temperature carbonization (800°C, 2h, 5°C / min), omitting the freeze-drying and two-step carbonization steps.

[0038] The test results of the sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared in Comparative Example 3 are as follows: Material characterization data: Specific surface area: 1250 m² 2 / g. Pore volume: 0.45 cm³ 3 / g. Elemental content: N: 3.0 wt%, S: 1.5 wt% (significant loss of sulfur and nitrogen). The proportion of unstable SOx- in the S species is too high, and the proportion of CSC is low.

[0039] Electrochemical performance data: SI: Capacity 280 mAh / g. ZAB: E1 / 2 = 0.78 V. CO2RR: FE_CO = 75%. Note that all performance values ​​are significantly lower than in Example 1, indicating that the two-step carbonization and freeze-drying process is crucial for retaining dopant elements, controlling dopant morphology, and achieving the desired shape.

[0040] In summary, the sulfur-nitrogen co-doped porous carbon nanosheet electrode material and its preparation method proposed in this invention have the following advantages: 1. The sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared by this invention has a high specific surface area (≥1800 m²). 2The material possesses a rich hierarchical pore structure ( / g), providing ample contact interfaces and rapid transport channels for electrolyte ions. Sulfur-nitrogen co-doping introduces abundant active sites, significantly enhancing the material's capacitance and catalytic activity. Experiments show that this material exhibits high specific capacity and excellent rate performance in sodium-ion batteries, high oxygen reduction catalytic activity in zinc-air batteries, and high selectivity and stability in the carbon dioxide electroreduction reaction.

[0041] 2. By combining two-dimensional nanosheet morphology with three-dimensional interconnected hierarchical pore structure, both abundant edge active sites are ensured and continuous electron conduction paths are provided; the sheet thickness is controlled at 20-30 nanometers, which effectively shortens the ion diffusion distance and improves the material's kinetic properties.

[0042] 3. By optimizing the preparation process, uniform co-doping of sulfur and nitrogen elements was achieved, and the ratio of different nitrogen species (pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen) and sulfur species (CSC, -SOx-) was precisely controlled. This allows for the regulation of the electronic structure and surface properties of the material to meet the needs of different application scenarios. Furthermore, using waste shiitake mushroom substrate as a carbon source achieves high-value utilization of waste resources. The preparation process employs a water-based system and low-temperature freeze-drying, avoiding the use of organic solvents and reducing energy consumption and environmental pollution. The overall process is simple and easy to scale up for production.

[0043] 4. The sulfur-nitrogen co-doped porous carbon nanosheet electrode material prepared by this invention is not only suitable for traditional supercapacitors and lithium-ion batteries, but also exhibits excellent performance in emerging fields such as sodium-ion batteries, zinc-air batteries and carbon dioxide electroreduction, and has broad application prospects.

[0044] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A sulfur-nitrogen co-doped porous carbon nanosheet electrode material, characterized in that, It is prepared by using waste shiitake mushroom logs as a carbon source through a combination of in-situ doping and template method; The sulfur-nitrogen co-doped porous carbon nanosheet electrode material has a nitrogen content of 3-8 wt%, a sulfur content of 1-5 wt%, and a specific surface area of ​​not less than 1800 m². 2 / g, pore volume not less than 1.2 cm³ 3 / g, and nitrogen exists in the form of pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen, while sulfur exists in the form of CSC covalent bonds and -SOx- functional groups.

2. The sulfur-nitrogen co-doped porous carbon nanosheet electrode material according to claim 1, characterized in that, It has a two-dimensional nanosheet morphology with a sheet thickness of 20-30 nanometers. The sheets form a three-dimensional interconnected hierarchical pore structure, which includes: micropores (0.5-2 nm) accounting for 40-60%, mesopores (2-50 nm) accounting for 30-50%, and macropores (50-200 nm) accounting for 5-15%.

3. The sulfur-nitrogen co-doped porous carbon nanosheet electrode material according to claim 1, characterized in that, The ratio of pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen in the material is (30-50):(25-40):(20-35), and the molar ratio of CSC to -SOx- is (1.5-3):

1.

4. A method for preparing a sulfur-nitrogen co-doped porous carbon nanosheet electrode material as described in any one of claims 1-3, characterized in that, Includes the following steps: S01. Raw material pretreatment: Wash, crush, and sieve the waste shiitake mushroom logs to obtain raw material powder of 80-200 mesh. S02. Mixing and impregnation: Mix the raw material powder with thiourea and zinc chloride at a mass ratio of 1:0.5-2:1-3, add deionized water and stir to form a slurry, and impregnate for 6-24 hours; S03, freeze-drying: freeze-dry the impregnated mixture at -50 to -80°C for 12-36 hours; S04, Two-step carbonization: The dried precursor is subjected to two-step heat treatment in a tube furnace: the first step is to hold at 300-500°C for 0.5-2 hours, and the second step is to hold at 700-900°C for 1-3 hours, with a heating rate of 2-10°C / min. S05. Post-treatment: The cooled product is acid-washed and water-washed until neutral, and finally vacuum-dried at 60-100°C for 6-12 hours.

5. The method for preparing the sulfur-nitrogen co-doped porous carbon nanosheet electrode material according to claim 4, characterized in that, Step S02 also includes adding a transition metal salt accounting for 2-5% of the raw material mass, wherein the transition metal salt is at least one of ferric chloride, nickel nitrate or ammonium molybdate.

6. The method for preparing the sulfur-nitrogen co-doped porous carbon nanosheet electrode material according to claim 4, characterized in that, In step S04, both carbonization processes are carried out under nitrogen / argon atmosphere protection, with a gas flow rate of 50-200 mL / min.

7. The method for preparing the sulfur-nitrogen co-doped porous carbon nanosheet electrode material according to claim 4, characterized in that, In step S05, acid washing is performed using a 0.5-2 mol / L sulfuric acid or nitric acid solution, and the washing is repeated 2-4 times.

8. The method for preparing the sulfur-nitrogen co-doped porous carbon nanosheet electrode material according to claim 4, characterized in that, The preparation method further includes: Step S06: The dried material is reactivated at 300-500°C in a carbon dioxide or water vapor atmosphere for 0.5-2 hours.

9. An electrode, characterized in that, It comprises the sulfur-nitrogen co-doped porous carbon nanosheet electrode material as described in any one of claims 1-3.

10. The application of the electrode according to claim 9 in sodium-ion batteries, zinc-air batteries, or carbon dioxide electroreduction reactions.