A polyolefin-derived carbon-based single-atom catalyst and its preparation method and application

Abstract

The present application discloses a polyolefin-derived carbon-based single-atom catalyst, its preparation method, and application, which belong to the field of electrocatalysts. The present invention prepares a polyolefin-derived carbon-based single-atom catalyst comprising: preparing a polyolefin / calcium carbonate mixture, and mixing the polyolefin / calcium carbonate mixture with a nitrogen source and a sulfur source, and then sequentially performing high-temperature carbonization at 700-900°C and acid washing to obtain a polyolefin-derived porous carbon support; and mixing the polyolefin-derived porous carbon support with a transition metal salt, and then sequentially performing low-temperature pyrolysis at 300-450°C, washing with an ethanol / water mixture, and medium-temperature carbonization at 550-600°C, and the resulting product is acid washed. The present invention can optimize the electron transport capacity of the polyolefin-derived carbon-based single-atom catalyst while achieving a high load of metal single atoms, so that the prepared carbon-based single-atom catalyst has excellent redox electrocatalytic efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a polyolefin-derived carbon-based single-atom catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Carbon-based single-atom catalysts are electrocatalytic systems composed of atomically dispersed metal components anchored to a carbon support. They possess unique electronic structures and extremely high atomic utilization, demonstrating high selectivity and activity in applications such as redox electrocatalysis, fuel cells, and zinc-air batteries. However, traditional carbon-based single-atom catalysts rely on high-purity carbon sources such as graphene and carbon nanotubes, and the relatively high cost of these raw materials has limited their large-scale production and commercial application.

[0003] Currently, the relevant field has disclosed a low-cost preparation technology for preparing carbon-based single-atom catalysts using waste plastic-derived carbon supports. For example, Ma Shengjia et al. chemically modified waste polystyrene plastic with concentrated nitric acid to produce nitropolystyrene, and then co-pyrolyzed it with FeCl3·6H2O to prepare a nitrogen-doped porous carbon support-loaded Fe single-atom catalyst, achieving the goals of pollutant control and resource recycling.

[0004] However, this technical strategy of preparing carbon-based single-atom catalysts using plastic-derived carbon supports still has shortcomings or defects. For example, the iron loading of the prepared iron single-atom catalyst is extremely low (< 1wt%), resulting in low catalytic efficiency of the carbon-based iron single-atom catalyst and poor commercial prospects. In addition, chemical modification of polyolefins with concentrated nitric acid is prone to produce harmful gases or waste liquids, and the industrialization prospects are poor. Summary of the Invention

[0005] The present application discloses a polyolefin-derived carbon-based single-atom catalyst, a preparation method and application thereof, which are used to solve the technical problem of low metal single-atom loading faced by the existing preparation of single-atom catalysts using plastic-derived carbon supports.

[0006] In order to achieve the above objectives, this application provides the following technical solutions:

[0007] In a first aspect, the present application provides a method for preparing a polyolefin-derived carbon-based single-atom catalyst, comprising the steps of:

[0008] preparing a polyolefin / calcium carbonate mixture;

[0009] The polyolefin / calcium carbonate mixture is mixed with a nitrogen source and a sulfur source, and then subjected to high-temperature carbonization at 700-900° C. and acid washing in sequence to obtain a polyolefin-derived porous carbon support; and

[0010] The polyolefin-derived porous carbon support is mixed with a transition metal salt, and then subjected to low-temperature pyrolysis at 300-450°C, washing with an ethanol / water mixture, and medium-temperature carbonization at 550-600°C. The obtained product is acid-washed to obtain a polyolefin-derived carbon-based single-atom catalyst.

[0011] According to the preparation method disclosed herein, the polyolefin is selected from at least one of polystyrene, polyethylene, polypropylene, and polyvinyl chloride; and / or,

[0012] The mass ratio of polyolefin to calcium carbonate in the polyolefin / calcium carbonate mixture is 1:2-8.

[0013] According to the preparation method disclosed herein, the nitrogen source is selected from at least one of melamine, urea, thiourea, cyanamide, and dicyandiamide; and / or,

[0014] The mass ratio of the nitrogen source material to the polyolefin / calcium carbonate mixture is 1-4:1.

[0015] According to the preparation method disclosed herein, the sulfur source is selected from at least one of elemental sulfur, carbon disulfide, hydrogen sulfide, sodium thiosulfate, and thiourea; and / or,

[0016] The mass ratio of the sulfur source material to the polyolefin / calcium carbonate mixture is 1-4:1.

[0017] According to the preparation method disclosed herein, the transition metal salt is selected from chlorides and / or acetates containing at least one of Fe, Co, and Ni.

[0018] According to the preparation method disclosed herein, the transition metal salt is selected as cobalt chloride hexahydrate, and the mass ratio of the cobalt chloride hexahydrate to the polyolefin-derived porous carbon support is 2:1.

[0019] According to the preparation method disclosed herein, the preparation of the polyolefin / calcium carbonate mixture comprises ultrasonically dispersing the polyolefin and calcium carbonate in tetrahydrofuran, and then drying by rotary evaporation.

[0020] According to the preparation method disclosed herein, the pickling agent used for pickling is selected to have a concentration of 2 to 8 mol·L -1 At least one of hydrochloric acid, sulfuric acid, and nitric acid; and / or

[0021] The pickling temperature is 25-60°C and the time is 4-12 hours.

[0022] According to the preparation method disclosed herein, the high-temperature carbonization time is 2 to 4 hours; the low-temperature pyrolysis and the medium-temperature carbonization time are both 3 to 7 hours.

[0023] In a second aspect, the present application also provides a polyolefin-derived carbon-based single-atom catalyst prepared by the preparation method of the present invention, which comprises a nitrogen / sulfur co-doped polyolefin-derived porous carbon support;

[0024] Cobalt single atoms with a loading amount greater than 8 wt % are anchored on the nitrogen / sulfur co-doped polyolefin-derived porous carbon support.

[0025] In a third aspect, the present application also provides the use of the polyolefin-derived carbon-based single-atom catalyst prepared by the preparation method of the present invention in a fuel cell or a metal-air battery.

[0026] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application include at least:

[0027] The present invention uses a calcium carbonate template to assist in high-temperature carbonization of polyolefin to form a defect-rich N / S co-doped polyolefin-derived porous carbon support, and then mixes the N / S co-doped polyolefin-derived porous carbon support with a metal component and performs a gradient heat treatment of low-temperature pyrolysis and medium-temperature carbonization. This effectively solves the problem of low metal single-atom loading faced in the existing preparation of carbon-based single-atom catalysts using plastic-derived carbon supports, thereby achieving the purpose of improving the catalytic performance of polyolefin-derived carbon-based single-atom catalysts. Specifically, the combined effect of calcium carbonate template assistance and N / S co-doping can make the polyolefin-derived carbon carrier have rich mass transfer channels and loading sites, promote mass transfer and provide a loading environment for the metal component; at the same time, by sequentially performing the gradient heat treatment of low-temperature pyrolysis and medium-temperature carbonization, it can not only prevent the carbon carrier from being excessively graphitized and further optimize the coordination environment for the metal component to bind to the carbon carrier, effectively avoid the adsorption and binding of metal component nanoparticles, and ultimately achieve the effect of increasing the metal single atom loading, but also promote the ordering of the carbon carrier and eliminate unstable defects, effectively enhance the electron transport capacity of the carbon-based single atom catalyst, thereby giving the carbon-based single atom catalyst a better catalytic effect through the synergistic effect of high metal single atom loading and efficient electron transport. In addition, the chemical modification of concentrated nitric acid is avoided in the preparation process of the present invention, and the production is safe and environmentally friendly. At the same time, waste polyolefin rate can also be used as a carbon precursor raw material, which is expected to achieve high-value production of pollutant control and resource recycling, and has good industrialization and commercialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To more clearly illustrate the technical solutions of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some of the embodiments described in this application. Those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0029] Figure 1Transmission electron micrographs of the polystyrene-derived carbon-based cobalt single-atom catalysts prepared in Example 1(a), Comparative Example 2(b), and Comparative Example 3(c) provided herein;

[0030] Figure 2 Spherical aberration-corrected high-angle annular dark field scanning transmission images of the polystyrene-derived carbon-based cobalt single-atom catalysts prepared in Example 1(a), Comparative Example 2(b) and Comparative Example 3(c) provided in this application;

[0031] Figure 3 XRD spectra of the polystyrene-derived porous carbon support prepared in Comparative Example 1, the polystyrene-derived carbon-based cobalt single-atom catalysts prepared in Examples 1-3 and Comparative Examples 2-3, and the carbon-based cobalt nanoparticle catalyst prepared in Comparative Example 4 provided in this application;

[0032] Figure 4 This is the Co 2p XPS spectrum of the polystyrene-derived carbon-based cobalt single-atom catalyst prepared in Example 1 provided in this application;

[0033] Figure 5 Linear sweep voltammograms of the electrocatalytic oxygen reduction reaction of the polystyrene-derived porous carbon support prepared in Comparative Example 1, the polystyrene-derived carbon-based cobalt single-atom catalysts prepared in Examples 1 to 3 and Comparative Examples 2 to 3, and the carbon-based cobalt nanoparticle catalyst prepared in Comparative Example 4 provided in this application. DETAILED DESCRIPTION

[0034] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] In the relevant descriptions of this application, the term "and / or" is used to describe the association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural.

[0036] In the relevant description of this application, the term "at least one" refers to one or more, wherein "plurality" refers to two or more. "At least one of the following" or similar descriptions thereof refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of A, B or C", or "at least one of A, B and C" means one of A, B, C, or A+B, or A+C, or B+C, or A+B+C, wherein A, B, C can be single or multiple.

[0037] In the relevant description of this application, the order of serial numbers does not mean the order of execution. Some or all steps can be executed in parallel or sequentially. The execution order of each process should be determined based on its function and internal logic, and should not constitute a limitation on the implementation process of the present invention.

[0038] Throughout the description of this application, numerical ranges are understood to also specifically disclose each intervening value between the upper and lower limits of the range. Each smaller range between any stated value or intervening value within a stated range, and any other stated value or intervening value within that stated range, is also disclosed herein. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0039] Unless otherwise indicated, the technical / scientific terms used in this application have meanings and / or interpretations that are generally familiar to those of ordinary skill in the art. Although this application only describes possible materials and / or methods of the present invention, any materials and / or methods similar or equivalent to the present invention may also be used in the implementation or experiments disclosed in this application. In addition, all documents mentioned in this application are incorporated by reference to disclose and describe the materials and / or methods related to the documents. In the event of any conflict with any incorporated document, the technical content of the present invention shall prevail.

[0040] The present application provides a method for preparing a single-atom catalyst, which comprises steps S1 to S3:

[0041] S1: preparing a polyolefin / calcium carbonate mixture;

[0042] S2: mixing the polyolefin / calcium carbonate mixture obtained in the previous step with a nitrogen source and a sulfur source, and then sequentially carbonizing the mixture at a temperature of 700-900°C and acid washing the mixture to obtain a polyolefin-derived porous carbon support;

[0043] S3: After mixing the polyolefin-derived porous carbon support in the previous step with a transition metal salt, the mixture is subjected to low-temperature pyrolysis at 300-450°C, washing with an ethanol / water mixture, and medium-temperature carbonization at 550-600°C. The resulting product is acid-washed to obtain a polyolefin-derived carbon-based single-atom catalyst.

[0044] It should be noted that, when washing with an ethanol / water mixture, an ethanol / water mixture (volume ratio of 1:1) can be used for immersion, and after washing, the mixture can be dried at 60° C. to remove the ethanol / water mixture.

[0045] The design logic and technical principles of the present invention are provided in this application. Specifically, polyolefin plastic carbon precursors generally lack suitable anchoring sites for metal atoms to attach, making it unsuitable to prepare carbon carriers by directly pyrolyzing plastics. At the same time, although nitrogen-doped carbon carriers can regulate the electronic structure of metal components and improve the durability of carbon-based single-atom catalysts, the existing preparation of carbon-based single-atom catalysts by combining nitrogen-doped carbon carriers with transition metal salts often causes the destruction of the anchoring structure, restricting the anchoring binding of the metal component in the form of a single atom, resulting in an extremely low metal single-atom loading. To this end, the present invention carbonizes a mixture of components containing polyolefins, calcium carbonate templates, nitrogen sources and sulfur sources at high temperature into defect-rich N / S co-doped polyolefin-derived porous carbon carriers, so that the carbon carrier has abundant mass transfer channels and loading sites, thereby promoting mass transfer while providing a loading environment for the metal components. On this basis, the present invention also provides for the first time a carbon-based single-atom synthesis strategy of a two-step gradient heat treatment and washing with an ethanol / water mixture between the two heat treatments, specifically:

[0046] First, a mixture of N / S co-doped polyolefin-derived porous carbon support and transition metal salt is subjected to a set low-temperature pyrolysis. First, the transition metal salt (cobalt chloride hexahydrate / CoCl2·6H2O) is dehydrated and partially decomposed to form transition metal intermediates (CoO, CoCl2), which coordinate with the N and S doping sites (pyridinic nitrogen / sulfide groups) in the carbon support to form a coordination structure such as Co-N3-S1; second, the reduction process of the transition metal component (Co) is regulated, so that the transition metal component (Co) is in a highly dispersed state, facilitating the subsequent formation of single-atom sites; third, excessive graphitization of the carbon support is avoided and sufficient defects and loading sites (micropores, edge sites) are retained, thereby providing a rich coordination environment for the anchoring of the transition metal component (Co).

[0047] Secondly, the washing treatment of the set ethanol / water mixture can selectively remove unbound metal precursors, prevent the formation of metal nanoparticles due to thermal migration during the subsequent medium-temperature carbonization, and ensure that the final loaded metal components are mainly metal single atoms rather than nanoparticles, which effectively regulates the loading amount of metal single atoms.

[0048] Thirdly, medium-temperature carbonization is carried out to promote the graphitization of the carbon support, thereby enhancing the coordination effect between the defect sites (pyridinic nitrogen and sulfur sites) and the cobalt metal, forming a stable Co-N3-S1 coordination structure, and achieving the effect of firmly anchoring the cobalt single atom; at the same time, it also improves the conductivity and chemical stability of the carbon support, thereby optimizing the electron transport ability of the catalyst while eliminating some unstable defects and improving the overall durability of the material.

[0049] It should be understood by those skilled in the art that the high-temperature carbonization, low-temperature pyrolysis and medium-temperature carbonization provided in the present invention are all carried out in an inert atmosphere such as nitrogen, argon or helium to reduce the generation of by-products. For example, in the present invention, the gas flow rate is 100-300 mL·min -1 , heating rate is 2~5 ℃·min -1 in a nitrogen atmosphere.

[0050] In the exemplary embodiments of the present disclosure, the polyolefin used is selected from at least one of polystyrene, polyethylene, polypropylene, and polyvinyl chloride, preferably polystyrene. The present disclosure does not specify the specific source or grade of the polyolefin; it can be commercially available raw materials of various grades or waste recycled materials of various grades. Furthermore, the mass ratio of polyolefin to calcium carbonate in the polyolefin / calcium carbonate mixture of the present invention is 1:2 to 8, with examples including but not limited to 1:2, 1:4, and 1:8.

[0051] In an exemplary embodiment of the present disclosure, the nitrogen source used in the present invention is selected from at least one of melamine, urea, thiourea, cyanamide, and dicyandiamide, preferably melamine. The nitrogen source used in the present invention is added at a mass ratio of 1 to 4:1 to the polyolefin / calcium carbonate mixture, with examples including but not limited to 1:1, 2:1, and 4:1.

[0052] In the exemplary embodiments of the present disclosure, the sulfur source used in the present invention is at least one of elemental sulfur, carbon disulfide, hydrogen sulfide, sodium thiosulfate, and thiourea, preferably elemental sulfur. The sulfur source is added to the polyolefin / calcium carbonate mixture at a mass ratio of 1 to 4:1, with examples including but not limited to 1:1, 2:1, and 4:1.

[0053] In an exemplary embodiment of the present disclosure, the transition metal salt is a chloride and / or acetate containing at least one of Fe, Co, and Ni, including but not limited to ferric chloride hexahydrate, cobalt chloride hexahydrate, nickel chloride hexahydrate, ferric acetate, cobalt acetate, and nickel acetate tetrahydrate, preferably cobalt chloride hexahydrate. The mass ratio of cobalt chloride hexahydrate to the polyolefin-derived porous carbon support is 2:1.

[0054] In an exemplary embodiment of the present disclosure, the preparation of the polyolefin / calcium carbonate mixture comprises ultrasonically dispersing the polyolefin and calcium carbonate in tetrahydrofuran, followed by rotary evaporation drying. The present invention does not particularly limit the specific parameters of the rotary evaporation drying, so long as the tetrahydrofuran can be sufficiently removed.

[0055] In the exemplary embodiment of the present disclosure, the pickling agent used for pickling is selected to have a concentration of 2 to 8 mol·L -1 At least one of hydrochloric acid, sulfuric acid, and nitric acid, for example, 2 mol·L -1 、3 mol·L -1 , 4 mol·L -1 , 5 mol·L -1 , 6 mol·L -1 , 7 mol·L -1 , 8 mol·L -1 The pickling temperature is selected to be 25-60°C, and the pickling time is 4-12 h, which can be exemplified as 25°C / 12 h, 25°C / 15 h, etc.

[0056] It should be noted that the pickling treatment mentioned here includes the pickling in step S2 and / or S3. The pickling treatments in steps S2 and S3 may be the same or different, specifically based on the removal of calcium carbonate by pickling in step S2 and the removal of unbound metal components and metal nanoparticles by pickling in step S3.

[0057] In the exemplary embodiment of the present disclosure, the high-temperature carbonization time is 2 to 4 hours, preferably 3 hours to ensure sufficient carbonization of the polyolefin while avoiding excessive graphitization; and

[0058] The time for the low-temperature pyrolysis and the medium-temperature carbonization is 3 to 7 hours, preferably 5 hours to ensure that the effects described above in each step are fully achieved.

[0059] The present application also provides a polyolefin-derived carbon-based single-atom catalyst prepared by the preparation method of the present invention, which comprises a nitrogen / sulfur co-doped polyolefin-derived porous carbon support, on which a cobalt single atom with a loading of greater than 8 wt% is anchored. Among them, since the preparation method of the present invention can increase the metal atom loading and optimize the electron transport capacity, and can use waste polyolefin plastic as a carbon precursor, the carbon-based single-atom catalyst prepared by the present invention has the advantages of high catalytic efficiency and low cost, and is suitable for industrial production.

[0060] The present application also provides an application of the polyolefin-derived carbon-based single-atom catalyst prepared by the preparation method of the present invention, specifically, using the polyolefin-derived carbon-based single-atom catalyst prepared by the present invention in a fuel cell or a metal-air battery.

[0061] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0062] Example 1

[0063] This embodiment provides a method for preparing a polystyrene-derived carbon-based cobalt single-atom catalyst, the steps of which include:

[0064] S1: 0.5 g polystyrene and 2.0 g calcium carbonate template were dissolved in tetrahydrofuran solution, sonicated for 20 min, and rotary evaporated to dry to prepare a polystyrene / calcium carbonate mixture.

[0065] S2: 1.0 g of melamine and 2.0 g of sublimed sulfur powder were added to the polystyrene / calcium carbonate mixture and ground uniformly. -1 In a nitrogen atmosphere, the -1 The temperature was raised to 800℃ at a rate of 1000℃ and kept at that temperature for 3 h. -1 The calcium carbonate template was removed by pickling with hydrochloric acid for 12 h to obtain a polystyrene-derived porous carbon support.

[0066] S3: The polystyrene-derived porous carbon support and cobalt chloride hexahydrate were dispersed in anhydrous ethanol solution at a mass ratio of 1:2, ultrasonicated for 20 min, and dried by rotary evaporation to prepare a transition metal salt / carbon support mixture. -1 In a nitrogen atmosphere, first -1 The temperature was raised to 300 °C at a rate of 100 °C and kept at that temperature for 5 h, then washed with ethanol and water and dried in an oven at 60 °C for 8 h; then the temperature was increased at 2 °C·min -1 The temperature was raised to 550 °C at a rate of 5 h and then heated to 6 mol·L -1 The catalyst was washed with hydrochloric acid for 12 h to remove unbound metal ligands and metal nanoparticles, and then dried in an oven at 60 °C for 8 h to obtain a polystyrene-derived carbon-based cobalt single-atom catalyst.

[0067] Example 2

[0068] This embodiment provides a method for preparing a polystyrene-derived carbon-based cobalt single-atom catalyst, the steps of which include:

[0069] S1: 0.5 g polystyrene and 1.0 g calcium carbonate template were dissolved in tetrahydrofuran solution, sonicated for 20 min, and rotary evaporated to dry to prepare a polystyrene / calcium carbonate mixture.

[0070] S2: 1.0 g of melamine and 2.0 g of sublimed sulfur powder were added to the polystyrene / calcium carbonate mixture and ground uniformly.-1 In a nitrogen atmosphere, the -1 The temperature was raised to 800℃ at a rate of 1000℃ and kept at that temperature for 3 h. -1 The calcium carbonate template was removed by pickling with hydrochloric acid for 12 h to obtain a polystyrene-derived porous carbon support.

[0071] S3: The polystyrene-derived porous carbon support and cobalt chloride hexahydrate were dispersed in anhydrous ethanol solution at a mass ratio of 1:2, ultrasonicated for 20 min, and dried by rotary evaporation to prepare a transition metal salt / carbon support mixture. -1 In a nitrogen atmosphere, first -1 The temperature was raised to 300 °C at a rate of 100 °C and kept at that temperature for 5 h, then washed with ethanol and water and dried in an oven at 60 °C for 8 h; then the temperature was increased at 2 °C·min -1 The temperature was raised to 550 °C at a rate of 5 h and then heated to 6 mol·L -1 The catalyst was washed with hydrochloric acid for 12 h to remove unbound metal ligands and metal nanoparticles, and then dried in an oven at 60 °C for 8 h to obtain a polystyrene-derived carbon-based cobalt single-atom catalyst.

[0072] Example 3

[0073] This embodiment provides a method for preparing a polystyrene-derived carbon-based cobalt single-atom catalyst, the steps of which include:

[0074] S1: 0.5 g polystyrene and 4.0 g calcium carbonate template were dissolved in tetrahydrofuran solution, sonicated for 20 min, and rotary evaporated to dry to prepare a polystyrene / calcium carbonate mixture.

[0075] S2: 1.0 g of melamine and 2.0 g of sublimed sulfur powder were added to the polystyrene / calcium carbonate mixture and ground uniformly. -1 In a nitrogen atmosphere, the -1 The temperature was raised to 800℃ at a rate of 1000℃ and kept at that temperature for 3 h. -1 The calcium carbonate template was removed by pickling with hydrochloric acid for 12 h to obtain a polystyrene-derived porous carbon support.

[0076] S3: The polystyrene-derived porous carbon support and cobalt chloride hexahydrate were dispersed in anhydrous ethanol solution at a mass ratio of 1:2, ultrasonicated for 20 min, and dried by rotary evaporation to prepare a transition metal salt / carbon support mixture. -1 In a nitrogen atmosphere, first -1The temperature was raised to 300 °C at a rate of 100 °C and kept at that temperature for 5 h, then washed with ethanol and water, and dried in an oven at 60 °C for 8 h; then the temperature was raised to 550 °C at a rate of 2 °C·min-1 and kept at that temperature for 5 h, and finally heated to 6 mol·L -1 The catalyst was washed with hydrochloric acid for 12 h to remove unbound metal ligands and metal nanoparticles, and then dried in an oven at 60 °C for 8 h to obtain a polystyrene-derived carbon-based cobalt single-atom catalyst.

[0077] Example 4

[0078] This embodiment provides a method for preparing a polystyrene-derived carbon-based cobalt single-atom catalyst, the steps of which include:

[0079] S1: 0.5 g polystyrene and 2.0 g calcium carbonate template were dissolved in tetrahydrofuran solution, sonicated for 20 min, and rotary evaporated to dry to prepare a polystyrene / calcium carbonate mixture.

[0080] S2: 2.0 g of melamine and 2.0 g of sublimed sulfur powder were added to the polystyrene / calcium carbonate mixture and ground uniformly. -1 In a nitrogen atmosphere, the -1 The temperature was raised to 800℃ at a rate of 1000℃ and kept at that temperature for 3 h. -1 The polystyrene-derived porous carbon support was prepared by pickling with hydrochloric acid for 12 h to remove the calcium carbonate template.

[0081] S3: The polystyrene-derived porous carbon support and cobalt chloride hexahydrate were dispersed in anhydrous ethanol solution at a mass ratio of 1:2, ultrasonicated for 20 min, and dried by rotary evaporation to prepare a transition metal salt / carbon support mixture. -1 In a nitrogen atmosphere, first -1 The temperature was raised to 300 °C at a rate of 100 °C and kept at that temperature for 5 h, then washed with ethanol and water and dried in an oven at 60 °C for 8 h; then the temperature was increased at 2 °C·min -1 The temperature was raised to 550 °C at a rate of 5 h and then heated to 6 mol·L -1 The catalyst was washed with hydrochloric acid for 12 h to remove unbound metal ligands and metal nanoparticles, and then dried in an oven at 60°C for 8 h to obtain a polystyrene-derived carbon-based cobalt single-atom catalyst.

[0082] In order to illustrate the technical effect of the preparation method of the present invention, this application also provides comparative examples 1 to 4.

[0083] Comparative Example 1

[0084] The difference between this comparative example and Example 1 is that step S3 is omitted, and the rest is the same as Example 1.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that the addition of melamine is omitted in step S2, and the rest is the same as Example 1.

[0087] Comparative Example 3

[0088] The difference between this comparative example and Example 1 is that the addition of sublimed sulfur powder is omitted in step S2, and the rest is the same as Example 1.

[0089] Comparative Example 4

[0090] The difference between this comparative example and Example 1 is that in step S3, the transition metal salt / carbon support mixture is subjected to low-temperature carbonization at 400°C / 0.5 h and high-temperature pyrolysis at 900°C / 2 h in sequence. The rest is the same as Example 1, and the product is a carbon-based cobalt nanoparticle catalyst.

[0091] The polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Example 1 and Comparative Examples 2-3 were structurally characterized. Figures 1-3 As shown. Among them, Figure 1 Transmission electron micrographs of the polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Example 1 and Comparative Examples 2-3 (a, b, c correspond to Example 1, Comparative Example 2, and Comparative Example 3, respectively); Figure 2 Spherical aberration-corrected high-angle annular dark-field scanning transmission images of the polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Example 1 and Comparative Examples 2-3 (a, b, c correspond to Example 1, Comparative Example 2, and Comparative Example 3, respectively); Figure 3 XRD spectra of the polystyrene-derived porous carbon support obtained in Comparative Example 1, the polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Comparative Examples 2-3, the carbon-based cobalt nanoparticle catalyst obtained in Comparative Example 4, and the polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Examples 1-3; Figure 4 2p XPS spectrum of the polystyrene-derived carbon-based cobalt single-atom catalyst obtained in Example 1; Figure 5 Linear sweep voltammetric characteristic curves of the electrocatalytic oxygen reduction reaction of the polystyrene-derived porous carbon support obtained in Comparative Example 1, the polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Comparative Examples 2-3, the carbon-based cobalt nanoparticle catalyst obtained in Comparative Example 4, and the polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Examples 1-3.

[0092] according to Figure 1 It can be seen that the polystyrene-derived carbon-based cobalt single-atom catalysts prepared in Example 1 and Comparative Examples 2-3 have a good three-dimensional porous carbon structure.

[0093] according to Figure 2It can be seen that the polystyrene-derived carbon-based cobalt single-atom catalysts of Example 1 and Comparative Examples 2-3 have isolated bright spot portions, indicating that Co is dispersed in the form of single atoms on the polystyrene-derived carbon support.

[0094] according to Figure 3 As can be seen, the polystyrene-derived carbon-based cobalt single-atom catalysts prepared in Example 1 and Comparative Examples 2-3 exhibit only a broad diffraction peak corresponding to the (002) plane, with no detectable diffraction peaks for Co metal, indicating the absence of Co metal species. In contrast, the carbon-based cobalt nanoparticles prepared in Comparative Example 4 exhibit distinct diffraction peaks for Co metal, indicating the presence of metal nanoparticle agglomeration.

[0095] according to Figure 4 It can be seen that the peak of the polystyrene-derived carbon-based cobalt single-atom catalyst prepared in Example 1 at 781.1 eV is higher than that of Co 0 (778.1~778.8 eV), indicating that cobalt does not appear in a metallic state, further proving the isolated state of a single cobalt atom. In addition, the cobalt loading measured by XPS is approximately 9.41 wt%. The cobalt loading measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) is approximately 8.01~8.08 wt%.

[0096] The present application also tested the redox electrocatalytic performance of the polystyrene-derived porous carbon support obtained in Comparative Example 1 and the polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Examples and Comparative Examples. The specific testing process is as follows: in a three-electrode system, 0.1 M KOH is used as the electrolyte and the test is carried out under saturated oxygen. The scanning range is 0.2~1.0 V (vs. RHE) and the scanning rate is 10 mV·s -1 , the speed is 1600 rpm. According to the Nernst equation: , all measured potentials were converted to reversible hydrogen electrode (RHE) standards, and the results were Figure 5 As shown. Among them, Figure 5 This is the ORR linear sweep voltammetric characteristic curve.

[0097] according to Figure 5It can be seen that the polystyrene-derived porous carbon supports, polystyrene-derived carbon-based cobalt single-atom catalysts, and carbon-based cobalt nanoparticles prepared in the embodiments of the present invention and the comparative examples have different redox electrocatalytic properties. The reasons for the differences in electrocatalytic oxygen reduction reaction performance of different samples may be: in the carbon-based cobalt single-atom catalyst prepared in Example 1, due to the moderate amount of template, the pore distribution is optimized, the density of active sites and the conductivity are balanced, so that it has a high density of active sites and an optimized porous structure, showing an optimal half-wave potential (0.89V); in the carbon-based cobalt single-atom catalyst prepared in Example 2, due to insufficient amount of template, the support structure is underdeveloped, the active sites are reduced, and its half-wave potential is (0.82V); in the carbon-based cobalt single-atom catalyst prepared in Example 3, due to excessive template, the pore distribution is optimized, the density of active sites and the conductivity are balanced, and the active sites are balanced. Plate agent, slightly reduces the structural efficiency, but still has a high active site density, and its half-wave potential is (0.86V); in Comparative Example 1, due to the lack of cobalt single atom loading, it only relies on the catalytic activity of the carbon support and shows the worst half-wave potential (0.72V); in the carbon-based cobalt single-atom catalyst prepared in Comparative Example 2, due to the lack of nitrogen doping, it only relies on the sulfur-cobalt interaction and has limited activity, and its half-wave potential is (0.79V); in the carbon-based cobalt single-atom catalyst prepared in Comparative Example 3, due to the lack of sulfur doping, it only relies on the nitrogen-cobalt interaction and lacks sulfur-induced carbon substrate charge redistribution, and its half-wave potential is (0.78V); in the carbon-based cobalt nanoparticle catalyst prepared in Comparative Example 4, due to the presence of cobalt nanoparticle agglomeration, its half-wave potential (0.76V) is greatly reduced compared with Example 1.

[0098] The above analysis demonstrates that the present invention, through sulfur-nitrogen co-doping and optimization of an appropriate template, constructs highly dispersed active sites and an efficient mass transfer pore structure, resulting in a carbon-based single-atom catalyst with excellent electrocatalytic performance. This demonstrates that the present invention can significantly enhance the oxygen reduction performance of the electrocatalyst by regulating the amount of template, metal salt precursor, sulfur source, and nitrogen source, along with a gradient heat treatment process consisting of low-temperature pyrolysis, ethanol / water washing, and moderate-temperature carbonization.

[0099] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0100] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for preparing a polyolefin-derived carbon-based single-atom catalyst, characterized in that: The following steps are included: preparing a polyolefin / calcium carbonate mixture, wherein the polyolefin is selected from at least one of polystyrene, polyethylene, polypropylene, and polyvinyl chloride, and the mass ratio of the polyolefin to calcium carbonate in the polyolefin / calcium carbonate mixture is 1:2-8; The polyolefin / calcium carbonate mixture is mixed with a nitrogen source and a sulfur source, followed by sequentially performing high-temperature carbonization at 700-900° C. and acid washing to produce a polyolefin-derived porous carbon support, wherein the mass ratio of the nitrogen source to the polyolefin / calcium carbonate mixture is 1-4:1, the mass ratio of the sulfur source to the polyolefin / calcium carbonate mixture is 1-4:1, and the high-temperature carbonization time is 2-4 hours; and After mixing the polyolefin-derived porous carbon support with a transition metal salt, the mixture is sequentially subjected to low-temperature pyrolysis at 300-450°C, washing with an ethanol / water mixture, and medium-temperature carbonization at 550-600°C. The resulting product is acid-washed to obtain a polyolefin-derived carbon-based single-atom catalyst. The polyolefin-derived carbon-based single-atom catalyst comprises a nitrogen / sulfur co-doped polyolefin-derived porous carbon support, on which a cobalt single atom with a loading amount greater than 8 wt% is anchored. The transition metal salt is selected as a chloride and / or acetate containing Co, and the time for the low-temperature pyrolysis and the medium-temperature carbonization is both 3-7 h.

2. The preparation method according to claim 1, wherein The nitrogen source is selected from at least one of melamine, urea, thiourea, cyanamide and dicyandiamide.

3. The preparation method according to claim 1, wherein The sulfur source material is selected from at least one of elemental sulfur, carbon disulfide, hydrogen sulfide, sodium thiosulfate, and thiourea.

4. The preparation method according to claim 1, wherein The transition metal salt is cobalt chloride hexahydrate, and the mass ratio of the cobalt chloride hexahydrate to the polyolefin-derived porous carbon support is 2:

1.

5. The preparation method according to claim 1, wherein The preparation of the polyolefin / calcium carbonate mixture comprises ultrasonically dispersing the polyolefin and calcium carbonate in tetrahydrofuran, and then drying by rotary evaporation.

6. The preparation method according to claim 1, wherein The pickling agent used for pickling is selected to have a concentration of 2 to 8 mol·L -1 At least one of hydrochloric acid, sulfuric acid, and nitric acid; And / or, the pickling temperature is 25-60° C. and the time is 4-12 h.

7. A polyolefin-derived carbon-based single-atom catalyst prepared according to the preparation method according to any one of claims 1 to 6.

8. Use of the polyolefin-derived carbon-based single-atom catalyst prepared by the preparation method according to any one of claims 1 to 6 in a fuel cell or a metal-air battery.

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