Nitrogen and sulfur co-doped Fe-based diatomic catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the field of catalysts, and particularly relates to a nitrogen-sulfur co-doped Fe-based diatomic catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: by taking hexamethylenetetramine and 2, 4-dihydroxybenzoic acid as hard templates and sodium oleate, P123 and polyethylene glycol with the molecular weight of 4000 as soft templates, uniformly mixing, carrying out hydrothermal reaction to prepare HBP, loading Fe ions, and carrying out nitrogen and sulfur doping with thiourea through high-temperature calcination to obtain the nitrogen and sulfur doped hollow carbon bowl loaded Fe-based diatomic catalyst. The catalyst shows excellent ORR catalytic activity under an alkaline condition and shows excellent application performance in a zinc-air battery.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts, and in particular relates to a nitrogen-sulfur co-doped Fe-based diatomic catalyst, a preparation method and applications thereof. Background Art

[0002] At this critical juncture of energy transition and environmental protection, hydrogen-oxygen fuel cells and metal-air batteries, as highly promising new energy technologies, demonstrate numerous shared advantages. Both rely on chemical reactions to efficiently convert chemical energy into electrical energy. They possess high energy conversion efficiency and excellent energy density, effectively meeting modern society's demand for efficient energy utilization. Furthermore, they produce virtually no greenhouse gases or other harmful pollutants during operation, making them extremely environmentally friendly and consistent with global sustainable development strategies.

[0003] However, the cathode oxygen reduction reaction (ORR) of these two types of batteries involves a complex proton coupling process and is limited by slow reaction kinetics, which affects its overall working efficiency. Therefore, the development of low-cost, high-efficiency ORR cathode catalysts has become the focus of current research. In recent years, single-atom catalysts (SACs) with atomically dispersed iron-nitrogen-carbon (Fe-NC) coordination structures have received widespread attention in the field of electrocatalytic oxygen reduction due to their highly customizable coordination environment, unique electronic structure and nearly 100% atomic utilization. However, due to the existence of a single active site, single-atom catalysts find it difficult to break through the linear relationship of the adsorption energy of oxygen reduction intermediates, thereby limiting the further improvement of their catalytic activity.

[0004] As an extension of the Fe-NC system, the Fe-based diatomic catalyst (Fe2-NC) benefits from the synergistic effect between the two Fe atoms and can enhance the catalytic activity to a certain extent. CN115487847A discloses a method for preparing a heteroatom-doped carbon material with a multi-level ordered pore structure that is adjustable. The method utilizes a dual-mode method of a hard template and a soft template, and adjusts the particle size of the hard template microspheres and the particle size of the soft template micelles to obtain an ordered multi-level porous carbon material with coexistence of macropores, mesopores and micropores; the material is immersed in a transition metal salt solution to prepare a multi-level ordered pore structure that is adjustable. The heteroatom-doped carbon material. CN108695521A discloses a double-level porous Fe-N co-doped carbon material, which is prepared by mixing and dissolving ethyl orthosilicate, a nonionic surfactant, resorcinol, and formaldehyde, and hydrothermally reacting to obtain a silicon template / phenolic resin. After low-temperature carbonization to remove the silicon template, the material is mixed with a metal salt inorganic substance and melamine for calcination, acid leaching, protonating the phenolic resin, removing unstable and inactive substances, and finally carbonizing at high temperature.

[0005] However, conventional nitrogen-coordinated Fe2-NCs have limitations in manipulating the coordination environment to optimize catalytic activity. Precisely controlling the coordination environment is a key strategy for optimizing the electronic structure of metal active sites and enhancing catalytic performance. Therefore, the development of Fe-based diatomic catalysts with tunable coordination environments will provide new insights into the design of efficient ORR catalysts. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention uses a hydrothermal method to prepare a hollow polymer bowl-shaped material (Hollowpolymer bowl, HPB), loads Fe ions, and then performs nitrogen and sulfur doping through high-temperature calcination to obtain a nitrogen- and sulfur-doped hollow carbon bowl-loaded Fe-based diatomic catalyst, which exhibits excellent ORR catalytic activity under alkaline conditions and excellent application performance in zinc-air batteries.

[0007] The present invention adopts the following technical solutions:

[0008] A method for preparing a nitrogen-sulfur co-doped Fe-based diatomic catalyst comprises the following steps:

[0009] (1) HPB was prepared by mixing hexamethylenetetramine and 2,4-dihydroxybenzoic acid as hard templates, sodium oleate, P123, and polyethylene glycol (molecular weight 4000) as soft templates through hydrothermal reaction.

[0010] (2) dispersing a certain amount of HPB in a solvent, adding an iron salt solution, mixing, evaporating, and drying to obtain a HPB-loaded Fe ion precursor;

[0011] (3) The HPB-loaded Fe ion precursor is fully ground with a nitrogen source and a sulfur source, and calcined at a high temperature to obtain the nitrogen-sulfur co-doped Fe-based diatomic catalyst.

[0012] Furthermore, in step (1), the hard template and the soft template are dissolved separately, then fully mixed, and transferred to a reactor for hydrothermal reaction at a temperature of 120-170° C. for 1-3 h.

[0013] Furthermore, in step (1), after the hydrothermal reaction, the mixture is centrifuged and washed multiple times, and then vacuum dried to obtain HPB powder. The HPB powder is in the shape of a hollow bowl.

[0014] Furthermore, in step (2), the solvent is pentane and ultrapure water; and HPB is dispersed in the solvent by ultrasound.

[0015] Furthermore, in step (2), the iron salt is selected from ferric chloride hexahydrate.

[0016] Furthermore, in step (2), stirring is continued during the evaporation process, and vacuum drying is performed after the solvent is completely evaporated. The evaporation of the solvent generates capillary force, which causes Fe 3+ interacts with the hydrophilic groups on the HPB surface and adsorbs to form Fe 3+ Loaded HPB precursor.

[0017] Furthermore, in step (3), the nitrogen source is melamine or thiourea, and the sulfur source is thiourea; preferably, thiourea is used as both the nitrogen source and the sulfur source.

[0018] Furthermore, in step (3), the high-temperature calcination is performed by heating to 800-1200°C at a heating rate of 1-5°C / min under a nitrogen atmosphere and maintaining the temperature for 2-5 hours. After high-temperature calcination, a nitrogen-sulfur co-doped hollow carbon bowl-supported Fe-based diatomic catalyst is obtained.

[0019] The present invention also provides a nitrogen-sulfur co-doped Fe-based diatomic catalyst prepared by the preparation method of any of the above embodiments.

[0020] The present invention also provides the use of the nitrogen-sulfur co-doped Fe-based diatomic catalyst as a cathode oxygen reduction reaction catalyst.

[0021] Furthermore, the cathode oxygen reduction reaction catalyst is used in a fuel cell or a metal-air battery.

[0022] Compared with the prior art, the beneficial effects of the present invention include at least:

[0023] 1. The present invention prepares a hollow polymer bowl-shaped material using hexamethylenetetramine and 2,4-dihydroxybenzoic acid as hard templates and sodium oleate, P123 and polyethylene glycol with a molecular weight of 4000 as soft templates.

[0024] 2. The present invention uses HPB to load iron ions after carbonization, forming a "bowl-shaped cavity" inside the molecule, and there are some specific functional groups around the cavity, which gives it unique molecular recognition and selectivity and high catalytic efficiency.

[0025] 3. Nitrogen and sulfur co-doping can regulate the elemental composition of the diatomic catalyst. While maintaining the morphology of the polymer substrate unchanged, it can adjust the coordination structure of the metal atoms, thereby improving the catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 (a) is a transmission electron microscopy image of Fe-N,S-HCB; Figure 1 Middle (b) is a high-resolution transmission electron microscopy image of Fe-N,S-HCB; Figure 1(c) and (d) are the annular scanning dark-field transmission electron microscopy and elemental mapping of Fe, N, S, and C elements of Fe-N, S-HCB, respectively.

[0027] Figure 2 This is the spherical aberration corrected annular scanning dark-field transmission electron microscopy image of the Fe-N,S-HCB catalyst, in which the diatomic sites are marked by circles.

[0028] Figure 3 (a) is the synchrotron radiation XANES spectrum of Fe-N,S-HCB catalyst; Figure 3 (b) is the synchrotron radiation X-ray extended edge absorption structure R space spectrum of Fe-N,S-HCB catalyst. Figure 3 (c) is the fitted spectrum diagram.

[0029] Figure 4 (a) is the electron paramagnetic resonance spectra of Fe-N,S-HCB catalyst and control catalyst Fe-N-HCB; Figure 4 (b) is a graph showing the temperature dependence of the Fe-N,S-HCB catalyst and the control catalyst Fe-N-HCB - analysis results of the magnetic needle test of the vibrating sample.

[0030] Figure 5 (a) is the linear sweep voltammetry (LSV) curve of Fe-N,S-HCB catalyst, comparative catalyst Fe-N-HCB and commercial Pt / C catalyst in O2-saturated 0.1M KOH solution; Figure 5 (b) is the Tafel slope curve of Fe-N,S-HCB catalyst, comparative catalyst Fe-N-HCB and commercial Pt / C catalyst; Figure 5 (c) is the chronoamperometric (It) test curve of Fe-N,S-HCB catalyst and commercial Pt / C catalyst to evaluate the stability of the catalyst; Figure 5 (d) is the open circuit voltage (OCV) curve of zinc-air batteries (ZABs) assembled with Fe-N,S-HCB catalyst; Figure 5 (e) shows the discharge curve and corresponding power density curve of Fe-N,S-HCB catalyst-based ZABs; Figure 5 (f) is the voltage curve obtained from the cyclic stability test of Fe-N,S-HCB catalyst-based ZABs at different current densities. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and beneficial effects of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. Examples of the embodiments are shown in the accompanying drawings. It should be understood that the specific embodiments described in the following embodiments of the present invention are only exemplary descriptions of the specific embodiments of the present invention, intended to be used for explaining the present invention, and do not constitute a limitation of the present invention.

[0032] The endpoints of ranges and any values ​​disclosed herein are not limited to the exact range or value, and these ranges or values ​​should be understood to include approximations to these ranges.

[0033] Example 1: Preparation of catalyst

[0034] A method for preparing a nitrogen-sulfur co-doped Fe-based diatomic catalyst comprises the following steps:

[0035] (1) Preparation of hollow polymer bowl-shaped materials by hydrothermal method

[0036] First, using hexamethylenetetramine and 2,4-dihydroxybenzoic acid as hard templates, and sodium oleate, P123, and 4000 molecular weight polyethylene glycol as soft templates, 0.088g of hexamethylenetetramine and 0.231g of 2,4-dihydroxybenzoic acid were weighed and dissolved in 75mL of water in beaker A. 0.09g of sodium oleate, 10.875mL of a 5mg / mL aqueous P123 solution, and 10.875mL of a 5mg / mL aqueous polyethylene glycol solution were dissolved in beaker B. The two solutions were stirred at 800 rpm for 30 minutes to thoroughly mix and achieve a homogeneous phase. The resulting solution was then combined in beaker C. After stirring for another 30 minutes, the resulting solution was transferred to a reactor and hydrothermally reacted at 160°C for 120 minutes. After completion of the reaction, the reaction product was washed with deionized water and separated by centrifugation. Subsequently, the obtained product was dried in a vacuum drying oven and fully ground to obtain HPB powder.

[0037] (2) Synthesis of Fe-ion-loaded hollow polymer bowl-shaped materials

[0038] 50.6 mg of HPB was dispersed in pentane and uniformly dispersed under ultrasonic conditions. Then, it was transferred to a constant speed stirrer for stirring. Subsequently, 200 μL of 5 mg / mL FeCl3·6H2O solution was added and stirred continuously until the solvent was completely evaporated. During this process, the evaporation of pentane generated capillary force, which caused the Fe 3+ interacts with the hydrophilic groups on the HPB surface and adsorbs to form Fe 3+ Finally, the obtained material was placed in a vacuum drying oven and dried at 60°C to obtain Fe-HPB powder precursor.

[0039] (3) Synthesis of Nitrogen-Sulfur Co-doped Hollow Polymer Bowls Supported with Fe-Based Catalysts

[0040] The Fe-HPB powder obtained in step (2) was thoroughly ground with 364 mg of thiourea (as a nitrogen and sulfur source), placed in a porcelain boat, and placed in a tube furnace. Under a nitrogen atmosphere, the mixture was heated to 900°C at a heating rate of 2°C / min and held at that temperature for 180 min. After cooling, a nitrogen-sulfur co-doped hollow carbon bowl-supported Fe-based diatomic catalyst, designated Fe-N,S-HCB, was obtained.

[0041] As a control, the catalyst Fe-N-HCB containing only nitrogen doping was synthesized using the same preparation method and melamine as the nitrogen source.

[0042] Example 2: Fe-N,S-HCB catalyst

[0043] (1) Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to preliminarily observe the morphology of the material and the existence form of metallic Fe. The results are as follows: Figure 1 No Fe-based nanoparticles were detected in the TEM images, suggesting that Fe atoms may be dispersed atomically on the carbon substrate surface. Furthermore, the morphology of the hollow carbon bowl substrate was maintained after high-temperature calcination.

[0044] (2) Spherical aberration corrected annular dark field scanning transmission electron microscopy (HAADF-STEM) is used to further reveal the actual existence state of metal atoms, such as Figure 2 As shown, the HAADF-STEM image clearly shows that there are a large number of metal bright spots on the surface of the carbon substrate, and these metal bright spots are distributed in the form of atomic pairs, further confirming the existence of the diatomic structure.

[0045] (3) X-ray absorption spectroscopy (XAS) was used to fit the specific coordination environment of Fe atoms. The spectrum results are shown in the figure below. Figure 3 The fitting result parameters are shown in Table 1.

[0046] The structural analysis results show that in the Fe-N,S-HCB catalyst, two Fe atoms are embedded in the carbon matrix in the form of Fe2N6S1 structure. Among them, each Fe atom exists in the FeN3S1 coordination structure, and the average bond length of Fe-N coordination is The average bond length of Fe-S coordination is In addition, the two Fe atoms are connected by Fe-S-Fe coordination, and the distance between Fe-Fe is

[0047] Table 1. EXAFS fitting results of Fe-N,S-HCB catalyst

[0048]

[0049] (4) The electronic structure of Fe-N,S-HCB catalyst after the introduction of S atoms was analyzed by electron paramagnetic resonance (EPR) spectroscopy and temperature-dependent vibrating sample magnetometer (VSM). The EPR spectral results are shown in Figure 4. Figure 4 (a) shows that after the introduction of S atoms into the N-coordinated Fe-based diatomic structure, the electronic structure spin polarization of Fe atoms is effectively suppressed. In addition, according to the temperature dependence analysis of VSM test, as shown in Figure 4 (b) The number of unpaired electrons in the Fe-N,S-HCB catalyst is 1.6, while that in the comparative catalyst Fe-N-HCB is 1.2, which is consistent with the EPR characterization results. This phenomenon indicates that the introduction of S atoms plays an important role in regulating the electronic structure of Fe-based catalysts.

[0050] Example 3: Oxygen reduction catalytic performance of Fe-N,S-HCB catalyst

[0051] (1) Preparation of catalyst test dispersion

[0052] 2 mg of Fe-N,S-HCB catalyst powder was added to a mixture of 0.78 mL of ultrapure water, 0.2 mL of isopropanol and 0.02 mL of 5% Nafion solution, and ultrasonic dispersion was performed for several minutes to obtain a uniform catalyst dispersion.

[0053] (2) Electrochemical testing

[0054] 42 μL of the prepared Fe-N,S-HCB catalyst dispersion was evenly drop-coated onto the surface of a rotating disk glassy carbon electrode (RDE) as the working electrode. A platinum wire served as the counter electrode, and Ag / AgCl served as the reference electrode. All electrochemical tests were performed on a CHI842 electrochemical workstation.

[0055] (3) Practical application verification

[0056] To further verify the application potential of Fe-N,S-HCB, zinc-air batteries (ZABs) were assembled using it as the air cathode catalyst, zinc flakes as the anode material, and 6M KOH aqueous solution as the electrolyte. All battery tests were performed on a CHI 660 electrochemical workstation.

[0057] The electrochemical performance test and actual application performance test results are as follows Figure 5 As shown:

[0058] (a) Linear sweep voltammetry (LSV) test results curve, the test sweep rate is 100mV / s. The results show that the Fe-N,S-HCB catalyst has high catalytic activity, the onset potential (E onset ) is 0.98 V, and the half-wave potential (E1 / 2) is 0.91 V, both higher than those of commercial Pt / C catalysts (E onset =0.97V; E1 / 2=0.87V).

[0059] (b) Tafel slope curve, obtained from LSV analysis, is used to evaluate the reaction kinetics of the Fe-N,S-HCB catalyst during the reaction. As shown in the figure, the Tafel slope of the Fe-N,S-HCB catalyst is 48.6 mV / dec, which is lower than the 64.9 mV / dec of the commercial Pt / C catalyst, indicating that the Fe-N,S-HCB catalyst has higher reaction kinetics.

[0060] (c) Current-time curve obtained from a chronoamperometric test, demonstrating the current retention performance of the Fe-N,S-HCB catalyst over extended periods of operation. As shown, after 30,000 seconds of stable operation, the Fe-N,S-HCB catalyst maintained a current retention rate of 91.6% of the initial current density, significantly exceeding the 72.9% of the commercial Pt / C catalyst.

[0061] (d) Open-circuit voltage (OCV) curves of zinc-air batteries (ZABs) assembled with Fe-N,S-HCB catalysts. As shown in the figure, ZABs assembled with Fe-N,S-HCB catalysts can provide a high open-circuit voltage of 1.45 V, which is better than ZABs assembled with commercial Pt / C (1.42 V).

[0062] (e) Discharge curves and corresponding power density curves of ZABs assembled with Fe-N,S-HCB catalysts. As shown in the figure, ZABs assembled with Fe-N,S-HCB and Pt / C catalysts can provide 135.3 and 113.3 mW / cm 2 The power density of Fe-N,S-HCB catalyst is shown to be superior.

[0063] (f) Cyclic voltage curves of ZABs assembled with Fe-N,S-HCB catalyst at different current densities. After three cycles, the cell voltage remained stable with no significant attenuation, demonstrating the excellent long-term stability of the Fe-N,S-HCB catalyst in practical applications.

[0064] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and do not constitute a limitation of the present invention. Within the technical concept of the present invention, the technical solutions of the present invention may be subjected to various simple modifications, including combining the various technical features in any other appropriate manner. These simple modifications and combinations should also be considered as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-sulfur co-doped Fe-based diatomic catalyst, characterized in that: The steps include: (1) HPB was prepared by mixing hexamethylenetetramine and 2,4-dihydroxybenzoic acid as hard templates, sodium oleate, P123, and polyethylene glycol (molecular weight 4000) as soft templates through hydrothermal reaction. (2) dispersing a certain amount of HPB in a solvent, adding an iron salt solution, mixing, evaporating, and drying to obtain a HPB-loaded Fe ion precursor; (3) The HPB-loaded Fe ion precursor is fully ground with a nitrogen source and a sulfur source, and calcined at a high temperature to obtain the nitrogen-sulfur co-doped Fe-based diatomic catalyst.

2. The preparation method according to claim 1, wherein In step (1), the hard template and the soft template are dissolved separately, then fully mixed, and transferred to a reactor for hydrothermal reaction at a temperature of 120-170° C. for 1-3 h.

3. The preparation method according to claim 1, wherein In step (1), after the hydrothermal reaction, the product is centrifuged and washed multiple times, and then vacuum dried to obtain HPB powder.

4. The preparation method according to claim 1, wherein The solvent is pentane and ultrapure water, and HPB is dispersed in the solvent by ultrasound; and the iron salt is ferric chloride hexahydrate.

5. The preparation method according to claim 1, wherein In step (2), stirring is continued during the evaporation process, and vacuum drying is performed after the solvent is completely evaporated.

6. The preparation method according to claim 1, wherein In step (3), the nitrogen source is thiourea or melamine, and the sulfur source is thiourea.

7. The preparation method according to claim 1, wherein In step (3), the high-temperature calcination operation is: heating to 800-1200°C at a heating rate of 1-5°C / min under N2 atmosphere, and keeping the temperature for 2-5h.

8. A nitrogen-sulfur co-doped Fe-based diatomic catalyst, characterized in that: The preparation method is described in any one of claims 1 to 7.

9. Use of the nitrogen-sulfur co-doped Fe-based diatomic catalyst according to claim 8 as a cathode oxygen reduction reaction catalyst.

10. The use according to claim 9, characterized in that The cathode oxygen reduction reaction catalyst is used in a fuel cell or a metal-air battery.

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