Carbon nano tube for packaging M-NC single atoms and M3C nano particles as well as preparation method and application of carbon nano tube

Abstract

The invention discloses a carbon nano tube for packaging M-NC single atoms and M3C nano particles as well as a preparation method and application of the carbon nano tube, and belongs to the field of composite materials and electrochemistry. The method comprises the following steps: preparing a mixed solution containing an organic ligand, a metal salt and a zinc salt; performing solvent heat treatment on the mixed solution to obtain a precursor; and mixing the precursor with dicyandiamide, and carrying out high-temperature heat treatment in an inert atmosphere to obtain a final product. According to the final product, the bamboo-shaped carbon nano tube is used as an outer frame, the packaged metal element M is wrapped in the outer frame of the carbon nano tube in the form of M-NC single atoms and M3C nano particles, and the metal element M is iron or cobalt. The product is low in cost, high in efficiency and good in stability when being used as an oxygen reduction electrocatalyst of a battery.

Description

Technical Field

[0001] This invention belongs to the field of composite materials and electrochemical technology, specifically relating to a carbon nanotube encapsulating M-NC single atoms and M3C nanoparticles, its preparation method and application. Background Technology

[0002] Zinc-air batteries (ZABs) have become a focal point for sustainable energy solutions due to their affordability and environmental friendliness. The core of ZAB efficacy lies in the oxygen reduction reaction (ORR) efficiency on the air electrode, where slow kinetics typically degrade practical performance. While platinum group metal-based catalysts (PGMs) can effectively enhance ORR kinetics, their high price, scarcity, limited availability, and poor cycling performance severely restrict their commercial application. This has spurred the search for alternative non-precious metal electrocatalysts for ORR.

[0003] In the oxygen reduction reaction (ORR), the performance of MNC catalysts (metal-nitrogen-carbon) is closely related to the adsorption / desorption behavior of reaction intermediates at single metal sites. This process largely depends on the interaction between the d orbitals of metal atoms and the adsorbed oxygen intermediates. Therefore, the key to designing efficient ORR electrocatalysts lies in the precise control of the local electronic environment of the MNC active sites. Optimization of the electronic environment can be achieved by introducing synergistic metal-based components near the MNC sites. Components such as metal carbides, sulfides, nitrides, nanoclusters, and nanoparticle oxides can lower the ORR reaction energy barrier by changing the charge density. Taking an iron-, nitrogen-, and carbon-containing precursor as an example, its pyrolysis process generates FeN... X In addition to conventional structures such as nitrogen-doped carbon, Fe3C can also form cementite (Fe3C) and metallic Fe nanoparticles. Recent studies have found that Fe3C species can significantly enhance the catalytic efficiency of active sites through synergistic effects, thereby promoting the efficiency of oxygen reduction reactions. Therefore, composite systems of single-atom Fe-NC and metal carbides such as Fe3C have become a research hotspot.

[0004] Carbon nanotubes (CNTs) possess excellent electrical conductivity due to their graphite-like sheet structure, enabling the construction of highly efficient conductive pathways to accelerate ORR kinetics. However, current CNT preparation techniques lack synergistic design between the catalytic phase and the carbon support, making it difficult to meet application requirements. Existing CNT-encapsulated ORR electrocatalysts suffer from complex synthesis, unsatisfactory catalytic efficiency, and poor cycling stability. Summary of the Invention

[0005] 1. The problem to be solved

[0006] To address the problems of high price, low efficiency, and poor stability of existing oxygen reduction electrocatalysts, this invention provides an economical, efficient, and stable carbon nanotube encapsulated with M-NC single atoms and M3C nanoparticles, along with its preparation method and applications. M-NC represents the single metal atom sites on a nitrogen-doped carbon support, and M3C represents cementite, exhibiting a nanoscale orthorhombic crystal structure.

[0007] 2. Technical Solution

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a carbon nanotube encapsulating M-NC single atoms and M3C nanoparticles, wherein the carbon nanotube serves as the outer framework, and the encapsulated metal element M is wrapped in the carbon nanotube in the form of M-NC single atoms and M3C nanoparticles.

[0010] Furthermore, the aforementioned metallic element M is either iron or cobalt.

[0011] Furthermore, the aforementioned carbon nanotubes are bamboo-like in shape and have a diameter of 50-200 nm.

[0012] Furthermore, the diameter of the aforementioned carbon nanotubes is 50-100 nm.

[0013] Furthermore, the mass of the aforementioned metallic element M accounts for 10%-30% of the total mass.

[0014] Furthermore, the mass of the aforementioned metallic element M accounts for 20%-30% of the total mass.

[0015] Furthermore, the mass of the aforementioned metallic element M accounts for 20%-25% of the total mass.

[0016] This invention also provides a method for preparing carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles, comprising the following steps:

[0017] S1, Mixed solution preparation: Prepare a mixed solution containing organic ligands, metal salts, and zinc salts; as a further explanation of this application, the density of metal sites is controlled during the preparation process, and it is used as a template agent for generating metal single atoms (iron single atoms or cobalt single atoms);

[0018] S2, Solvent heat treatment: The mixed solution is heated to 100-150°C at a heating rate of 1-5°C per minute, and reacted at a constant temperature for 5-10 hours. After cooling, the precursor is obtained.

[0019] S3, High-temperature heat treatment: Mix the precursor with dicyandiamide and heat it to 800-1000℃ at a heating rate of 1-5℃ per minute under an inert atmosphere, hold for 2-3 hours, and then cool to obtain the final product.

[0020] Furthermore, the aforementioned organic ligands are cyano-containing organic ligands.

[0021] Furthermore, the aforementioned cyano-containing organic ligands include 4,5-dicyanimidazole.

[0022] Furthermore, the aforementioned metal salts include iron salts or cobalt salts.

[0023] Furthermore, the aforementioned iron salts include ferric nitrate.

[0024] Furthermore, the aforementioned cobalt salts include cobalt nitrate.

[0025] Furthermore, the aforementioned zinc salts include zinc nitrate.

[0026] Furthermore, the molar ratio of the zinc salt to the metal salt is (5-10):1.

[0027] Furthermore, the molar ratio of the above-mentioned organic ligand to metal salt is 4:(0.1-0.5).

[0028] Furthermore, in S2 above, the mixed solution is heated to 120°C at a heating rate of 1°C per minute and reacted at a constant temperature for 8 hours.

[0029] Furthermore, in S2 above, the cooled product also includes washing with ethanol.

[0030] Furthermore, in S2 above, washing also includes drying.

[0031] Furthermore, in S3 above, the mass ratio of the precursor to dicyandiamide is 1:(5-8). Even further, the mass ratio of the precursor to dicyandiamide is 1:5.

[0032] Furthermore, in the above S3, the heating temperature is 900-1000℃.

[0033] Furthermore, in S3 above, the heating temperature is 900 or 1000°C.

[0034] Furthermore, in S3 above, the heating rate is 5°C per minute.

[0035] Furthermore, in S3 above, the holding time is 2 hours.

[0036] Furthermore, the inert atmosphere in S3 above includes nitrogen or argon.

[0037] The present invention also provides an application of the above-described carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles as an oxygen reduction electrocatalyst.

[0038] Furthermore, the above applications include its use as an oxygen reduction electrocatalyst in zinc-air batteries.

[0039] The present invention also provides a zinc-air battery comprising carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles as described above.

[0040] 3. Beneficial effects

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] (1) The carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles of the present invention and their preparation method utilize organic ligands rich in cyano groups to prepare precursors. After adding dicyandiamide, carbon nanotubes with a diameter of 50-200 nm can be obtained by high-temperature heat treatment. They also have abundant pyridine nitrogen and graphitic nitrogen, which can provide oxygen reduction active sites.

[0043] (2) The carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles of the present invention and their preparation method are low cost.

[0044] (3) The carbon nanotube of the present invention encapsulates M-NC single atoms and M3C nanoparticles, wherein M-NC single atoms have a large number of active sites and good cycling stability; Fe3C promotes efficient four-electron oxygen reduction reaction (ORR) by regulating the electronic structure of the surface carbon shell, ensuring rapid electron transfer, and this structure has better tolerance to alkaline solutions and methanol.

[0045] (4) The application of the carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles of the present invention, when used as a cathode catalyst in a zinc-air battery, exhibits a higher power density (145.5 mW·cm⁻¹). -2 It also offers superior cycle stability. Attached Figure Description

[0046] Figure 1 SEM image of Fe3C / FeN@CNT-900.

[0047] Figure 2 STEM image of Fe3C / FeN@CNT-900.

[0048] Figure 3 The following are SEM images of other products, including (a) Fe3C / FeN@CNT-800; (b) Fe3C / FeN@CNT-1000; (c) Fe / Fe3C@CNT; and (d) Fe-NC.

[0049] Figure 4 SEM image of Co3C / CoN@CNT.

[0050] Figure 5The images are TEM and STEM images of each sample. The top image is the TEM image and the bottom image is the STEM image. (a) Fe3C / FeN@CNT-800; (b) Fe3C / FeN@CNT-900; (c) Fe3C / FeN@CNT-1000.

[0051] Figure 6 Here are the XRD patterns for each sample.

[0052] Figure 7 Here are the XAFS images for each sample.

[0053] Figure 8 The images are FT-EXAFS plots for each sample.

[0054] Figure 9 XPS plots for each sample.

[0055] Figure 10 High-resolution XPS images of Fe 2p for each sample.

[0056] Figure 11 LSV diagrams for Fe3C / FeN@CNT-900 at different rotational speeds.

[0057] Figure 12 RRDE plots for Fe3C / FeN@CNT-900 and Pt / C.

[0058] Figure 13 The power density diagram of a zinc-air battery using Fe3C / FeN@CNT-900 and the noble metal catalyst Pt / C+RuO2 is shown.

[0059] Figure 14 The graph shows the chronoamperometry test results for Fe3C / FeN@CNT-900.

[0060] Figure 15 The graph shows the cyclic stability test results of each sample after 10,000 CV cycles.

[0061] Figure 16 Figures showing the methanol resistance test results for Fe3C / FeN@CNT-900 and commercial Pt / C. Detailed Implementation

[0062] The present application will be further described below with reference to specific embodiments.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0064] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0065] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0066] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0067] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as “less than about 4.5,” which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0068] Example 1

[0069] This embodiment provides a carbon nanotube encapsulating M-NC single atoms and M3C nanoparticles and its preparation method, wherein the metal element M is selected as Fe.

[0070] The method includes the following steps:

[0071] (1) Preparation of mixed solution: Dissolve 20 mmol of 4,5-dicyanimidazolium (DCI), 0.5 mmol of ferric nitrate nonahydrate and 5 mmol of zinc nitrate hexahydrate in 50 mL of methanol and stir thoroughly; mix the above solutions and continue stirring for 1 hour to obtain a mixed solution containing organic ligands, metal salts and zinc salts;

[0072] (2) Solvent heat treatment: The mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene and stainless steel. After sealing, the reactor was placed in an oven and heated to 120°C at a heating rate of 1°C per minute. The reaction was kept at a constant temperature for 8 hours and then cooled to room temperature naturally. The product was washed three times with ethanol and dried at 60°C for 12 hours to obtain the precursor ZnFe-DCI.

[0073] (3) High temperature heat treatment: 300 mg of precursor ZnFe-DCI and 1500 mg of dicyandiamide (DCD) were thoroughly mixed and placed in a tube furnace; the temperature was increased to 900 °C at a rate of 5 °C per minute under an argon atmosphere and held for 2 hours; after natural cooling to room temperature, the final product was obtained and labeled as Fe3C / FeN@CNT-900.

[0074] In this embodiment, the density of metallic zinc sites is controlled during the preparation process to serve as a template agent for the generation of iron single atoms. Fe accounts for 23.9% by mass in the final product.

[0075] Example 2

[0076] This embodiment provides a carbon nanotube encapsulating M-NC single atoms and M3C nanoparticles and its preparation method, wherein the metal element M is selected as Fe.

[0077] The specific steps of this method are as described in Example 1, except that the high-temperature heat treatment temperature in step (3) is 800℃, and the resulting product is labeled as Fe3C / FeN@CNT-800.

[0078] Fe accounts for 24.6% of the mass of the final product.

[0079] Example 3

[0080] This embodiment provides a carbon nanotube encapsulating M-NC single atoms and M3C nanoparticles and its preparation method, wherein the metal element M is selected as Fe.

[0081] The specific steps of this method are as described in Example 1, except that the high-temperature heat treatment temperature in step (3) is 1000℃, and the resulting product is labeled as Fe3C / FeN@CNT-1000.

[0082] Fe accounts for 22.8% of the mass of the final product.

[0083] Example 4

[0084] This embodiment provides a carbon nanotube encapsulating M-NC single atoms and M3C nanoparticles and its preparation method, wherein the metal element selected is Co.

[0085] The specific steps of this method are as described in Example 1, except that step (1) ferric nitrate nonahydrate is replaced with 0.5 mmol cobalt nitrate hexahydrate, and the resulting product is labeled as Co3C / CoN@CN-900.

[0086] Comparative Example 1

[0087] This comparative example provides a carbon nanotube catalyst and its preparation method.

[0088] The method steps are the same as in Example 1, except that: dicyandiamide is not added during the high-temperature heat treatment in step (3), and the rest are the same as in Example 1. The resulting product (carbon nanotube catalyst) is labeled as Fe / Fe3C@CNT.

[0089] Comparative Example 2

[0090] This comparative example provides an oxygen reduction electrocatalyst and its preparation method.

[0091] The oxygen reduction electrocatalyst of this comparative example was prepared as follows: Fe-doped ZIF-8 (Fe-ZIF-8) was synthesized via a simple precipitation method according to conventional preparation methods. 20 mmol of 2-methylimidazole was dissolved in 50 mL of methanol, and then 0.5 mmol of ferric nitrate nonahydrate and 5 mmol of zinc nitrate hexahydrate were added to another 50 mL methanol solution. The mixture was stirred vigorously for 2 hours. The suspension was washed three times with methanol and dried overnight at 60 °C to obtain a light yellow Fe-ZIF-8 powder. 300 mg of Fe-ZIF-8 was thoroughly mixed with 1500 mg of DCD and placed in a horizontal tube furnace. The temperature was increased to 900 °C at a rate of 5 °C per minute under an argon atmosphere and maintained for 2 hours. After natural cooling to room temperature, the Fe-NC catalyst was obtained.

[0092] Example 5

[0093] This embodiment provides structural and compositional analysis of the materials prepared in Examples 1-4.

[0094] like Figure 1 SEM image of Fe3C / FeN@CNT-900, showing that Fe3C / FeN@CNT-900 has a uniform carbon nanotube structure.

[0095] like Figure 2 STEM image of Fe3C / FeN@CNT-900: Aberration-corrected transmission electron microscopy (AC-TEM) image, showing the simultaneous presence of isolated bright spots and nanoparticles (NPs) in the Fe3C / FeN@CNT-900 catalyst within the carbon matrix, revealing that Fe3C / FeN@CNT-900 is composed of single-atom Fe and nanoscale Fe3C phases. Figure 3 As shown, this morphology can also be observed in Fe / Fe3C@CNT, Fe3C / FeN@CNT-800, and Fe3C / FeN@CNT-1000. Notably, Fe-NC exhibits a mixed morphology of partially formed carbon nanotubes and irregular carbon particles, a stark contrast to the carbon nanotube structure of Fe3C / FeN@CNT-900. Figure 4 We can also see that Co3C / CoN@CN-900 has a similar carbon nanotube structure. Through... Figure 5TEM clearly shows that Fe3C nanoparticles are encapsulated in carbon nanotubes.

[0096] like Figure 5 The calculated nanotube structure diameters were 89 nm for Fe3C / FeN@CNT-800, 85 nm for Fe3C / FeN@CNT-900, and 62 nm for Fe3C / FeN@CNT-1000.

[0097] like Figure 6 The XRD patterns of all samples showed that they contained the Fe phase (JCPDS No. 00-0006-0696), Fe3C phase (JCPDS No. 00-35-0772), and graphitic carbon GC phase (JCPDS No. 00-041-1487). The XRD spectrum of Fe / Fe3C@CNT showed the most prominent characteristic peaks of the Fe and Fe3C phases. In contrast, the diffraction peak intensities of metallic iron (Fe) and Fe3C in the Fe3C / FeN@CNT-800, Fe3C / FeN@CNT-900, and Fe3C / FeN@CNT-1000 samples were weaker. This phenomenon highlights the crucial role of dicyandiamide in the formation of Fe single atoms under high Fe content conditions. Sharp diffraction peaks detected in the 40°–50° range confirmed the presence of Fe3C. The presence of dicyandiamide effectively inhibited the formation of Fe nanoparticles and promoted the incorporation of more Fe atoms into the carbon matrix. Notably, the enhanced graphitic carbon (GC) diffraction peaks in the dicyandiamide-containing samples indicate a higher degree of graphitization, which is attributed to the role of dicyandiamide in promoting the ordered carbon structure. Samples without dicyandiamide exhibit a broad peak at approximately 26°, corresponding to amorphous carbon; while samples with added dicyandiamide (Fe3C / FeN@CNT-800, Fe3C / FeN@CNT-900, and Fe3C / FeN@CNT-1000) show sharper graphitic carbon (GC) diffraction peaks, indicating a higher degree of carbon structural order and improved electrical conductivity.

[0098] like Figure 7 and Figure 8 The coordination state and atomic arrangement of Fe species in Fe3C / FeN@CNT-900 were investigated using X-ray absorption spectroscopy, and Fourier transform extended X-ray absorption fine structure (FT-EXAFS) analysis was performed. The FeK-edge absorption energies of Fe3C / FeN@CNT-900 and Fe / Fe3C@CNT fall between those of Fe foil and iron phthalocyanine (FePc), clearly indicating that the average valence state of Fe is between 0 and +2. The FT-EXAFS spectra of the FeK-edge show that Fe3C / FeN@CNT-900 has an average valence state of approximately... A shoulder peak exists at this location, clearly indicating Fe-N or Fe-O coordination. At approximately... The significant peak at this location lies between that of the Fe foil and the FeN reference, confirming the mixed Fe-N bonding and Fe-Fe coordination. Crucially, no metallic Fe-Fe peak (typically located at...) was observed. This eliminates the possibility of bulk Fe aggregation. The weak coordination peak at the point further indicates that the Fe-Fe interaction within the Fe3C nanoparticles is mediated by the Fe-C-Fe scattering pathway.

[0099] like Figure 9 and Figure 10 XPS analysis was used to examine the electronic structure and chemical state of various atoms. XPS full-spectrum analysis confirmed the presence of C, N, O, and Fe elements in all samples. However, Zn almost evaporates at 1000℃, resulting in an undetectable Zn signal peak in the XPS spectrum. A small amount of zinc was found in the 1020-1050 eV range in the XPS full spectra of Fe3C / FeN@CNT-800, Fe3C / FeN@CNT-900, and Fe / Fe3C@CNT. High-resolution C1s spectra indicated the formation of N-doped carbon. The high-resolution N1s spectra of all catalysts could be deconvoluted into five states, attributed to graphitic N, pyrrole N, N oxide, Fe-N, and pyridine N, respectively. Pyridine N played a more critical role than any other type of nitrogen-containing substance, exhibiting higher activity in reducing the ORR overpotential. The Fe2p spectrum could be deconvoluted into eight different binding energy peaks, corresponding to Fe... 3+ 2p 3 / 2, Fe 3+ 2p1 / 2, Fe 2+ 2p 3 / 2, Fe 2+ 2p 1 / 2 and Fe 0 The appearance of the Fe-N morphological peak in Fe 2+ The fact that 2p 3 / 2 can be attributed to is that Fe 2+ The high content of Fe is believed to be due to coupling with adjacent N atoms. Fe-N is a highly efficient active site for catalytic oxygen reduction. 0 The signal further indicates that Fe-based nanoparticles (e.g., Fe, Fe3C) are anchored on the surface of the graphite carbon layer.

[0100] The surface elements and their relative contents in different catalysts are shown in Table 1 below, including C1s, O1s, N1s, Fe2p and Zn2p (wt%).

[0101] Table 1

[0102] <![CDATA[Fe3C / FeN@CNT-800]]> <![CDATA[Fe3C / FeN@CNT-900]]> <![CDATA[Fe3C / FeN@CNT-1000]]> <![CDATA[Fe3 / Fe3C@CNT]]> Fe-NC C1s 74.12 78.52 88.75 78.01 86.82 O1s 8.75 7.86 4.88 6.89 8.49 N1s 9.32 8.9 2.51 8.82 3.993 Zn2p 2.63 0.14 0.00 5.10 0.10 Fe2p 5.18 4.58 3.86 1.18 0.66

[0103] Example 6

[0104] This embodiment studies the oxygen reduction catalytic activity. All electrochemical measurements were performed using a CS2350M electrochemical workstation (Wuhan Keruit Instrument Co., Ltd.) in a three-electrode system. ORR measurements used 0.1M KOH as the electrolyte. The test system consisted of a working electrode (RDE or RRDE), a reference electrode (Hg / HgO), and a counter electrode (graphite rod), all of which were calibrated before recording. To prepare the working electrode, 5 mg of Fe3C / FeN@CNT-900 catalyst was mixed with 200 μL of isopropanol, 760 μL of ultrapure water, and 40 μL of 5 wt% Nafion solution. After sonication for 1 hour, the homogeneous catalyst ink was drop-cast onto a 5 mm diameter polished glassy carbon (GC) disk (RDE) or a 5.6 mm diameter RRDE, with a catalyst loading of 0.37 mg·cm³. -2 Pt / C catalysts (JM-40wt%) were prepared under the same conditions. The experimental setup was continuously purged with O2. Initial activation of all catalysts was performed using cyclic voltammetry (CV) curves from 1 to 0.2 V. Linear sweep voltammetry (LSV) curves were obtained at 5 mV·s. -1 The scan rate and rotation speed were 1600 rpm, and the results were used to evaluate catalyst performance. LSV curves were collected under N2 saturation conditions at the same scan rate to eliminate background current interference.

[0105] All potentials were converted to the reversible hydrogen electrode (RHE) scale using the Nernst equation:

[0106] E RHE =E (Hg / HgO) +E 0(Hg / HgO) +0.0592*pH

[0107] The oxygen reduction catalytic performance test results for all samples are shown in Table 2 below.

[0108] Table 2

[0109] sample <![CDATA[E onset ]]> <![CDATA[E 1 / 2 ]]> <![CDATA[Fe3C / FeN@CNT-800]]> 0.97 0.83 <![CDATA[Fe3C / FeN@CNT-900]]> 0.99 0.89 <![CDATA[Fe3C / FeN@CNT-1000]]> 0.97 0.87 <![CDATA[Fe / Fe3C@CNT]]> 0.86 0.78 <![CDATA[Co3C / CoN@CNT]]> 0.99 0.88 Fe-NC 0.89 0.79 Pt / C 0.98 0.86

[0110] like Figure 11 Fe3C / FeN@CNT-900 exhibited excellent ORR activity, achieving a half-wave potential of 0.89V (E0.05). 1 / 2 It is superior to Fe3C / FeN@CNT-800 (E) 1 / 2 =0.83V), Fe3C / FeN@CNT-1000(E 1 / 2 =0.87V) and JM-40%Pt / C(E 1 / 2 =0.86V). The lowest Tafel slope of Fe3C / FeN@CNT-900 is 72mV·dec. -1Similar to JM-40%Pt / C.

[0111] like Figure 12 The mass loading of 0.4 mg·cm³ was measured using a rotating ring-disc electrode (RRDE). -2 The Fe3C / FeN@CNT-900 further confirms the ability of the four-electron ORR pathway, with an electron transfer number (n) of approximately 3.9, close to 4.0, demonstrating that the ORR of this catalyst follows a four-electron pathway.

[0112] like Figure 13 The Fe3C / FeN@CNT-900 electrode exhibits a higher power density (145.5 mW·cm-2) compared to Pt / C-based cells.

[0113] like Figure 14 As shown, after 100 hours of continuous operation, Fe3C / FeN@CNT-900 maintained a current retention rate of 94.3% at 0.87V, demonstrating excellent durability.

[0114] like Figure 15 As shown, in an O2-saturated 0.1M KOH solution, at 50 mV·s -1 After 10,000 CV cycles at a scan rate within a potential range of 0.2-1.2V vsRHE, the E of Fe3C / FeN@CNT-900 was... 1 / 2 The value decreased by only 9mV, which is far superior to commercial Pt / C (JM-40%).

[0115] like Figure 16 As shown, Fe3C / FeN@CNT-900 exhibits excellent tolerance to methanol, with only a slight decrease in current density in 0.5M methanol, while the commercial Pt / C (JM-40%) catalyst shows a sharp decrease in current density after contact with methanol.

[0116] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A carbon nanotube encapsulating M-NC single atoms and M3C nanoparticles, characterized in that, The carbon nanotubes serve as the outer framework, and the encapsulated metal element M is wrapped in the carbon nanotubes in the form of M-NC single atoms and M3C nanoparticles.

2. The carbon nanotube encapsulating M-NC single atoms and M3C nanoparticles according to claim 1, characterized in that, The metallic element M is either iron or cobalt.

3. A method for preparing carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles as described in claim 1 or 2, characterized in that, Includes the following steps: S1, Preparation of mixed solution: Prepare a mixed solution containing organic ligands, metal salts, and zinc salts; S2, Solvent heat treatment: The mixed solution is heated to 100-150°C at a heating rate of 1-5°C per minute, and reacted at a constant temperature for 5-10 hours. After cooling, the precursor is obtained. S3, High-temperature heat treatment: The precursor is mixed with dicyandiamide and heated to 800-1000℃ for 2-3 hours at a heating rate of 1-5℃ per minute under an inert atmosphere. After cooling, the final product is obtained.

4. The method for preparing carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles according to claim 3, characterized in that, The organic ligand is a cyano-containing organic ligand.

5. The method for preparing carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles according to claim 4, characterized in that, The cyano-containing organic ligand includes 4,5-dicyanimidazole.

6. The method for preparing carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles according to claim 4 or 5, characterized in that, The metal salt includes iron salt or cobalt salt, and the molar ratio of zinc salt to metal salt is (5-10):1; the molar ratio of organic ligand to metal salt is 4:(0.1-0.5).

7. The method for preparing carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles according to claim 6, characterized in that, In S3, the mass ratio of the precursor to dicyandiamide is 1:(5-8).

8. The application of the carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles as described in claim 1 or 2 as an oxygen reduction electrocatalyst.

9. The application according to claim 8, characterized in that, The applications include: use as an oxygen reduction electrocatalyst in zinc-air batteries.

10. A zinc-air battery, characterized in that, The battery comprises carbon nanotubes encapsulating M-NC single atoms and M3C nanoparticles as described in claim 1 or 2.

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