A (MnO2) cluster Process for the preparation of / Fe,Mn-N-C catalysts and use thereof

Abstract

The application relates to a (MnO2) cluster Preparation method of / Fe,Mn-N-C catalyst and application thereof, the preparation method comprises the following steps: glycine and dicyanediamine are used as organic ligands to perform a coordination reaction with manganese salt and iron salt, FeMn-Precursor powder is obtained through drying; the FeMn-Precursor powder is calcined under an inert atmosphere, and the calcined powder is ground to obtain FeMn-complex; the FeMn-complex is subjected to acid pickling and water washing, and is calcined again under an inert atmosphere after drying, so that the (MnO2) cluster / Fe,Mn-N-C catalyst is obtained. In the application, the interaction between Fe and Mn can retain more metal active sites, and the MnO2 cluster can regulate the electronic structure of the metal active sites around the cluster, so that the catalyst has extremely high oxygen reduction reaction electrocatalytic activity, stability, methanol resistance and excellent zinc-air battery performance.

Description

Technical Field

[0001] The present invention relates to the field of non-precious metal catalysts; more specifically, to a preparation method and application of nitrogen-doped carbon NC-loaded MnO2 nanoclusters and Fe and Mn single-atom catalysts. Background Art

[0002] Nowadays, efficient, green, and sustainable catalytic technologies have become one of the keys to the development of the chemical industry. Among them, single-atom catalysts (SACs), as a new type of catalytic material, have attracted much attention due to their high atom utilization, tunable electronic structure, and unique catalytic properties.

[0003] However, single-component single-atom catalysts often find it difficult to meet the diverse needs of complex reaction systems. Therefore, regulating and optimizing catalytic performance by introducing a second single-atom component has become a research hotspot in the current field of catalytic science. Dual Atom Catalysts (DACs) are an emerging research direction in the field of catalytic science in recent years. DACs exhibit excellent performance in catalytic chemical reactions due to their unique atomic-level dispersion and dual catalytic active sites. DACs not only combine the high atomic utilization and catalytic activity of SACs, but also achieve multiple regulation and optimization of catalytic functions by introducing a second single-atom component. Depending on the different bimetallic structures in DSACs, the bimetallic sites in DACs can be divided into two separated heterometallic sites, two connected homometallic sites, and two connected heterometallic sites.

[0004] In recent years, the introduction of clusters to regulate single-atom catalysts has become a research hotspot in the field of catalysis science. It combines the advantages of single-atom catalysis and cluster regulation, providing a new path for efficient and green chemical reactions. First, the research background of cluster-regulated single-atom catalysts stems from the limitations of traditional catalysts and the rise of single-atom catalysts. Traditional catalysts often have problems such as unclear active sites, low catalytic efficiency, and insufficient stability. Single-atom catalysts achieve atomic-level control of active sites by dispersing metal atoms on a support, thereby improving the activity and selectivity of the catalyst. However, the preparation and stability of single-atom catalysts still face challenges, and there is a scaling relationship limit (SRL) problem. The introduction of cluster regulation strategies provides new possibilities for the performance optimization of single-atom catalysts. At the same time, the study of cluster-regulated single-atom catalysts also helps to gain a deeper understanding of the structure-activity relationship of catalysts, reveal the intrinsic mechanism of catalytic reactions, and provide theoretical support for the design and development of new catalysts.

[0005] The Chinese invention patent application No. CN202310911323.5 submitted by the applicant discloses a Mncluster / Mn DAC The invention discloses a preparation method of a MnO / Mn-NC catalyst, which comprises the following steps: reacting glycine with manganese chloride to form a complex, and drying to obtain a Glycine-MnCl2 powder; calcining the Glycine-MnCl2 powder under an inert atmosphere, and grinding the calcined powder to obtain MnO / Mn-NC; acid-washing and water-washing the MnO / Mn-NC, and then drying to obtain a MnO / Mn-NC catalyst. DAC -NC powder; Mn DAC -NC powder was calcined again under inert atmosphere to obtain Mn cluster / Mn DAC -NC catalyst, in which Mn cluster Clusters and Mn DAC Double single atoms are dispersed on nitrogen-doped carbon support NC.

[0006] Although the Mn cluster / Mn DAC -NC catalyst has good electrocatalytic activity, stability and methanol tolerance for ORR reaction, but there is still room for further optimization. The present invention is an improvement based on the above-mentioned prior application. Summary of the Invention

[0007] The main purpose of the present invention is to provide a preparation method and application of a catalyst containing MnO2 clusters and Fe, Mn single atoms, wherein the MnO2 clusters and Fe, Mn single atoms are dispersed on a nitrogen-doped carbon support NC with a high specific surface area, and have extremely high electrocatalytic activity, stability and methanol resistance for the ORR reaction, and at the same time exhibit excellent performance in zinc-air batteries.

[0008] In order to achieve the above main purpose, the present invention discloses a (MnO2) cluster A method for preparing a Fe, Mn-NC catalyst comprises the following steps:

[0009] (1) Glycine and dicyandiamide are used as organic ligands to react with manganese salt and iron salt, and then dried to obtain FeMn-Precursor powder;

[0010] (2) calcining the FeMn-Precursor powder under an inert atmosphere and grinding the calcined powder to obtain the FeMn-complex;

[0011] (3) The FeMn-complex is acid-washed and water-washed, dried and then calcined again under an inert atmosphere to obtain the (MnO2) cluster / Fe,Mn-NC catalyst, in which MnO2 clusters and Fe, Mn single atoms are dispersed on the nitrogen-doped carbon support NC.

[0012] In the above technical solution, Fe and Mn each play different roles in the catalyst material and jointly optimize and regulate the catalyst structure: Fe is the main source for regulating the catalyst's specific surface area and increasing the nitrogen content in the catalyst, while Mn is the main source of defects in the catalyst material. The interaction between Fe and Mn can retain more metal active sites in the catalyst. At the same time, the introduction of MnO2 clusters into the catalyst can regulate the electronic structure of the metal active sites surrounding the clusters, further controlling the adsorption strength of the adsorbate, resulting in the catalyst having extremely high electrocatalytic activity, stability, and methanol tolerance for the ORR reaction.

[0013] According to a specific embodiment of the present invention, in step (1), glycine, dicyandiamide, manganese salt and iron salt are coordinated in a molar ratio of 2:2:1:1.

[0014] Furthermore, in step (1), glycine, dicyandiamide, manganese salt and iron salt are first ultrasonically dispersed in an alcohol-water mixed solution, and then heated to 60-90° C. and stirred and dried to obtain FeMn-Precursor powder.

[0015] Preferably, the alcohol-water mixed solution is a mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is less than 1.

[0016] Preferably, the manganese salt and the iron salt are manganese chloride and ferric chloride, respectively.

[0017] Furthermore, the calcination temperature in step (2) is 850-950° C., and the holding time is 1-3 h; the calcination temperature in step (3) is 850-950° C., and the holding time is 1-3 h.

[0018] According to a specific embodiment of the present invention, the calcination temperature in step (2) and step (3) is 900°C, and the holding time is 2 hours. The calcination temperature and holding time in step (2) and step (3) are consistent, which is beneficial for maintaining the uniformity and structural stability of the carbon material. Furthermore, when calcined at this temperature, the degree of graphitization and defect level of the carbon support are moderate, which is beneficial for anchoring the active sites and maintaining the stability of the catalyst material.

[0019] According to a specific embodiment of the present invention, in step (3), the FeMn-complex is acid-washed at room temperature using an HCl solution with a concentration of 0.5 to 1.5 mol / L, so that the nanoparticles in the catalyst can be washed away while retaining the active sites to the greatest extent.

[0020] The present invention also discloses (MnO2) obtained by the above preparation method cluster Application of / Fe,Mn-NC catalysts in ORR reaction.

[0021] As described in detail below, the technical solution of the present invention has the following beneficial effects:

[0022] 1. In the present invention, the addition of a Mn source helps to increase the degree of defects in the material. The more defect sites, the more metal active sites. The addition of an Fe source helps to increase the nitrogen content in the catalyst. N is a species directly associated with the active sites in the catalyst. The higher the nitrogen content, the more metal active sites that can be anchored. At the same time, the amino group in glycine and dicyandiamide provide a rich nitrogen source to form the single-atom structure of FeN4 and MnN4. The oxygen in the carboxyl group of glycine is the key to the formation of MnO2 clusters.

[0023] 2. In the present invention, the addition of Fe source is also beneficial to increase the specific surface area of ​​the material, which is conducive to the full exposure of active sites, especially the carbon support forms an amorphous porous carbon nanosheet structure, and the pore types mainly exist in the form of micropores and mesopores. Micropores are conducive to the distribution of more active sites, and mesopores are conducive to the mass transfer of ORR intermediates, thereby improving the catalyst performance.

[0024] 3. In the present invention, MnO2 clusters and Fe and Mn single atoms are highly dispersed on the nitrogen-doped carbon support NC. The MnO2 clusters are primarily formed through the secondary calcination in step (3). The MnO2 clusters regulate the surrounding Fe and Mn single atoms, reducing the reaction energy barrier of the catalyst during the oxygen reduction reaction. This results in the catalyst having excellent electrocatalytic activity, stability, and methanol tolerance for the ORR reaction. The stability, in particular, is significantly superior to that of the prior application. Zinc-air batteries assembled using this catalyst also exhibit superior performance compared to the prior application.

[0025] In order to more clearly illustrate the purpose, technical solutions and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 In: a is the FT-IR image of the FeMn-Precursor, Fe-Precursor, and Mn-Precursor precursor powders in Example 1, Comparative Example 2, and Comparative Example 3; b is the FT-IR image of the (MnO2) precursor powders in Example 1, Comparative Example 2, and Comparative Example 3. cluster / XRD patterns of Fe,Mn-NC, Fe-NC, and Mn-NC catalysts;

[0027] Figure 2 In: ab is Example 1 (MnO2) cluster / Fe,Mn-NC catalyst SEM images; cf is its TEM image; gk is its element mapping distribution map;

[0028] Figure 3 In: a is the Mn obtained in Example 7 cluster / Mn DAC -SEM images of NC catalyst, bc are its STEM images;

[0029] Figure 4 In: a is the Mn obtained in Example 7 cluster / Mn DAC -element mapping distribution diagram of NC catalyst, b its spherical aberration electron microscope image;

[0030] Figure 5 Where: a is (MnO2) obtained in Example 1 cluster / Fe, Mn-NC catalyst spherical aberration electron microscopy image; b is the corresponding electron energy loss spectrum (EELS);

[0031] Figure 6 In: ad are FeMn-complex and (MnO2) prepared in Example 1 and Comparative Examples 1-3 respectively. cluster / Nitrogen adsorption-desorption curves and pore size distribution of Fe,Mn-NC, Fe-NC, and Mn-NC catalysts;

[0032] Figure 7 (MnO2) obtained in Example 1, Comparative Example 2 and Comparative Example 3 cluster / Raman images of Fe,Mn-NC, Fe-NC, and Mn-NC catalysts;

[0033] Figure 8 (MnO2) obtained in Example 1 cluster Fourier transform EXAFS spectra of Fe (a) and Mn (b) of / Fe,Mn-NC catalyst;

[0034] Figure 9 The Mn obtained in Comparative Example 7 cluster / Mn DAC -Fourier transform EXAFS spectrum of Mn of NC catalyst;

[0035] Figure 10a 1 is a comparison diagram of the linear sweep voltammetry (LSV) curves of Example 1, Comparative Examples 2 to 6 and a commercial Pt / C catalyst;

[0036] Figure 10b The catalyst (MnO2) obtained in Example 1 cluster Comparison of chronoamperometric curves (it) of / Fe,Mn-NC and commercial Pt / C catalysts;

[0037] Figure 10c The catalyst (MnO2) obtained in Example 1 clusterComparison of the chronoamperometric curves (it) of the methanol crossover effect of Fe,Mn-NC and commercial Pt / C catalysts;

[0038] Figure 10d The catalyst (MnO2) obtained in Example 1 cluster LSV comparison of Fe, Mn-NC and commercial Pt / C catalysts before and after 10,000 CV cycles;

[0039] Figure 11 a is the Mn obtained in Comparative Example 7 cluster / Mn DAC -Comparison of chronoamperometric curves (it) of NC catalyst and commercial Pt / C catalyst; Figure 11 b is the LSV comparison diagram of the two before and after 10,000 CV cycles;

[0040] Figure 12 In: a is Example 1 (MnO2) cluster The open circuit voltage diagram of the zinc-air battery assembled with / Fe,Mn-NC and commercial Pt / C+RuO2 catalyst, b is a comparison diagram of its power density; cd are comparison diagrams of its charge and discharge cycle stability;

[0041] Figure 13 In: a is the Mn obtained in Example 7 cluster / Mn DAC -NC and commercial Pt / C+RuO2 catalyst assembled zinc-air battery open circuit voltage diagram, b is a comparison diagram of its power density; cd are comparison diagrams of its charge and discharge cycle stability. DETAILED DESCRIPTION

[0042] An embodiment of the present invention provides a method for preparing a MnO2 nanocluster and Fe, Mn single-atom catalyst. In the catalyst obtained by the preparation method, Mn is highly dispersed in the form of MnO2 nanoclusters and Mn single atoms in a nitrogen-doped carbon nanosheet carrier with a rich specific surface area, and Fe is highly dispersed in the carrier in the form of Fe single atoms. The MnO2 nanoclusters and the surrounding Fe and Mn single atoms cooperate with each other, so that the catalyst has extremely high electrocatalytic activity, stability and methanol resistance.

[0043] Exemplarily, the preparation method of the embodiment of the present invention includes the following steps:

[0044] (1) Make glycine and dicyandiamide react with manganese salt and iron salt, and obtain FeMn-Precursor powder after drying.

[0045] Specifically, glycine, dicyandiamide, manganese chloride tetrahydrate, and ferric chloride hexahydrate can be first ultrasonically dispersed uniformly in an alcohol-water mixed solution at a predetermined molar ratio (for example, 2:2:1:1), and then stirred and reacted at 60-90°C and dried to obtain a gray-brown FeMn-Precursor powder; wherein the alcohol-water mixed solution can be a mixed solution of ethanol and water, and the volume ratio of ethanol to water is preferably less than 1 (for example, 4:5).

[0046] ⑵ calcining the FeMn-Precursor powder under an inert atmosphere (such as N2), and grinding the calcined powder to obtain the FeMn-complex;.

[0047] (3) The FeMn-complex is pickled (for example, with a 0.5-1.5 mol / L HCI solution at room temperature) and washed with water, and then the powder obtained after drying is calcined again under an inert atmosphere to obtain (MnO2) cluster / Fe,Mn-NC catalyst, in which MnO2 clusters and Fe, Mn single atoms are dispersed on the nitrogen-doped carbon support NC.

[0048] In the embodiment, the calcination temperature in step (2) and step (3) can be 850-950° C. (e.g., 900° C.), and the holding time can be 1-3 hours (e.g., 2 hours). Preferably, the calcination temperature, holding time, and other process parameters in step (3) and step (2) are preferably kept consistent, which is beneficial to maintaining the uniformity and structural stability of the carbon support material.

[0049] Hereinafter, the present invention will be described in more detail based on specific examples and comparative examples.

[0050] Example 1 (MnO2) cluster Preparation of / Fe,Mn-NC catalyst

[0051] The preparation method of Example 1 comprises the following steps:

[0052] ⑴1.5g glycine, 1.68g dicyandiamide, 1.98g manganese chloride tetrahydrate, and 2.7g ferric chloride hexahydrate were ultrasonically dispersed in 100mL of aqueous solution, and then 80ml of ethanol was added. The mixture was ultrasonically mixed for 2h and dried at 80℃ to obtain a gray-brown solid powder FeMn-Precursor.

[0053] ⑵ Place the FeMn-Precursor powder in a tube furnace, heat it to 900℃ at 5℃ / min under N2 atmosphere and keep it at this temperature for 2 hours. Take it out and grind it to obtain FeMn-complex.

[0054] (3) The FeMn-complex was acid-washed with 1 mol / L HCl solution at room temperature for 6 hours, filtered and washed with deionized water 3-4 times, and then dried at 60°C in a forced air drying oven. After that, it was placed in a tube furnace and heated to 900°C at 5°C / min under N2 atmosphere and kept warm for 2 hours to obtain (MnO2) with rich surface area. cluster / Fe,Mn-NC catalyst.

[0055] Comparative Example 1 Preparation of FeMn-complex catalyst

[0056] The difference between this comparative example and Example 1 is that this comparative example only performs steps (1) and (2) and does not perform step (3).

[0057] Comparative Example 2 Preparation of Fe-NC Catalyst

[0058] The main difference between this comparative example and Example 1 is that manganese chloride tetrahydrate is not added in the preparation process.

[0059] ⑴1.5g glycine, 1.68g dicyandiamide and 5.4g ferric chloride hexahydrate were ultrasonically dispersed in 100mL of aqueous solution, and then 80ml of ethanol was added. The mixture was ultrasonically mixed for 2h and dried at 80℃ to obtain a gray-brown solid powder Fe-Precursor.

[0060] ⑵ Place the Fe-Precursor powder in a tube furnace, heat it to 900℃ at 5℃ / min under N2 atmosphere and keep it at this temperature for 2 hours. Take it out and grind it to obtain Fe-complex.

[0061] ⑶ The Fe-complex was acid-washed with 1 mol / L HCl solution at room temperature for 6 hours, filtered and washed with deionized water 3-4 times, then dried at 60°C in a forced air drying oven, placed in a tube furnace, and heated to 900°C at 5°C / min under a N2 atmosphere and kept warm for 2 hours to obtain the catalyst Fe-NC.

[0062] Comparative Example 3 Preparation of Mn-NC Catalyst

[0063] The main difference between this comparative example and Example 1 is that ferric chloride hexahydrate is not added in the preparation process.

[0064] ⑴1.5g glycine, 1.68g dicyandiamide and 3.96g manganese chloride tetrahydrate were ultrasonically dispersed in 100mL of aqueous solution, and then 80ml of ethanol was added. The mixture was ultrasonically mixed for 2h and dried at 80℃ to obtain light purple solid powder Mn-Precursor.

[0065] ⑵ Place the Mn-Precursor powder in a tube furnace, heat it to 900℃ at 5℃ / min under N2 atmosphere and keep it warm for 2 hours. Take it out and grind it to obtain Mn-complex.

[0066] ⑶ The Mn-complex was acid-washed with 1 mol / L HCl solution at room temperature for 6 hours, filtered and washed with deionized water 3-4 times, then dried at 60°C in a forced air drying oven and placed in a tube furnace. The temperature was raised to 900°C at 5°C / min under a N2 atmosphere and kept at this temperature for 2 hours to obtain the catalyst Mn-NC.

[0067] Comparative Example 4 (MnO2) cluster Preparation of / Fe,Mn-NC-(Glycine) catalyst

[0068] The main difference between this comparative example and Example 1 is that only glycine is used as the organic ligand, and no dicyandiamide is used.

[0069] ⑴ 3.36 g of glycine, 1.98 g of manganese chloride tetrahydrate, and 2.7 g of ferric chloride hexahydrate were ultrasonically dispersed in 100 mL of aqueous solution, and then 80 mL of ethanol was added. The mixture was ultrasonically mixed for 2 h and dried at 80 ° C to obtain a gray-brown solid powder FeMn-Precursor.

[0070] ⑵ Place the FeMn-Precursor powder in a tube furnace, heat it to 900℃ at 5℃ / min under N2 atmosphere and keep it at this temperature for 2 hours. Take it out and grind it to obtain FeMn-complex.

[0071] (3) The FeMn-complex was acid-washed with 1 mol / L HCl solution at room temperature for 6 hours, filtered and washed with deionized water 3-4 times, and then dried in a blast drying oven at 60°C. The mixture was placed in a tube furnace and heated to 900°C at 5°C / min under N2 atmosphere and kept at this temperature for 2 hours to obtain the catalyst (MnO2). cluster / Fe,Mn-NC-(Glycine).

[0072] Comparative Example 5 (MnO2) cluster Preparation of Fe,Mn-NC-(Dihydrodiammine) catalyst

[0073] The main difference between this comparative example and Example 1 is that only dicyandiamide is used as the organic ligand, and glycine is not used.

[0074] ⑴ 3 g of dicyandiamide, 1.98 g of manganese chloride tetrahydrate, and 2.7 g of ferric chloride hexahydrate were ultrasonically dispersed in 100 mL of aqueous solution, and then 80 ml of ethanol was added. The mixture was ultrasonically mixed for 2 h and dried at 80 ° C to obtain a gray-brown solid powder FeMn-Precursor.

[0075] ⑵ Place the FeMn-Precursor powder in a tube furnace, heat it to 900℃ at 5℃ / min under N2 atmosphere and keep it at this temperature for 2 hours. Take it out and grind it to obtain FeMn-complex.

[0076] ⑶ The FeMn-complex was acid-washed with 1 mol / L HCl solution at room temperature for 6 hours, filtered and washed with deionized water 3-4 times, then dried at 60°C in a forced air drying oven, placed in a tube furnace and heated to 900°C at 5°C / min under N2 atmosphere and kept warm for 2 hours to obtain the catalyst (MnO2)cluster / Fe,Mn-NC-(Dihydrodiammine).

[0077] Comparative Example 6 Preparation of N-OC Catalyst

[0078] The difference between this comparative example and Example 1 is that manganese chloride tetrahydrate and ferric chloride hexahydrate are not used.

[0079] (1) Disperse 1.5 g of glycine and 1.68 g of dicyandiamide in 100 mL of aqueous solution by ultrasonication, then add 80 mL of ethanol, mix thoroughly by ultrasonication for 2 h, and dry by stirring at 80 °C to obtain a white solid powder NOC-Precursor.

[0080] (2) Place the NOC-Precursor powder in a tube furnace, heat it to 900°C at 5°C / min under a N2 atmosphere and keep it at that temperature for 2 hours. Then take it out and grind it to obtain NOC-900.

[0081] ⑶ NC was acid-washed with 1 mol / L HCl solution at room temperature for 6 hours, filtered and washed with deionized water 3-4 times, then dried at 60°C in a forced air drying oven and placed in a tube furnace. The temperature was raised to 900°C at 5°C / min under a N2 atmosphere and kept at this temperature for 2 hours to obtain catalyst NOC.

[0082] Comparative Example 7Mn cluster / Mn DAC Preparation of -NC catalyst

[0083] ⑴ Ultrasonic dispersion of 1.5 g of glycine and 1.98 g of manganese chloride tetrahydrate in 25 mL of aqueous solution was performed, and then 40 mL of ethanol was added. Ultrasonic mixing was performed for 2 h, and the mixture was dried at 60 ° C to obtain a white solid powder Glycine-MnCl2.

[0084] ⑵ Place the Glycine-MnCl2 powder in a tube furnace and heat it to 900℃ at 5℃ / min under N2 atmosphere and keep it at this temperature for 2 hours. Then take it out and grind it to obtain MnO / Mn-NC.

[0085] (3) MnO / Mn-NC was acid-washed with 1 mol / L HCl solution at room temperature for 6 hours, filtered and washed with deionized water for 3-4 times, and then dried in a blast drying oven at 60° to obtain Mn DAC -NC.

[0086] (4) Mn DAC -NC was placed in a tube furnace and heated to 900℃ at 5℃ / min under N2 atmosphere and kept at this temperature for 2 hours to obtain carbon nanosheet catalyst Mn with rich surface area. cluster / Mn DAC -NC.

[0087] Morphology, size and phase analysis of examples and comparative examples

[0088] Figure 1 a is the Fourier transform infrared spectrum (FTIR) of three precursor powders: FeMn-Precursor, Fe-Precursor, and Mn-Precursor. Figure 1 As shown in a, Fe-Precursor is at 2220 cm -1 There is no absorption peak of C=N, Mn-Precursor and Fe, Mn-Precursor at 2220cm -1 There is an obvious C=N absorption peak, and the C=N absorption peak of Mn-Precursor is the strongest, and at 1685cm -1 The absorption peak of Fe-Precursor C=O is the strongest at 1100cm. The changes of these two peaks indicate that Fe and Mn play different roles in the coordination process with glycine and dicyandiamide. -1 and 3400cm -1 The corresponding absorption peaks of CO and OH did not change significantly. In general, by simultaneously introducing Fe and Mn into glycine and dicyandiamide, the contents of C=N and CO in the catalyst precursor can be changed, thereby modifying the molecular structure of the catalyst.

[0089] Figure 1 b is (MnO2) cluster From the XRD results of the three catalysts, Fe, Mn-NC, Fe-NC and Mn-NC, it can be seen that they all have only two characteristic peaks of carbon at 26° and 42°, which can be attributed to the (002) and (101) planes of graphitic carbon.

[0090] Figure 2 af in the middle is (MnO2) cluster / The SEM and TEM images of the Fe,Mn-NC catalyst show that the catalyst has a loose flake-like structure and no nanoparticles exist on the surface; Figure 2 Figure gk is the element mapping image of the catalyst, from which it can be seen that the C, N, O, Mn, and Fe elements are evenly distributed.

[0091] Figure 3 ac is comparative example 7 (MnO2) cluster From the SEM and TEM images of the / Fe,Mn-NC catalyst, it can be seen that the catalyst has a flake-like structure and there are no nanoparticles on the surface.

[0092] Figure 4 a is a comparative example 7Mn cluster / Mn DAC -NC catalyst TEM element distribution diagram, it can be seen that the elements C, N, O, and Mn are evenly distributed. Figure 4 b is Mn cluster / Mn DAC -NC spherical aberration corrected high-angle annular dark field scanning transmission electron microscopy (AC-HAADF-STEM) shows that Mn is mainly distributed on the surface of the carbon material in the form of clusters (circled in yellow in the figure) and double single atoms (circled in red in the figure).

[0093] Figure 5 a is the catalyst (MnO2) obtained in Example 1 cluster Spherical aberration corrected high-angle annular dark field scanning transmission electron microscopy (AC-HAADF-STEM) of / Fe,Mn-NC shows that Fe and Mn are distributed on the surface of carbon materials in the form of clusters (large yellow circles in the figure) and single atoms (small red circles in the figure). Figure 5 In the electron energy loss spectrum of b, peaks of Fe and Mn were observed, and the peak of Fe was stronger than that of Mn. Most of the metal in the surface catalyst was Fe.

[0094] Table 1 below shows the contents of Fe and Mn in the catalysts of Example 1 and Comparative Examples 1-3.

[0095] Table 1 ICP-OES analysis of metal Fe and Mn content in the catalyst

[0096]

[0097] Figure 6 The nitrogen adsorption and desorption curves (inset) and the corresponding pore size distribution diagrams of the catalysts prepared in Example 1 and Comparative Examples 1-3 are shown. clusterThe pore types in Fe,Mn-NC are mainly in the form of micropores and mesopores. Micropores are conducive to the distribution of more active sites, while mesopores are conducive to the mass transfer of ORR intermediates. It can also be seen that Fe-NC has the highest specific surface area (1709m 2 g -1 ), while the specific surface area of ​​Mn-NC is only 501m 2 g -1 , (MnO2) cluster / Fe,Mn-NC is 1023m 2 g -1 , which indicates that (MnO2) cluster The main source of the specific surface area of ​​ / Fe,Mn-NC catalyst is attributed to the introduction of Fe during the calcination process.

[0098] Figure 7 Fe-NC, Mn-NC and (MnO2) cluster Raman spectra of the three catalysts: Fe / Mn-NC, which has a peak at 1334 cm -1 Showing a characteristic disordered D band, 1590 cm -1 The G band related to graphite carbon is shown. Among them, Fe-NC, Mn-NC, (MnO2) cluster I / Fe,Mn-NC D :I G The ratios are 0.64, 1.20 and 1.00 respectively. The I D :I G The value is the lowest, indicating that it has the highest degree of graphitization. D :I G The value is the highest, indicating that it has a low degree of graphitization, but there are abundant defect sites. The defects in the catalyst are closely related to the distribution of active sites, which plays a vital role in electrocatalytic ORR. (MnO2) cluster I / Fe,Mn-NC catalyst D :I G The graphitization degree and defect degree of the catalyst are between those of Fe-NC and Mn-NC. This result indicates that the presence of Fe is conducive to improving the graphitization degree of the catalyst, while the presence of Mn is conducive to increasing the defect sites in the catalyst.

[0099] Figure 8 a is (MnO2) cluster Fourier transform (FT) k of Fe K-edge of / Fe,Mn-NC 2 Weighted X-ray Absorption Fine Spectroscopy (EXAFS), (MnO2) cluster / Fe,Mn-NC The peak at corresponds to the Mn-N bond in FePc. Figure 8 In b, the Fourier transform (FT) k of the Mn K-edge 2 Weighted EXAFS spectrum shows that (MnO2) cluster / Fe,Mn-NC The peak at corresponds to the Mn-N bond in MnPc, but with a slight positive shift, indicating that Mn in (MnO2) cluster There may be multiple coordination situations in / Fe,Mn-NC. In addition, there is no The characteristic peak of the metallic Mn-Mn bond corresponding to the Mn foil is found near A broad bulge peak was found nearby, which corresponds to MnO2, indicating that (MnO2) cluster In / Fe,Mn-NC, Mn may exist in Mn-Mn and Mn-O structures similar to MnO2.

[0100] Comprehensive Figure 5 The results of the atomic distribution observed in (MnO2) cluster In the / Fe,Mn-NC catalyst, Fe is mainly in the form of FeN x In the form of Mn, Mn mainly exists in the form of MnN x , Mn-Mn and Mn-O-Mn exist in the carbon framework.

[0101] Figure 9 For comparative example 7Mn cluster / Mn DAC Fourier transform (FT) k of the Mn K-edge of -NC 2 Weighted X-ray Absorption Spectroscopy (EXAFS), which The peak at corresponds to the Mn-N bond in MnPc. There is no Mn-O bond corresponding to MnO nearby, indicating that the oxygen in the catalyst is not coordinated with Mn. cluster / Mn DAC -NC in There is a characteristic peak at , which is similar to the Mn-Mn bond in Mn foil, however, this peak has a positive shift compared to that of Mn foil. Figure 4 The spherical aberration observed results, it is speculated that in Mn cluster / Mn DAC Mn in NC is mainly in the form of double single-atom Mn2N x and Mn clusters exist in the carbon framework structure.

[0102] Catalytic performance testing

[0103] Test conditions: Measurements were performed using a three-electrode system in an O2-saturated 0.1 mol / L KOH solution; the reference electrode was an Ag / AgCl electrode, and the counter electrode was a platinum electrode. All potentials in the accompanying figures are converted to standard hydrogen electrode potentials. Commercial Pt / C and RuO2 catalysts used for comparison were purchased from Johnson Matthey.

[0104] Figure 10a The linear sweep voltammetry (LSV) curves of Example 1, Comparative Examples 2-6 and commercial Pt / C (20%) catalyst are compared. It can be seen intuitively that the (MnO2) of Example 1 cluster The onset potential and half-wave potential of the Pt / C / Fe,Mn-NC catalyst are significantly higher than those of the comparative example and commercial Pt / C catalyst.

[0105] In addition, from Figure 10a It can also be seen that the catalyst (MnO2) prepared with glycine as the metal organic ligand cluster / Fe,Mn-NC-(Glycine) and catalysts prepared with only dicyandiamide as metal organic ligand (MnO2) cluster The performance of / Fe,Mn-NC-(Dihydrodiammine) is much lower than that when glycine and dicyandiamide are used as metal organic ligands at the same time, indicating that when glycine and dicyandiamide are used as metal complex synthesis catalysts at the same time, the best coordination effect can be achieved on metal Fe and Mn, showing better performance.

[0106] At the same time, compared with Fe-NC with only metallic Fe and Mn-NC with only metallic Mn, the coexistence of Fe and Mn (MnO2) cluster / Fe,Mn-NC also has the best catalytic performance, indicating the synergistic effect of Fe and Mn. However, the ORR performance of NOC without metal source is almost the same, which also indicates that the catalyst (MnO2) cluster Fe and Mn in / Fe,Mn-NC are the real active sites.

[0107] Figure 10b (MnO2) obtained in Example 1 cluster The comparison of the chronoamperometric curves (it) of the / Fe,Mn-NC catalyst and the commercial Pt / C catalyst shows that the current of the commercial Pt / C catalyst decayed by 12.9% after 30,000s, while the (MnO2) cluster / Fe,Mn-NC catalyst only decayed by 3.3%, which indicates that (MnO2 cluster / Fe,Mn-NC catalysts have better durability than commercial Pt / C catalysts.

[0108] Figure 10c (MnO2) of Example 1 cluster Comparison of the chronoamperometric curves (it) of the methanol cross-resistance of the Fe,Mn-NC catalyst and the commercial Pt / C catalyst. Methanol was added at 200s to test the methanol cross-resistance of the catalyst. As can be seen from the figure, the commercial Pt / C catalyst responds very quickly to methanol and immediately turns to methanol oxidation reaction, while (MnO2) cluster / Fe,Mn-NC catalyst has almost no reaction to methanol oxidation and is very effective in resisting methanol cross-effect.

[0109] Figure 10d (MnO2) obtained in Example 1 cluster / Fe,Mn-NC catalyst cycle durability test diagram, after 10,000 CV cycles, (MnO2) cluster The half-wave potential of the / Fe,Mn-NC catalyst only decayed by 1mV. While that of the commercial Pt / C decayed by 19mV. The above results show that (MnO2 cluster / Fe,Mn-NC catalysts have better long-term stability than commercial Pt / C catalysts and have more obvious advantages in practical applications.

[0110] Figure 11 a is the Mn obtained in Comparative Example 7 cluster / Mn DAC The comparison of the chronoamperometric curves (it) of the -NC catalyst and the commercial Pt / C catalyst shows that after 25000s, the Mn cluster / Mn DAC The current density of the -NC catalyst decayed by 7.4%. Figure 11 b is Mn cluster / Mn DAC -NC and commercial Pt / C catalyst cycle durability test diagram, after 10,000 CV cycles, Mn cluster / Mn DAC -NC half-wave potential was attenuated by 9mV. Figure 10b The test results of and d show that (MnO2) cluster / Fe,Mn-NC relative to the Mn in Comparative Example 7 cluster / Mn DAC -NC has been significantly improved in stability.

[0111] Figure 12 a is obtained using (MnO2) from Example 1 clusterThe open circuit voltage comparison of zinc-air batteries assembled with / Fe,Mn-NC catalyst and commercial Pt / C+RuO2 catalyst shows that (MnO2) cluster The open circuit voltage of the zinc-air battery assembled with Pt / Fe,Mn-NC catalyst is 1.52V, which is significantly higher than the open circuit voltage of the zinc-air battery assembled with commercial Pt / C+RuO2 catalyst (1.42V). Figure 12 b is a comparison chart of power density, from which we can see that (MnO2) cluster The power density of the zinc-air battery assembled with Pt / Fe,Mn-NC is 200 mW, which is higher than that of commercial Pt / C+RuO2.

[0112] In addition, the charge-discharge cycle test was conducted to compare the ZAB-(MnO2) cluster / Fe,Mn-NC and ZAB-Pt / C+RuO2 stability, such as Figure 12 As shown in d, ZAB-(MnO2) cluster / Fe,Mn-NC has good stability. After 97h of charge and discharge cycle, the performance does not decrease significantly, while the performance of ZAB-Pt / C+RuO2 decreases significantly. In the first 300min, ZAB-(MnO2) cluster The charge-discharge voltage gap of / Fe,Mn-NC is 0.8V, which is lower than the charge-discharge voltage gap of ZAB-Pt / C+RuO2 (1.25V), indicating that it has good charge and discharge properties.

[0113] Figure 13 a is the Mn obtained in Comparative Example 7 cluster / Mn DAC -NC catalyst assembled zinc-air battery and commercial Pt / C+RuO2 open circuit voltage comparison chart, Mn cluster / Mn DAC -NC open circuit voltage is 1.48V. Figure 12 c is a comparison chart of its power density, Mn cluster / Mn DAC -NC power density is 180mW. Figure 13 d is ZAB-Mn cluster / Mn DAC -NC charge and discharge curve within 50h, in the first 300min, the charge and discharge voltage gap is 1.02V. Figure 12 The test results show that compared with the Mn cluster / Mn DAC -NC, (MnO2) cluster / Fe,Mn-NC exhibits higher open circuit voltage and power density and lower charge-discharge voltage gap in zinc-air batteries, and exhibits better performance in zinc-air batteries.

[0114] In summary, the present invention combines the advantages of double single atoms and cluster-controlled single atoms, uses Fe and Mn as double metal active sites, and then synthesizes a catalyst (MnO2) with double metal active sites and nanoclusters in a carbon framework through high-temperature heat treatment. cluster / Fe,Mn-NC. Among them, the synergistic effect between Fe and Mn can retain more metal active sites. Fe is the main source of increasing the specific surface area of ​​the catalyst and the content of N in the catalyst, and Mn is the main source of increasing the degree of defects in the catalyst material. Fe and Mn play different roles in the catalyst material, and together optimize and regulate the structure of the catalyst, making (MnO2) cluster / Fe,Mn-NC catalysts exhibited excellent ORR performance under alkaline (0.1M KOH) conditions. cluster / Fe,Mn-NC assembled zinc-air batteries also showed excellent performance. (MnO2) cluster The excellent catalytic performance of / Fe,Mn-NC is mainly attributed to the interaction between Fe and Mn that retains more metal active sites and the synergistic effect between MnO2 nanoclusters and single atoms.

[0115] In particular, compared with the Mn cluster / Mn DAC -NC catalyst, (MnO2) of the present invention cluster / Fe,Mn-NC catalysts exhibited better stability and significantly improved performance in assembled zinc-air batteries.

[0116] Although the present invention has been described above through specific embodiments, it should be understood that any equivalent improvements made by a person skilled in the art in accordance with the present invention without departing from the scope of the present invention should be covered by the protection scope of the present invention.

Claims

1. A (MnO2) cluster / Fe, Mn-NC catalyst preparation method, characterized in that The steps include: (1) Glycine and dicyandiamide are used as organic ligands to react with manganese salt and iron salt, and then dried to obtain FeMn-Precursor powder; (2) calcining the FeMn-Precursor powder under an inert atmosphere and grinding the calcined powder to obtain the FeMn-complex; (3) The FeMn-complex is acid-washed and water-washed, dried and then calcined again under an inert atmosphere to obtain the (MnO2) cluster / Fe,Mn-NC catalyst, in which MnO2 clusters and Fe, Mn single atoms are dispersed on the nitrogen-doped carbon support NC.

2. The preparation method according to claim 1, wherein: In step (1), glycine, dicyandiamide, manganese salt and iron salt are subjected to coordination reaction in a molar ratio of 2:2:1:

1.

3. The preparation method according to claim 2, wherein: In step (1), the glycine, dicyandiamide, manganese salt and iron salt are first ultrasonically dispersed in an alcohol-water mixed solution, and then heated to 60-90° C. and stirred and dried to obtain FeMn-Precursor powder.

4. The preparation method according to claim 3, wherein: The alcohol-water mixed solution is a mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is less than 1.

5. The preparation method according to claim 2, wherein: The manganese salt and the iron salt are manganese chloride and iron chloride respectively.

6. The preparation method according to claim 1, wherein: The calcination temperature in step (2) is 850-950° C., and the holding time is 1-3 hours.

7. The preparation method according to claim 1, wherein: The calcination temperature in step (3) is 850-950° C., and the holding time is 1-3 hours.

8. The preparation method according to claim 1, wherein: The calcination temperature and holding time in step (2) and step (3) are both 900° C., and the holding time is both 2 h.

9. The preparation method according to claim 1, wherein: In step (3), the FeMn-complex is pickled at room temperature using a 0.5-1.5 mol / L HCl solution.

10. (MnO2) obtained by the preparation method according to any one of claims 1 to 9 cluster Application of / Fe,Mn-NC catalysts in ORR reaction.

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