A method for preparing heteroatom-doped single-atom catalysts based on waste plastics and its application

Abstract

This invention discloses a method for preparing heteroatom-doped single-atom catalysts based on waste plastics and its application. First, a porous carbon support is synthesized from waste plastics. Then, the carbon support is stirred with a transition metal complex and a heteroatom source until dry to obtain a uniform precursor. Finally, the precursor is pyrolyzed in an inert atmosphere to prepare the heteroatom-doped single-atom catalyst. The raw materials used in this invention are widely available and readily available, the process is simple, and it is easy to scale up. The oxygen reduction onset potential of the catalyst Fe-N-C-S-1 is 1.0 V, the half-wave potential is 0.90 V, and the maximum power density of the zinc-air cell can reach 203.0 mW / cm². ‑2 Furthermore, the four catalysts prepared in the examples exhibited good cyclic stability over 300 hours. Their oxygen reduction catalytic performance was superior to that of commercial Pt / C catalysts, demonstrating significant theoretical and practical value.

Description

Technical Field

[0001] This invention relates to the technical field of single-atom catalyst preparation methods, specifically to a method for preparing heteroatom-doped single-atom catalysts based on waste plastics and its application. Background Technology

[0002] The widespread use of plastic products has greatly facilitated people's production and lives, but the resulting large amount of non-degradable waste plastics (referred to as "waste plastics") has become a global environmental problem. Therefore, the efficient resource utilization of waste plastics has become an important issue that urgently needs to be addressed. Waste plastics are rich in carbon, and using waste plastics as raw materials to prepare high-value-added carbon materials is an important way to achieve the resource-based recycling of waste plastics. Meanwhile, carbon nanomaterials, due to their outstanding advantages such as large specific surface area, good conductivity, excellent structural tunability, and stable chemical properties, have shown broad application prospects in many fields such as adsorption separation, catalytic reactions, and lithium-ion batteries. They have received particular attention in the field of energy storage and conversion, and have become an important direction for related research.

[0003] Metal-air batteries, as a promising candidate for next-generation energy storage systems, possess significant potential for application in portable electronic devices, electric vehicles, and distributed energy storage due to their advantages such as high theoretical energy density, good safety, and low cost. However, the slow kinetics of their cathode oxygen reduction reaction (ORR) result in poor overall performance, limiting their widespread commercialization. Therefore, developing low-cost, highly active, and highly stable ORR catalysts is an urgent priority for promoting the industrialization of metal-air batteries. Heteroatom-doped single-atom catalysts, with their advantages of high atomic utilization and tunable electronic structure, are a highly promising class of ORR catalysts. Based on this, using abundant and inexpensive waste plastics as a carbon source, we prepare heteroatom-doped single-atom catalysts and apply them to ORR and metal-air batteries. This not only enables high-value-added resource utilization of waste plastics and solves the environmental pollution problems they cause, but also effectively reduces catalyst preparation costs and improves ORR catalytic performance, thereby promoting the development of high-efficiency metal-air batteries. This has significant theoretical and practical application value in the intersection of energy and environmental protection, which is the technical problem and core research focus of this invention.

[0004] The existing ORR catalysts currently have the following main defects: (1) The preparation process is relatively complicated, involving activation and segmented pyrolysis, etc.; (2) The prepared catalysts are only transition metal-nitrogen-carbon type single-atom catalysts with low metal single-atom loading, and doping of heteroatoms (other than nitrogen) has not been achieved. It is impossible to further improve the ORR catalytic performance by controlling the electronic structure of the catalyst through heteroatoms, and it has not been clearly extended to the preparation and application of heteroatom-doped single-atom catalysts, which is essentially different from the heteroatom-doped single-atom catalysts targeted by this invention.

[0005] Therefore, there is an urgent need to develop a single-atom catalyst with good oxygen reduction catalytic performance and cycle stability. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing heteroatom-doped single-atom catalysts based on waste plastics and their applications. First, a porous carbon support is synthesized from waste plastics. Then, the carbon support is stirred with a transition metal complex and a heteroatom source until dry to obtain a uniform precursor. Finally, the precursor is pyrolyzed in an inert atmosphere to prepare the heteroatom-doped single-atom catalyst. The raw materials used in this invention are widely available and readily available, the process is simple, and it is easy to scale up. The oxygen reduction catalytic performance of the four prepared catalysts is superior to that of commercial Pt / C catalysts, which has significant theoretical and practical application value, expanding the application of waste plastic-derived heteroatom-doped single-atom catalysts in metal-air batteries.

[0007] To achieve the above technical effects, the following technical solution is adopted: A method for preparing heteroatom-doped single-atom catalysts based on waste plastics includes the following steps: (1) Take waste plastic and template agent and ball mill them to obtain a homogeneous mixture; (2) The mixture obtained in step (1) is placed in a high-temperature tube furnace and calcined in an inert atmosphere. After the reaction is completed, the calcined powder is obtained. (3) The powder calcined in step (2) is washed and dried to obtain nitrogen-doped carbon material; (4) Disperse the transition metal salt and ligand in a solvent to form a metal complex solution. Add the heteroatom source and the nitrogen-doped carbon material obtained in step (3) to the above metal complex solution, mix evenly by ultrasonication, and stir dry at 60~80 °C to obtain the precursor. (5) The precursor was placed in a high-temperature tube furnace and calcined in an inert atmosphere. After the reaction was completed, a black powder was obtained. (6) The black powder was treated in an acidic solution. After the treatment, the powder was filtered, washed with water and dried to obtain a heteroatom-doped single-atom catalyst. Furthermore, the waste plastic is one of polyvinyl chloride, polyethylene terephthalate, high-density polyethylene, low-density polyethylene, and polycarbonate; Furthermore, in step (1), the template agent is a mixture of potassium chloride and lithium chloride, and the mass ratio of waste plastic to potassium chloride to lithium chloride is 1~2:2~6:2~6; Furthermore, the ball milling time is 1.5 to 2.5 hours, and the ball milling speed is 350 to 500 rpm; Furthermore, in step (2), the inert gas is nitrogen or argon, the gas flow rate is 20~50 mL / min, the heating rate is 5~10 ℃ / min, the calcination reaction temperature is 800~1000 ℃, and the reaction time is 1~2 hours; Furthermore, in step (4), the transition metal salt is ferrous chloride dihydrate, copper chloride, or nickel chloride; the ligand is 1,10-phenanthroline; the heteroatom source is thiourea; and the solvent is anhydrous ethanol. Furthermore, in step (4), the mass ratio of the transition metal salt: ligand: heteroatom source: nitrogen-doped carbon is 3~5: 15~30: 150~350: 20~35, and the stirring time is 10~12 hours; Furthermore, in step (5), the inert gas is either nitrogen or argon, the gas flow rate is 40~80 ml / min, the heating rate is 3~8 ℃ / min, the calcination reaction temperature is 700~1000 ℃, and the reaction time is 1~3 hours. Furthermore, in step (6), the acid solution is one of perchloric acid, sulfuric acid, and hydrochloric acid, the concentration of the acid solution is 0.4~1 mol / L, and the acid solution treatment time is 10~24 hours; This invention also provides the application of the above-mentioned waste plastics in the preparation of heteroatom-doped single-atom catalysts in metal-air batteries.

[0008] The beneficial effects of this invention are as follows: 1) The preparation process of this invention is convenient to operate and has strong versatility. It can be applied to a variety of waste plastic raw materials, expanding the scope of raw material application and the flexibility of catalyst preparation. It realizes the high-value-added resource utilization of waste plastics, effectively solves the environmental pollution problem caused by waste plastics, and at the same time, it significantly reduces the cost of catalyst preparation by using waste plastics as a carbon source, taking into account both energy utilization and environmental protection benefits, which meets the development needs of the intersection of energy and environmental protection. 2) This invention realizes the preparation of heteroatom-doped metal-nitrogen-carbon single-atom catalysts. The electronic structure of the catalyst can be controlled by heteroatoms, which can significantly improve the ORR catalytic performance of the catalyst and overcome the defects of the existing technology that can only prepare transition metal-nitrogen-carbon type single-atom catalysts and whose catalytic performance is difficult to further optimize. 3) This invention expands the application of waste plastic-derived heteroatom-doped single-atom catalysts in metal-air batteries. The prepared catalyst exhibits excellent ORR catalytic activity, with an optimal upper half-wave potential of 0.90 V, outperforming commercial Pt / C catalysts. Simultaneously, the zinc-air battery achieves a maximum power density of 203.0 mW / cm². -2 It also has good stability and broad application prospects. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0010] Figure 1 This is a scanning electron microscope image of the catalyst Fe-NCS-1 prepared in Example 1 of the present invention; Figure 2 This is a transmission electron microscope image of the catalyst Fe-NCS-1 prepared in Example 1 of the present invention; Figure 3 This is a high-angle annular dark-field scanning transmission electron microscope image of the catalyst Fe-NCS-1 prepared in Example 1 of this invention; Figure 4 The S 2p high-resolution XPS spectrum of the catalyst Fe-NCS-1 prepared in Example 1 of this invention; Figure 5 The graph shows the oxygen reduction electrocatalytic performance of the catalyst Fe-NCS-1 prepared in Example 1 of this invention. Figure 6 This is a zinc-air cell test image of the catalyst Fe-NCS-1 prepared in Example 1 of this invention; Figure 7 The figure shows the zinc-air battery cycling stability of the catalyst Fe-NCS-1 prepared in Example 1 of this invention. Figure 8 This is a transmission electron microscope image of the catalyst Fe-NCS-2 prepared in Example 2 of the present invention; Figure 9 This is a high-angle annular dark-field scanning transmission electron microscope image of the catalyst Fe-NCS-2 prepared in Example 2 of this invention; Figure 10 The graph shows the oxygen reduction electrocatalytic performance of the catalyst Fe-NCS-2 prepared in Example 2 of this invention. Figure 11 This is a transmission electron microscope image of the Ni-NCS catalyst prepared in Example 3 of the present invention; Figure 12 Here is a high-resolution transmission electron microscope image of the Ni-NCS catalyst prepared in Example 3 of this invention; Figure 13 The graph shows the oxygen reduction electrocatalytic performance of the Ni-NCS catalyst prepared in Example 3 of this invention. Figure 14 This is a transmission electron microscope image of the Cu-NCS catalyst prepared in Example 4 of the present invention; Figure 15 Here is a high-resolution transmission electron microscope image of the Cu-NCS catalyst prepared in Example 4 of this invention; Figure 16 The graph shows the oxygen reduction electrocatalytic performance of the Cu-NCS catalyst prepared in Example 4 of this invention. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0012] 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 herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0013] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0014] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used are conventional methods and techniques in the art.

[0015] The technical solutions provided by the present invention will be described below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0016] Example 1: 1 g of waste PET plastic, 2.75 g of KCl, and 2.25 g of LiCl were ball-milled at 400 rpm for 2 hours. The mixture was then placed in a high-temperature tube furnace at a gas flow rate of 30 mL / min and heated to 900 °C at a rate of 5 °C / min under an Ar atmosphere. After calcination for two hours, the molten salt template was washed off with deionized water, and the mixture was thoroughly dried to obtain PET-NC. 7.6 mg of FeCl2·H2O and 46.6 mg of 1,10-phenanthroline were dissolved in 45 mL of anhydrous ethanol to form an iron complex solution. Then, 50 mg of PET-NC and 400 mg of thiourea were added to the iron complex solution. After ultrasonic mixing for 10 minutes, the mixture was stirred dry at 80 °C for 12 hours. The resulting precursor was placed in a high-temperature tube furnace at a gas flow rate of 50 mL / min and heated to 700 °C at a rate of 5 °C / min under an argon atmosphere. The mixture was then calcined for 2 hours. After h, the product was acid-washed with 0.5 mol / L perchloric acid solution at 80 ℃. After acid treatment for 16 h, the product was filtered, washed with water and dried for 12 h to obtain catalyst Fe-NCS-1.

[0017] Example 2: 1 g of waste PC plastic, 3 g of KCl, and 2 g of LiCl were ball-milled at 350 rpm for 2 hours. The mixture was then placed in a high-temperature tube furnace at a gas flow rate of 20 mL / min and heated to 800 °C at a rate of 5 °C / min under an Ar atmosphere. After calcination for two hours, the molten salt template was washed away with deionized water, and the mixture was thoroughly dried to obtain PC-NC. 8.4 mg of FeCl2·H2O and 48.2 mg of 1,10-phenanthroline were dissolved in 45 mL of anhydrous ethanol to form an iron complex solution. Then, 50 mg of PC-NC and 600 mg of thiourea were added to the iron complex solution. After ultrasonic mixing for 10 minutes, the mixture was stirred dry at 80 °C for 10 hours. The resulting precursor was placed in a high-temperature tube furnace at a gas flow rate of 40 mL / min and heated to 700 °C at a rate of 3 °C / min under an argon atmosphere. After calcination for 2 hours, the mixture was then heated to 80 °C. The product was acid-washed with 0.4 mol / L perchloric acid solution at ℃ for 16 h. After acid treatment, the product was filtered, washed with water and dried for 12 h to obtain the catalyst Fe-NCS-2.

[0018] Example 3: 1 g of waste PVC plastic, 3.2 g of KCl, and 2.7 g of LiCl were ball-milled at 450 rpm for 2 hours. The mixture was then placed in a high-temperature tube furnace at a gas flow rate of 40 mL / min and heated to 800 °C at a rate of 5 °C / min under an Ar atmosphere. After calcination for two hours, the molten salt template was washed away with deionized water, and the mixture was thoroughly dried to obtain PVC-NC. 6 mg of NiCl2 and 30 mg of 1,10-phenanthroline were dissolved in 45 mL of anhydrous ethanol to form a nickel complex solution. Then, 40 mg of PVC-NC and 300 mg of thiourea were added to the nickel complex solution. After ultrasonic mixing for 10 minutes, the mixture was stirred dry at 80 °C for 11 hours. The resulting precursor was placed in a high-temperature tube furnace at a gas flow rate of 60 mL / min and heated to 800 °C at a rate of 3 °C / min under an argon atmosphere. After calcination for 3 hours, the mixture was then heated at 80 °C with 0.8... The product was acid-washed with mol / L perchloric acid solution, and after acid treatment for 16 h, it was filtered, washed with water and dried for 12 h to obtain the catalyst Ni-NCS.

[0019] Example 4: 1 g of waste PET plastic, 2.75 g of KCl, and 2.25 g of LiCl were ball-milled at 500 rpm for 2 hours. The mixture was then placed in a high-temperature tube furnace at a gas flow rate of 50 mL / min and heated to 900 °C at a rate of 5 °C / min under an Ar atmosphere. After calcination for two hours, the molten salt template was washed off with deionized water, and the mixture was thoroughly dried to obtain PET-NC. 8 mg of CuCl2 and 50 mg of 1,10-phenanthroline were dissolved in 45 mL of anhydrous ethanol to form a copper complex solution. 54 mg of PET-NC and 500 mg of thiourea were added to the copper complex solution. After ultrasonic mixing for 10 minutes, the mixture was stirred dry at 80 °C for 12 hours. The resulting precursor was placed in a high-temperature tube furnace at a gas flow rate of 80 mL / min and heated to 700 °C at a rate of 3 °C / min under an argon atmosphere. After calcination for 2 hours, the mixture was then heated to 80 °C. The product was acid-washed with 0.8 mol / L perchloric acid solution at ℃ for 16 h. After acid treatment, the product was filtered, washed with water and dried for 12 h to obtain the catalyst Cu-NCS.

[0020] The present invention characterized the structure and morphology of the catalysts Fe-NCS-1, Fe-NCS-2, Ni-NCS, and Cu-NCS prepared in Examples 1-4 above using scanning electron microscopy and transmission electron microscopy. The characterization results are as follows: Figure 1-3 , Figure 8-9 , Figure 11-12 , Figure 14-15 As shown.

[0021] This invention employs linear scanning voltammetry to test the oxygen reduction reaction (ORR) of the prepared catalyst. The specific steps are as follows: 5 mg of the prepared catalyst is accurately weighed and dispersed in 2 ml of anhydrous ethanol. After ultrasonic dispersion for 10-20 minutes, 50 μL of a 5 wt.% Nafion solution is transferred, and ultrasonication continues for 20-30 minutes to obtain a homogeneous catalyst slurry. 25 μL of the catalyst slurry is accurately pipetted onto a polished glassy carbon electrode (5 mm in diameter). After drying at room temperature, it serves as the working electrode. An Hg / HgO electrode and a graphite rod are used as the reference and counter electrodes, respectively. A three-electrode system is assembled for ORR performance testing. The test conditions are: 0.1 M KOH electrolyte solution, test potential range of 0.2-1.1 V (vs. RHE), and scan rate of 10 mV / s. -1 .

[0022] A self-assembled zinc-air battery was constructed using carbon paper (1.5 × 1.5 cm) with a catalyst supported. 2 Loading capacity 0.5 mg cm -2 The zinc-air battery used an air cathode and zinc foil as the anode, with a 6 M KOH aqueous solution containing 0.2 M Zn(Ac)₂ as the electrolyte. Performance tests of the zinc-air battery were performed on a CHI 760E workstation. Charging polarization curves were obtained using the linear sweep voltammetry (LSV) method at a scan rate of 10 mV / s. -1 The charge-discharge cycle stability was evaluated using a constant current charge-discharge method at 5 mA cm⁻¹. -2 The current density was subjected to alternating 900-second discharge and 900-second charge cycles.

[0023] The morphology, surface composition, oxygen reduction reaction, and zinc-air cell performance of the catalysts Fe-NCS-1, Fe-NCS-2, Ni-NCS, and Cu-NCS prepared in Examples 1-4 are as follows: Figure 1-16 As shown. From Figure 1-2 As can be seen, the catalyst Fe-NCS-1 prepared in Example 1 is assembled into a three-dimensional porous structure from nanosheets, and no metal particles are observed in the high-resolution transmission electron microscopy image. Figure 3 It can be proven that iron single atoms exist in the catalyst Fe-NCS-1. Figure 4 This demonstrates that S was successfully incorporated into the Fe-NCS-1 catalyst, from Figure 5-7 The results show that the oxygen reduction onset potential of the Fe-NCS-1 catalyst is 1.0 V, and the half-wave potential is 0.90 V, which is superior to that of commercial Pt / C catalysts. Furthermore, the maximum power density of the zinc-air cell can reach 203.0 mW / cm². -2 Furthermore, it exhibits good stability during 300 hours of cycling; from Figure 8-10 It can be seen that the catalyst Fe-NCS-2 prepared in Example 2 exhibits a porous structure without metal particles, and the iron element exists in the form of single atoms. Its oxygen reduction half-wave potential is 0.89 V, which is superior to that of commercial Pt / C catalysts. Figure 11-13 It can be seen that the catalyst Ni-NCS prepared in Example 3 exhibits a three-dimensional structure composed of stacked porous nanosheets and no metal particles are observed, and the half-wave potential for oxygen reduction is 0.90 V. Figure 14-16 It can be seen that the Cu-NCS catalyst prepared in Example 4 exhibits a nanoporous morphology and has no metal particles on the carbon support, with an oxygen reduction half-wave potential of 0.89 V. In summary, the oxygen reduction catalytic performance of the catalysts Fe-NCS-1, Fe-NCS-2, Ni-NCS, and Cu-NCS prepared in Examples 1-4 is superior to that of commercial Pt / C catalysts.

[0024] Therefore, those skilled in the art will recognize that although embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A method for preparing heteroatom-doped single-atom catalysts based on waste plastics, characterized in that, Includes the following steps: (1) Take waste plastic and template agent and ball mill them to obtain a homogeneous mixture; (2) The mixture obtained in step (1) is placed in a high-temperature tube furnace and calcined in an inert atmosphere. After the reaction is completed, the calcined powder is obtained. (3) The powder calcined in step (2) is washed and dried to obtain nitrogen-doped carbon material; (4) Disperse the transition metal salt and ligand in a solvent to form a metal complex solution. Add the heteroatom source and the nitrogen-doped carbon material obtained in step (3) to the above metal complex solution, mix evenly by ultrasonication, and stir dry at 60~80 °C to obtain the precursor. (5) The precursor was placed in a high-temperature tube furnace and calcined in an inert atmosphere. After the reaction was completed, a black powder was obtained. (6) The black powder is treated in an acidic solution. After the treatment, the powder is filtered, washed with water and dried to obtain a heteroatom-doped single-atom catalyst.

2. The method for preparing heteroatom-doped single-atom catalysts based on waste plastics as described in claim 1, characterized in that, In step (1), the waste plastic is one of polyvinyl chloride (PVC), polyethylene terephthalate (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polycarbonate (PC).

3. The method for preparing heteroatom-doped single-atom catalysts from waste plastics as described in claim 1, characterized in that, In step (1), the template agent is a mixture of potassium chloride and lithium chloride, and the mass ratio of waste plastic: potassium chloride: lithium chloride is 1~2:2~6:2~6.

4. The method for preparing heteroatom-doped single-atom catalysts from waste plastics as described in claim 1, characterized in that, In step (1), the ball milling time is 1.5 to 2.5 hours and the ball milling speed is 350 to 500 rpm.

5. The method for preparing heteroatom-doped single-atom catalysts from waste plastics as described in claim 1, characterized in that, In step (2), the inert gas is nitrogen or argon, the gas flow rate is 20~50 mL / min, the heating rate is 5~10 ℃ / min, the calcination reaction temperature is 800~1000 ℃, and the reaction time is 1~2 hours.

6. The method for preparing heteroatom-doped single-atom catalysts from waste plastics as described in claim 1, characterized in that, In step (4), the transition metal salt is one of ferrous chloride dihydrate, copper chloride, and nickel chloride, the ligand is 1,10-phenanthroline, the heteroatom source is thiourea, and the solvent is anhydrous ethanol.

7. The method for preparing heteroatom-doped single-atom catalysts from waste plastics as described in claim 1, characterized in that, In step (4), the mass ratio of transition metal salt: ligand: heteroatom source: nitrogen-doped carbon is 3~5: 15~30: 150~350: 20~35, and the stirring time is 10~12 hours.

8. The method for preparing heteroatom-doped single-atom catalysts from waste plastics as described in claim 1, characterized in that, In step (5), the inert gas is either nitrogen or argon, the gas flow rate is 40~80 ml / min, the heating rate is 3~8℃ / min, the calcination reaction temperature is 700~1000 ℃, and the reaction time is 1~3 hours.

9. The method for preparing heteroatom-doped single-atom catalysts from waste plastics as described in claim 1, characterized in that, In step (6), the acid solution is one of perchloric acid, sulfuric acid, or hydrochloric acid, the concentration of the acid solution is 0.4~1 mol / L, and the acid solution treatment time is 10~24 hours.

10. The application of the heteroatom-doped single-atom catalyst prepared from waste plastics as described in claims 1-10 in metal-air batteries.

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