A metal and non-metal cascade catalyst with Fe-B dual sites and its preparation method and application

Abstract

The present invention relates to a metal and non-metal cascade catalyst with an Fe-B dual site and a preparation method thereof, comprising the following steps: adding a boron source to a graphene oxide solution, then adding an iron source, ultrasonicating, obtaining a precursor solution, subjecting the precursor solution to a hydrothermal reaction, and obtaining a reaction product; freeze-drying the reaction product, and then performing high-temperature nitridation using a chemical vapor deposition method to obtain a metal and non-metal cascade catalyst with an Fe-B dual site. The metal and non-metal cascade catalyst with an Fe-B dual site prepared by the present invention exhibits excellent four-electron oxygen reduction electrocatalytic performance in an alkaline environment, with high activity and stable performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical catalysis, and particularly relates to a metal and non-metal cascade catalyst with Fe-B dual sites, and a preparation method and application thereof. Background Art

[0002] The cathodic oxygen reduction reaction (ORR) is a crucial half-reaction that determines the performance and efficiency of various electrochemical energy devices, such as hydrogen fuel cells and rechargeable metal-air batteries. However, achieving efficient and fast ORR kinetics remains a major challenge due to the complexity of the multi-electron transfer process. To date, platinum group metal (PGM) materials have served as benchmark electrocatalysts for ORR, but their high cost and natural scarcity have severely hindered their large-scale application. Consequently, efforts have been underway to explore inexpensive, efficient, and durable alternatives to PGM materials. Currently, atomically dispersed metal-nitrogen-carbon (MNC, M = Fe, Co, Ni, etc.) materials with minimal economic cost and variable coordination structures have attracted significant interest. In particular, Fe-NC catalysts with the FeN4 structure are considered the most promising alternative to PGM materials due to their excellent ORR performance. However, in practical applications, the performance of Fe-NC still needs to be further optimized due to challenges such as low site density, inefficient desorption of oxygen intermediates from Fe centers, and severe catalyst deactivation. Therefore, there is an urgent need to develop efficient ORR electrocatalysts with dense active sites to regulate the adsorption behavior of intermediates, thereby achieving excellent activity and stability. Summary of the Invention

[0003] The purpose of the present invention is to provide a metal and non-metal cascade catalyst with Fe-B dual sites and its preparation method and application, so as to solve the technical problem that the Fe-B dual site coordination structure is difficult to control;

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A metal and non-metal cascade catalyst with Fe-B dual sites and a preparation method and application thereof, comprising the following steps:

[0006] S1. Adding boric acid to the graphene oxide solution, and then adding ferric nitrate, and ultrasonicating to obtain a homogeneous precursor solution. The precursor solution is subjected to a hydrothermal reaction to obtain a black columnar reaction product;

[0007] S2. The reaction product is freeze-dried and then subjected to high-temperature nitridation using a chemical vapor deposition method to obtain a metal and non-metal cascade catalyst with Fe-B dual sites.

[0008] Preferably, the percentage of iron in the ferric nitrate to the mass of graphene oxide in the graphene oxide solution is 1-10%; the percentage of boron in the boric acid to the mass of graphene oxide in the graphene oxide solution is 1-7%, wherein deionized water is used to dissolve the ferric nitrate nonahydrate and the boric acid.

[0009] Preferably, the preparation method of the graphene oxide solution is: dissolving graphene oxide solid in deionized water, ultrasonicating for 4-6 hours to obtain a uniformly dispersed graphene oxide solution; the concentration of the graphene oxide solution is 1-3 mg mL -1 .

[0010] Preferably, in step S1, the ultrasonic time is 10 minutes.

[0011] Preferably, in step S1, the temperature of the hydrothermal reaction is 170-190° C., and the time of the hydrothermal reaction is 8-14 h.

[0012] Preferably, in step S2, the freeze-drying treatment time is 5-10 hours.

[0013] Preferably, in step S2, the high-temperature nitridation using the chemical vapor deposition method includes the following steps: nitridation is performed in a mixed atmosphere of argon and ammonia, the reaction temperature is 700-900°C, the reaction time is 1-3h, the argon flow rate is 100±10sccm, and the ammonia flow rate is 50±10sccm.

[0014] In another aspect, the present invention provides a metal and non-metal cascade catalyst having a Fe-B dual site, which is prepared by the above-mentioned preparation method.

[0015] In another aspect, the present invention provides the use of the above-mentioned metal and non-metal cascade catalyst having Fe-B dual sites as a catalyst for a four-electron oxygen reduction reaction.

[0016] In another aspect, the present invention provides the use of the above-mentioned metal and non-metal cascade catalyst having Fe-B dual sites as a cathode catalyst for a zinc-air battery.

[0017] The present invention uses ferric nitrate (Fe(NO3)3) as an iron source, boric acid (H3BO3) as a boron source, and ammonia (NH3) as a nitrogen source, and adopts hydrothermal synthesis and chemical vapor deposition technology (CVD) to synthesize a metal and non-metal cascade catalyst with Fe-B dual sites. The catalyst exhibits excellent four-electron oxygen reduction electrocatalytic performance in an alkaline environment.

[0018] The present invention uses graphene as a carrier and boric acid as a modifier of the carbon substrate in a hydrothermal reaction, which not only provides a large number of anchoring sites for Fe atoms but also facilitates the formation of Fe-OB structures. During the hydrothermal reaction, the high temperature effectively catalyzes the dehydration condensation reaction between the hydroxyl functional groups in graphene oxide and H3BO3, allowing the B atoms to be uniformly incorporated into the graphite structure in the form of BO3 oxygen anions. Afterwards, these oxygen anions are gradually converted into boron carbide (BC 3-x O x ,x=0-2), destroying sp 2 The electrical neutrality of carbon creates additional anchoring sites for iron ions. The Fe-OB bridge bond is obtained through the hydrothermal self-assembly process, which significantly improves the utilization rate and site density of Fe. During the CVD process, ammonia easily decomposes to produce N radicals with lone pairs of electrons, which easily coordinate with Fe ions. Ultimately, the Fe cation is coordinated with two BC2O groups and two N radicals; these same groups are located in the para position, destroying the D 4h symmetry, thus forming a Fe-B double-site structure.

[0019] The synthesis method of the present invention is simple, the preparation cycle is short, the precursor is cheap and the reserves are abundant, and it has good application prospects; the metal and non-metal cascade catalyst with Fe-B dual sites can be obtained through simple hydrothermal and chemical vapor deposition. When the catalyst is used as a cathode catalyst for anion exchange membrane fuel cells and zinc-air batteries, it exhibits excellent power density and stability, and has very broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the XRD pattern of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1;

[0021] Figure 2 This is a Raman spectrum of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1;

[0022] Figure 3 This is an infrared spectrum of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1;

[0023] Figure 4 TEM image of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1, where: a-500nm, b-200nm;

[0024] Figure 5 Schematic diagram of the element contents of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1;

[0025] Figure 6 This is the XPS pattern of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1, where: a-Fe 2p, bB 1s, cN 1s, dO 1s;

[0026] Figure 7 The basic 4e of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 - ORR performance, where: a-polarization curve, b-corresponding Koutecky-Levich (KL) plot;

[0027] Figure 8 The basic 4e of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 - ORR performance, where: a-Tafel slope plot, b-stability curve;

[0028] Figure 9 The discharge polarization curve and power density diagram of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 in a zinc-air battery device;

[0029] Figure 10 Polarization curves and power density curves of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 under a back pressure of 1.0 bar for H2-O2 AEMFCs;

[0030] Figure 11 The metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 was tested in AEMFCs at 0.6 V under H2-air conditions for a long time. DETAILED DESCRIPTION

[0031] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0032] The graphene oxide in the following examples was prepared by a modified Hummers method, which is as follows: 3 g of graphite powder and a mixed solution of concentrated H2SO4 and H3PO4 (volume ratio 9:1) were added to a three-necked flask, and 18 g of KMnO4 solid was slowly added at a rotation speed of 200-350 rpm.

[0033] The water bath temperature was set at 50°C, the stirring speed was 200-350 rpm, and the stirring time was 12 h. After the reaction, the solution temperature dropped to room temperature, poured into 400 mL of pre-chilled deionized water and stirred evenly. H2O2 was slowly added to the solution in small amounts several times until the solution changed from purple to bright yellow. The solution was repeatedly washed with 30% by mass HCl solution, deionized water, anhydrous ethanol and ether in sequence. A light yellow graphene oxide solid was obtained after vacuum drying at room temperature for 24 h.

[0034] Example 1

[0035] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0036] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 3 mL of boric acid solution and 6 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 6% and 3% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0037] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0038] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 800°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 2 hours. A metal and non-metal cascade catalyst (Fe-BNC-3) with Fe-B dual sites was obtained.

[0039] Example 2

[0040] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0041] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 7 mL of boric acid solution and 6 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 6% and 7% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0042] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0043] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 800°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 2 hours. A metal and non-metal cascade catalyst (Fe-BNC-7) with Fe-B dual sites was obtained.

[0044] Example 3

[0045] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0046] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 3 mL of boric acid solution and 6 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 6% and 3% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0047] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0048] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 800°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 1 hour. This resulted in a metal-nonmetal cascade catalyst (Fe-BNC@1) with a dual Fe-B site.

[0049] Example 4

[0050] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0051] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 3 mL of boric acid solution and 6 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 6% and 3% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0052] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0053] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 800°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 3 hours. This resulted in a metal and non-metal cascade catalyst (Fe-BNC@3) with Fe-B dual sites.

[0054] Example 5

[0055] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0056] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 3 mL of boric acid solution and 6 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 6% and 3% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0057] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0058] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 850°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 2 hours. A metal and non-metal cascade catalyst (Fe-BNC / 850) with Fe-B dual sites was obtained.

[0059] Example 6

[0060] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0061] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 3 mL of boric acid solution and 6 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 6% and 3% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0062] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0063] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 950°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 2 hours. A metal and non-metal cascade catalyst (Fe-BNC / 950) with Fe-B dual sites was obtained.

[0064] Example 7

[0065] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0066] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 3 mL of boric acid solution and 10 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 10% and 3% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0067] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0068] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 800°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 2 hours. A metal and non-metal cascade catalyst (Fe-BNC-3) with Fe-B dual sites was obtained.

[0069] Example 8

[0070] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0071] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 1 mL of boric acid solution and 6 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 6% and 1% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0072] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0073] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 800°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 2 hours. A metal and non-metal cascade catalyst (Fe-BNC-1) with Fe-B dual sites was obtained.

[0074] Example 9

[0075] A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, comprising the following steps:

[0076] 0.16 g of graphene oxide solid was added to 80 ml of deionized water. After ultrasonication for 6 hours, 3 mL of boric acid solution and 1 mL of ferric nitrate nonahydrate solution were added to the graphene oxide solution in sequence, where the mass of iron and boron elements accounted for 1% and 3% of the mass of graphene oxide, respectively. After ultrasonication for 10 minutes, a uniformly dispersed precursor solution was obtained.

[0077] The precursor solution was transferred to the inner lining of the reactor, and the hydrothermal temperature was set to 180°C and the hydrothermal time was set to 12 h.

[0078] After freeze-drying the hydrothermal product for 10 hours, the resulting product was placed in a CVD furnace and subjected to a high-temperature nitridation reaction in a mixed atmosphere of Ar and NH3 using chemical vapor deposition technology. The reaction parameters were set as follows: temperature: 800°C, gas flow rate: NH3: 50sccm, Ar: 100sccm, and nitridation time: 2 hours. A metal and non-metal cascade catalyst (Fe-BNC-3) with Fe-B dual sites was obtained.

[0079] The catalyst performance evaluation and characterization of Example 1 are as follows:

[0080] A cascade of metal and nonmetal catalysts with Fe-B dual sites was used as 4e - ORR catalyst material: The test instrument uses a pine rotating disk electrode device (Rotating disk electrode, RDE and Rotating ring-diskelectrode, RRDE; electrode model: AFE6R2) to perform relevant electrochemical tests. The dispersion liquid is formulated as follows: 10 mg of catalyst is added to 1 mL of deionized water, 1 mL of anhydrous ethanol and 200 μL of Nafion solution and then ultrasonicated for 1 hour. Take 2.5 μL of the dispersion droplet and apply it to the disk electrode (disk area of ​​RDE: 0.196 cm 2 Or the disk area of ​​RRDE: 0.2376 cm 2 The area of ​​the platinum ring is 0.2356 cm 2), after the first dispersion was dried, 2.5 μL of dispersion was drop-coated (the area mass loading of the electrocatalyst was 0.12 mg cm -2 (RDE) or 0.10 mg cm -2 (RRDE)), after natural drying for 6-10 hours, relevant experimental tests can be carried out. Three-electrode system: platinum wire electrode as counter electrode, Ag / AgCl (3M KCl solution as salt bridge) as reference electrode, disk electrode or ring disk electrode coated with metal and non-metal cascade catalyst with Fe-B dual site as working electrode. Before the experiment, nitrogen or oxygen was introduced into 0.1M KOH electrolyte until saturated, and the electrolyte was tested at 100mV s -1 The cyclic voltammetry (CV) test was used to activate the catalyst for 30-60 min until there was no air on the catalyst surface. In an oxygen-saturated electrolyte, different speeds (225-2025 rpm) were set, and the voltage range was 0.1-1.1 V at a rate of 5 mV s -1 Linear voltammetry (LSV) was performed at a low sweep rate.

[0081] Membrane electrode assembly (MEA) and anion exchange membrane fuel cell testing: First, 10 mg of electrocatalyst, 2000 μL of isopropyl alcohol, 200 μL of ultrapure water, and 200 μL of PiperION-B5-HCO3 solution (5 wt%) were mixed and ultrasonicated for 2 hours to prepare catalyst ink. Then, the catalyst ink was sprayed on one side of polytetrafluoroethylene-treated carbon paper (Sigracet, 29BC) with a microporous layer (MPL), maintaining an electrode area of ​​2*2 cm 2 Fe-BNC or commercial Pt / C was used as cathode catalyst, with the final catalyst loading of 2.0 mg cm -2 and 0.4 mg cm -2 Pt / C (60%, Johnson Matthey) was used as the anode catalyst with a loading of 0.4 mg cm -2 The prepared carbon paper containing anode and cathode catalysts was placed on both sides of an anion exchange membrane (Versogen, PiperION-A-20HCO3) to prepare MEA. Polarization curve and stability tests were carried out under H2-O2 or H2-Air conditions using an NBT-FEM-100W fuel cell test system equipped with a back pressure module. During the test, the anode and cathode humidity was adjusted to 100%, and the H2 and O2 or air flow was maintained at 0.6 L min -1 The stability of the H2-Air fuel cell was evaluated at a constant cell voltage of 0.6V.

[0082] Zinc-air battery assembly and testing: Cathode electrode: 5 mg of homemade catalyst and 5 mg of carbon black powder were added to 50 μL of isopropyl alcohol, 25 μL of polytetrafluoroethylene (PTFE) solution, and 0.95 mL of deionized water. Ultrasonic dispersion was performed for 3 to 5 hours to disperse the mixture uniformly. The resulting dispersion was drop-coated on a 2.5 × 2.5 cm hydrophilic carbon paper surface with a drop-coating area of ​​1 × 1 cm and a loading of 1.0 mg cm. -2 Anode: Ultrasonic clean the polished zinc plate with anhydrous ethanol and then acetone for 30 minutes. Battery electrolyte: A mixed solution of 6M KOH and 0.2M ZnCl2.

[0083] After testing, the half-wave potential can reach 0.91V, and the kinetic current density at 0.85V is 16.98mA cm -2 , with good stability and extremely low H2O2 selectivity, proving that the catalyst has good 4e - ORR performance.

[0084] Figure 1 Shown is the XRD pattern of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1. The two broad diffraction peaks near 25° and 44° are assigned to graphitized carbon, and no peaks of iron-related substances are detected, indicating that iron elements exist in the lattice of graphitic carbon in the form of isolated atoms or clusters.

[0085] Figure 2 The Raman spectrum of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 is shown. In the Raman spectrum, the intensity ratio of the D band to the G band of Fe-BNC (I D / I G ) is 1.17. This is because boron atoms are generally in the form of BC 3-x O x Compared with N elements, B atoms cause greater lattice distortion and form defect-rich materials.

[0086] Figure 3 The figure shows the infrared spectrum of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1. Fe-BNC has abundant functional groups, such as CN and CO groups, which effectively alleviate the inherent inertness of the graphene basal surface.

[0087] Figure 4 a and 4b are the low-magnification and high-magnification TEM images of the metal-nonmetal cascade catalyst with Fe-B dual sites prepared in Example 1, respectively. The morphology of Fe-BNC presents an ultrathin nanosheet structure with abundant wrinkles and ripples, which is conducive to the adsorption and activation of oxygen in the ORR process.

[0088] Figure 5The figure shows the element content of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1, wherein Fe: 0.73, B: 0.98, C: 87.32, N: 5.81, O: 5.15, indicating that iron, boron, and nitrogen elements are successfully doped into graphene.

[0089] Figure 6 The XPS graph of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 is shown. In the Fe 2p spectrum, the Fe 2p at 710.6eV and 714.7eV 3 / 2 The XPS peaks are assigned to Fe 2+ and Fe 3+ state, and Fe 2+ The peak intensity of Fe 3+ The strong peaks confirm that the Fe atoms exist mainly in the form of divalent cations. The B 1s spectrum is deconvoluted into three peaks, belonging to the structures of BC3 (189.4eV), BC2O (190.6eV), and BCO2 (192.0eV). The samples all have a large amount of BC2O structure and no Fe-B signal. In addition, the N 1s spectrum shows that the main nitrogen species are pyridinic-N and Fe-N, which constitute the key active sites for ORR. The O 1s spectrum indicates the presence of various oxygen functional groups in the sample, such as Fe-O (530.3eV), C=O (531.6eV), OB (532.8eV), and CO (533.5eV).

[0090] Figure 7 The results show that the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 is - The ORR performance, polarization curves and corresponding Koutecky-Levich (KL) plots in 0.1 M KOH electrolyte, where the catalyst has a high half-wave potential (E 1 / 2 , 0.91 V) and kinetic current density (J K At 0.85 V, 16.98 mA cm -2 ). Furthermore, the electron transfer number (n) was calculated from the KL plot, and the n value of the catalyst was 4.00, indicating an ideal 4-electron transfer pathway.

[0091] Figure 8 The results show that the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 is - ORR performance, where Figure 8 a and Figure 8 b are the Tafel slope and stability curve in 0.1 M KOH electrolyte, respectively. The Tafel slope of the catalyst is 74 mV dec-1 , demonstrating the fast kinetics. After 110 h of long-term stability testing, the current density of Fe-BNC only decreased by 5%, highlighting the superior electrocatalytic stability of Fe-BNC.

[0092] Figure 9 The figure shows the discharge polarization curve and power density diagram of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1 in a zinc-air battery device. The above catalyst is used as the cathode catalyst of the zinc-air battery, which can provide 195mW cm -2 The peak power density of 1.5 wt% catalytic activity was 2.3 wt% and 1.5 wt% catalytic activity, respectively, which proves that the catalyst has both excellent catalytic activity and stable performance and has the prospect of practical application.

[0093] Figure 10 The figure shows the polarization curve and power density curve of the metal and non-metal cascade catalyst with Fe-B dual sites prepared in Example 1. The H2-O2 AEMFCs polarization curve and power density curve under 1.0 bar back pressure are shown. The peak power density of the AEMFCs with Fe-BNC as the cathode is 690 mW cm -2 .

[0094] Figure 11 The figure shows the long-term testing of the dual-site Fe-BNC metal and non-metal cascade catalyst prepared in Example 1 in AEMFCs at 0.6 V under H₂-air conditions. Specifically, the Fe-BNC-based AEMFCs exhibited excellent durability, with only a 12% loss in current density after 350 hours. These results demonstrate the excellent ORR activity and exceptional stability of Fe-BNCs under practical AEMFC operating conditions, highlighting their broad potential for energy device applications.

Claims

1. A method for preparing a metal and non-metal cascade catalyst having a Fe-B dual site, characterized in that: The following steps are involved: S1. Adding boric acid to a graphene oxide solution, and then adding ferric nitrate, and ultrasonicating to obtain a precursor solution, and subjecting the precursor solution to a hydrothermal reaction to obtain a reaction product; S2. The reaction product is freeze-dried and then subjected to high-temperature nitridation by chemical vapor deposition to obtain a metal and non-metal cascade catalyst having a Fe-B dual site, wherein the nitrogen source used in the high-temperature nitridation process is ammonia.

2. The preparation method according to claim 1, characterized in that The percentage of iron in the ferric nitrate to the mass of the graphene oxide in the graphene oxide solution is 1-10%; the percentage of boron in the boric acid to the mass of the graphene oxide in the graphene oxide solution is 1-7%.

3. The preparation method according to claim 1, characterized in that In step S1, the ultrasonication time is 10 min.

4. The preparation method according to claim 1, characterized in that In step S1, the temperature of the hydrothermal reaction is 170-190° C., and the time of the hydrothermal reaction is 8-14 h.

5. The preparation method according to claim 1, characterized in that In step S2, the freeze-drying treatment time is 5-10 h.

6. The preparation method according to claim 1, characterized in that In step S2, the high-temperature nitridation using the chemical vapor deposition method includes the following steps: nitridation is performed in a mixed atmosphere of argon and ammonia, the reaction temperature is 700-900°C, the reaction time is 1-3 hours, the argon flow rate is 100±10 sccm, and the ammonia flow rate is 50±10 sccm.

7. A metal and non-metal cascade catalyst having a Fe-B dual site, prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the metal and non-metal cascade catalyst having Fe-B dual sites according to claim 7 as a catalyst for a four-electron oxygen reduction reaction.

9. Use of the metal and non-metal cascade catalyst having Fe-B dual sites as claimed in claim 7 as a cathode catalyst for zinc-air batteries.

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