Preparation of transition metal element doped Fe3-N-C few-atomic cluster catalyst and research on oxygen reduction performance of transition metal element doped Fe3-N-C few-atomic cluster catalyst

Abstract

The invention provides a transition metal element doped Fe3-N-C few-atomic-cluster catalyst and a preparation method and application thereof, and belongs to the technical field of new energy. The preparation method comprises the following steps: performing primary pyrolysis on a ZIF-8 catalytic precursor, dispersing into water, respectively dropwise adding a ferroferric dodecacarbonyl solution and a transition metal salt solution into a nitrogen-doped porous carbon material dispersion liquid, performing liquid-phase adsorption, and performing secondary pyrolysis to obtain the transition metal element doped Fe3-N-C few-atomic cluster catalyst. The Fe3-N-C few-atomic-cluster catalyst is used as a substrate material, on the basis of ensuring the intrinsic activity of a monatomic catalyst, a single active center is amplified by three times to form a new active center with three iron atoms as the center, transition metal elements are introduced into the Fe3-N-C few-atomic-cluster catalyst, and by means of the synergistic effect of metal atoms, the activity of the Fe3-N-C few-atomic-cluster catalyst is improved. The activity and stability of the catalyst are regulated and controlled, and finally high activity and high stability are achieved.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to the preparation of a transition metal element-doped Fe3-NC few-atom cluster catalyst and the study of its oxygen reduction performance. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) and metal-air batteries (MABs) are currently a class of highly promising clean energy conversion devices. Their development has not only significantly alleviated the current energy shortage problem but also paved a new path for the sustainable development and application of clean energy in the future. Among these, the oxygen reduction reaction (ORR) in PEMFCs and MABs is the decisive step in their energy conversion process; however, the kinetics of ORR occurring at the cathode are slow and highly dependent on noble metal platinum-based catalysts. The low abundance and high cost of noble metals (such as Pt, Ru, Ir, and Rh) severely hinder their widespread application.

[0003] To date, most researchers have focused on optimizing the kinetics of cathode catalysts or searching for bifunctional, noble metal-free catalysts with catalytic performance comparable to or even better than platinum-based catalysts to reduce costs and improve energy conversion efficiency. Transition metal nitrogen-carbon catalysts (Fe-NC), formed by combining transition metals (such as Fe, Pt, Co, Ni, Cu, and Mn) with a nitrogen-doped carbon substrate, have shown initial performance superior to other non-noble metal catalysts (NPMCs) and even comparable to currently commercialized platinum-carbon catalysts. However, research on transition metal nitrogen-carbon catalysts has primarily focused on single-atom catalysts (SACs). While single-atom catalysts offer maximized atom utilization, unique coordination environments and electronic configurations, and high catalytic activity, their high specific surface area leads to insufficient stability, making further development extremely challenging. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a transition metal element-doped Fe3-NC few-atom cluster catalyst, its preparation method, and its application. The transition metal element-doped Fe3-NC few-atom cluster catalyst prepared by this invention maintains high activity while regulating its stability, ultimately achieving the goal of high activity and high stability.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a transition metal element-doped Fe3-NC few-atom cluster catalyst, comprising the following steps: The ZIF-8 catalytic precursor was pyrolyzed once to obtain nitrogen-doped porous carbon material; The nitrogen-doped porous carbon material is dispersed in water to obtain a nitrogen-doped porous carbon material dispersion. The dodecyltriferric oxide solution and the transition metal salt solution were respectively added dropwise to the nitrogen-doped porous carbon material dispersion for liquid-phase adsorption to obtain the adsorbed carbon material. The adsorbed carbon material is subjected to secondary pyrolysis to obtain the transition metal element-doped Fe3-NC few-atom cluster catalyst.

[0006] Preferably, the temperature of the first pyrolysis is 800~1000℃ and the time is 2~3h.

[0007] Preferably, the heating rate from room temperature to the temperature of the first pyrolysis is 3~5℃ / min.

[0008] Preferably, the ZIF-8 catalytic precursor has a dodecahedral microstructure and a specific surface area of ​​1500~2000 m². 2 / g.

[0009] Preferably, the mass ratio of dodecyltriferrite in the dodecyltriferrite solution, the transition metal salt in the transition metal salt solution, and the nitrogen-doped porous carbon material in the nitrogen-doped porous carbon material dispersion is 8:50:1~35.

[0010] Preferably, the transition metal element in the transition metal salt solution includes one or more of Pt, Co, Ni, Cu and Mn.

[0011] Preferably, the temperature of the secondary pyrolysis is 600~1000℃ and the time is 2~3h.

[0012] Preferably, the heating rate from room temperature to the temperature of the secondary pyrolysis is 3~5℃ / min.

[0013] The present invention also provides a transition metal element-doped Fe3-NC few-atom cluster catalyst prepared by the preparation method described above.

[0014] This invention also provides the application of the transition metal element-doped Fe3-NC few-atom cluster catalyst described above in the field of electrochemical energy conversion.

[0015] This invention provides a method for preparing a transition metal element-doped Fe3-NC few-atom cluster catalyst, comprising the following steps: pyrolyzing a ZIF-8 catalyst precursor to obtain a nitrogen-doped porous carbon material; dispersing the nitrogen-doped porous carbon material in water to obtain a nitrogen-doped porous carbon material dispersion; adding a dodecyltriferric oxide solution and a transition metal salt solution dropwise to the nitrogen-doped porous carbon material dispersion for liquid-phase adsorption to obtain adsorbed carbon material; and subjecting the adsorbed carbon material to a second pyrolysis to obtain the transition metal element-doped Fe3-NC few-atom cluster catalyst.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses Fe3-NC few-atom cluster catalyst as the substrate material. While maintaining the intrinsic activity of single-atom catalysts, it increases the active sites of the active center, forming a new active center centered on three iron atoms. Transition metal elements (such as Pt, Co, Ni, Cu, and Mn), which inherently contribute significantly to the oxygen reduction reaction, are introduced into the Fe3-NC few-atom cluster catalyst. Utilizing the synergistic effect between metal atoms, the activity and stability of the catalyst are regulated, ultimately achieving the goals of high activity, high stability, and low cost. Specific advantages are as follows: The present invention is scientifically and rationally designed. First, the ZIF-8 catalytic precursor is pyrolyzed to obtain nitrogen-doped porous carbon material. The ZIF-8 catalytic precursor is easy to prepare and can be mass-produced. It has a high specific surface area and a specific pore structure, which provides a large number of active sites and channels for the preparation of subsequent catalysts, which is beneficial to the adsorption, diffusion and desorption of reactants and products. Compared to currently commercialized platinum-carbon catalysts, this invention uses transition metals as the main active source, replacing the precious metals commonly used in traditional catalysts. This significantly reduces the cost of catalyst preparation and breaks through the limitations imposed on the further development and widespread application of catalysts by the high cost and low abundance of precious metals. Secondly, by using Fe3 low-atom clusters as the main active centers, the number of active sites on the catalyst is multiplied. Compared to the currently popular single-atom and diatomic catalysts, this invention improves upon their problems of single active sites, weak adsorption capacity, difficulty in controlling selectivity, susceptibility to side reactions and undesirable products, and high synthesis difficulty. While ensuring the intrinsic activity of catalysts, catalyst stability has always been a major challenge for non-precious metal catalysts. To alleviate this problem, transition metal elements with good oxygen reduction properties are introduced into Fe3 low-atom clusters. By utilizing the synergistic effect between atoms, the stability of the catalyst is improved. The introduction of transition metal elements causes the originally stable Fe3 low-atom cluster structure to redistribute, the interatomic bonds to shorten and become more tightly bound, transforming into a more stable coordination structure, thus improving the stability of the catalyst.

[0017] In summary, this invention improves the catalytic activity of the oxygen reduction reaction catalyst while also enhancing its stability. Compared to traditional oxygen reduction reaction catalysts, it significantly reduces the catalyst preparation cost. Furthermore, the catalyst preparation process is relatively simple and easy to implement, without involving highly precise or complex operations. The final catalyst exhibits good overall catalytic performance, with a half-wave potential of 0.92V (alkaline), which is superior to Pt / C (0.85V). In the stability test of an assembled zinc-air battery, no significant degradation in catalytic performance was observed within 300 hours. Attached Figure Description

[0018] Figure 1 This is a flowchart of the preparation of the Co-Fe3-NC catalyst in Example 1; Figure 2 The images shown are TEM images and elemental mappings of the Co-Fe3-NC catalyst prepared in Example 1 at different magnifications, where a~d are TEM images at different magnifications and e~i are different elemental mappings. Figure 3 The electrochemical performance test results of Co-Fe3-NC catalyst, Fe3-NC, NC and Pt / C in 0.5 M H2SO4 are shown in the figure. a is the linear sweep voltammetry curve, b is the Tafel slope curve, c is the hydrogen peroxide and electron transfer number curve, and d is the stability curve of the catalyst tested by chronoamperometry. Figure 4 The electrochemical performance test results of Co-Fe3-NC catalyst, Fe3-NC, NC and Pt / C in 0.1 M KOH are shown in the figure. a is the linear sweep voltammetry curve, b is the Tafel slope curve, c is the hydrogen peroxide and electron transfer number curve, and d is the stability curve of the catalyst tested by chronoamperometry. Figure 5 This is a picture of a zinc-air battery during testing. Figure 6 Open-circuit voltage results of zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC and Pt / C, tested by an electrochemical workstation; Figure 7 Power density curves of zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC and Pt / C; Figure 8 Specific capacity curves of zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC and Pt / C; Figure 9 Discharge voltage curves of zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC and Pt / C at different current densities; Figure 10 Cyclic stability testing of zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC and Pt / C; Figure 11 Linear sweep voltammetry curves of the catalysts prepared in Examples 1 and 2 in 0.5 M H2SO4; Figure 12 Linear sweep voltammetry curves of the catalysts prepared in Examples 1 and 2 in 0.1 M KOH; Figure 13 The linear sweep voltammetry curve of the catalyst prepared in Example 3 in 0.5 M H2SO4 is shown. Figure 14 The linear sweep voltammetry curve of the catalyst prepared in Example 3 in 0.1 M KOH is shown. Detailed Implementation

[0019] This invention provides a method for preparing a transition metal element-doped Fe3-NC few-atom cluster catalyst, comprising the following steps: The ZIF-8 catalytic precursor was pyrolyzed once to obtain nitrogen-doped porous carbon material (NC). The nitrogen-doped porous carbon material is dispersed in water to obtain a nitrogen-doped porous carbon material dispersion. The dodecyltriferric oxide solution and the transition metal salt solution were respectively added dropwise to the nitrogen-doped porous carbon material dispersion for liquid-phase adsorption to obtain the adsorbed carbon material. The adsorbed carbon material is subjected to secondary pyrolysis to obtain the transition metal element-doped Fe3-NC few-atom cluster catalyst.

[0020] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0021] This invention involves pyrolyzing the ZIF-8 catalytic precursor to obtain a nitrogen-doped porous carbon material. The nitrogen-doped porous carbon material has a high specific surface area and a specific pore structure, providing a large number of active sites and channels for the subsequent preparation of the catalyst, which is beneficial for the adsorption, diffusion and desorption of reactants and products.

[0022] In this invention, the microstructure of the ZIF-8 catalytic precursor is preferably dodecahedral, and the specific surface area is preferably 1500~2000 m². 2 / g.

[0023] In this invention, the particle size of the ZIF-8 catalytic precursor is preferably 80~120nm, specifically 80, 90, 100, 110 or 120nm. Theoretically, the smaller the particle size, the larger the specific surface area, which is beneficial to expose more active sites and improve the catalytic performance of the catalyst. However, it should not be too small, as too small a particle size will cause agglomeration when adsorbing metal atoms, reducing the atom utilization rate.

[0024] The present invention preferably prepares the ZIF-8 catalytic precursor by a liquid-phase method, and more preferably by the following steps: dissolving dimethylimidazole (3.24 g) and zinc nitrate (2.94 g) separately in beakers containing 100 mL of methanol. After complete dissolution, the zinc nitrate solution is poured into the dimethylimidazole solution while stirring. The beaker is then sealed and continuously stirred on a magnetic stirrer (600 rpm) for 2 to 5 hours (specifically 2, 2.5, 3, 4, or 5 hours). After the stirring is complete, the resulting mixed liquid is centrifuged, washed three times with methanol, and vacuum dried overnight at 80 °C to obtain the ZIF-8 catalytic precursor.

[0025] In this invention, the temperature of the first pyrolysis (the first pyrolysis) is preferably 800~1000℃, specifically 800, 850, 900, 950 or 1000℃, and the time is preferably 2~3h, specifically 2, 2.5 or 3h.

[0026] In this invention, the heating rate from room temperature to the temperature of the first pyrolysis is preferably 3~5℃ / min, specifically 3, 4 or 5℃ / min.

[0027] In this invention, the atmosphere for the primary pyrolysis is preferably a protective atmosphere, and more preferably argon.

[0028] In this invention, the primary pyrolysis is preferably carried out in a tubular furnace.

[0029] After obtaining nitrogen-doped porous carbon material, the present invention disperses the nitrogen-doped porous carbon material in water to obtain a nitrogen-doped porous carbon material dispersion.

[0030] In this invention, the preferred ratio of nitrogen-doped porous carbon material to water is 50 mg: 80 mL.

[0031] In this invention, the nitrogen-doped porous carbon material is preferably dispersed in a three-necked flask containing water and ultrasonically dispersed for 10 minutes to obtain a dispersion of the nitrogen-doped porous carbon material.

[0032] After obtaining a nitrogen-doped porous carbon material dispersion, the present invention adds a dodecyltriferrite solution and a transition metal salt solution dropwise into the nitrogen-doped porous carbon material dispersion for liquid-phase adsorption to obtain adsorbed carbon material. The dodecyltriferrite in the dodecyltriferrite solution is an iron source and has a triatomic cluster structure, which can be used to synthesize triatomic iron cluster catalysts.

[0033] Compared to commercially available platinum-carbon catalysts, this invention utilizes transition metals as the primary source of activity, replacing the precious metals commonly used in traditional catalysts. This significantly reduces catalyst preparation costs and overcomes the limitations imposed by the high cost and low abundance of precious metals on the further development and widespread application of catalysts. Secondly, by using Fe3 low-atom clusters as the main active centers, the number of active sites on the catalyst is multiplied. Compared to the currently popular single-atom and diatomic catalysts, this invention addresses issues such as single active sites, weak adsorption capacity, difficulty in controlling selectivity, susceptibility to side reactions and undesirable products, and high synthesis difficulty. While ensuring intrinsic catalyst activity, catalyst stability has always been a major challenge for non-precious metal catalysts. To alleviate this challenge, transition metal elements with good oxygen reduction properties are introduced into the Fe3 low-atom clusters. Utilizing interatomic synergy, the stability of the catalyst is improved. The introduction of transition metal elements redistributes the previously stable Fe3 low-atom cluster structure, shortening the interatomic bonds and creating a more compact and stable coordination structure, thus improving catalyst stability.

[0034] In this invention, the concentration of the dodecyltriferric solution is preferably 8 mg: 3 mL.

[0035] In this invention, the solvent of the dodecyltriferric solution preferably includes tetrahydrofuran or methanol.

[0036] The present invention dissolves dodecyltriferric oxide in tetrahydrofuran or methanol to obtain the dodecyltriferric oxide solution.

[0037] In this invention, the concentration of the transition metal salt solution is preferably 15 mg: 2 mL.

[0038] In this invention, the transition metal element in the transition metal salt solution preferably includes one or more of Pt, Co, Ni, Cu and Mn.

[0039] In this invention, the solvent for the transition metal salt solution preferably includes water or ethanol.

[0040] The present invention dissolves a transition metal salt in water or ethanol to obtain the transition metal salt solution.

[0041] In this invention, the transition metal salt preferably includes one or more of cobalt nitrate, cobalt acetate tetrahydrate, chloroplatinic acid hexahydrate, nickel nitrate, manganese nitrate, manganese chloride, and copper sulfate. When the transition metal salt is preferably chloroplatinic acid hexahydrate, the solvent for the transition metal salt solution is preferably ethanol; when the transition metal salt is preferably another salt, the solvent for the transition metal salt solution is preferably water.

[0042] In this invention, the nitrogen-doped porous carbon material dispersion is placed on a heating and stirring device. While stirring, the dodecyltriferric solution and the transition metal salt solution are dripped into the nitrogen-doped porous carbon material dispersion using a syringe. After complete addition, the dispersion is heated at 60°C for 1 hour. The product is then collected by filtration and vacuum dried at 40°C overnight to obtain the adsorbed carbon material.

[0043] In this invention, the dripping rate of both the dodecyltriferric solution and the transition metal salt solution is preferably 0.025 mL / min. The purpose of the dripping is to ensure that the transition metal elements are uniformly adsorbed on the nitrogen-doped porous carbon material.

[0044] In this invention, the preferred mass ratio of dodecyltriferrite in the dodecyltriferrite solution, the transition metal salt in the transition metal salt solution, and the nitrogen-doped porous carbon material in the nitrogen-doped porous carbon material dispersion is 8:50:1 to 35, specifically 8:50:1, 8:50:3, 8:50:5, 8:50:10, 8:50:15, 8:50:20, 8:50:25, 8:50:30, or 8:50:35.

[0045] After obtaining the adsorbed carbon material, the present invention performs secondary pyrolysis on the adsorbed carbon material to obtain the transition metal element doped Fe3-NC few atom cluster catalyst.

[0046] In this invention, the temperature of the secondary pyrolysis (secondary pyrolysis) is preferably 600~1000℃, specifically 600, 650, 700, 750, 800, 850, 900, 950 or 1000℃, and the time is preferably 2~3h, specifically 2, 2.5 or 3h.

[0047] In this invention, the heating rate from room temperature to the temperature of the secondary pyrolysis is preferably 3~5℃ / min, specifically 3, 4 or 5℃ / min.

[0048] After the secondary pyrolysis is completed, the present invention preferably cools the obtained product naturally to room temperature to obtain the transition metal element doped Fe3-NC few atom cluster catalyst.

[0049] The present invention also provides a transition metal element-doped Fe3-NC few-atom cluster catalyst prepared by the preparation method described above.

[0050] This invention also provides the application of the transition metal element-doped Fe3-NC few-atom cluster catalyst described above in the field of electrochemical energy conversion.

[0051] In this invention, the preferred application is to use the transition metal element-doped Fe3-NC few-atom cluster catalyst in a proton exchange membrane fuel cell or a metal-air battery.

[0052] In this invention, the water is preferably deionized water.

[0053] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] Electrochemical performance testing procedure: Electrochemical experimental data were obtained using an electrochemical workstation (CHI 760E) from Shanghai Chenhua Instruments Co., Ltd., coupled with a rotating ring-disk electrode (RRDE, Pine Research Instrumentation, USA) technology. The tests were conducted at room temperature (25℃) using a standard three-electrode system, with a saturated calomel electrode (SCE) as the reference electrode and a platinum sheet as the counter electrode. Tests were performed in Ar and O2-saturated 0.5 M H2SO4 and 0.1 M KOH aqueous solutions, respectively, at an electrode rotation speed of 1600 rpm. According to the Nernst equation: E RHE =E SCE + 0.0591 × pH + 0.244 (pH = 0.3 in 0.5 M H2SO4 solution, pH = 13.98 in 0.1 M KOH solution), all potentials are converted to the reversible hydrogen electrode (RHE) scale.

[0055] The catalyst ink was prepared as follows: 2 mg of catalyst was mixed with 5 μL of Nafion solution (5 wt.%), 70 μL of deionized water, and 80 μL of isopropanol, and ultrasonically dispersed for 10 min. The catalyst ink was then loaded onto the surface of a glassy carbon electrode at a loading rate of 0.4 mg·cm³. -2 The concentration of the Pt / C (Pt / C-40, Pt content 40wt%) catalyst ink is 0.5 mg·mL. -1 The platinum loading on the glassy carbon electrode is 20 µg·cm⁻¹ -2Cyclic voltammetry (CV) curves were obtained at a scan rate of 50 mV·s. -1 The measurements were obtained using linear sweep voltammetry (LSV) with a rotating disk electrode (RRDE) at a scan rate of 10 mV·s. -1 The rotational speed was 1600 r / min. The LSV polarization curve was calculated by subtracting the background current from the argon-saturated 0.5 M H2SO4 and 0.1 M KOH solution.

[0056] Before each electrochemical test, O2 was continuously introduced into the electrolyte for 30 min to achieve oxygen saturation. Stable polarization curves were obtained by performing 20 cycles of cyclic voltammetry activation followed by recording linear sweep voltammetry (LSV). The oxygen reduction current was obtained by subtracting the capacitance background in the argon-saturated electrolyte. The ring electrode potential was set to 1.25 V vs. RHE. Stability tests were performed using chronoamperometry in O2-saturated 0.5 M H2SO4 or 0.1 M KOH solutions. Simultaneously, the hydrogen peroxide yield (H2O2) and electron transfer number (n) were calculated using a rotating ring electrode test. The H2O2 yield and electron transfer number n were calculated using the following formula based on RRDE measurements: The hydrogen peroxide yield was calculated using the formula (1) for ring current and disk current: Equation (1); The number of electrons transferred is calculated using formula (2): Formula (2); In formulas (1) and (2): I d and I r These represent disk current and ring current, respectively, while the collection efficiency of the ring electrode N is 0.37.

[0057] Zinc-air battery testing process The catalyst ink is prepared as follows: 2 mg catalyst, 10 μL Nafion solution (5 wt.%), 70 μL deionized water and 80 μL isopropanol are mixed and ultrasonically dispersed for 10 min.

[0058] Liquid zinc-air batteries (ZABs) are assembled using a 0.5 mm thick polished zinc foil as the anode, an aqueous solution containing 6 mol / L KOH and 0.2 mol / L Zn(C₂H₃O₂)₂·2H₂O as the electrolyte, and a catalyst coated on a composite matrix material and 100 μL of commercial platinum-carbon (Pt / C-40, 40 wt% Pt) as the air cathode. The catalyst mass loading is 1.27 mg·cm⁻¹. -2The constant discharge, specific capacity, and charge-discharge cycle performance of the batteries at different current densities were evaluated using the Xinwei Battery Testing System at room temperature. Open-circuit voltage, discharge polarization curves, and power density were evaluated using an electrochemical analysis workstation (CHI760D, Shanghai Chenhua Instruments Co., Ltd.). Discharge performance was assessed at a range of current densities (2, 5, 10, 20, and 50 mA·cm⁻¹). -2 Constant current discharge was performed at 5 mA·cm⁻¹, and then returned sequentially to 5 mA·cm⁻¹. -2 The zinc-air battery was evaluated using a constant current discharge method, normalized to the mass of zinc consumed. Each cycle of this zinc-air battery test lasted 20 minutes (10 minutes for each charge and discharge cycle).

[0059] Specific capacity is calculated according to formula (3): Formula (3); Energy density is calculated according to formula (4): Formula (4); In formulas (3) and (4), I Indicates the discharge current. t Indicates the discharge time. M zn This indicates the mass of zinc consumed. U This represents the average discharge voltage.

[0060] Example 1 Preparation of transition metal element-doped Fe3-NC few-atom cluster catalysts Figure 1 The flowchart for the preparation of the Co-Fe3-NC catalyst in Example 1 includes the following steps: Step 1: Dissolve dimethylimidazole (3.24 g) and zinc nitrate (2.94 g) separately in beakers containing 100 mL of methanol. Once completely dissolved, pour the zinc nitrate solution into the dimethylimidazole solution while stirring. Seal the beaker and stir continuously at 600 rpm for 2.5 h using a magnetic stirrer. After stirring, centrifuge the resulting mixture (7000 rpm, 10 min), wash three times with methanol, and vacuum dry overnight at 80 °C to obtain the ZIF-8 catalytic precursor. The ZIF-8 catalytic precursor has a particle size of 100 nm, a dodecahedral microstructure, and a specific surface area of ​​2000 m². 2 / g.

[0061] Step 2: The obtained ZIF-8 catalytic precursor was pyrolyzed in a tube furnace at 850℃ (under Ar protective atmosphere, with a heating rate of 5℃ / min from room temperature) for 3 hours to obtain nitrogen-doped porous carbon material.

[0062] Step 3: Weigh 50 mg of nitrogen-doped porous carbon material and disperse it in a three-necked flask containing 80 mL of deionized water. Sonicate the dispersion for 10 min to obtain a dispersion. Dissolve 8 mg of dodecyltriferric oxide in 3 mL of tetrahydrofuran and 15 mg of cobalt nitrate in 2 mL of deionized water. Then, place the dispersion on a heating and stirring apparatus. While stirring, use a syringe to dropwise add the cobalt nitrate solution and the dodecyltriferric oxide solution separately into the three-necked flask at a rate of 0.025 mL / min. After complete addition, heat at 60 °C for 1 h. Collect the product by filtration and vacuum dry at 40 °C overnight to obtain the adsorbed carbon material.

[0063] Step 4: The adsorbed carbon material is placed in a tube furnace for secondary pyrolysis at 850℃ for 3 hours (under Ar protective atmosphere, with a heating rate of 5℃ / min from room temperature). After the secondary pyrolysis is completed, it is naturally cooled to room temperature, and the final product is collected to obtain the Co-Fe3-NC catalyst, also known as Co15-850 (where 15 refers to the amount of cobalt nitrate used, 15 mg, and 850 refers to the temperature of the secondary pyrolysis, 850℃).

[0064] Figure 2 The images shown are TEM images and elemental mappings of the Co-Fe3-NC catalyst prepared in Example 1 at different magnifications. The images a to d are TEM images at different magnifications. It can be seen that cobalt atoms were successfully doped into the NC substrate containing Fe3 atom clusters. The images e to i are different elemental mappings. It can be seen from the elemental mappings that iron and cobalt elements are uniformly distributed on the NC substrate and there is no agglomeration.

[0065] Comparative Example 1 Same as Example 1, except that cobalt nitrate was not added to obtain Fe3-NC.

[0066] Comparative Example 2 Same as Example 1, except that dodecyltriferric oxide is replaced with ferric chloride to prepare Co-Fe-NC.

[0067] The zinc-air battery prepared by Co-Fe-NC showed a half-wave potential in a linear sweep voltammetry curve in 0.1 M KOH electrolyte that was 15 mV lower than that of Co-Fe3-NC in Example 1, indicating that the oxygen reduction performance of Co-Fe3-NC in Example 1 was superior to that of Co-Fe-NC.

[0068] Figure 3The electrochemical performance of Co-Fe3-NC catalyst, Fe3-NC, NC, and Pt / C in 0.5 M H2SO4 is shown in Figure 1. Linear sweep voltammetry curves show that the Co-Fe3-NC catalyst has the largest half-wave potential (0.807 V), indicating the best oxygen reduction performance. Tafel slope curves show that the Co-Fe3-NC catalyst has the smallest Tafel slope, indicating the fastest kinetics and the fastest oxygen reduction reaction rate. Hydrogen peroxide and electron transfer curves show that Co-Fe3-NC approaches four-electron transfer, resulting in the lowest hydrogen peroxide yield. The closer the catalyst is to four-electron transfer, the lower the hydrogen peroxide yield, which is more conducive to the oxygen reduction reaction. Stability curves tested by chronoamperometry show that Co-Fe3-NC exhibits a current loss of only 6.23% in the stability test, significantly better than commercial platinum-carbon catalysts, indicating good cycle stability.

[0069] Figure 4 The electrochemical performance test results of Co-Fe3-NC catalyst, Fe3-NC, NC, and Pt / C in 0.1 M KOH are shown in Figure a. Linear sweep voltammetry curves show that the Co-Fe3-NC catalyst has the largest half-wave potential (0.92 V), indicating that it has the best oxygen reduction performance. Figure b. Tafel slope curves show that the Co-Fe3-NC catalyst has the smallest Tafel slope, indicating that it has the fastest kinetics and the fastest oxygen reduction reaction rate. Figure c. Hydrogen peroxide and electron transfer curves show that Co-Fe3-NC is close to four electron transfer, resulting in the lowest hydrogen peroxide yield. The closer the catalyst is to four electron transfer, the lower the hydrogen peroxide yield, which is more conducive to the oxygen reduction reaction. Figure d. Stability curves of the catalysts tested by chronoamperometry show that Co-Fe3-NC has a current loss of only 2.95% in the stability test, which is significantly better than commercial platinum-carbon catalysts, indicating that it has good cycle stability.

[0070] Figure 5 The image shows a test case of a zinc-air battery. It can be seen that connecting two zinc-air batteries in series can power a 3V LED display for several days, demonstrating its good practical application capability.

[0071] Figure 6 The open-circuit voltage results of zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC and Pt / C were tested by an electrochemical workstation. It can be seen that the open-circuit voltage of the zinc-air battery assembled with Co-Fe3-NC can reach 1.507V, which is significantly better than the 1.488V of commercial platinum-carbon.

[0072] Figure 7The power density curves of zinc-air batteries prepared using Co-Fe3-NC catalyst, Fe3-NC, and Pt / C show that the power density of the zinc-air battery assembled with Co-Fe3-NC can reach 230 mW·cm⁻¹. -2 It is significantly superior to commercial platinum-carbon.

[0073] Figure 8 The specific capacity curves of zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC, and Pt / C show that the specific capacity of the zinc-air battery assembled with Co-Fe3-NC can reach 782.3 mA·h·g. zn -1 It is significantly superior to commercial platinum-carbon.

[0074] Figure 9 The discharge voltage curves of zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC and Pt / C at different current densities show that the zinc-air battery assembled with Co-Fe3-NC exhibits a stable discharge voltage at different current densities, indicating that it has good discharge performance at both high and low current densities.

[0075] Figure 10 Cyclic stability tests were conducted on zinc-air batteries prepared with Co-Fe3-NC catalyst, Fe3-NC, and Pt / C. The results showed that the catalytic performance of the battery prepared with Co-Fe3-NC catalyst did not show significant degradation within 300 hours.

[0076] Example 2 Same as Example 1, except that the amount of cobalt nitrate used was 25 mg, and the resulting catalyst was designated Co25-850.

[0077] Same as Example 1, except that the amount of cobalt nitrate used was 35 mg, and the resulting catalyst was designated Co35-850.

[0078] Same as Example 1, except that the temperature of the secondary pyrolysis was 900°C, and the resulting catalyst was denoted as Co15-900.

[0079] Similar to Example 1, the only difference is that the temperature of the secondary pyrolysis is 900°C and the amount of cobalt nitrate used is 35 mg. The resulting catalyst is denoted as Co35-900.

[0080] Figure 11 The linear sweep voltammetry curves of the catalysts prepared in Examples 1 and 2 in 0.5 M H2SO4 are shown. The test results show that when the cobalt loading is 15 mg, it exhibits the largest half-wave potential in the 0.5 M H2SO4 electrolyte, indicating that the Co-Fe3-NC catalyst has the best oxygen reduction reaction performance at this loading.

[0081] Figure 12 The linear sweep voltammetry curves of the catalysts prepared in Examples 1 and 2 in 0.1 M KOH are shown. The test results show that when the cobalt loading is 15 mg, it exhibits the largest half-wave potential in the 0.1 M KOH electrolyte, indicating that the Co-Fe3-NC catalyst has the best oxygen reduction reaction performance at this loading.

[0082] Example 3 Same as Example 1, except that cobalt nitrate was replaced with 1 mg of chloroplatinic acid hexahydrate, and the resulting catalyst was designated Pt1-850.

[0083] Same as Example 1, except that cobalt nitrate was replaced with 3 mg of chloroplatinic acid hexahydrate, and the resulting catalyst was designated Pt3-850.

[0084] Same as Example 1, except that cobalt nitrate was replaced with 5 mg of chloroplatinic acid hexahydrate, and the resulting catalyst was designated Pt5-850.

[0085] Same as Example 1, except that cobalt nitrate was replaced with 10 mg of chloroplatinic acid hexahydrate, and the resulting catalyst was designated Pt10-850.

[0086] Same as Example 1, except that cobalt nitrate was replaced with 1 mg of chloroplatinic acid hexahydrate and the temperature of the secondary pyrolysis was 900°C. The resulting catalyst was denoted as Pt1-900.

[0087] Similar to Example 1, except that cobalt nitrate was replaced with 3 mg of chloroplatinic acid hexahydrate and the secondary pyrolysis temperature was 900°C. The resulting catalyst was designated Pt3-900.

[0088] Figure 13 The linear sweep voltammetry curve of the catalyst prepared in Example 3 in 0.5 M H2SO4 is shown. The test results show that when the platinum loading is 3 mg, it exhibits the largest half-wave potential in the 0.5 M H2SO4 electrolyte, indicating that the Pt-Fe3-NC catalyst has the best oxygen reduction reaction performance at this loading.

[0089] Figure 14 The linear sweep voltammetry curve of the catalyst prepared in Example 3 in 0.1 M KOH was obtained. The test results showed that when the platinum loading was 1 mg, it exhibited the largest half-wave potential in the 0.1 M KOH electrolyte, indicating that the Pt-Fe3-NC catalyst had the best oxygen reduction reaction performance at this loading.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the 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 method for preparing a transition metal element-doped Fe3-NC few-atom cluster catalyst, characterized in that, Includes the following steps: The ZIF-8 catalytic precursor was pyrolyzed once to obtain nitrogen-doped porous carbon material; The nitrogen-doped porous carbon material is dispersed in water to obtain a nitrogen-doped porous carbon material dispersion. The dodecyltriferric oxide solution and the transition metal salt solution were respectively added dropwise to the nitrogen-doped porous carbon material dispersion for liquid-phase adsorption to obtain the adsorbed carbon material. The adsorbed carbon material is subjected to secondary pyrolysis to obtain the transition metal element-doped Fe3-NC few-atom cluster catalyst.

2. The preparation method according to claim 1, characterized in that, The temperature of the first pyrolysis is 800~1000℃, and the time is 2~3h.

3. The preparation method according to claim 1 or 2, characterized in that, The heating rate from room temperature to the temperature of the first pyrolysis is 3~5℃ / min.

4. The preparation method according to claim 1, characterized in that, The ZIF-8 catalytic precursor has a dodecahedral microstructure and a specific surface area of ​​1500~2000 m². 2 / g.

5. The preparation method according to claim 1, characterized in that, The mass ratio of dodecyltriferrite in the dodecyltriferrite solution, the transition metal salt in the transition metal salt solution, and the nitrogen-doped porous carbon material in the nitrogen-doped porous carbon material dispersion is 8:50:1~35.

6. The preparation method according to claim 1 or 5, characterized in that, The transition metal element in the transition metal salt solution includes one or more of Pt, Co, Ni, Cu and Mn.

7. The preparation method according to claim 1, characterized in that, The secondary pyrolysis is performed at a temperature of 600~1000℃ for 2~3 hours.

8. The preparation method according to claim 1 or 7, characterized in that, The heating rate from room temperature to the temperature of the secondary pyrolysis is 3~5℃ / min.

9. The transition metal element-doped Fe3-NC few-atom cluster catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the transition metal element-doped Fe3-NC few-atom cluster catalyst according to claim 9 in the field of electrochemical energy conversion.

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