A method for synthesizing a single-atom catalyst and an electrocatalytic application of the single-atom catalyst

Abstract

The application discloses a method for synthesizing a single-atom catalyst, which comprises the following steps of mixing raw materials: taking dimethyl imidazole, zinc nitrate and graphene oxide as solutes, and taking anhydrous methanol as a solvent to form ZIF-8@GO through stirring; taking ZIF-8@GO and thiourea as solutes, and taking anhydrous methanol as a solvent to form S / ZIF-8@GO through stirring and adsorption; first-stage pyrolysis: pyrolyzing S / ZIF-8@GO in a protective gas atmosphere to form porous carbon (S, N-C); precursor preparation: after the porous carbon is cooled, phenanthroline (Phen) and a transition metal source (M) are added into the porous carbon to form a precursor M / S, N-C@Phen; and second-stage pyrolysis: pyrolyzing the M / S, N-C@Phen precursor in a protective gas atmosphere to obtain a M / S, N-C single-atom catalyst. The synthesis method is simple and effective, can be used for large-scale synthesis of a single-atom catalyst, is suitable for synthesis of various metal single-atom catalysts, and solves the problems of complexity in the prior art and difficulty in large-scale preparation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysts, in particular to a method for synthesizing a single-atom catalyst and an electrocatalytic application of the single-atom catalyst. BACKGROUND

[0002] The overconsumption of fossil energy has led to increasingly serious energy and environmental crises, and thus a "clean, low-carbon, safe, and efficient" energy revolution is imperative. Fuel cells, compared with other energy conversion devices, have the advantages of a wide fuel source, no pollution, and high efficiency, and thus are considered one of the most effective green energy conversion technologies. In a fuel cell, the oxygen reduction reaction (ORR) pathway at the cathode is complex, has many intermediate products, and has a high activation energy, which leads to slow chemical kinetics and greatly reduces the efficiency. Although noble metal catalysts have excellent ORR performance, their application is greatly limited by high cost, scarcity of reserves, and poor stability.

[0003] The existing synthesis methods of single-atom catalysts still have many problems, such as a complex synthesis method, difficulty in large-scale preparation, expensive precursors, and poor performance of single-atom catalysts with non-noble metal active sites, and the preparation method is often only effective for one kind of metal, and there is a lack of a general strategy for preparing single-atom catalysts for multiple metals. SUMMARY

[0004] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract, and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0005] In view of the above and / or existing problems in the prior art, the present application is proposed.

[0006] Therefore, the technical problem to be solved by the present application is to develop a general strategy for preparing single-atom catalysts with a simple synthesis method, inexpensive precursors, and effectiveness for multiple metals.

[0007] To solve the above technical problems, the present application provides the following technical solutions: a method for synthesizing a single-atom catalyst, comprising,

[0008] Raw material mixing: taking dimethyl imidazole, zinc nitrate, and graphene oxide as solutes, and anhydrous methanol as a solvent, and forming ZIF-8@GO by stirring;

[0009] Sulfur doping: taking ZIF-8@GO and thiourea as solutes, and anhydrous methanol as a solvent, and forming S / ZIF-8@GO by stirring and adsorption;

[0010] First-stage pyrolysis: pyrolysis of S / ZIF-8@GO in a protective gas atmosphere to form porous sulfur-doped carbon (S, N-C);

[0011] Precursor preparation: after S, N-C is cooled, phenanthroline (Phen) and a transition metal source (M) are added to S, N-C to form a precursor M / S, N-C@Phen;

[0012] Second-stage pyrolysis: pyrolysis of the M / S, N-C@Phen precursor in a protective gas atmosphere to obtain a single-atom catalyst.

[0013] As a preferred scheme of the method for synthesizing a single-atom catalyst described in the present application, wherein: the transition metal source is selected from one or more of Fe(II), Cu(II), Co(II), and Ni(II) metal salts.

[0014] As a preferred scheme of the method for synthesizing a single-atom catalyst described in the present application, wherein: the transition metal source is one or more of FeCl2, CuCl2, CoCl2, and NiCl2.

[0015] As a preferred scheme of the method for synthesizing a single-atom catalyst described in the present application, wherein: in the raw material mixing, the stirring temperature is 22-26°C, and the stirring time is 10 h.

[0016] As a preferred scheme of the method for synthesizing a single-atom catalyst described in the present application, wherein: in the first-stage pyrolysis, the pyrolysis temperature is 800-1100°C, and the holding time is 1-3 h.

[0017] As a preferred scheme of the method for synthesizing a single-atom catalyst described in the present application, wherein: in the second-stage pyrolysis, the pyrolysis temperature is 400-600°C, and the holding time is 1-3 h.

[0018] As a preferred scheme of the method for synthesizing a single-atom catalyst described in the present application, wherein: in the raw material mixing, the molar ratio of zinc nitrate to dimethylimidazole is 1:(4-10).

[0019] As a preferred scheme of the method for synthesizing a single-atom catalyst described in the present application, wherein: in the sulfur doping process, the mass ratio of thiourea to ZIF-8@GO is (3-5):1.

[0020] As a preferred scheme of the method for synthesizing a single-atom catalyst described in the present application, wherein: in the precursor preparation, the mass ratio of phenanthroline to the transition metal source is 1:(0.5-1).

[0021] As a preferred solution of the method for synthesizing the single-atom catalyst according to the application, in the first-stage pyrolysis, the heating rate is 1-5 ℃ / min, and the cooling rate is 3-8 ℃ / min.

[0022] A single-atom catalyst is prepared by any of the above methods.

[0023] The synthetic method of the application is simple and effective, can be used for large-scale synthesis of single-atom catalysts, and is suitable for synthesis of various metal single-atom catalysts, solving the problems of complexity and difficulty in scale production in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0025] Figure 1 A columnar graph for comparing the catalyst activity (half-wave potential) of Examples 1, 7-9 and Comparative Example 1 of the application;

[0026] Figure 2 An LSV curve for comparing the catalyst activity of Examples 1 and Comparative Example 2 of the application;

[0027] Figure 3 A columnar graph for comparing the catalyst activity (half-wave potential) of Examples 1 and Comparative Example 4 of the application;

[0028] Figure 4 A columnar graph for comparing the catalyst activity (half-wave potential) of Examples 1-4 of the application;

[0029] Figure 5 A columnar graph for comparing the catalyst activity (half-wave potential) of Examples 1, 5 and 6 of the application;

[0030] Figure 6 A spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) photo of the Fe single-atom catalyst prepared in Example 1 of the application;

[0031] Figure 7 A spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) photo of the Fe catalyst prepared in Comparative Example 3 of the application, in which Fe nanoparticles appear. DETAILED DESCRIPTION

[0032] In order to make the above objectives, characteristics and advantages of the present application more apparent, a detailed description of the specific embodiments of the present application will be given below with reference to the accompanying drawings.

[0033] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. The present application, however, can be practiced in a variety of ways other than those specifically described herein, and the scope of the present application is not limited to the specific embodiments described herein.

[0034] Secondly, the present application is described in detail in conjunction with the schematic diagram. In the detailed description of the embodiments of the present application, the cross-sectional view of the device structure is locally enlarged without the general proportion for the convenience of description, and the schematic diagram is only an example, which should not limit the scope of protection of the present application herein. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in actual manufacture.

[0035] Thirdly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. The "in one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent of or mutually exclusive with other embodiments.

[0036] Embodiment 1

[0037] The present embodiment provides a single-atom catalyst, which is prepared by the following steps:

[0038] (1) 3.5 g of 2-methylimidazole was weighed into a 100 mL beaker, and 80 mL of anhydrous methanol was added to the beaker. Ultrasonic dispersion was performed for 30 min to obtain a uniform colorless solution A.

[0039] (2) 4.2 g of Zn(NO3)2·6H2O was weighed into a 100 mL beaker, and 80 mL of anhydrous methanol was added to the beaker. Ultrasonic dispersion was performed for 30 min to obtain a uniform solution B.

[0040] (3) The A solution was slowly poured into a 250 mL three-necked flask, and then the B solution was poured into the flask. Stirring was performed at 25°C for 30 min, and then 70 mL of graphene oxide was added. Stirring was continued for 20 h, and centrifugation and washing were performed to obtain ZIF-8@GO.

[0041] (4) 500 mg of ZIF-8@GO and 1500 mg of thiourea were weighed into a 100 mL beaker, and 80 mL of anhydrous methanol was added to the beaker. Stirring was continued for 5 h, and centrifugation was performed to obtain S / ZIF-8@GO.

[0042] (5) Under the nitrogen atmosphere, the S / ZIF-8@GO is pyrolyzed at 900℃ for 2h at a heating rate of 3℃ / min to form porous S, N-C, and then cooled to room temperature at a cooling rate of 5℃ / min.

[0043] (6) 100mg of the porous S, N-C is dissolved in 100mL of ethanol to obtain a uniform solution C by ultrasonic dispersion for 30min, and 5mg of phenanthroline and 2mg of FeCl2 are dissolved in 20mL of ethanol to obtain solution D.

[0044] (7) The solution C is first slowly poured into a 200mL three-necked flask, and then the solution D is poured into the flask, stirred at 25℃ for 10h to form Fe / S, N-C@Phen, centrifuged and washed with methanol for three times, and dried in a drying oven at 70℃ overnight to obtain a Fe / S, N-C@Phen powder sample.

[0045] (8) The Fe / S, N-C@Phen powder is placed in a quartz boat and heated to 500℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, kept for 2h, and cooled to room temperature to obtain a black powder. The obtained solid is ground into a fine powder to obtain a N, S-doped porous carbon supported Fe-S, N-C single-atom catalyst.

[0046] Example 2

[0047] The present example provides a single-atom catalyst, which is prepared by the following steps:

[0048] (1) 3.5g of 2-methylimidazole is weighed into a 100mL beaker, and 80mL of anhydrous methanol is added to the beaker. Ultrasonic dispersion is performed for 30min to obtain a uniform colorless solution A.

[0049] (2) 4.2g of Zn(NO3)2·6H2O is weighed into a 100mL beaker, and 80mL of anhydrous methanol is added to the beaker. Ultrasonic dispersion is performed for 30min to obtain a uniform solution B.

[0050] (3) The solution A is first slowly poured into a 250mL three-necked flask, and then the solution B is poured into the flask. Stirring is performed at 25℃ for 30min, and then 70mL of graphene oxide is added. Stirring is continuously performed for 20h, and then centrifugation and washing are performed to obtain ZIF-8@GO.

[0051] (4) 500mg of ZIF-8@GO and 1500mg of thiourea are weighed into a 100mL beaker, and 80mL of anhydrous methanol is added to the beaker. Stirring is continuously performed for 5h, and then centrifugation is performed to obtain S / ZIF-8@GO.

[0052] (5) Under the nitrogen atmosphere, the S / ZIF-8@GO is pyrolyzed at 800℃ for 2h at a heating rate of 3℃ / min to form porous S, N-C, and then cooled to room temperature at a cooling rate of 5℃ / min.

[0053] (6) Take 100 mg of porous S, N-C and dissolve it in 100 mL of ethanol, ultrasonic dispersion for 30 min to obtain a uniform solution C, take 5 mg of phenanthroline and 2 mg of FeCl2 and dissolve them in 20 mL of ethanol to obtain solution D.

[0054] (7) First, slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h to form Fe / S, N-C@Phen, centrifuge and wash with methanol three times, dry in a 70°C drying oven overnight to obtain Fe / S, N-C@Phen powder sample.

[0055] (8) Place the Fe / S, N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen atmosphere, keep for 2 h, cool to room temperature to obtain a black powder, grind the obtained solid into fine powder to obtain N, S doped porous carbon supported Fe-S, N-C single atom catalyst.

[0056] Example 3

[0057] This example provides a single atom catalyst, which is prepared by the following steps:

[0058] (1) Take 3.5 g of 2-methylimidazole and place it in a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0059] (2) Take 4.2 g of Zn(NO3)2·6H2O and place it in a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0060] (3) First, slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, continue to stir for 20 h, centrifuge and wash to obtain ZIF-8@GO.

[0061] (4) Take 500 mg of ZIF-8@GO and 1500 mg of thiourea and place them in a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, continue to stir for 5 h, centrifuge to obtain S / ZIF-8@GO.

[0062] (5) Under a nitrogen atmosphere, pyrolyze S / ZIF-8@GO at a heating rate of 3°C / min to 1000°C for 2 h to form porous S, N-C, then cool to room temperature at a cooling rate of 5°C / min.

[0063] (6) Take 100 mg of porous S, N-C and dissolve it in 100 mL of ethanol, and ultrasonic dispersion for 30 min to obtain a uniform solution C. Take 5 mg of phenanthroline and 2 mg of FeCl2 and dissolve them in 20 mL of ethanol to obtain solution D.

[0064] (7) First, slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h to form Fe / S, N-C@Phen, centrifuge and wash with methanol three times, and place it in a drying oven at 70°C overnight to dry to obtain Fe / S, N-C@Phen powder sample.

[0065] (8) Place the Fe / S, N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen atmosphere, and keep the temperature for 2 h, and cool to room temperature to obtain a black powder. Grind the obtained solid into a fine powder to obtain a N, S-doped porous carbon supported Fe-S, N-C monatomic catalyst.

[0066] Example 4

[0067] This example provides a monatomic catalyst, which is prepared by the following steps:

[0068] (1) Take 3.5 g of 2-methylimidazole and place it in a 100 mL beaker. Add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0069] (2) Take 4.2 g of Zn(NO3)2·6H2O and place it in a 100 mL beaker. Add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0070] (3) First, slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, and continue to stir for 20 h. Centrifuge and wash to obtain ZIF-8@GO.

[0071] (4) Take 500 mg of ZIF-8@GO and 1500 mg of thiourea and place them in a 100 mL beaker. Add 80 mL of anhydrous methanol to the beaker. Continue to stir for 5 h. Centrifuge to obtain S / ZIF-8@GO.

[0072] (5) Under a nitrogen atmosphere, pyrolyze the S / ZIF-8@GO at a heating rate of 3°C / min to 1100°C for 2 h to form porous S, N-C, and then cool to room temperature at a cooling rate of 5°C / min.

[0073] (6) Take 100 mg of porous S, N-C and dissolve it in 100 mL of ethanol, and ultrasonic dispersion for 30 min to obtain a uniform solution C. Take 5 mg of phenanthroline and 2 mg of FeCl2 and dissolve them in 20 mL of ethanol to obtain solution D.

[0074] (7) First, slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h to form Fe / S, N-C@Phen, centrifuge and wash with methanol three times, and place it in a drying oven at 70°C overnight to dry to obtain Fe / S, N-C@Phen powder sample.

[0075] (8) Place the Fe / S, N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen atmosphere, and keep the temperature for 2 h, and cool to room temperature to obtain a black powder. Grind the obtained solid into a fine powder to obtain a N, S-doped porous carbon supported Fe-S, N-C monatomic catalyst.

[0076] Example 5

[0077] This example provides a monatomic catalyst, which is prepared by the following steps:

[0078] (1) Take 3.5 g of 2-methylimidazole and place it in a 100 mL beaker. Add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0079] (2) Take 4.2 g of Zn(NO3)2·6H2O and place it in a 100 mL beaker. Add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0080] (3) First, slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, and continue to stir for 20 h. Centrifuge and wash to obtain ZIF-8@GO.

[0081] (4) Take 500 mg of ZIF-8@GO and 2000 mg of thiourea and place them in a 100 mL beaker. Add 80 mL of anhydrous methanol to the beaker. Continue to stir for 5 h. Centrifuge to obtain S / ZIF-8@GO.

[0082] (5) Under a nitrogen atmosphere, pyrolyze the S / ZIF-8@GO at a heating rate of 3°C / min to 900°C for 2 h to form porous S, N-C, and then cool to room temperature at a cooling rate of 5°C / min.

[0083] (6) Take 100 mg of porous S, N-C and dissolve in 100 mL of ethanol, ultrasonic dispersion for 30 min to obtain a uniform solution C, take 5 mg of phenanthroline and 2 mg of FeCl2 and dissolve in 20 mL of ethanol to obtain solution D.

[0084] (7) First, slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h to form Fe / N-C@Phen, centrifuge and wash with methanol three times, dry in a 70°C drying oven overnight to obtain Fe / N-C@Phen powder sample.

[0085] (8) Place the Fe / N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen atmosphere, keep for 2 h, cool to room temperature to obtain a black powder, grind the obtained solid into fine powder to obtain N-doped porous carbon supported Fe-N-C single-atom catalyst.

[0086] Example 6

[0087] This example provides a single-atom catalyst, which is prepared by the following steps:

[0088] (1) Take 3.5 g of 2-methylimidazole and place it in a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0089] (2) Take 4.2 g of Zn(NO3)2·6H2O and place it in a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0090] (3) First, slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, continue to stir for 20 h, centrifuge and wash to obtain ZIF-8@GO.

[0091] (4) Take 500 mg of ZIF-8@GO and 2500 mg of thiourea and place them in a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, continue to stir for 5 h, centrifuge to obtain S / ZIF-8@GO.

[0092] (5) Under a nitrogen atmosphere, pyrolyze the S / ZIF-8@GO at a heating rate of 3°C / min to 900°C for 2 h to form porous S, N-C, then cool to room temperature at a cooling rate of 5°C / min.

[0093] (6) Take 100 mg of porous S, N-C and dissolve in 100 mL of ethanol, ultrasonic dispersion for 30 min to obtain a uniform solution C, take 5 mg of phenanthroline and 2 mg of FeCl2 and dissolve in 20 mL of ethanol to obtain solution D.

[0094] (7) First, slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h to form Fe / S, N-C@Phen, centrifuge and wash with methanol three times, and dry in a 70°C drying oven overnight to obtain Fe / S, N-C@Phen powder sample.

[0095] (8) Place the Fe / S, N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen atmosphere, and keep the temperature for 2 h, and cool to room temperature to obtain a black powder. Grind the obtained solid into fine powder to obtain N, S-doped porous carbon supported Fe-S, N-C monatomic catalyst.

[0096] Example 7

[0097] This example provides a monatomic catalyst, which is prepared by the following steps:

[0098] (1) Weigh 4.0 g of 2-methylimidazole into a 100 mL beaker, and add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0099] (2) Weigh 5.1 g of Zn(NO3)2·6H2O into a 100 mL beaker, and add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0100] (3) First, slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, and continue to stir for 20 h. Centrifuge and wash to obtain ZIF-8@GO.

[0101] (4) Weigh 500 mg of ZIF-8@GO and 2500 mg of thiourea into a 100 mL beaker, and add 80 mL of anhydrous methanol to the beaker. Stir for 5 h, centrifuge to obtain S / ZIF-8@GO.

[0102] (5) Under a nitrogen atmosphere, pyrolyze S / ZIF-8@GO at a heating rate of 3°C / min to 900°C for 2 h to form porous S, N-C, and then cool to room temperature at a cooling rate of 5°C / min.

[0103] (6) Dissolve 80 mg of porous S, N-C in 100 mL of ethanol, and ultrasonic dispersion for 30 min to obtain a uniform solution C. Dissolve 6 mg of phenanthroline and 1 mg of CuCl2 in 20 mL of ethanol to obtain solution D.

[0104] (7) First, slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h, form Cu / S, N-C@Phen, centrifuge and wash with methanol three times, place in a drying oven at 70°C overnight to dry to obtain Cu / S, N-C@Phen powder sample.

[0105] (8) Place the Cu / S, N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen environment, keep for 3 h, cool to room temperature to obtain a black powder, grind the obtained solid into fine powder to obtain a N, S-doped porous carbon supported Cu-S, N-C monatomic catalyst.

[0106] Example 8

[0107] This example provides a monatomic catalyst, which is prepared by the following steps:

[0108] (1) Weigh 5.1 g of 2-methylimidazole into a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0109] (2) Weigh 6.4 g of Zn(NO3)2·6H2O into a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0110] (3) First, slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, continue to stir for 20 h, centrifuge and wash to obtain ZIF-8@GO.

[0111] (4) Weigh 500 mg of ZIF-8@GO and 2500 mg of thiourea into a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, continue to stir for 5 h, centrifuge to obtain S / ZIF-8@GO.

[0112] (5) Under a nitrogen atmosphere, pyrolyze S / ZIF-8@GO at a heating rate of 3°C / min to 900°C for 2 h to form porous S, N-C, then cool to room temperature at a cooling rate of 5°C / min.

[0113] (6) Dissolve 110 mg of porous S, N-C in 100 mL of ethanol, ultrasonic dispersion for 30 min to obtain a uniform solution C, dissolve 7 mg of phenanthroline and 4 mg of CoCl2 in 20 mL of ethanol to obtain solution D.

[0114] (7) First, slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h, form Co / S, N-C@Phen, centrifuge and wash with methanol three times, place in a drying oven at 70°C overnight to dry to obtain Co / S, N-C@Phen powder sample.

[0115] (8) Place the Co / S, N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen environment, keep for 3 h, cool to room temperature to obtain a black powder, grind the obtained solid into fine powder to obtain a N, S-doped porous carbon supported Co-S, N-C monatomic catalyst.

[0116] Example 9

[0117] The present embodiment provides a monatomic catalyst, which is prepared by the following steps:

[0118] (1) Weigh 4.8 g of 2-methylimidazole into a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0119] (2) Weigh 5.5 g of Zn(NO3)2·6H2O into a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0120] (3) First, slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, continue to stir for 20 h, centrifuge and wash to obtain ZIF-8@GO.

[0121] (4) Weigh 500 mg of ZIF-8@GO and 2500 mg of thiourea into a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, continue to stir for 5 h, centrifuge to obtain S / ZIF-8@GO.

[0122] (5) Under a nitrogen atmosphere, pyrolyze S / ZIF-8@GO at a heating rate of 3°C / min to 900°C for 2 h to form porous S, N-C, then cool to room temperature at a cooling rate of 5°C / min.

[0123] (6) Dissolve 120 mg of porous S, N-C in 100 mL of ethanol, ultrasonic dispersion for 30 min to obtain a uniform solution C, dissolve 7 mg of phenanthroline and 3 mg of NiCl2 in 20 mL of ethanol to obtain solution D.

[0124] (7) First, slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h to form Ni / S, N-C@Phen, centrifuge and wash with methanol three times, and dry in a 70°C drying oven overnight to obtain a Ni / S, N-C@Phen powder sample.

[0125] (8) Put the Ni / S, N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen environment, keep for 3 h, cool to room temperature to obtain a black powder, and grind the obtained solid into a fine powder to obtain a N, S-doped porous carbon supported Ni-S, N-C monatomic catalyst.

[0126] Comparative Example 1

[0127] The present comparative example uses an ORR commercial benchmark Pt / C catalyst.

[0128] Comparative Example 2

[0129] The present comparative example differs from Example 1 in that the first-stage pyrolysis and the second-stage pyrolysis are combined into one-step pyrolysis in the present comparative example.

[0130] Comparative Example 3

[0131] The present example provides a monatomic catalyst, which is prepared by the following steps:

[0132] (1) Weigh 3.5 g of 2-methylimidazole into a 100 mL beaker, and add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0133] (2) Weigh 4.2 g of Zn(NO3)2·6H2O into a 100 mL beaker, and add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0134] (3) First, slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, continue to stir for 20 h, centrifuge and wash to obtain ZIF-8@GO.

[0135] (4) Weigh 500 mg of ZIF-8@GO and 2500 mg of thiourea into a 100 mL beaker, and add 80 mL of anhydrous methanol to the beaker. Stir for 5 h, centrifuge to obtain S / ZIF-8@GO.

[0136] (5) Under a nitrogen atmosphere, pyrolyze S / ZIF-8@GO at a heating rate of 3°C / min to 900°C for 2 h to form porous S, N-C, and then cool to room temperature at a rate of 5°C / min.

[0137] (6) Take 100 mg of porous S, N-C and dissolve in 100 mL of ethanol, ultrasonic dispersion for 30 min to obtain a uniform solution C, take 7 mg of phenanthroline and 3 mg of Fe(NO3)3 and dissolve in 20 mL of ethanol to obtain solution D.

[0138] (7) First slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h to form Fe / S, N-C@Phen, centrifugal and wash with methanol three times, dry in a drying oven at 70°C overnight to obtain Fe / S, N-C@Phen powder sample.

[0139] (8) Place the Fe / S, N-C@Phen powder in a quartz boat, heat to 500°C at a heating rate of 2°C / min in a nitrogen environment, keep for 2 h, cool to room temperature to obtain a black powder, grind the obtained solid into fine powder to obtain N, S doped porous carbon loaded Fe-S, N-C catalyst.

[0140] Comparative Example 4

[0141] (1) Take 3.5 g of 2-methylimidazole and place in a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker. Ultrasonic dispersion for 30 min to obtain a uniform colorless solution A.

[0142] (2) Take 4.2 g of Zn(NO3)2·6H2O and place in a 100 mL beaker, add 80 mL of anhydrous methanol to the beaker, ultrasonic dispersion for 30 min to obtain a uniform solution B.

[0143] (3) First slowly pour the A solution into a 250 mL three-necked flask, then pour the B solution into the flask, stir at 25°C for 30 min, then add 70 mL of graphene oxide, continue to stir for 20 h, centrifugal and wash to obtain ZIF-8@GO.

[0144] (5) Under a nitrogen atmosphere, pyrolyze the ZIF-8@GO at a heating rate of 3°C / min to 900°C for 2 h to form porous S, N-C, then cool to room temperature at a cooling rate of 5°C / min.

[0145] (6) Take 100 mg of porous N-C and dissolve in 100 mL of ethanol, ultrasonic dispersion for 30 min to obtain a uniform solution C, take 5 mg of phenanthroline and 2 mg of FeCl2 and dissolve in 20 mL of ethanol to obtain solution D.

[0146] (7) First slowly pour the C solution into a 200 mL three-necked flask, then pour the D solution into the flask, stir at 25°C for 10 h to form Fe / N-C@Phen, centrifugal and wash with methanol three times, dry in a drying oven at 70°C overnight to obtain Fe / N-C@Phen powder sample.

[0147] (8) The Fe / N-C@Phen powder was placed in a quartz boat and heated to 500℃ at a rate of 2℃ / min in a nitrogen environment, and kept for 2h. The black powder obtained was cooled to room temperature, and the obtained solid was ground into fine powder to obtain a N-doped porous carbon supported Fe-N-C single-atom catalyst.

[0148] Catalyst performance detection

[0149] 5mg of the catalyst powder prepared in Examples 1-7 and Comparative Examples 1-2 was weighed, mixed with 250μL of water, 250μL of anhydrous ethanol and 25μL of a 0.05% Nafion solution, and ultrasonically dispersed to obtain a test solution. 2μL of the test solution was taken and deposited on a polished working electrode, and dried at room temperature to obtain a uniform black film. The ORR performance was then tested in 0.1M KOH, and the LSV curve was scanned at 5mV / s. At the same potential, the greater the half-wave potential and the kinetic current density, the better the catalytic activity. The test results are shown in Table 1. Figures 1-3

[0150] Conclusion analysis:

[0151] (1) Referring to Table 1, it can be seen that the catalyst prepared in the present application is superior to or close to the ORR commercial benchmark Pt / C catalyst, which proves that the catalyst prepared by the present application has good superiority and stability. Figure 1

[0152] At the same time, the single-atom catalysts prepared by different types of metals all show good catalytic performance. It can be proved that the preparation method provided by the present application is suitable for a variety of metals and has good universality.

[0153] (2) Referring to Table 1, it can be seen that the catalyst prepared by two-step pyrolysis is significantly better than the catalyst prepared by one-step pyrolysis. Figure 2

[0154] This is because in the one-step pyrolysis method, the doping of the metal and the anchoring of the single atom are completed simultaneously. Among them, the doping of the metal will affect the growth and synthesis of the MOF material, and different pyrolysis temperatures, feeding ratios, solvents and other conditions will simultaneously produce effects, causing complexity and uncertainty of the experiment. In the two-step pyrolysis, the synthesis of the MOF material and the doping and anchoring of the metal are carried out separately, avoiding the complexity of the experiment.

[0155] (3) Referring to Table 1, it can be seen that the catalyst prepared by two-step pyrolysis is significantly better than the catalyst prepared by one-step pyrolysis. Figure 3 ​​​From the experimental data of Comparative Example 1 and Comparative Example 4, it can be found that the doping of S species into the MOF material causes lattice distortion, changes the electron density, and thus changes the electronic structure and improves the catalytic performance.

[0156] (4) Refer to Figure 4 From the experimental data of Comparative Examples 1-4, it can be found that adjusting the pyrolysis temperature of the first stage has a significant effect on the catalytic performance of the catalyst. Among them, when the pyrolysis temperature is 900 DEG C, the catalyst shows the best catalytic performance.

[0157] This is because different pyrolysis temperatures will affect the carbonization process of the MOF material, and the melting point of zinc is 905 DEG C. Therefore, at a carbonization temperature of 900 DEG C, the sublimation and precipitation of zinc can be completed, and below 900 DEG C is not conducive to the sublimation of zinc, and above 900 DEG C will affect the graphitization degree of the carbon material.

[0158] (4) Refer to Figure 6 and Figure 7 , Figure 6 The spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the Fe single-atom catalyst prepared in Example 1. In the HAADF mode, the brightness of the atom is proportional to the 1.8th power of the atomic number, so the metal on the carbon-nitrogen carrier will be very bright, Figure 4 The small bright spots in the figure are single Fe atoms, indicating that the metal elements are atomically dispersed in the catalyst.

[0159] Figure 7 The spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the Fe catalyst prepared in Comparative Example 4. In the HAADF mode, the metal atoms form clusters and form metal nanoparticles, so the single-atom catalyst cannot be successfully synthesized.

[0160] This is because divalent iron, cobalt, nickel, etc. can form complexes with Phen and have a positive charge, while the N-C material formed by one-step pyrolysis has a negative charge, so the electrostatic adsorption between them is conducive to the combination of metal complexation and carbon material. Trivalent metals cannot form complexes and are prone to aggregation during pyrolysis, forming metal nanoparticles. Therefore, during preparation, divalent metal salts should be selected for the preparation of single-atom catalysts.

[0161] In summary, the method for synthesizing a single-atom catalyst provided by the present application has the following beneficial effects:

[0162] (1) The method of the present application is a general method that is effective for Fe, Cu, Co, Ni and other metals, solving the defect that other methods are only effective for one kind of metal.

[0163] (2) The precursor used in the application is dimethyl imidazole, zinc nitrate, thiourea, graphene oxide, a transition metal source (M), and phenanthroline, which has the advantages of cheap raw materials and low cost compared with other methods, and has cost advantages in practical application.

[0164] (3) The synthesis method of the application is simple and effective, and can be used for large-scale synthesis of single-atom catalysts, solving the problem of complex synthesis and difficulty in large-scale preparation of other existing technologies.

[0165] (4) The catalyst synthesized by the synthesis method of the application has excellent performance, in addition to good activity, it can also effectively improve the energy conversion efficiency of zinc-air batteries.

[0166] It should be noted that the above examples are only used to illustrate the technical solutions of the application and are not limiting, although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the application, which should be covered in the scope of the claims of the application.

Claims

1. A method for synthesizing a single-atom catalyst, characterized in that: include, Raw material mixing: Using dimethylimidazole, zinc nitrate, and graphene oxide as solutes and anhydrous methanol as solvent, ZIF-8@GO is formed by stirring. Sulfur doping: Using ZIF-8@GO and thiourea as solutes and anhydrous methanol as solvent, S / ZIF-8@GO is formed through stirring and adsorption. First stage pyrolysis: In a protective gas atmosphere, S / ZIF-8@GO is pyrolyzed to form porous sulfur-doped carbon, denoted as S and NC; Precursor preparation: After S and NC are cooled, phenanthroline Phen and transition metal source M are added to S and NC to form precursors M / S and NC@Phen; Second-stage pyrolysis: In a protective gas atmosphere, the M / S and NC@Phen precursors are pyrolyzed to obtain a single-atom catalyst; The transition metal source is one or more of FeCl2, CuCl2, CoCl2, and NiCl2; In the first stage of pyrolysis, the pyrolysis temperature is 800–1100℃, and the holding time is 1–3 hours; During sulfur doping, the mass ratio of thiourea to ZIF-8@GO is 3 to 5:

1. In the preparation of the precursor, the mass ratio of phenanthroline to transition metal source is 1:0.5-1.

2. The method for synthesizing a single-atom catalyst according to claim 1, characterized in that: The transition metal source is selected from one or more of Fe(II), Cu(II), Co(II), and Ni(II) metal salts.

3. The method for synthesizing a single-atom catalyst according to claim 1, characterized in that: During the mixing of the raw materials, the stirring temperature is 22-26℃ and the stirring time is 20h.

4. The method for synthesizing a single-atom catalyst according to claim 1, characterized in that: In the second stage of pyrolysis, the pyrolysis temperature is 400–600℃, and the temperature is maintained for 1–3 hours.

5. The method for synthesizing a single-atom catalyst according to claim 1, characterized in that: In the raw material mixture, the molar ratio of zinc nitrate to dimethylimidazole is 1:4 to 10.

6. A single-atom catalyst, characterized in that: It is prepared by the method described in any one of claims 1 to 5.

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