An iron-nitrogen-carbon catalyst and its preparation method and application

Abstract

The present invention relates to the technical field of ORR catalyst preparation, and in particular to an iron-nitrogen-carbon catalyst and its preparation method and application. The present invention provides a method for preparing an iron-nitrogen-carbon catalyst, characterized in that it comprises: dispersing a zinc salt and a ferrous salt in methanol to obtain a mixed solution A; under heating conditions, dispersing 2-methylimidazole and 1,4-terephthalonitrile in methanol to obtain a mixed solution B; stirring and mixing the mixed solution A and the mixed solution B to obtain a precursor powder, and calcining the precursor powder under an inert atmosphere to obtain an iron-nitrogen-carbon catalyst with a hierarchical porous structure. The present invention provides a new preparation method for preparing an iron-nitrogen-carbon catalyst with a hierarchical pore structure, which prepares the iron-nitrogen-carbon catalyst with a hierarchical pore structure by introducing a 1,4-terephthalonitrile molecular template.

Description

Technical Field

[0001] The present invention relates to the technical field of ORR catalyst preparation, and in particular to an iron-nitrogen-carbon catalyst and a preparation method and application thereof. Background Art

[0002] Oxygen reduction reaction (ORR) is an important electrochemical process related to energy devices such as fuel cells and metal-air batteries, which has attracted extensive attention in the past few decades. It is well known that platinum-based electrocatalysts can perfectly solve the 4e - The ORR reaction is slow, but its high cost, resource scarcity, and susceptibility to poisoning make it difficult to apply on a large scale. Therefore, there is an urgent need to develop efficient, durable, and non-precious electrocatalysts to not only replace platinum-based materials in ORR, but also to achieve breakthroughs in large-scale applications.

[0003] Transition metal-nitrogen-carbon (MNC, M = Fe, Co, Mn, etc.) catalysts exhibit excellent electrocatalytic performance and good stability for the organic reaction reaction (ORR). Notably, iron-nitrogen-carbon (Fe-NC) catalysts, particularly those based on ZIF8 zeolite, have emerged as the most promising MNC-based ORR catalysts due to their high electrochemical potential and low reaction energy barrier. However, the carbonization process of ZIF8-derived Fe-NC catalysts typically produces a microporous structure characterized by insufficient porosity and limited mass transfer pathways, leading to a rapid decline in catalytic performance during the reaction. Therefore, it is imperative to develop new, efficient Fe-NC catalysts with hierarchical pore structures to enhance their catalytic activity.

[0004] The strategic design of hierarchical pore structures is considered to be an efficient method to enhance catalyst mass transfer and optimize the utilization of active sites. Specifically, micropores are crucial for exposing catalytic active sites, mesopores improve molecular mass efficiency, and macropores significantly improve mass transfer efficiency. Xie Y, Yu X, Jin Z, et al. Dual-template strategy synthesis of hierarchically porous electrocatalysts for oxygen reduction reaction [J]. Advanced Sensor and Energy Materials, 2022, 1(2): 100006. et al. used silica and sodium chloride as templates to create mesopores and synthesized (FeCo)HPNC@NaCl catalysts, which exhibited ORR activity comparable to commercial Pt / C under acidic conditions. Zhu C, Shi Q, Xu B, et al. Hierarchically Porous M-NC (M = Co and Fe) Single-Atom Electrocatalysts with Robust MNx Active Moieties Enable Enhanced ORR Performance [J]. Advanced Energy Materials, 2018, 8(29): 1801956. et al. used a combination of silica colloid and zinc chloride as a pore-inducing template to synthesize MNC (M = Fe, Co), producing a porous structure and atomically dispersed MN2 active sites, which showed excellent activity and stability in ORR performance.

[0005] Therefore, current methods primarily rely on hard-template, soft-template, and hybrid-template approaches, which result in complex synthetic procedures, reduced productivity, and increased costs, hindering large-scale commercial manufacturing. Furthermore, the structural integrity and porosity of synthesized catalysts can be compromised during the template removal process, especially when using environmentally harmful solvents such as hydrofluoric acid and hot alkaline solutions. Summary of the Invention

[0006] The present invention provides an iron-nitrogen-carbon catalyst, its preparation method, and its application. The invention provides a novel synthesis method for an iron-nitrogen-carbon catalyst with a hierarchical pore structure. The preparation method is simple and efficient, and does not require harmful reagents to obtain a complete hierarchical pore structure. Furthermore, the obtained iron-nitrogen-carbon catalyst exhibits excellent ORR activity.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing an iron-nitrogen-carbon catalyst, which is characterized by comprising:

[0009] S1. A zinc salt and a ferrous salt are dispersed in methanol to obtain a mixture A. Under heating conditions, 2-methylimidazole and 1,4-terephthalonitrile are dispersed in methanol to obtain a mixture B.

[0010] S2. Mixed solution A and mixed solution B are stirred and mixed to obtain a precursor powder, which is calcined under an inert atmosphere to obtain an iron-nitrogen-carbon catalyst having a hierarchical porous structure.

[0011] During the initial preparation of the ZIF8 material, the applicant introduced 1,4-terephthalonitrile as a molecular template, which facilitated the aggregation of smaller ZIF8 precursors into larger catalyst particles. This process promoted the aggregation of individual catalytic molecules during the pyrolysis phase, helping to establish a more stable solid catalytic interface, manifested in a hierarchical porous structure and improved graphitization, ultimately resulting in an iron-nitrogen-carbon catalyst with a hierarchical porous structure.

[0012] Preferably, the zinc salt is zinc nitrate, and the ferrous salt is ferrous sulfate.

[0013] Preferably, in S1, the molar ratio of zinc in the zinc salt, iron in the ferrous salt, 2-methylimidazole and 1,4-terephthalonitrile is 5:0.2:(40-42):(0.3-2).

[0014] More preferably, the molar ratio of zinc in the zinc salt, iron in the ferrous salt, 2-methylimidazole and 1,4-terephthalonitrile is 5:0.2:(40-42):(0.7-1).

[0015] Preferably, in S1, the heating condition is: heating to 60-70° C. in an oil bath.

[0016] Preferably, in S2, the stirring and mixing time is 6 to 8 hours, and after stirring and mixing, the precursor powder is dried in vacuum at 60 to 80° C. for 12 to 24 hours.

[0017] Preferably, in said S2, the inert atmosphere is nitrogen and / or argon.

[0018] Preferably, in S2, the calcination method is: heating to 180-200° C. and keeping the temperature for 2-3 hours, and then continuing to heat to 800-900° C. and keeping the temperature for 2-3 hours.

[0019] Preferably, the temperature is increased to 180-200° C. at a rate of 8-10° C. / min, and then continued to be increased to 800-900° C. at a rate of 3-5° C. / min.

[0020] Further preferably, in S2, the calcination method is: heating to 200°C at 10°C / min and keeping it at that temperature for 2 hours, and then heating to 900°C at 5°C / min and keeping it at that temperature for 2 hours.

[0021] The present invention also provides an iron-nitrogen-carbon catalyst having a hierarchical porous structure of micropores and mesopores, a defect density ≥0.97, and a particle size of 550-650 nm.

[0022] Preferably, the specific surface area of the iron-nitrogen-carbon catalyst is 600-800 m 2 / g, and the mesopore area is 420~440 m 2 / g, pore volume is 1.0~1.5 cm 3 / g.

[0023] The iron-nitrogen-carbon catalyst prepared by the above method exhibits a hierarchical porous structure. Combined Raman and XPS characterization results demonstrate that the obtained iron-nitrogen-carbon catalyst possesses a hierarchical porous structure that enhances the mass transfer efficiency of the catalyst's active sites and a high defect density that promotes oxygen adsorption. Furthermore, the hierarchical porous structure enhances the content of pyridinic and graphitic nitrogen, resulting in an iron-nitrogen-carbon catalyst with excellent ORR activity.

[0024] The present invention also provides a zinc-air battery, which uses the iron-nitrogen-carbon catalyst as a catalyst material for the cathode.

[0025] The use of an iron-nitrogen-carbon catalyst with a hierarchical porous structure can effectively help zinc-air batteries improve their open-circuit voltage, specific capacity, stability, and other performance. This has been shown to have significant battery performance and holds broad application prospects in zinc-air fuel cells.

[0026] Therefore, the present invention has the following beneficial effects:

[0027] (1) The present invention provides a new preparation method for preparing an iron-nitrogen-carbon catalyst with a hierarchical pore structure, wherein the iron-nitrogen-carbon catalyst with a hierarchical pore structure is prepared by introducing a 1,4-terephthalonitrile molecular template.

[0028] (2) The iron-nitrogen-carbon catalyst provided by the present invention has a hierarchical porous structure, which can help improve the mass transfer efficiency of the catalyst active sites, and its high defect density can promote the adsorption of oxygen; in addition, the emergence of the hierarchical porous structure helps to enhance the content of pyridinic N and graphitic N, and the iron-nitrogen-carbon catalyst finally obtained has excellent ORR activity.

[0029] (3) The zinc-air battery provided by the present invention utilizes an iron-nitrogen-carbon catalyst as a cathode catalyst, which significantly improves the open circuit voltage, specific capacity, stability and other performance of the battery, proving that the iron-nitrogen-carbon catalyst can be widely used as a catalyst source for zinc-air batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Fe-N / C 1,4-DB Schematic diagram of the preparation of a series of catalysts;

[0031] Figure 2 The scanning electron microscope image of the Fe-N / C series catalyst, where a is Fe-ZIF8 1,4-DB-0.1 SEM images of b and Fe-N / C 1,4-DB-0.1 SEM images of Fe-N / C at different magnifications. 1,4-DB-0.1 HRTEM image of Fe-N / C 1,4-DB-0.1 Mapping diagram;

[0032] Figure 3 Fe-ZIF8 and Fe-ZIF8 / 1,4-DB-0.1 FT-IR spectrum of

[0033] Figure 4 Fe-N / C 1.4-DB-Y Performance characterization diagrams of a series of catalysts, where a is the nitrogen adsorption-desorption isotherm curve, b is the pore size distribution curve, c is the XRD pattern, d is the Raman spectrum, e is the high-resolution XPS spectrum of N 1s, and f is the high-resolution XPS spectrum of Fe 2p;

[0034] Figure 5 Fe-N / C 1,2-DB-0.1 Nitrogen adsorption-desorption isotherm curve of the catalyst;

[0035] Figure 6 Fe-N / C 1,2-DB-0.1 Pore size distribution curve of the catalyst;

[0036] Figure 7 Fe-N / C 1.4-DB-Y XPS spectra of a series of catalysts;

[0037] Figure 8 Fe-N / C 1,4-DB-0.1 Changes in N content of the catalyst;

[0038] Figure 9 Fe-N / C 1,2-DB-0.1 XPS spectrum of the catalyst;

[0039] Figure 10Figure 3 is the electrochemical performance diagram of the catalyst, where a is the cyclic voltammetry curve, b is the linear sweep voltammetry curve, c is the Tafel slope diagram, d is the electron transfer number and hydrogen peroxide yield, e is the chronoamperometric response, and f is the current-time chronoamperometric response;

[0040] Figure 11 Fe-N / C 1.4-DB-Y ORR performance diagram of a series of catalysts;

[0041] Figure 12 Fe-N / C 1,2-DB-0.1 Linear sweep voltammetry curves of the catalyst;

[0042] Figure 13 Fe-N / C 1,3-DB-0.1 Linear sweep voltammetry curves of the catalyst;

[0043] Figure 14 The performance test diagram of the zinc-air battery, where a is the schematic diagram of the zinc-air battery device, b is the open circuit voltage curve, c is the polarization curve and power density, and d is the Fe-N / C 1,2-DB-0.1 Photo of a red LED lit by a zinc-air battery with a catalyst, e is the full discharge curve and its corresponding specific capacity, and f is the constant current discharge curve at different current densities. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below generally represent only a portion of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0045] In this work, FeSO₄·7H₂O, 2-methylimidazole (AR 98%), methanol (AR 99.5%), 1,4-terephthalonitrile (AR 98%), 1,4-ophthalonitrile (AR 98%), and 1,4-isophthalonitrile (AR 98%) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Zn(NO₃)₂·6H₂O was purchased from Sinopharm Chemical Reagent Co., Ltd.; Pt / C catalyst (20%) was purchased from Suzhou Sinero Technology Co., Ltd.; and Nafion D520 (5%) was purchased from DuPont China Holdings Co., Ltd. All reagents used in this work were not further purified.

[0046] [Example]

[0047] Example 1

[0048] S1. Zn(NO3)2·6H2O (1.5024 g, 5 mmol) and FeSO4·7H2O (0.0561 g, 0.2 mmol) were dispersed in 30 mL of methanol to obtain mixed solution A. 2-Methylimidazole (3.3510 g, 40.8 mmol) and 1,4-terephthalonitrile (0.10 g, 0.78 mmol) were dispersed in 30 mL of methanol and then stirred in an oil bath at 60°C to obtain mixed solution B.

[0049] S2. Add mixed solution A to mixed solution B and stir for 6 h. Centrifuge to obtain a reddish-yellow precipitate, then wash it three times with methanol to remove impurities in the precipitate, and dry it in a vacuum drying oven at 80°C for 12 h to obtain Fe-ZIF8 / 1,4-DB-0.1 Precursor powder.

[0050] S3. Under nitrogen atmosphere, Fe-ZIF8 / 1,4-DB-0.1 The precursor powder was pyrolyzed in a tube furnace. The temperature was first raised to 200°C at 10°C / min and kept at this temperature for 2 h, then continued to rise to 900°C at 5°C / min and kept at this temperature for 2 h. 1,4-DB-0.1 catalyst.

[0051] Example 2

[0052] S1. Zn(NO3)2·6H2O (1.5024 g, 5 mmol) and FeSO4·7H2O (0.0561 g, 0.2 mmol) were dispersed in 30 mL of methanol to obtain mixed solution A. 2-Methylimidazole (3.3510 g, 40.8 mmol) and 1,4-terephthalonitrile (0.05 g, 0.39 mmol) were dispersed in 30 mL of methanol and then stirred in an oil bath at 60°C to obtain mixed solution B.

[0053] S2. Add mixed solution A to mixed solution B and stir for 6 h. Centrifuge to obtain a reddish-yellow precipitate, then wash it three times with methanol to remove impurities in the precipitate, and dry it in a vacuum drying oven at 80°C for 12 h to obtain Fe-ZIF8 / 1,4-DB-0.05 Precursor powder.

[0054] S3. Under nitrogen atmosphere, Fe-ZIF8 / 1,4-DB-0.1 The precursor powder was pyrolyzed in a tube furnace. The temperature was first raised to 200°C at 10°C / min and kept at this temperature for 2 h, then continued to rise to 900°C at 5°C / min and kept at this temperature for 2 h. 1,4-DB-0.05 catalyst.

[0055] Example 3

[0056] S1. Zn(NO3)2·6H2O (1.5024 g, 5 mmol) and FeSO4·7H2O (0.0561 g, 0.2 mmol) were dispersed in 30 mL of methanol to obtain mixed solution A. 2-Methylimidazole (3.3510 g, 40.8 mmol) and 1,4-terephthalonitrile (0.25 g, 1.95 mmol) were dispersed in 30 mL of methanol and then stirred in an oil bath at 60°C to obtain mixed solution B.

[0057] S2. Add mixed solution A to mixed solution B and stir for 6 h. Centrifuge to obtain a reddish-yellow precipitate, then wash it three times with methanol to remove impurities in the precipitate, and dry it in a vacuum drying oven at 80°C for 12 h to obtain Fe-ZIF8 / 1,4-DB-0.25 Precursor powder.

[0058] S3. Under nitrogen atmosphere, Fe-ZIF8 / 1,4-DB-0.1 The precursor powder was pyrolyzed in a tube furnace. The temperature was first raised to 200°C at 10°C / min and kept at this temperature for 2 h, then continued to rise to 900°C at 5°C / min and kept at this temperature for 2 h. 1,4-DB-0.25 catalyst.

[0059] Comparative Example 1

[0060] S1. Zn(NO3)2·6H2O (1.5024 g, 5 mmol) and FeSO4·7H2O (0.0561 g, 0.2 mmol) were dispersed in 30 mL of methanol to obtain mixed solution A. 2-Methylimidazole (3.3510 g, 40.8 mmol) was dispersed in 30 mL of methanol and then stirred in an oil bath at 60°C to obtain mixed solution B.

[0061] S2. Add Mixture A to Mixture B and stir for 6 h. Centrifuge to obtain a reddish-yellow precipitate. Wash the precipitate three times with methanol to remove impurities and dry it in a vacuum oven at 80°C for 12 h to obtain Fe-ZIF8 precursor powder.

[0062] S3. Under nitrogen atmosphere, Fe-ZIF8 / 1,4-DB-0.1 The precursor powder was pyrolyzed in a tube furnace. The temperature was first raised to 200°C at 10°C / min and held for 2 hours. The temperature was then further increased to 900°C at 5°C / min and held for 2 hours. The Fe-N / C catalyst was calcined.

[0063] Comparative Example 2

[0064] S1. Zn(NO3)2·6H2O (1.5024 g, 5 mmol) and FeSO4·7H2O (0.0561 g, 0.2 mmol) were dispersed in 30 mL of methanol to obtain mixed solution A. 2-Methylimidazole (3.3510 g, 40.8 mmol) and 1,2-phthalonitrile (0.10 g, 0.78 mmol) were dispersed in 30 mL of methanol and then stirred in an oil bath at 60°C to obtain mixed solution B.

[0065] S2. Add mixed solution A to mixed solution B and stir for 6 h. Centrifuge to obtain a reddish-yellow precipitate, then wash it three times with methanol to remove impurities in the precipitate, and dry it in a vacuum drying oven at 80°C for 12 h to obtain Fe-ZIF8 / 1,2-DB-0.1 Precursor powder.

[0066] S3. Under nitrogen atmosphere, Fe-ZIF8 / 1,4-DB-0.1 The precursor powder was pyrolyzed in a tube furnace. The temperature was first raised to 200°C at 10°C / min and kept at this temperature for 2 h, then continued to rise to 900°C at 5°C / min and kept at this temperature for 2 h. 1,2-DB-0.1 catalyst.

[0067] Comparative Example 3

[0068] S1. Zn(NO3)2·6H2O (1.5024 g, 5 mmol) and FeSO4·7H2O (0.0561 g, 0.2 mmol) were dispersed in 30 mL of methanol to obtain mixed solution A. 2-Methylimidazole (3.3510 g, 40.8 mmol) and 1,3-isophthalonitrile (0.10 g, 0.78 mmol) were dispersed in 30 mL of methanol and then stirred in an oil bath at 60°C to obtain mixed solution B.

[0069] S2. Add mixed solution A to mixed solution B and stir for 6 h. Centrifuge to obtain a reddish-yellow precipitate, then wash it three times with methanol to remove impurities in the precipitate, and dry it in a vacuum drying oven at 80°C for 12 h to obtain Fe-ZIF8 / 1,3-DB-0.1 Precursor powder.

[0070] S3. Under nitrogen atmosphere, Fe-ZIF8 / 1,4-DB-0.1 The precursor powder was pyrolyzed in a tube furnace. The temperature was first raised to 200°C at 10°C / min and kept at this temperature for 2 h, then continued to rise to 900°C at 5°C / min and kept at this temperature for 2 h. 1,3-DB-0.1 catalyst.

[0071]

Performance test

[0072] 1. Morphology and structure

[0073] The Fe-ZIF8 precursor powder and Fe-ZIF8 / 1,4-DB-0.1 The functional groups contained in the precursor powder are as follows Figure 3 As shown. It can be seen that Fe-ZIF-8 / 1,4-DB-0.1 In the FT-IR spectrum, at about 2450 cm −1 There is an obvious characteristic peak of -CN bond at , which indicates that C and N have successfully entered the framework of ZIF8.

[0074] Furthermore, the Fe-N / C 1,4-DB-0.1 The catalyst was characterized by scanning electron microscopy and transmission electron microscopy. Figure 2 shown. Figure 2 b in the equation is Fe-ZIF8 / 1,4-DB-0.1 The SEM image of the precursor powder shows that Fe-ZIF8 / 1,4-DB-0.1 The precursor powder has a regular hexahedral structure and a particle size of about 250 nm. 1,4-DB-0.1 The precursor powder was calcined and carbonized to obtain Fe-N / C 1,4-DB-0.1 Catalyst, its structure is as Figure 2 As shown in Figure c, after carbonization, its surface changes from a smooth hexahedral structure to a rough spherical structure, and the particle size increases to 600 nm. 1,4-DB-0.1 After the catalyst was characterized by transmission electron microscopy, it was found that the carbonized Fe-N / C 1,4-DB-0.1 The catalyst showed an obvious porous structure, which can explain the increase in the particle size of the catalyst particles after carbonization due to the appearance of a loose porous structure.

[0075] Figure 2 g in Fe-N / C 1,4-DB-0.1 Catalyst mapping diagram, it can be observed that C, N, and Fe are evenly distributed in the Fe-N / C 1,4-DB-0.1 The results of FT-IR spectrum show that C and N have successfully entered into the framework of ZIF8, and the basic framework of ZIF8 is retained after carbonization, while C and N have successfully doped into the Fe-N / C 1,4-DB-0.1 In the catalyst.

[0076] 2. Microstructure Characterization

[0077] The nitrogen physical adsorption technology was used to 1.4-DB-Y (Y=0.05, 0.1, 0.25) catalyst, Fe-N / C 1.2-DB-0.1 and Fe-N / C 1.3-DB-0.1The specific surface area and pore size of Figure 4 a in Figure 4 b in Figure 5 and Figure 6 shown.

[0078] Figure 4 a in Fe-N / C and Fe-N / C 1.4-DB-Y Nitrogen adsorption-desorption isotherm curves of the catalyst (Y=0.05, 0.1, 0.25) show that: all Fe-N / C 1.4-DB-Y All catalysts exhibited micropores and mesopores. At higher N₂ pressures (P / P₀ = 0.4-0.95), the presence of micropores led to a pronounced hysteresis curve. In contrast, the Fe-N / C catalyst exhibited a type IV isotherm at relatively low N₂ pressures (P / P₀ = 0-0.015) and lacked mesoporous structures. Figure 4 b in Fe-N / C and Fe-N / C 1.4-DB-Y The pore size distribution of the catalyst (Y = 0.05, 0.1, 0.25) and the specific surface area data in Table 1 show that: Fe-N / C 1.4-DB-Y0.1 Catalyst specific surface area (762 m 2 / g) and the highest pore volume (1.24 cm 3 / g), mesopore area (430.64 m 2 / g) is the largest. After introducing 1,4-terephthalonitrile as a molecular template, Fe-N / C 1.4-DB-Y Compared with Fe-N / C catalyst, the specific surface area, pore volume and mesopore area of the catalyst are improved to varying degrees. This shows that by using 1,4-terephthalonitrile as a molecular template, mesopores can be introduced into ZIF-8, and the change in the pore structure of the catalyst helps to improve the mass transfer efficiency of the catalyst active site. Figure 5 and Figure 6 The results showed that 1,2-phthalonitrile with similar structure could not achieve the same effect as 1,4-terephthalonitrile. Fe-N / C using 1,2-phthalonitrile as molecular template 1,2-DB-0.1 The catalyst does not show a hierarchical structure of micropores and mesopores.

[0079] Table 1 BET result data table

[0080]

[0081] After obtaining the above internal pore structure distribution results, the Fe-N / C 1,2-DB-0.1 Catalyst and Fe-N / C 1.4-DB-Y0.1 The catalyst was characterized by XPS. Figure 4 e in Figure 4 f and Figures 7-9 shown.

[0082] like Figure 4 As shown in Figure e: The Fe 2p spectrum has characteristic peaks at 710.6 eV and 723.6 eV, corresponding to Fe 2+ (III) and Fe 2+ (II). In addition, the peaks at 714.6 eV and 727.6 eV are attributed to Fe 3+ (III) and Fe 3+ (II). Figure 4 f and Figure 7 It shows that pyridinic N (398.5 eV), pyrrolic N (400.3 eV), graphitic N (401.0 eV) and oxidized N (402.7 eV) are present in all samples. It is worth noting that pyridinic N and graphitic N constitute the main peaks of the N 1s XPS spectrum, which not only helps to improve the ORR activity, but also pyridinic N and graphitic N can serve as anchor points for Fe atoms to enhance the stability of the catalytic material. Figure 8 The results show that the incorporation of molecular template 1,4-terephthalonitrile leads to the formation of Fe-NC / 1，4-DB-0.1 The increased contents of pyridinic N and graphitic N in the catalyst provide a large number of coordinated environments that are conducive to the formation of active sites, thereby enhancing the ORR performance of the catalyst.

[0083] Furthermore, for Fe-N / C 1.4-DB-Y (Y=0.05, 0.1, 0.25) The catalysts were characterized by XRD and Raman. Figure 4 Figure c shows the corresponding XRD results, revealing two prominent diffraction peaks (24.2° and 42.3°), both characteristic of carbon. Furthermore, diffraction peaks of varying intensities were observed at 35.4°, 53.5°, and 56.7°, corresponding to the crystalline structure of ferroferric oxide. In summary, the intensity of the ferroferric oxide diffraction peaks decreases with increasing 1,4-terephthalonitrile content. Figure 4 The d in the figure is the Raman spectrum at 1335 cm -1 and 1594 cm -1 There are two characteristic peaks at the d-band and g-band. The degree of carbon defects is usually quantified by the ratio of the d-band to the g-band intensities (ID / IG). Comparing the ID / IG values of different catalysts, it is found that Fe-N / C 1,4-DB-0.1 The defect density of Fe-N / C (0.98) is greater than that of Fe-N / C (0.96). These results indicate that the incorporation of molecular templates can increase the defect density in the catalyst, thereby promoting oxygen adsorption and enhancing the ORR performance of the catalyst.

[0084] 3. Electrochemical performance

[0085] The tests in this section were conducted on a CHI760E electrochemical workstation using 0.1 M potassium hydroxide solution as the electrolyte. A three-electrode setup was employed: a platinum (Pt) counter electrode, a glassy carbon electrode (GCE) coated with the catalyst ink as the working electrode, and a saturated calomel electrode (SCE) as the reference electrode. The catalyst ink was prepared by dispersing 5 mg of the catalyst in 1 mL of a solution containing 985 μL of ethanol, 5 μL of 5% Nafion solution, and 10 μL of water. The solution was sonicated for at least 30 minutes.

[0086] Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) experiments were performed in the potential range of 0–1.2 V at a scan rate of 100 mV·s. -1 Before the experiment, the sample was purged with O2 / N2 gas for 30 min at ambient temperature. Then, the sample was rotated at 1600 rpm and scanned at a rate of 5 mV·s. -1 The oxygen reduction polarization curves (ORR polarization curves) of the catalysts were obtained under the conditions of a voltage range of 0–1.2 V vs. RHE. The potential cycling was repeated until a stable linear sweep voltammogram was obtained. ORR polarization curves were generated under the same test conditions using a platinum ring electrode with the ring voltage set to 1.5 V (vs RHE). These curves can be used to calculate the electron transfer number and hydrogen peroxide yield using equations (1) and (2).

[0087] (1)

[0088] (2)

[0089] In the above formula, n is the number of electron transfers, HO 2 - is the peroxide yield, %; I d is the current of the glassy carbon disk, A; I r is the current of the platinum ring, A; N is the current collection efficiency of the RRDE platinum ring (N = 0.37).

[0090] The electrocatalytic stability was evaluated using the constant current (IT) method for the oxygen reduction reaction. A constant voltage of 0.8 V (vs RHE) was applied to the catalyst-loaded glassy carbon electrode in an oxygen-saturated 0.1 M potassium hydroxide solution. 5000 cycles were performed at a scan rate of 50 mV·s. -1 The cyclic voltammogram curves were used to induce catalyst aging.

[0091] The Fe-N / C 1,4-DB-0.1 ORR performance of the catalysts. A comparative analysis of Fe-N / C and Pt / C catalysts was performed. All tested potentials were calibrated to a reversible hydrogen electrode (RHE). Figure 11 and Figure 10 a in the figure is the cyclic voltammetry curve, Fe-N / C doped with 1,4-terephthalonitrile molecular template 1,4-DB-0.1 The catalyst has a large curve area. By adjusting the amount of 1,4-terephthalonitrile added, it was found that when the amount of 1,4-terephthalonitrile was 0.1 g, the Fe-N / C 1,4-DB-0.1 In addition, combined with Figure 11 and Figure 10 From b in the figure, we can see that Fe-N / C 1,4-DB-0.1 The catalyst also has the highest half-potential (E 1 / 2 =0.90 V vs RHE) and the maximum limiting current density. Compared with Fe-N / C (0.85 V vs RHE) and 20 wt% Pt / C (0.86 V vs RHE), Fe-N / C 1,4-DB-0.1 The improvement of the catalyst is very significant. In addition, Figure 11 and Figure 10 The ORR performance data of b in the figure can confirm that the addition of 1,4-terephthalonitrile molecular template can effectively improve the ORR activity, which is consistent with the Raman results: it proves that the addition of 1,4-terephthalonitrile molecular template can increase the defect density in the catalyst and promote the adsorption of oxygen, which ultimately manifests as an improvement in ORR activity. At the same time, this is consistent with the Fe-N / C 1,4-DB-0.1 The structural characteristics of the hierarchical pores in the catalyst are also closely related. The hierarchical pore structure helps improve the mass transfer efficiency of the catalyst active sites and helps improve the ORR activity. Figure 12 and Figure 13 When 1,2-phthalonitrile and 1,3-isophthalonitrile were used as molecular templates, their ORR activity was lower than that when 1,4-terephthalonitrile was used. The reason for this may be that 1,2-phthalonitrile did not show a hierarchical pore structure when used as a molecular template, and it was not an effective template. In addition, the change trend of its N site was different from that of 1,4-terephthalonitrile, and Fe-N x , ultimately leading to reduced ORR activity. When 1,3-isophthalonitrile was used as a molecular template, ORR activity decreased directly. This is speculated to be due to the lack of a hierarchical pore structure, similar to 1,2-phthalonitrile, which ultimately leads to suboptimal ORR activity. Therefore, forming a hierarchical pore structure is the most critical factor in selecting a molecular template.

[0092] Furthermore, the kinetic performance of ORR was evaluated using the Tafel slope, and the results were recorded in Figure 10 In the c. It can be seen that Fe-N / C 1,4-DB-0.1 The Tafel slope of is the lowest, indicating that it experiences the lowest overpotential during the ORR catalysis process, thus exhibiting fast dynamic characteristics. Figure 10 The d in the figure is the comparison data of electron transfer number and hydrogen peroxide yield. It is found that Fe-N / C 1,4-DB-0.1 The hydrogen peroxide yield was always less than 3%, while the electron transfer efficiency was about 4.0. These data indicate that the Fe-N / C 1,4-DB-0.1 In the catalytic oxidation process, the electron transfer mechanism dominates the occurrence of the catalytic reaction.

[0093] Furthermore, the constant current method was used to evaluate the Fe-N / C 1,4-DB-0.1 The cyclic stability of Figure 10 Figure e shows that after 50,000 s of cycling, the Fe-N / C 1,4-DB-0.1 The current density of the Fe-N / C catalyst decreased by only 7.5%; the control current density decreased by 31.5%, which showed strong cycling stability. In actual catalytic applications, stability is a key factor affecting the commercial feasibility of catalysts. Another ideal catalyst evaluation parameter is methanol resistance. 1,4-DB-0.1 The methanol resistance test was conducted in 0.1 M KOH with 20 wt% Pt / C, and 1 mL of methanol was injected at 200 s. Figure 10 As shown in Figure f, the current change of the catalyst with 1,4-terephthalonitrile molecular template is almost invisible, while the current of 20% Pt / C is significantly reduced, indicating that the Fe-N / C 1,4-DB-0.1 The catalyst has strong methanol resistance.

[0094] 4. Zinc-air battery

[0095] Based on the electrochemical performance test results of the above catalysts, Figure 14 A Zn-air battery was assembled to further evaluate the Fe-N / C 1,4-DB-0.1 Potential applications of catalysts in practical battery systems. 1,4-DB-0.1 The performance test of the zinc-air battery was completed using a catalyst as the cathode catalyst (the electrode carrier was a glassy carbon electrode, GCE), a platinum (Pt) electrode as the counter electrode, a saturated calomel electrode (SCE) as the reference electrode, and a 6 M potassium hydroxide solution as the electrolyte.

[0096] observe Figure 14 b and Figure 14 From the c in the figure, we can see that using Fe-N / C 1,4-DB-0.1The Zn-air battery with the catalyst exhibited an open circuit voltage of 1.467 V and a peak power density of 321 mW cm -2 The zinc-air battery prepared with Pt / C catalyst has an open circuit voltage of 1.459 V and a peak power density of 221 mW cm -2 By comparison, it can be seen that the use of Fe-N / C 1,4-DB-0.1 After adding the catalyst, the performance of the battery is effectively improved. Figure 14 The figure d in the figure is the phenomenon of zinc-air battery. It is found that the application of Fe-NC / 1 ,4-DB-0.1 Zinc-air batteries with Fe-NC / 1,4-DB-0.1 The specific capacity of the zinc-air battery with the catalyst is 807 mAh·g -1 , while the ZAB-based zinc-air battery based on Pt / C is only 715 mAh·g -1 . Figure 14 The f in the figure is the constant current discharge curve of the zinc-air battery assembled at different current densities. It can be seen that the Fe-NC / 1,4-DB-0.1 The catalyst-assembled zinc-air battery exhibited stable discharge capacity, maintaining a consistent plateau at each discharge current density.

[0097] The above results show that Fe-NC / 1,4-DB-0.1 The catalyst exhibits remarkable battery performance and has broad application prospects in zinc-air fuel cells.

Claims

1. A method for preparing an iron-nitrogen-carbon catalyst, characterized in that: include: S1. A zinc salt and a ferrous salt are dispersed in methanol to obtain a mixed solution A. 2-Methylimidazole and 1,4-terephthalonitrile are dispersed in methanol and heated in an oil bath to 60-70°C to obtain a mixed solution B. The molar ratio of zinc in the zinc salt, iron in the ferrous salt, 2-methylimidazole, and 1,4-terephthalonitrile is 5:0.2:(40-42):(0.3-2). S2. Mixed solutions A and B are stirred to obtain a precursor powder. The precursor powder is heated to 180-200°C under an inert atmosphere and maintained for 2-3 hours. The temperature is then further raised to 800-900°C and maintained for 2-3 hours to obtain an iron-nitrogen-carbon catalyst with a hierarchical porous structure.

2. The preparation method according to claim 1, wherein In S2, the stirring and mixing time is 6 to 8 hours, and after stirring and mixing, the precursor powder is dried in a vacuum at 60 to 80° C. for 12 to 24 hours.

3. The preparation method according to claim 1, wherein In the above-mentioned S2, the inert atmosphere is nitrogen and / or argon.

4. The preparation method according to claim 1, wherein Raise the temperature to 180~200℃ at 8~10℃ / min, and continue to raise the temperature to 800~900℃ at 3~5℃ / min.

5. The iron-nitrogen-carbon catalyst prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The iron-nitrogen-carbon catalyst has a hierarchical porous structure of micropores and mesopores, a defect density of ≥0.97, and a particle size of 550-650 nm.

6. The iron-nitrogen-carbon catalyst according to claim 5, characterized in that The specific surface area of the iron-nitrogen-carbon catalyst is 600-800 m 2 / g, and the mesopore area is 420~440 m 2 / g, pore volume is 1.0~1.5 cm 3 / g.

7. A zinc-air battery, characterized in that: The iron-nitrogen-carbon catalyst according to claim 5 or 6 is used as a catalyst material for the cathode.

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