Polyolefin derived carbon-based monatomic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a polyolefin derived carbon-based monatomic catalyst as well as a preparation method and application thereof, and belongs to the field of electrocatalysts. The method for preparing the polyolefin-derived carbon-based monatomic catalyst comprises the following steps: preparing a polyolefin / calcium carbonate mixture, mixing the polyolefin / calcium carbonate mixture with a nitrogen source substance and a sulfur source substance, and sequentially performing high-temperature carbonization and acid pickling at 700-900 DEG C to prepare a polyolefin-derived porous carbon carrier; and mixing the polyolefin-derived porous carbon carrier with a transition metal salt, sequentially carrying out low-temperature pyrolysis at 300-450 DEG C, washing with an ethanol / water mixed solution, and carrying out medium-temperature carbonization at 550-600 DEG C, and carrying out acid pickling on the obtained product. According to the present invention, the electron transmission ability of the polyolefin derived carbon-based monatomic catalyst can be optimized while the high metal monatomic loading is achieved, such that the prepared carbon-based monatomic catalyst has excellent oxidation reduction electro-catalysis efficiency.

Description

Technical Field

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

[0002] Carbon-based single-atom catalysts are electrocatalytic systems composed of metal components anchored on carbon carriers in an atomically dispersed form. They have a unique electronic structure and extremely high atomic utilization, and can show the advantages of high selectivity and high activity in the fields of redox electrocatalysis, fuel cells, and zinc-air batteries. However, traditional carbon-based single-atom catalysts mostly rely on high-purity carbon sources such as graphene and carbon nanotubes, and the relatively high cost of raw materials limits their large-scale production and commercial use.

[0003] At present, the relevant field has disclosed a low-cost preparation technology for preparing carbon-based single-atom catalysts by deriving carbon carriers from waste plastics. For example, Ma Shengjia et al. chemically modified waste polystyrene plastics with concentrated nitric acid to make nitropolystyrene, and then reacted with FeCl 3 6H 2 O was co-pyrolyzed to prepare nitrogen-doped porous carbon supports loaded with Fe single-atom catalysts, achieving the goals of pollutant control and resource recycling.

[0004] However, the technical strategy of preparing carbon-based single-atom catalysts through plastic-derived carbon carriers 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 and a preparation method and application thereof, which are used to solve the technical problem of low metal single-atom loading in the existing preparation of single-atom catalysts through plastic-derived carbon carriers.

[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] After mixing the polyolefin / calcium carbonate mixture with a nitrogen source and a sulfur source, the mixture is sequentially carbonized at a high temperature of 700 to 900° C. and acid-washed to obtain a polyolefin-derived porous carbon carrier; and

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

[0011] According to the preparation method disclosed in the present invention, 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 in the present invention, 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 in the present invention, the sulfur source material 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 in the present invention, the transition metal salt is selected as a chloride and / or acetate containing at least one of Fe, Co, and Ni.

[0018] According to the preparation method disclosed in the present invention, 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 carrier is 2:1.

[0019] According to the preparation method disclosed in the present invention, 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 in the present invention, 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 in the present invention, the time of the high-temperature carbonization is 2 to 4 h; the time of the low-temperature pyrolysis and the medium-temperature carbonization are both 3 to 7 h.

[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] The nitrogen / sulfur co-doped polyolefin-derived porous carbon support has cobalt single atoms with a loading amount greater than 8 wt %.

[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 at least include:

[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 carrier, and mixes the N / S co-doped polyolefin-derived porous carbon carrier with a metal component and then performs a gradient heat treatment of low-temperature pyrolysis and medium-temperature carbonization, thereby effectively solving the problem of low metal single atom loading in the existing preparation of carbon-based single-atom catalysts using plastic-derived carbon carriers, 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 abundant 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 excessive graphitization and further optimize the coordination environment of the metal component to the carbon carrier, effectively avoid the adsorption and binding of the metal component nanoparticles, and finally achieve the effect of increasing the loading amount of metal single atoms, but also promote the ordering of the carbon carrier and eliminate unstable defects, effectively improve the electron transmission 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 loading and efficient electron transmission of metal single atoms. 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, the 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] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in this application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[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 in the present application;

[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 the present application;

[0031] Figure 3 XRD spectra of the polystyrene-derived porous carbon support prepared in Comparative Example 1 provided in the present application, 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;

[0032] Figure 4 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 provided in the present application, 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. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of this application.

[0035] In the relevant description of this application, the term "and / or" is used to describe the association relationship of associated objects, indicating that there may be three relationships. 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 the present 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", all mean 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, respectively.

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

[0038] In the relevant description of the application, the numerical range is understood to also specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the range also belongs to the disclosure of the application. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0039] Unless otherwise stated, the technical / scientific terms used in this application have the meanings and / or interpretations that are generally known 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 experiment 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 a 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 and acid washing at 700-900°C to obtain a polyolefin-derived porous carbon support;

[0043] S3: After mixing the polyolefin-derived porous carbon support in the previous step with the transition metal salt, low-temperature pyrolysis at 300-450°C, washing with an ethanol / water mixture, and medium-temperature carbonization at 550-600°C are sequentially performed. The obtained 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, the present application can use an ethanol / water mixture (volume ratio of 1:1) for immersion washing, and after washing, dry 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 directly pyrolyze plastics to prepare carbon carriers. At the same time, although nitrogen-doped carbon carriers can adjust 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 and binding of metal components in the form of single atoms, making the metal single-atom loading extremely low. To this end, the present invention carbonizes a mixture containing components of 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 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 low-temperature pyrolysis to make the transition metal salt (cobalt chloride hexahydrate / CoCl 2 6H 2 O) may undergo dehydration and partial decomposition to form transition metal intermediates (CoO, CoCl 2 ) and coordinate with the N and S doping sites (pyridinic nitrogen / sulfide groups) in the carbon support to form, for example, Co-N 3 -S 1 The first is to adjust the reduction process of the transition metal component (Co) so that the transition metal component (Co) is in a highly dispersed state, which is convenient for the subsequent formation of single atomic sites; the second is to avoid excessive graphitization of the carbon carrier and retain sufficient defects and loading sites (micropores, edge sites), 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 the 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, thereby effectively regulating the loading amount of metal single atoms.

[0048] Secondly, the set medium temperature carbonization is carried out to promote the graphitization of the carbon support, so that the coordination effect between the defect sites (pyridinic nitrogen and sulfur sites) and the cobalt metal is enhanced to form a stable Co-N 3 -S 1 The coordination structure can achieve the effect of firmly anchoring the cobalt single atom; at the same time, it also improves the conductivity and chemical stability of the carbon carrier, thereby optimizing the electron transmission capacity 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 scheme of the present disclosure, the polyolefin used in the present invention is selected from at least one of polystyrene, polyethylene, polypropylene, and polyvinyl chloride, and polystyrene may be preferred. The present disclosure does not specifically limit the specific source and brand of the polyolefin, and it may be either commercially available raw materials of various brands or waste recycled materials of various brands. At the same time, the mass ratio of polyolefin to calcium carbonate in the polyolefin / calcium carbonate mixture of the present invention is 1:2 to 8, and examples include but are not limited to 1:2, 1:4, and 1:8.

[0051] In the exemplary scheme 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, and melamine is preferred. 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, and examples include but are not limited to 1:1, 2:1, and 4:1.

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

[0053] In the 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 specifically limit the specific parameters of the rotary evaporation drying, so long as the tetrahydrofuran can be fully removed.

[0055] In the exemplary embodiment of the present disclosure, the pickling agent used for pickling has 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 hydrochloric acid, sulfuric acid, nitric acid, etc.; the pickling temperature is selected to be 25~60℃, and the time is 4~12 h, which can be exemplified as 25℃ / 12 h, 25℃ / 15 h, etc.

[0056] It should be noted that the pickling treatment mentioned here includes the pickling in step S2 and / or S3, and the pickling treatments in steps S2 and S3 may be the same or different, specifically, 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 that the polyolefin is fully carbonized 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 in each step above 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 carrier, on which a cobalt single atom with a loading amount greater than 8 wt% is anchored. Among them, since the preparation method of the present invention can increase the metal atom loading amount and optimize the electron transmission capacity, and can use waste polyolefin plastics as carbon precursors, 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, ultrasonicated for 20 min, and rotary evaporated to dry to obtain a polystyrene / calcium carbonate mixture.

[0065] S2: 1.0 g melamine and 2.0 g sublimated sulfur powder were added to the polystyrene / calcium carbonate mixture and ground evenly. -1 In a nitrogen atmosphere, the temperature was 5 °C·min -1 The temperature was raised to 800 °C at a rate of 1.5 % 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 obtain a transition metal salt / carbon support mixture. -1 In a nitrogen atmosphere, the -1 The temperature was raised to 300 °C at a rate of 1.5 °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. -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, ultrasonicated for 20 min, and rotary evaporated to dry to obtain a polystyrene / calcium carbonate mixture.

[0070] S2: 1.0 g melamine and 2.0 g sublimated sulfur powder were added to the polystyrene / calcium carbonate mixture and ground evenly.-1 In a nitrogen atmosphere, the temperature was 5 °C·min -1 The temperature was raised to 800 °C at a rate of 1.5 % 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 obtain a transition metal salt / carbon support mixture. -1 In a nitrogen atmosphere, the -1 The temperature was raised to 300 °C at a rate of 1.5 °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. -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, ultrasonicated for 20 min, and rotary evaporated to dry to obtain a polystyrene / calcium carbonate mixture.

[0075] S2: 1.0 g melamine and 2.0 g sublimated sulfur powder were added to the polystyrene / calcium carbonate mixture and ground evenly. -1 In a nitrogen atmosphere, the temperature was 5 °C·min -1 The temperature was raised to 800 °C at a rate of 1.5 % 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 obtain a transition metal salt / carbon support mixture. -1 In a nitrogen atmosphere, the -1The temperature was raised to 300 °C at a rate of 1.5 °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, ultrasonicated for 20 min, and rotary evaporated to dry to obtain a polystyrene / calcium carbonate mixture.

[0080] S2: Add 2.0 g melamine and 2.0 g sublimated sulfur powder to the polystyrene / calcium carbonate mixture and grind it evenly. Place it at 200 mL min -1 In a nitrogen atmosphere, the temperature was 5 °C·min -1 The temperature was raised to 800 °C at a rate of 1.5 % 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 obtain a transition metal salt / carbon support mixture. -1 In a nitrogen atmosphere, the -1 The temperature was raised to 300 °C at a rate of 1.5 °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. -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 pickled 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, the present 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 sublimated 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 carrier mixture is subjected to low-temperature carbonization at 400°C / 0.5 h and high-temperature pyrolysis at 900°C / 2 h in sequence, and 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 to 3 As shown. Among them, Figure 1 TEM 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, Comparative Example 3, respectively); Figure 2 The 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, 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 catalysts obtained in Comparative Example 4, and the polystyrene-derived carbon-based cobalt single-atom catalysts obtained in Examples 1-3; Figure 4 is the Co 2p XPS spectrum of the polystyrene-derived carbon-based cobalt single-atom catalyst obtained in Example 1; Figure 5 It is a linear sweep voltammetric characteristic curve 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 catalyst 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 catalyst 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 It can be seen that the polystyrene-derived carbon-based cobalt single-atom catalysts prepared in Example 1 and Comparative Examples 2-3 only have broad diffraction peaks corresponding to the (002) plane, and no diffraction peaks of Co metal are detected, indicating that there are no Co metal species. In contrast, the carbon-based cobalt nanoparticles prepared in Comparative Example 4 have obvious diffraction peaks of Co metal detected, indicating the occurrence 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 about 9.41 wt%. The cobalt loading measured by inductively coupled plasma emission spectroscopy ICP-OES is about 8.01~8.08 wt%

[0096] The present application also tests the redox electrocatalytic performance of the polystyrene-derived porous carbon carrier obtained in Comparative Example 1 and the polystyrene-derived carbon-based cobalt single-atom catalyst obtained in Examples and Comparative Examples. The specific test process is to use 0.1 M KOH as the electrolyte in a three-electrode system and perform the test 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) standard, and the result was 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 carriers, 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 performances. The reasons for the difference 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, and exhibits 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 carrier 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 carrier and exhibits 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 its activity is limited, 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] From the above analysis, it can be seen that the present invention constructs highly dispersed active sites and efficient mass transfer pore structures through the optimization of sulfur-nitrogen co-doping and appropriate template agents, thereby obtaining a carbon-based single-atom catalyst with excellent electrocatalytic performance. It shows that the present invention can significantly improve the oxygen reduction performance of the electrocatalyst by regulating the amount of template, the amount of metal salt precursor, the amount of sulfur source, and the amount of nitrogen source, as well as the gradient heat treatment process of low-temperature pyrolysis, ethanol / water washing, and medium-temperature carbonization.

[0099] The various embodiments in this specification are described in a progressive manner, and 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 of ordinary skill in the art should understand that the technical solutions recorded in the aforementioned embodiments may still be modified, or some or all of the technical features therein may 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; After mixing the polyolefin / calcium carbonate mixture with a nitrogen source and a sulfur source, the mixture is sequentially carbonized at a high temperature of 700 to 900° C. and acid-washed to obtain a polyolefin-derived porous carbon carrier; and After the polyolefin-derived porous carbon support is mixed with a transition metal salt, low-temperature pyrolysis at 300-450°C, washing with an ethanol / water mixture, and medium-temperature carbonization at 550-600°C are sequentially performed. The obtained product is acid-washed to obtain a polyolefin-derived carbon-based single-atom catalyst.

2. The preparation method according to claim 1, characterized in that: The polyolefin is selected from at least one of polystyrene, polyethylene, polypropylene and polyvinyl chloride; And / or, the mass ratio of polyolefin to calcium carbonate in the polyolefin / calcium carbonate mixture is 1:2-8.

3. The preparation method according to claim 1, characterized in that: The nitrogen source is selected from at least one of melamine, urea, thiourea, cyanamide and dicyandiamide; And / or, the mass ratio of the nitrogen source substance to the polyolefin / calcium carbonate mixture is 1-4:

1.

4. The preparation method according to claim 1, characterized in that: The sulfur source material is selected from at least one of elemental sulfur, carbon disulfide, hydrogen sulfide, sodium thiosulfate, and thiourea; And / or, the mass ratio of the sulfur source material to the polyolefin / calcium carbonate mixture is 1-4:

1.

5. The preparation method according to claim 1, characterized in that: The transition metal salt is selected from chlorides and / or acetates containing at least one of Fe, Co, and Ni; And / or, 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.

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

7. The preparation method according to claim 1, characterized in that: The pickling agent used for pickling is selected to have a concentration of 2-8 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.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The high temperature carbonization time is 2 to 4 hours; and The time for the low-temperature pyrolysis and the medium-temperature carbonization is 3 to 7 hours.

9. A polyolefin-derived carbon-based single-atom catalyst prepared according to the preparation method of any one of claims 1 to 8, characterized in that: comprising a nitrogen / sulfur co-doped polyolefin-derived porous carbon support; The nitrogen / sulfur co-doped polyolefin-derived porous carbon support has cobalt single atoms with a loading amount greater than 8 wt %.

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

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