Transition metal single-atom catalyst for cathodic oxygen reduction reaction and preparation method thereof

Abstract

This invention provides a transition metal single-atom catalyst for the cathode oxygen reduction reaction and its preparation method, belonging to the field of catalyst and preparation technology. It solves the technical problems of existing transition metal single-atom catalysts, such as complex preparation methods, large particle size, easy aggregation, poor versatility, and inability to be mass-produced. The method involves adding p-phenylenediamine and 2-aminoterephthalic acid to water, stirring for several minutes to obtain a first solution, and simultaneously adding a transition metal source and zinc chloride to the first solution; after stirring and polymerization in an oil bath, a first suspension is obtained, which is then centrifuged and dried to obtain catalyst precursor one. Precursor one is then calcined under a nitrogen atmosphere to obtain catalyst precursor two. Finally, precursor two is acid-washed and dried to obtain the transition metal single-atom catalyst. This preparation method is simple, efficient, and highly versatile, suitable for high-consistency industrial mass production. The prepared catalyst is atomically dispersed, exhibiting good stability, good dispersibility, and good performance.

Description

Technical Field

[0001] This invention belongs to the field of catalyst and its preparation technology, specifically relating to a transition metal single-atom catalyst for cathode oxygen reduction reaction and its preparation method. Background Technology

[0002] Since Academician Zhang Tao of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, synthesized isolated Pt atom catalysts anchored on the surface of iron oxide nanoparticles in 2011, single-atom catalysis has become a major research hotspot in energy catalysis. Meanwhile, due to their near-100% atom utilization efficiency and tunable electronic structure, single-atom catalysts exhibit high activity in various energy conversion reactions, especially oxygen reduction reactions. (B.Qiao, A.Wang, X.Yang, L.Allard, Z.Jiang, Y.Cui, J.Liu, J.Li, T.Zhang; Single-atom catalysis of CO oxidation using Pt1 / FeO) x(Nature Chemistry, 2011, 3, 634-641). In recent years, ORR reaction catalysts have been widely used in metal-air batteries and fuel cells. Due to the sluggish kinetics of the oxygen reduction reaction, noble metal platinum-based catalysts are commonly used, but this also leads to high costs. Therefore, researchers are looking for alternatives to platinum-based catalysts. Among them, transition metal single-atom catalysts have been widely studied due to their high catalytic activity, low cost, and high stability. In addition, they are superior to platinum-based catalysts in terms of poisoning resistance. (K. Song, Y. Feng, W. Zhang, W. Zheng; MOFsfertilized transition-metallic single-atom electrocatalysts for highly-efficient oxygen reduction: Spreading the synthesis strategies and advanced identification; Journal of Energy Chemistry, 2022, 67, 391-422). However, in the process of preparing single-atom catalysts, the metal particles shrink, and the specific surface free energy of the metal surface increases sharply, which makes it easy for transition metal catalysts to agglomerate during preparation. Therefore, there are still some difficulties in preparing highly loaded and high-performance transition metal atom catalysts. Currently, most synthesis of transition metal single-atom catalysts is based on metal-organic frameworks (MOFs). MOFs provide highly dispersed metal sites, making them ideal precursors or templates for preparing transition metal single-atom catalysts. Compared to other MOFs, zinc-rich zeolite imidazole ester frameworks (ZIF-8) have the potential to support MN4 groups as key structural elements, making them particularly attractive for achieving high-density MN4 sites in catalysts obtained using a one-step high-temperature thermal activation method (H. Zhang, H.T. Chung, D.A. Dullen, S. Wagner, I.U. Kramm, K.L. More, P. Zelenay, G. Wu; High-performance fuel cell cathodes exclusively containing atomically dispersed iron active sites; Energy & Environmental Science, 2019 12 2548-2558). Professor Gang Wu's research group at the State University of New York at Buffalo has chemically doped ZIF-8 precursors by replacing a small portion of the Zn ions with Fe ions.Then, by adjusting and optimizing the Fe content, a model Fe-NC catalyst with atomically dispersed and nitrogen-coordinated FeN4 sites was successfully synthesized. These sites were uniformly dispersed in the partially graphitized carbon phase and did not form any iron-rich aggregates (H. Zhang, HT Chung, DACullen, S. Wagner, UI Kramm, KL More, P. Zelenay, G. Wu; High-performance fuel cell cathodes exclusively containing atomically dispersed iron active sites; Energy Environmental Science, 2019 12 2548-2558). Professor Wang Dingsheng's research group at Tsinghua University successfully prepared a highly active cobalt single-atom catalyst by pyrolyzing ZIF-8 followed by adsorption of metallic cobalt (Co) (Y.Chen,R.Gao,S.Ji,H.Li,K.Tang,P.Jiang,H.Hu,Z.Zhang,H.Hao,Q.Qu,X.Liang,W.Chen,J.Dong,D.Wang,Y.Li; Atomic-Level Modulation of Electronic Density at Cobalt Single-Atom Sites Derived from Metal-Organic Frameworks: Enhanced Oxygen Reduction Performance; Angew Chem Int Ed,2021 60(6)3212-3221). Furthermore, the morphology and structure of the catalyst can be controlled through a template strategy to further optimize its activity. Polystyrene spheres (PS) are a commonly used organic template and a good precursor for constructing ordered mesoporous structures. Studies have shown that electrocatalytic activity mainly depends on the intrinsic activity of the catalytic sites and the number of catalytic sites. The construction of ordered hierarchical porous structures is crucial for increasing the number of catalytic sites. Mesopores facilitate mass transfer and improve the accessibility of active sites, while micropores can accommodate active sites and increase site density, thereby achieving high catalytic activity (Z. Zhang, M. Dou, H. Liu, L. Dai, F. Wang; A Facile Route to Bimetal and Nitrogen-Codoped 3D Porous Graphitic Carbon Networks for Efficient Oxygen Reduction; Small, 2016 12 4193).Professor Wang Shuangyin's research group at Hunan University prepared atomically dispersed FeN4-doped ordered mesoporous carbon using a dual-solvent induced heterogeneous nucleation and polystyrene sphere template method. The resulting iron single-atom catalyst possessed a 3D interconnected hierarchical porous carbon framework. The introduction of polystyrene spheres effectively protected the Fe-doped ZIF-8 crystal, preventing the collapse of the ZIF-8 structure and the aggregation of single-atom sites during pyrolysis (M.Qiao, Y.Wang, Q.Wang, G.Hu, X.Mamat, S.Zhang, S.Wang; Hierarchically Ordered Porous Carbon with Atomically Dispersed FeN4 for Ultraefficient Oxygen Reduction Reaction in Proton-Exchange MembraneFuel Cell; Angew Chem Int Ed, 2020 59 2688). Professor Liu Junfeng's research at Beijing University of Chemical Technology yielded a single-atom manganese (Mn) catalyst via one-step pyrolysis of the precursor Mn(CH3COO)2@ZIF-8. The pyrolyzed catalyst maintained the dodecahedral morphology of ZIF-8 (X.Han,T.Zhang,W.Chen,B.Dong,G.Meng,L.Zheng,C.Yang,X.Sun,Z.Zhuang,D.Wang,A.Han,J.Liu; Mn-N4 Oxygen Reduction Electrocatalyst:OperandoInvestigation of Active Sites and High Performance in Zinc–Air Battery;Advanced Energy Materials,2021 11 2002753). Although MOFs have made significant breakthroughs in the preparation of single-atom catalysts, several problems remain to be solved. First, structural instability, which leads to structural collapse during pyrolysis. Second, the synthesis methods are complex and polluting, especially since precursor preparation typically requires organic solvents. Furthermore, the preparation of highly loaded single-atom catalysts still faces significant challenges. Therefore, developing a convenient, rapid, universal, and easily scalable method for synthesizing high-site-density single-atom catalysts is of great importance for the development of fuel cells and zinc-air batteries. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problems in the prior art of preparing transition metal single-atom catalysts, such as poor stability, easy aggregation of the formed single atoms, and complex preparation methods, poor universality, and inability to mass-produce the catalysts. The invention provides a transition metal single-atom catalyst for the cathode oxygen reduction reaction and its preparation method.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows.

[0005] This invention provides a method for preparing a transition metal single-atom catalyst for the cathode oxygen reduction reaction, comprising:

[0006] Step 1: Disperse the transition metal salt and o-phenanthroline evenly in water to obtain the first solution;

[0007] Step 2: Add zinc chloride to water and sonicate to obtain a second solution;

[0008] Step 3: Add p-phenylenediamine and 2-aminoterephthalic acid solid to a container, add water, and stir under oil bath conditions to obtain the third solution;

[0009] Step 4: Add the second solution to the third solution, and simultaneously add the first solution. Maintain the oil bath, stir and polymerize, centrifuge and dry to obtain catalyst precursor 1.

[0010] Step 5: Calcine the catalyst precursor 1 to obtain the catalyst precursor 2;

[0011] Step 6: The catalyst precursor No. 2 is acid-washed in hydrochloric acid solution, filtered and dried after acid washing to obtain the transition metal single-atom catalyst for the cathode oxygen reduction reaction.

[0012] Preferably, in step one, the transition metal salt is a nitrate, chloride, acetate, or sulfate.

[0013] Preferably, the molar ratio of the transition metal salt and o-phenanthroline in step one is 1:1 to 4:1.

[0014] Preferably, the ratio of zinc chloride (g) to deionized water (mL) added in step two is 1–3:20.

[0015] Preferably, the molar ratio of p-phenylenediamine to 2-aminoterephthalic acid added in step three is 1:1.

[0016] Preferably, in step three, the stirring temperature is 80–100°C and the stirring time is 3–5 minutes.

[0017] Preferably, in step four, the polymerization temperature is 80–100°C and the polymerization time is 12–24 h.

[0018] Preferably, the calcination temperature in step five is 800–1000°C, and the heating rate is 5°C / min.

[0019] Preferably, the pickling temperature in step six is ​​60–80°C, and the pickling time is 8–12 hours.

[0020] The present invention also provides a transition metal single-atom catalyst prepared by the above preparation method, wherein the metal element in the transition metal single-atom catalyst is in a monodisperse state.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention provides a transition metal single-atom catalyst for the cathode oxygen reduction reaction and its preparation method. The method involves coordinating a transition metal salt with o-phenanthroline, followed by polymerization with p-phenylenediamine and 2-aminoterephthalic acid. This invention avoids the use of organic solvents, thus preventing environmental pollution, and successfully prepares a transition metal single-atom catalyst without utilizing MOFs, saving costs. The prepared catalyst exhibits good stability and monodispersity; furthermore, compared with existing commercial platinum black catalysts, this catalyst demonstrates superior oxygen reduction activity and stability.

[0023] The preparation method of the transition metal single-atom catalyst of the present invention is simple, environmentally friendly and highly universal, suitable for large-scale industrial production, and lays a solid foundation for the mass production of transition metal single-atom catalysts. Attached Figure Description

[0024] Figure 1 The image is a transmission electron microscope (TEM) image of the iron single-atom catalyst prepared in Example 1 of this invention under a 200 nm scale.

[0025] Figure 2 Transmission electron microscopy (TEM) image of the iron single-atom catalyst prepared in Example 1 of the present invention after 10000 CV in the electrochemical stability test at a scale of 200 nm.

[0026] Figure 3 This is a high-resolution transmission electron microscope (HRTEM) image of the iron single-atom catalyst prepared in Example 1 of the present invention under a 2 nm scale.

[0027] Figure 4 High-resolution transmission electron microscopy (HRTEM) image of the iron single-atom catalyst prepared in Example 1 of this invention after 10000 CV in the electrochemical stability test at a 2 nm scale.

[0028] Figure 5 The X-ray diffraction (XRD) pattern of the iron single-atom catalyst prepared in Example 1 of this invention;

[0029] Figure 6 The oxygen reduction LSV curves of the iron single-atom catalyst prepared in Example 1 of this invention and Pt / C in 0.1 MkOH electrolyte are shown. Detailed Implementation

[0030] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with specific embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention and not for limiting the claims of the present invention.

[0031] This invention provides a method for preparing a transition metal single-atom catalyst for the cathode oxygen reduction reaction, comprising:

[0032] Step 1: At room temperature, the transition metal salt and o-phenanthroline are uniformly dispersed in water to obtain the first solution;

[0033] The transition metal salt is preferably a nitrate, chloride, acetate, or sulfate; the transition metal is preferably iron, cobalt, nickel, chromium, manganese, copper, or zinc. The transition metal salt solution is uniformly dispersed in water by first mixing o-phenanthroline with water, then sonicating for 15 minutes, and finally adding the transition metal salt and continuing sonication to ensure uniform dispersion. The water used is deionized water, and the molar ratio of the metal salt to o-phenanthroline is preferably 1:1 to 4:1, with the metal element concentration preferably being 0.5 to 4 mg / mL.

[0034] Step 2: Add zinc chloride to water and sonicate to obtain a second solution;

[0035] The ratio of zinc chloride (g) to deionized water (mL) is 1-3:20, and the preferred ultrasonic time is 15 minutes.

[0036] Step 3: Add p-phenylenediamine and 2-aminoterephthalic acid solid to a round-bottom flask, add water, and stir under oil bath conditions to obtain the third solution;

[0037] The preferred molar ratio of p-phenylenediamine to 2-aminoterephthalic acid is 1:1, with masses of 1.08 g and 1.81 g respectively. The added water is 200-300 mL. The preferred stirring temperature is 80-100°C, and the preferred stirring time is 3-5 minutes.

[0038] Step 4: Add the second solution to the third solution, and simultaneously add the first solution. Maintain the oil bath, stir and polymerize, centrifuge and dry to obtain catalyst precursor 1.

[0039] The preferred oil bath polymerization temperature is 80–100°C, the preferred polymerization time is 12–24 h, and the preferred volume ratio of the first solution, the second solution, and the third solution is 1–2:5:50.

[0040] Step 5: Calcine the catalyst precursor 1 to obtain the catalyst precursor 2;

[0041] The preferred calcination temperature is 800–1000℃, the preferred calcination time is 2 h, the preferred reaction atmosphere is Ar or N2, and the preferred heating rate is 5℃ / min.

[0042] Step 6: Wash the catalyst precursor No. 2 in hydrochloric acid solution, filter and dry after washing to obtain the transition metal single-atom catalyst.

[0043] The pickling temperature is preferably 60–80℃; the pickling time is preferably 8–12 h.

[0044] The present invention also provides a transition metal single-atom catalyst prepared by the above preparation method, wherein the metal element of the transition metal catalyst is in a monodisperse state.

[0045] The raw materials used in the following examples are all analytical grade, commercially available conventional chemicals, and do not require further processing.

[0046] Example 1

[0047] At room temperature, a complex solution of iron salt and o-phenanthroline was first prepared: 386.16 mg o-phenanthroline and 207.93 mg ferrous sulfate heptahydrate were dispersed in 20 mL of water and sonicated to obtain iron source solution 1. Then, 1.5 g zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g p-phenylenediamine and 1.81 g 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 80 °C for 3 minutes. Subsequently, 2 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 80 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 1000 °C under a nitrogen atmosphere for 2 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final iron single-atom catalyst.

[0048] Transmission electron microscopy was performed on the single-atom metallic iron catalyst of Example 1, and the results were as follows: Figure 1 and Figure 3 As shown in the figure, no particles were observed. Simultaneously, the stability of the metallic iron single-atom catalyst in Example 1 was tested (10,000 CV cycles) and observed using transmission electron microscopy. Figure 2 and Figure 4 As shown, no particle aggregation was observed.

[0049] X-ray analysis was performed on the metallic iron single-atom catalyst of Example 1, and the results are as follows: Figure 5 As shown, the XRD results indicate that only carbon diffraction peaks were observed in the prepared single-atom iron catalyst. No diffraction peaks of iron carbides, nitrides, or metal-metal were observed, indicating that the metal atoms did not agglomerate to form particles.

[0050] Electrochemical tests were performed on the single-atom metallic iron catalyst of Example 1, and the results are as follows: Figure 6 As shown in the LSV curve, the prepared metallic iron single-atom catalyst exhibits excellent performance, surpassing that of commercial Pt / C catalysts.

[0051] Example 2

[0052] At room temperature, a complex solution of cobalt salt and o-phenanthroline was first prepared: 386.16 mg o-phenanthroline and 132.39 mg cobalt acetate were dispersed in 20 mL of water and sonicated to obtain cobalt source solution 1. Then, 2 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 90 °C for 5 minutes. Subsequently, 2 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 90 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 1000 °C under a nitrogen atmosphere for 2 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final cobalt single-atom catalyst.

[0053] The cobalt single-atom catalyst of Example 2 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0054] Example 3

[0055] At room temperature, a complex solution of nickel chloride and o-phenanthroline was first prepared: 386.16 mg o-phenanthroline and 97.3 mg nickel chloride were dispersed in 20 mL of water and sonicated to obtain nickel source solution 1. Then, 2 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 80 °C for 3 minutes. Subsequently, 2 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 80 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 900 °C under a nitrogen atmosphere for 2 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final nickel single-atom catalyst.

[0056] The nickel single-atom catalyst of Example 3 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0057] Example 4

[0058] At room temperature, a complex solution of manganese salt and o-phenanthroline was first prepared: 386.16 mg o-phenanthroline and 189.63 mg manganese sulfate monohydrate were dispersed in 20 mL of water and sonicated to obtain manganese source solution 1. Then, 2 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 80 °C for 3 minutes. Subsequently, 2 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 80 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 1000 °C under a nitrogen atmosphere for 1 h. Finally, the pyrolysis product was acid-washed in a water bath at 80 °C for 8 h and dried to obtain the final manganese single-atom catalyst.

[0059] The single-atom manganese catalyst of Example 4 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0060] Example 5

[0061] At room temperature, a complex solution of iron salt and o-phenanthroline was first prepared: 386.16 mg o-phenanthroline and 202.17 mg ferric chloride hexahydrate were dispersed in 20 mL of water and sonicated to obtain iron source solution 1. Then, 2 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 80 °C for 3 minutes. Subsequently, 2 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 80 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 900 °C under a nitrogen atmosphere for 2 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final iron single-atom catalyst.

[0062] The single-atom iron catalyst of Example 5 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0063] Example 6

[0064] At room temperature, a complex solution of iron salt and o-phenanthroline was first prepared: 386.16 mg o-phenanthroline and 264.03 mg ferric acetylacetone were dispersed in 20 mL of water and sonicated to obtain iron source solution 1. Then, 2 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 80 °C for 3 minutes. Subsequently, 2 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 80 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 900 °C under a nitrogen atmosphere for 2 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final iron single-atom catalyst.

[0065] The single-atom iron catalyst of Example 6 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0066] Example 7

[0067] At room temperature, a complex solution of cobalt salt and o-phenanthroline was first prepared: 386.16 mg o-phenanthroline and 115.9 mg cobalt sulfate were dispersed in 20 mL of water and sonicated to obtain iron source solution 1. Then, 2 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 90 °C for 3 minutes. Subsequently, 3 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 90 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 900 °C under a nitrogen atmosphere for 2 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final cobalt single-atom catalyst.

[0068] The cobalt single-atom catalyst of Example 7 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0069] Example 8

[0070] At room temperature, a complex solution of iron salt and o-phenanthroline was first prepared: 514.88 mg o-phenanthroline and 202.17 mg ferric chloride hexahydrate were dispersed in 20 mL of water and sonicated to obtain iron source solution 1. Then, 2 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 80 °C for 3 minutes. Subsequently, 2 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 80 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 1000 °C under a nitrogen atmosphere for 1 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final iron single-atom catalyst.

[0071] The single-atom iron catalyst of Example 8 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0072] Example 9

[0073] At room temperature, a complex solution of iron salt and o-phenanthroline was first prepared: 514.88 mg of o-phenanthroline and 202.17 mg of ferric chloride hexahydrate were dispersed in 20 mL of water and sonicated to obtain iron source solution 1. Then, 3 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 90 °C for 3 minutes. Subsequently, 3 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 90 °C for 20 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 1000 °C under a nitrogen atmosphere for 1 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final iron single-atom catalyst.

[0074] The single-atom iron catalyst of Example 9 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0075] Example 10

[0076] At room temperature, a complex solution of iron salt and o-phenanthroline was first prepared: 386.16 mg o-phenanthroline and 404.34 mg ferric chloride hexahydrate were dispersed in 20 mL of water and sonicated to obtain iron source solution 1. Then, 3 g of zinc chloride was added to 20 mL of water and sonicated to obtain solution 2. 1.08 g of p-phenylenediamine and 1.81 g of 2-aminoterephthalic acid were added to a round-bottom flask, followed by 200 mL of water, and the mixture was heated and stirred at 100 °C for 3 minutes. Subsequently, 2 mL of solution 1 and all of solution 2 were added. The polymerization reaction was carried out under stirring in an oil bath at 100 °C for 24 h, followed by centrifugation with deionized water and drying. The resulting solid product was then calcined at 950 °C under a nitrogen atmosphere for 2 h. Finally, the pyrolysis product was acid-washed in a water bath at 60 °C for 8 h and dried to obtain the final iron single-atom catalyst.

[0077] The single-atom iron catalyst of Example 10 was characterized by transmission electron microscopy, XRD and electrochemical tests, and the results were similar to those of Example 1.

[0078] Obviously, the above embodiments are merely illustrative examples for clarity, and other variations or modifications can be made based on the above description. Therefore, obvious variations or modifications derived therefrom still fall within the protection scope of this invention.

[0079] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a transition metal single-atom catalyst for the cathode oxygen reduction reaction, characterized in that, include: Step 1: Disperse the transition metal salt and o-phenanthroline evenly in water to obtain the first solution; Step 2: Add zinc chloride to water and sonicate to obtain a second solution; Step 3: Add p-phenylenediamine and 2-aminoterephthalic acid solid to a container, add water, and stir under oil bath conditions to obtain the third solution; Step 4: Add the second solution to the third solution, and simultaneously add the first solution. Maintain the oil bath, stir and polymerize, centrifuge and dry to obtain catalyst precursor 1. Step 5: Calcine the catalyst precursor 1 to obtain the catalyst precursor 2; Step 6: The catalyst precursor No. 2 is acid-washed in hydrochloric acid solution, filtered and dried after acid washing to obtain the transition metal single-atom catalyst for the cathode oxygen reduction reaction. In step one, the transition metal is iron, cobalt, nickel, chromium, manganese, copper, or zinc; In step four, the polymerization temperature is 80~100℃ and the polymerization time is 12~24 h.

2. The method for preparing a transition metal single-atom catalyst for cathode oxygen reduction reaction according to claim 1, characterized in that, In step one, the transition metal salt is a nitrate, chloride, acetate, or sulfate.

3. The method for preparing a transition metal single-atom catalyst for cathode oxygen reduction reaction according to claim 1, characterized in that, In step one, the molar ratio of transition metal salt to o-phenanthroline is 1:1 to 4:

1.

4. The method for preparing a transition metal single-atom catalyst for cathode oxygen reduction reaction according to claim 1, characterized in that, The mass of zinc chloride in step two is: the volume of deionized water is (1~3) g: 20 mL.

5. The method for preparing a transition metal single-atom catalyst for cathode oxygen reduction reaction according to claim 1, characterized in that, The molar ratio of p-phenylenediamine to 2-aminoterephthalic acid added in step three is 1:

1.

6. The method for preparing a transition metal single-atom catalyst for cathode oxygen reduction reaction according to claim 1, characterized in that, In step three, the stirring temperature is 80~100℃ and the stirring time is 3~5 minutes.

7. The method for preparing a transition metal single-atom catalyst for cathode oxygen reduction reaction according to claim 1, characterized in that, In step five, the calcination temperature is 800~1000℃, and the heating rate is 5℃ / min.

8. The method for preparing a transition metal single-atom catalyst for cathode oxygen reduction reaction according to claim 1, characterized in that, In step six, the pickling temperature is 60~80℃ and the pickling time is 8~12 h.

9. The transition metal single-atom catalyst prepared by the method according to claim 1, characterized in that, In this transition metal single-atom catalyst, the metal elements are in a monodisperse state.

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