Ferrocarbide electro-catalytic material with monatomic anchoring defect state as well as preparation method and application of ferrocarbide electro-catalytic material

Abstract

The invention relates to the technical field of batteries, in particular to a ferrocarbide electrocatalytic material with a monatomic anchoring defect state as well as a preparation method and application of the ferrocarbide electrocatalytic material. The preparation method comprises the following steps: performing primary calcination on ferric salt and an organic precursor containing carbon and nitrogen to form a Fe3C composite material in which iron carbide nanoparticles are embedded in nitrogen-doped carbon nanotubes; dipping and etching to enable the iron carbide nanoparticles to become a defect-state iron carbide material containing iron vacancies; stirring and reacting with zinc salt and imidazole ligands, so that the defect-state iron carbide material containing the iron vacancy is coated with a metal organic framework material; and carrying out secondary calcination together with the cobalt source, so that the cobalt atoms are anchored in the iron vacancies. The catalyst has excellent oxygen reduction activity, fast reaction kinetics and excellent long-term stability, and still keeps excellent stability after 3000 CV cycle tests.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an iron carbide electrocatalytic material with single-atom anchored defect states, its preparation method, and its application. Background Technology

[0002] Currently, seeking green and clean new energy sources and developing efficient and environmentally friendly energy conversion systems have become crucial issues that must be addressed for sustainable social development. Metal-air batteries are an effective means of solving current energy shortages and environmental pollution problems, and their development hinges on the development of highly efficient electrode catalytic materials. The oxygen reduction reaction (ORR) is an essential half-reaction in various energy devices, including metal-air batteries. Developing electrocatalysts with high ORR activity and cost-effectiveness is key to realizing the commercial application of these energy technologies. Due to the high cost and scarcity of precious platinum-based metal materials, the development of non-platinum metal electrocatalysts for ORR has become a research hotspot in the renewable energy field in recent years.

[0003] Fe3C nanoparticles are promising candidates to replace noble metal catalysts due to their tunable electronic structure and good electrical conductivity. However, the inherent electronegativity difference between Fe and C atoms causes electrons to transfer from Fe to C, resulting in unfilled d orbitals in Fe. This electronic structure leads to the over-adsorption of oxygen intermediates at Fe sites, thereby reducing catalytic activity. Furthermore, the high surface energy of Fe3C nanoparticles makes them thermodynamically unstable, leading to Fe dissolution during ORR (Orbital Reduction) processes. This phenomenon not only disrupts active sites but also contaminates the electrolyte, further limiting their practical applications. These challenges indicate the need for innovative strategies to improve the activity and stability of Fe3C-based catalysts.

[0004] Therefore, existing technologies need to be improved. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide an iron carbide electrocatalytic material with single-atom anchored defect state, its preparation method and its application, aiming to solve the problem of inherent electronegativity difference defects in existing Fe3C materials.

[0006] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states, comprising the following steps: S1. Iron salt and organic precursors containing carbon and nitrogen are calcined for the first time under an inert atmosphere to form Fe3C composite material in which iron carbide nanoparticles are embedded in nitrogen-doped carbon nanotubes. S2. The Fe3C composite material obtained in S1 is immersed and etched in an acidic solution to remove some iron atoms from the iron carbide nanoparticles and introduce iron vacancies into the iron carbide nanoparticles, so that the iron carbide nanoparticles become defective iron carbide materials containing iron vacancies. S3. The defective iron carbide material containing iron vacancies is stirred and reacted with zinc salt and imidazole ligands to encapsulate the defective iron carbide material containing iron vacancies with a metal-organic framework material. S4. The product obtained in S3 and the cobalt source are placed in a vapor deposition apparatus and calcined for the second time under an inert atmosphere, so that the cobalt source volatilizes and deposits onto the iron vacancies of the defective iron carbide material containing iron vacancies, and the cobalt atoms are anchored to the iron vacancies, thus obtaining the electrocatalytic material of iron carbide with single-atom anchored defective state.

[0007] Optionally, the iron salt in S1 is at least one of anhydrous ferric chloride, ferric nitrate, and ferric acetate; The organic precursor containing carbon and nitrogen is at least one of dicyandiamine, cyanamide, and urea; Optionally, in S1, the first calcination temperature is 850–950°C, the time is 1–3 hours, and the heating rate is 3–10°C / min.

[0008] Specifically, during calcination, the carbon- and nitrogen-containing organic precursor is placed upstream of the reacting gas, while the iron salt is placed downstream, allowing the gas produced by the decomposition of the organic precursor to flow through the iron salt. Of course, to avoid environmental pollution, an anti-backflow device is connected to the gas outlet, and the exhaust gas is collected throughout the process using a pure aqueous solution.

[0009] Optionally, in S2, the acidic solution is at least one of hydrochloric acid, sulfuric acid, and nitric acid, with a concentration of 1 to 6 mol / L; the immersion etching temperature is 25°C, and the time is 3 hours.

[0010] It should be noted that after immersion etching, the resulting precipitate needs to be centrifuged and washed multiple times, and finally dried at 60°C.

[0011] Optionally, in S3, the zinc salt is zinc nitrate hexahydrate or zinc acetate; the imidazole ligand is one of dimethylimidazolium, imidazole, and 4-methylimidazolium; the stirring reaction temperature is 25°C and the time is 12 hours.

[0012] Specifically, the reaction of defective iron carbide material containing iron vacancies with zinc salt and imidazole ligands by stirring includes: dissolving the defective iron carbide material containing iron vacancies and zinc salt in methanol to obtain solution A; The imidazole ligand is then dissolved in methanol to obtain solution B; Solution B was poured into solution A, stirred and soaked for more than 12 hours, then centrifuged and washed to collect the precipitate, and finally dried at 60°C to obtain a defect-state iron carbide composite material encapsulated by a metal-organic framework.

[0013] Optionally, in S4, the cobalt source is at least one of cobalt nitrate hexahydrate, cobalt acetate, and cobalt acetylacetonate.

[0014] Optionally, in S4, the temperature of the second calcination is 850–950℃, the time is 1–3 hours, and the heating rate is 3–10℃ / min.

[0015] Secondly, the present invention provides a ferrocarbide electrocatalytic material with single-atom anchored defect states, prepared by the aforementioned preparation method. Alternatively, it may include nitrogen-doped carbon nanotubes and iron carbide nanoparticles; wherein the iron carbide nanoparticles are encapsulated within the nitrogen-doped carbon nanotubes; The iron carbide nanoparticles have iron vacancies, and cobalt single atoms are anchored at the iron vacancies to form a Co-NC coordination structure.

[0016] Thirdly, the present invention provides an application of iron carbide electrocatalytic material with single-atom anchored defect states in metal-air batteries.

[0017] Beneficial Effects: This invention provides an iron carbide electrocatalytic material with single-atom anchored defect states, its preparation method, and its applications. First, Fe3C is coated with a carbon layer within carbon nanotubes to obtain an Fe3C composite material. Then, iron vacancies are introduced into the iron carbide nanoparticles through acid etching. Finally, cobalt single atoms are directionally anchored to the vacancies using chemical vapor deposition. The catalyst obtained by this invention exhibits excellent oxygen reduction activity, with an onset potential of 1.022V and a half-wave potential (E1 / 2) of 0.91V, both exceeding those of commercial Pt / C and other comparative catalysts. The faster the reaction rate, the higher the Tafel slope (67mV dec). - ¹) Significantly lower than Pt / C (77mV dec) - ¹), Co SAc / -Fe3C (72mV dec) - ¹) and Fe3C (94mV dec - ¹). It exhibits excellent long-term stability, maintaining superior stability even after 3000 CV cycle tests. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process for preparing ferrocarbide electrocatalytic materials with single-atom anchored defect states, as described in an embodiment of the present invention.

[0019] Figure 2The process flow diagram for preparing iron carbide electrocatalytic materials with single-atom anchored defect states is shown in the embodiment of the present invention.

[0020] Figure 3 The figures show the morphology and structure characterization of each catalyst, where a is the X-ray diffraction pattern of each catalyst, and b is the Co... SAc / V Fe Transmission electron microscopy image (100 nm) of Fe3C catalyst, where c represents Co. SAc / V Fe Atomic-resolution HAADF-STEM image (2 nm) of Fe3C catalyst, d represents Co. SAc / V Fe Transmission electron microscopy image (50 nm) of Fe3C catalyst, e represents Co. SAc / V Fe Transmission electron microscopy image (5 nm) of Fe3C catalyst, f represents Co. SAc / V Fe -Atomic-resolution HAADF-STEM image (1 nm) of Fe3C catalyst, g is the FFT image of sites I and II in f, h is the Co SAc / V Fe -High-angle annular dark-field image of Fe3C catalyst-scanning transmission electron image, i is the two-dimensional EDS elemental distribution map of C, j is the two-dimensional EDS elemental distribution map of N, k is the two-dimensional EDS elemental distribution map of Fe, and l is the two-dimensional EDS elemental distribution map of Co.

[0021] Figure 4 The following are comparison diagrams of the electronic structures of various catalysts, where a is the XPS full spectrum, b is the high-resolution spectrum of C 1s, c is the high-resolution spectrum of Fe 2p, d is the high-resolution spectrum of N 1s, e is the UPS spectrum, and f is the EPR spectrum.

[0022] Figure 5 The graphs show a comparison of the electrochemical properties of the oxygen reduction reaction for various catalysts. In the graphs, a is the cyclic voltammetry curve, b is the redox polarization curve, c is the Tafel curve, d is the linear sweep voltammetry curve of the rotating ring disk electrode, e is the LSV curve of the cyclic stability test, and f is the characterization curve of the selectivity and electron transfer number of the rotating ring disk electrode.

[0023] Figure 6 The figures show the relevant properties of the zinc-air battery prepared using the catalyst obtained in Example 1. In the figures, a is a schematic diagram of the zinc-air battery structure, b is the discharge polarization curve, c is the polarization-power density curve, d is a physical image of the zinc-air battery, e is the open-circuit voltage stability curve, f is the rate performance / variable current discharge curve, and g is the long-term cycle stability curve. Detailed Implementation

[0024] This invention provides a ferrocarbide electrocatalytic material with single-atom anchored defect states, its preparation method, and its applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0025] In recent years, single-atom catalysts (SACs) have attracted widespread research interest in the field of electrocatalysis due to their near 100% atomic utilization, unique electronic structure, and excellent catalytic activity. Studies have shown that transition metals (such as Fe, Co, Cu, and Mn) possess abundant d-orbital electronic states. When their d-band centers are tuned to suitable positions, the adsorption energy for oxygen-containing intermediates (*OH, *O, *OOH) in the oxygen reduction reaction (ORR) can be optimized, thereby significantly improving catalytic performance. Based on this principle, researchers have developed various MNC (M=Fe, Co, Cu, Mn…) type single-atom catalysts, which have shown great application potential in energy devices such as fuel cells and metal-air batteries.

[0026] However, the intrinsic activity and stability of non-platinum-based catalytic materials remain key bottlenecks restricting their commercial application. Taking iron carbide (Fe3C) as an example, its good conductivity, tunable electronic structure, and low cost have made it a strong candidate to replace noble metal catalysts. However, Fe3C materials have an inherent drawback: due to the significant difference in electronegativity between Fe and C atoms, electrons transfer from Fe to C, resulting in unfilled d orbitals in Fe. This electronic structure leads to excessive adsorption of oxygen-containing intermediates at Fe active sites, not only reducing catalytic activity but also easily causing active site poisoning. Furthermore, the high surface energy of Fe3C nanoparticles makes them thermodynamically unstable, easily leading to Fe dissolution during ORR processes, resulting in the loss of active sites, severely limiting their practical application.

[0027] How to optimize the electronic structure of Fe3C, suppress Fe dissolution, and improve its catalytic activity and stability without sacrificing its conductivity and cost advantages has become a pressing technical challenge in this field.

[0028] Based on this, this embodiment provides a method for preparing a carbide iron electrocatalytic material with single-atom anchored defect states, such as... Figure 1 As shown, it includes the following steps: S1. Iron salt and an organic precursor containing carbon and nitrogen are calcined for the first time under an inert atmosphere to form an Fe3C composite material (denoted as Fe3C) in which iron carbide nanoparticles are embedded in nitrogen-doped carbon nanotubes. S2. The Fe3C composite material obtained in S1 is immersed and etched in an acidic solution to remove some iron atoms from the iron carbide nanoparticles and introduce iron vacancies into the iron carbide nanoparticles, making the iron carbide nanoparticles into defect-state iron carbide materials containing iron vacancies (denoted as V). Fe -Fe3C); S3. The defective iron carbide material containing iron vacancies is stirred and reacted with zinc salt and imidazole ligands to encapsulate the defective iron carbide material containing iron vacancies with a metal-organic framework material (denoted as ZIF-8 / V). Fe -Fe3C); S4. The product obtained in S3 and the cobalt source are placed in a vapor deposition apparatus and calcined a second time under an inert atmosphere, causing the cobalt source to volatilize and deposit onto the iron vacancies in the defective iron carbide material containing iron vacancies. Cobalt atoms are anchored to the iron vacancies, thus obtaining the electrocatalytic material with single-atom anchored defective state (denoted as Co). SAc / V Fe -Fe3C).

[0029] It should be noted that, as Figure 2 As shown, in this embodiment, an iron carbide composite nitrogen-doped carbon nanotube sample was first prepared. Then, iron vacancies V were introduced into the iron carbide nanoparticles through acid etching. Fe -Fe3C, and finally, cobalt single atoms are oriented and anchored to vacancy sites using chemical vapor deposition to obtain the Co carbide iron electrocatalyst material with single-atom anchored defect state. SAc / V Fe -Fe3C. Specifically, in S1, during the first calcination, the organic precursor decomposes and grows nitrogen-doped carbon nanotubes, while the iron salt is reduced and reacts with carbon to generate iron carbide nanoparticles. These iron carbide nanoparticles are in-situ coated during the growth of the nitrogen-doped carbon nanotubes, ultimately forming a composite structure of Fe3C coated within the nitrogen-doped carbon nanotubes. In S2, an acidic solution is used to etch some of the iron atoms in the Fe3C nanoparticles. By controlling the acid concentration, etching time, and temperature, the concentration and distribution of iron vacancies can be controllably introduced. These iron vacancies (V... Fe The formation of ) has a triple effect: first, it breaks the original periodic lattice structure of Fe3C, initially optimizing the local electron density; second, it serves as a "trap site" for subsequent anchoring of cobalt single atoms; and third, the vacancy itself can act as an active center to participate in the catalytic reaction. EPR test results ( Figure 4Figure f) confirms the successful introduction of iron vacancies, and the vacancy concentration can be controlled by etching conditions. In S3, iron vacancies, oxygen-containing functional groups, or residual nitrogen species on the defective iron carbide surface can serve as heterogeneous nucleation sites for ZIF-8, inducing ZIF-8 crystals to nucleate and grow independently on the material surface rather than in solution, thereby forming a uniform and dense encapsulation layer. The introduction of the ZIF-8 encapsulation layer has multiple functions: first, it protects iron vacancies from being destroyed or over-oxidized during subsequent high-temperature vapor deposition; second, after ZIF-8 is carbonized at high temperature, it provides an additional nitrogen source, providing an N4 coordination environment for the subsequently deposited Co single atoms; third, the confinement effect of the MOF layer can suppress the aggregation of cobalt atoms during the deposition process. In S4, the cobalt source (such as cobalt nitrate) volatilizes under heating conditions to produce gaseous cobalt. This gaseous cobalt diffuses to the material surface and tends to occupy lower-energy defect sites—i.e., pre-constructed iron vacancies. The "capture effect" of vacancies on cobalt atoms stems from the unsaturated coordination environment and high surface energy at the defect sites, causing cobalt atoms to preferentially anchor there rather than adsorb randomly. The anchored cobalt atoms then coordinate with surrounding nitrogen atoms (from ZIF-8 carbide products and nitrogen-doped carbon nanotubes) to form a stable Co-NC structure. This "vacancy-oriented anchoring" mechanism ensures precise placement of cobalt single atoms and nearly 100% atomic utilization.

[0030] In some embodiments, the iron salt in S1 is at least one of anhydrous ferric chloride, ferric nitrate, and ferric acetate; preferably, the iron salt is anhydrous ferric chloride. The carbon- and nitrogen-containing organic precursor is at least one of dicyandiamine, polycyanamide, and urea, preferably, the carbon- and nitrogen-containing organic precursor is dicyandiamine; In some embodiments, in S1, the first calcination temperature is 850-950°C, for example, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, or 950°C, the time is 1-3 hours, for example, 1 hour, 2 hours, or 3 hours, and the heating rate is 3-10°C / min, for example, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, or 10°C / min.

[0031] Specifically, during calcination, the carbon- and nitrogen-containing organic precursors are placed upstream of the reactant gases, while the iron salts are placed downstream. This allows the gases produced by the decomposition of the organic precursors to flow through the iron salts. The advantages of this arrangement are: the carbon and nitrogen source decomposition gases contact the iron salts in gaseous form, resulting in a large reaction interface and high mass transfer efficiency; the continuous flow of gas through the iron salts promptly removes reaction byproducts, promoting the forward reaction; and it avoids the localized uneven reaction problems that may occur during solid-liquid calcination. Of course, to avoid environmental pollution, an anti-backflow device is connected to the gas outlet, and the exhaust gas is collected throughout the process using a pure aqueous solution.

[0032] In some embodiments, in S2, the acidic solution is at least one of hydrochloric acid, sulfuric acid, and nitric acid, with a concentration of 1–6 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L. Preferably, the concentration is 3 mol / L. If the concentration is too low, H… + Insufficient concentration results in a slow etching rate and low vacancy introduction efficiency; excessively high concentration (>6 mol / L) leads to an excessively fast etching rate, which may cause excessive dissolution or even complete destruction of Fe3C particles.

[0033] The immersion etching temperature is 25-60℃, for example, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, and the time is 1-6h, for example, 1h, 2h, 3h, 4h, 5h, 6h.

[0034] It should be noted that after immersion etching, the resulting precipitate needs to be centrifuged and washed multiple times, and finally dried at 60°C.

[0035] In some embodiments, in S3, the zinc salt is zinc nitrate hexahydrate or zinc acetate; the imidazole ligand is one of dimethylimidazolium, imidazole, and 4-methylimidazolium, wherein different ligands can control the pore size and pore surface properties of the ZIF material; the stirring reaction temperature is 25-60°C, for example 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, and the time is 1-6h, for example 1h, 2h, 3h, 4h, 5h, 6h.

[0036] Specifically, the reaction of defective iron carbide material containing iron vacancies with zinc salt and imidazole ligands by stirring includes: dissolving the defective iron carbide material containing iron vacancies and zinc salt in methanol to obtain solution A; The imidazole ligand is then dissolved in methanol to obtain solution B; Solution B was poured into solution A, stirred and soaked for more than 12 hours, then centrifuged and washed to collect the precipitate, and finally dried at 60°C to obtain a defect-state iron carbide composite material encapsulated by a metal-organic framework.

[0037] This "stepwise mixing method" in this embodiment avoids a large amount of homogeneous nucleation between zinc ions and ligands before they contact the defective state of iron carbide, which is beneficial for ZIF-8 to preferentially nucleate and grow heterogeneously on the material surface. If all components are mixed in one pot, a large number of ZIF-8 crystal nuclei are easily formed in the solution, resulting in a thin and uneven coating layer.

[0038] In some embodiments, in S4, the cobalt source is at least one of cobalt nitrate hexahydrate, cobalt acetate, and cobalt acetylacetonate.

[0039] In some embodiments, in S4, the second calcination temperature is 850-950°C, for example, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, or 950°C, the time is 1-3 hours, for example, 1 hour, 2 hours, or 3 hours, and the heating rate is 3-10°C / min, for example, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, or 10°C / min.

[0040] This embodiment also provides a ferrocarbide electrocatalytic material with single-atom anchored defect states, prepared by the aforementioned method. Alternatively, it may include nitrogen-doped carbon nanotubes and iron carbide nanoparticles; wherein the iron carbide nanoparticles are encapsulated within the nitrogen-doped carbon nanotubes; The iron carbide nanoparticles have iron vacancies, and cobalt single atoms are anchored at the iron vacancies to form a Co-NC coordination structure.

[0041] In this embodiment, the nitrogen-doped carbon nanotubes of the iron carbide electrocatalytic material with single-atom anchored defect states have a one-dimensional hollow fiber structure. Iron carbide nanoparticles are encapsulated within these nitrogen-doped carbon nanotubes, each containing an iron vacancy anchored to a cobalt single atom. Through the synergistic effect of these multi-level structures, precise control of the material's electronic structure and a comprehensive improvement in its catalytic performance are achieved, specifically in the following aspects: Firstly, the embedded structure endows the material with excellent stability. Iron carbide nanoparticles are encapsulated within nitrogen-doped carbon nanotubes, forming a composite structure of "particles embedded in tubes." The walls of the carbon nanotubes physically confine the internal Fe3C particles, effectively inhibiting their migration, aggregation, and growth during high-temperature treatment and electrochemical reactions. The encapsulated carbon layer acts as a protective barrier, preventing corrosive species in the high-concentration KOH electrolyte from directly contacting the Fe3C surface during electrochemical reactions, significantly slowing down Fe dissolution. The tight heterogeneous interface formed between the carbon layer and Fe3C promotes interfacial charge transfer. As a result, the material maintains excellent activity after 3000 cycles and shows no significant performance degradation after 680 hours of continuous charge-discharge in a zinc-air battery.

[0042] Secondly, iron vacancies enable precise anchoring of single atoms. Iron vacancies (V0.05) introduced into the Fe3C lattice through acid etching are... FeWith its high surface energy and unsaturated coordination environment, the cobalt atom can act as a "trap" to directionally capture cobalt atoms deposited in the subsequent vapor phase, causing them to preferentially anchor at vacancies rather than being randomly distributed. Changes in the EPR signal and the EDS elemental distribution map jointly confirmed the successful occupation of vacancies by cobalt single atoms. This "vacancy anchoring" mechanism solves the problems of easy agglomeration of metal atoms and random loading sites in the preparation of traditional single-atom catalysts, achieving a near 100% atomic utilization rate. At the same time, the unoccupied iron vacancies and the anchored cobalt single atoms form defect-single-atom dual active centers, synergistically enhancing catalytic activity.

[0043] Third, while the cobalt single atom is anchored in the Fe3C particles, it coordinates with the N and C carbide products from ZIF-8, forming a stable Co-NC structure. This coordination structure hybridizes the d orbitals of cobalt with the p orbitals of nitrogen, optimizing the center position of the cobalt d band. UPS tests show that Co... SAc / V Fe -The d-band center of Fe3C is located at -5.57 eV, compared to Fe3C (-4.84 eV) and Co. SAc / Fe3C (-5.12 eV) shifted significantly downward, reaching the optimal ORR range. The downward shift of the d-band center optimized the adsorption energy of cobalt sites for oxygen-containing intermediates from "excessively strong" to "moderate," ensuring effective activation of O2 while avoiding difficulties in intermediate desorption, thereby significantly improving catalytic activity and reaction kinetics.

[0044] Fourth, nitrogen-doped carbon nanotubes provide both electrical conductivity and coordination functions. The one-dimensional hollow fiber structure of nitrogen-doped carbon nanotubes provides a fast axial electron transport channel, reducing charge transfer resistance. Furthermore, the doped species, such as pyridine nitrogen and graphitic nitrogen, not only improve the electron donor properties of carbon materials but also act as coordination sites to help stabilize cobalt single atoms. The hollow structure also provides additional channels for electrolyte permeation and oxygen diffusion, reducing mass transfer resistance and enabling the material to maintain high catalytic efficiency over a wide current density range.

[0045] This embodiment provides an application of iron carbide electrocatalytic material with single-atom anchored defect states in a metal-air battery.

[0046] Based on the excellent catalytic performance of the single-atom anchored defect state ferrocarbide electrocatalyst material in metal-air batteries according to this embodiment, it is expected to be applied in metal-air batteries.

[0047] The present invention will be further described below through specific embodiments.

[0048] Example 1 A method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states includes the following steps: 1. Synthesis of Fe3C: 0.08g of iron salt (anhydrous ferric chloride) and 3g of carbon and nitrogen-containing organic precursor (dicyandiamine) were placed in a sealed tube furnace. One end of the dicyandiamine was placed upstream of the tube furnace. The first calcination was carried out under a nitrogen atmosphere, with the temperature rising from room temperature to 900℃ at a rate of 5℃ / min. The temperature was maintained for 2 hours. An anti-backflow device was connected to the gas outlet, and the exhaust gas was collected throughout the process using a pure aqueous solution to avoid environmental pollution. After natural cooling, Fe3C composite material (denoted as Fe3C) with iron carbide nanoparticles embedded in nitrogen-doped carbon nanotubes was obtained.

[0049] 2. V Fe Synthesis of Fe3C: Prepare 200 ml of 3 mol / L hydrochloric acid by mixing 50 ml concentrated hydrochloric acid with 150 ml pure water. Immerse 120 mg of the Fe3C obtained in step 1 in the 3 mol / L hydrochloric acid solution at 25 °C for 3 hours. Then, centrifuge and wash three times, collect the precipitate, and dry it at 60 °C to obtain V. Fe -Fe3C; 3. ZIF-8 packaged V Fe - Synthesis of Fe3C: Take 0.1g of V obtained in step 2 Fe -Fe3C and 0.64g of zinc nitrate were dissolved in 25ml of methanol, referred to as solution A. Then, 1.46g of dimethylimidazole was dissolved in 25ml of methanol, referred to as solution B. At 25℃, solutions A and B were stirred separately for 5 minutes each. Then, solution B was quickly poured into solution A, and the reaction was stirred for 12 hours. Afterwards, the precipitate was collected by centrifugation and washing, and dried at 60℃ to obtain ZIF-8-encapsulated V. Fe -Fe3C.

[0050] 4. Co SAc / V Fe Synthesis of Fe3C: Take 0.25g of V wrapped in ZIF-8 Fe Fe3C and 0.1g of cobalt nitrate hexahydrate were placed at opposite ends of a ceramic boat and placed in a sealed tube furnace. The end containing cobalt nitrate hexahydrate was positioned upstream of the furnace. A second calcination was performed under a nitrogen atmosphere using chemical vapor deposition, with the temperature increased from room temperature to 900℃ at a rate of 5℃ / min. This temperature was maintained for 2 hours. The exhaust gas was collected throughout the process using a pure aqueous solution to prevent environmental pollution. After natural cooling, the desired iron carbide electrocatalytic material with single-atom anchored defect states (Co) was obtained. SAc / V Fe -Fe3C.

[0051] Comparative Example 1 A method for preparing an iron carbide electrocatalytic material includes the following steps: Synthesis of Fe3C: 0.08g of iron salt (anhydrous ferric chloride) and 3g of an organic precursor containing carbon and nitrogen (dicyandiamine) are placed in a sealed tube furnace. One end of the dicyandiamine is placed upstream of the tube furnace. The first calcination is carried out under a nitrogen atmosphere, with the temperature rising from room temperature to 900℃ at a rate of 5℃ / min. The temperature is maintained for 2 hours. An anti-backflow device is connected to the gas outlet, and the exhaust gas is collected throughout the process using a pure aqueous solution to avoid environmental pollution. After natural cooling, an Fe3C composite material (denoted as Fe3C) in which iron carbide nanoparticles are embedded in nitrogen-doped carbon nanotubes is obtained.

[0052] Compared with Example 1, this comparative example only yielded the Fe3C composite material (denoted as Fe3C) in which iron carbide nanoparticles were embedded in nitrogen-doped carbon nanotubes obtained in step 1.

[0053] Comparative Example 2 A method for preparing an iron carbide electrocatalytic material includes the following steps: Synthesis of Fe3C: 0.08g of iron salt (anhydrous ferric chloride) and 3g of carbon and nitrogen-containing organic precursor (dicyandiamine) were placed in a sealed tube furnace. One end of the dicyandiamine was placed upstream of the tube furnace. The first calcination was carried out under a nitrogen atmosphere, with the temperature rising from room temperature to 900℃ at a rate of 5℃ / min. The temperature was maintained for 2 hours. An anti-backflow device was connected to the gas outlet, and the exhaust gas was collected throughout the process using a pure aqueous solution to avoid environmental pollution. After natural cooling, Fe3C composite material (denoted as Fe3C) with iron carbide nanoparticles embedded in nitrogen-doped carbon nanotubes was obtained.

[0054] Synthesis of ZIF-8-coated Fe3C: 0.1 g of the obtained Fe3C and 0.64 g of zinc nitrate were dissolved in 25 ml of methanol, referred to as solution A. 1.46 g of dimethylimidazole was then dissolved in 25 ml of methanol, referred to as solution B. Solutions A and B were stirred separately for 5 min each. Solution B was then quickly poured into solution A, and the mixture was stirred and soaked for 12 hours. The precipitate was then collected by centrifugation and washing, and dried at 60 °C to obtain ZIF-8-coated Fe3C.

[0055] 4. Co SAc Synthesis of Fe3C: 0.25g of ZIF-8-encapsulated Fe3C and 0.1g of cobalt nitrate hexahydrate were placed at opposite ends of a ceramic boat and placed in a sealed tube furnace. The end containing cobalt nitrate hexahydrate was positioned upstream of the furnace. A second calcination was performed under a nitrogen atmosphere using chemical vapor deposition, raising the temperature from room temperature to 900℃ at a rate of 5℃ / min. This temperature was maintained for 2 hours. The exhaust gas was collected using a pure aqueous solution throughout the process to prevent environmental pollution. After natural cooling, the Fe3C electrocatalyst material with single-atom anchored defect states was obtained. SAc / Fe3C.

[0056] The difference between this comparative example and Example 1 is that this comparative example does not have step 2, that is, no acid etching is performed.

[0057] X-ray diffraction (XRD) was used to analyze the Fe3C obtained in step 1 and the V obtained in step 2 of this Example 1. Fe -Fe3C and Co obtained in step 4 SAc / V Fe The crystal structure of Fe3C was characterized, and the results are as follows: Figure 3 As shown in Figure a, Fe3C obtained in step 1 and V obtained in step 2 Fe -Fe3C and Co obtained in step 4 SAc / V Fe -Fe3C all showed clear diffraction peaks corresponding to the Fe3C phase (PDF number 00-035-0772), and no Co-related peaks were observed, confirming that the Co species are atomically dispersed in the matrix.

[0058] The Co obtained in Example 1 was further studied using transmission electron microscopy (TEM) images and atomic-resolution HAADF-STEM images. SAc / V Fe Morphological characteristics and corresponding elemental distribution of Fe3C catalysts. Figure 3 b, Figure 3 d, Figure 3 In the image, e represents a transmission electron microscope (TEM) image. Figure 3 From b, we can see Co SAc / V Fe -Fe3C catalysts exhibit a hollow bamboo-like structure. Figure 3 c, Figure 3 f is Co SAc / V Fe Atom-resolution HAADF-STEM images of the Fe3C catalyst can distinguish isolated bright spots (circled in red in the image) corresponding to single Co atoms. Figure 3 d and Figure 3 As shown in Figure e, iron carbide is surrounded by a carbon layer, exposing the (031), (210), and (112) crystal planes of iron carbide with lattice spacings of 0.201 nm, 0.238 nm, and 0.199 nm, respectively, and the (006) crystal plane of the carbon layer with a lattice spacing of 0.334 nm. Figure 3 The two sites I and II of f correspond to respectively Figure 3 In the image, g(Ⅰ and Ⅱ) are FFT images, which are diffraction spot patterns obtained by performing Fourier transform on high-resolution transmission electron microscopy (HRTEM) images, and iron vacancies can be seen from them.

[0059] To elucidate the atomic-scale spatial distribution of elements in the nanofiber structure, high-angle backscattering transmission electron microscopy was employed, and energy-dispersive X-ray spectroscopy elemental mapping results were simultaneously obtained, as shown below. Figure 3 As shown in Figure hl, the corresponding two-dimensional EDS elemental distribution map quantitatively verifies the uniform dispersion of all constituent elements (Fe, C, Co, and N) in the nanofiber matrix. The presence of Co at the central iron carbide site further confirms the successful anchoring of cobalt single atoms to the iron carbide.

[0060] Analysis of each catalyst using ultraviolet photoelectron spectroscopy (UPS) yielded the following results: Figure 4 As shown in Figure e, it reveals that the center of band d exhibits a gradual downward shift. Specifically, the Co obtained in Example 1... SAc / V Fe - The d-band center of Fe3C is located at -5.57 eV, compared to Fe3C obtained in Comparative Example 1 (-4.84 eV) and Co obtained in Comparative Example 2. SAc / Fe3C (-5.12eV) is closer to the Fermi level. Co SAc / V Fe The downward shift of the d-band center in the Fe3C catalyst optimizes the adsorption of hydroxyl intermediates at metal sites, enhances the protonation kinetics of hydroxyl intermediates, and inhibits the breaking of OO bonds, all of which contribute to the improvement of catalytic activity.

[0061] Electron paramagnetic resonance (EPR) spectroscopy was used to analyze Fe3C and Co. SAc / Fe3C, Co SAc / V Fe The defect structure of Fe3C was characterized. Figure 4 The XPS full spectrum of a in Co proves SAc / V Fe The presence of Co, C, Fe, and N elements in Fe3C within the catalyst. This is shown in the high-resolution C 1s spectrum, as... Figure 4 As shown in Figure b, the characteristic peaks at 289.1 eV, 285.9 eV, and 284.6 eV are attributed to carbon-oxygen double bonds, carbon-nitrogen bonds, and carbon-carbon single bonds, respectively. In the high-resolution spectrum of Fe2p, as shown... Figure 4 As shown in Figure c, the characteristic peaks at 733.5 eV and 720.3 eV correspond to satellite peaks, while the characteristic peaks at 726.9 eV and 710.6 eV correspond to the 2p-terminal peaks of divalent iron, respectively. 1 / 2 and 2p 3 / 2 The characteristic peaks at 723.8 eV and 713.8 eV correspond to the 2pe of trivalent iron, respectively. 1 / 2 and 2p 3 / 2 The characteristic peak at 707.9 eV corresponds to the Fe-C bond, and it can be observed that Co is higher than Fe3C. SAc / VFe The reduced peak area of ​​Fe3C indicates that etching caused some loss of iron carbide, leading to a weakening of the Fe-C signal. In the high-resolution N 1s spectrum, as shown... Figure 4 As shown in Figure d, the characteristic peaks at 404.5 eV, 402.6 eV, 400.8 eV, 399.2 eV, and 398.3 eV are attributed to nitrogen oxides, graphitic nitrogen, pyridine nitrogen, iron-nitrogen bonds, and pyrrole nitrogen, respectively. Figure 4 As shown in f, Co SAc / V Fe The EPR spectrum of Fe3C shows a paramagnetic absorption signal at g=1.99, which is attributed to Co. SAc / V Fe -Uncoordinated iron vacancies on the surface of Fe3C material, and V Fe Compared to Fe3C, Co SAc / V Fe -Fe3C showed a significantly weakened paramagnetic signal intensity, while Co showed a significantly weaker signal intensity compared to Fe3C. SAc / V Fe The significantly enhanced paramagnetic signal intensity of Fe3C indicates that acid etching successfully created iron vacancies and cobalt single atoms were anchored in the defective Fe3C state. The high content of iron vacancies can serve as accessible active sites, thereby accelerating the electrocatalytic reaction kinetics.

[0062] A rotating ring-disc electrode was used to treat Co in a 0.1 M KOH electrolyte. SAc / V Fe The oxygen reduction reaction (ORR) performance of the Fe3C catalyst was comprehensively tested and compared with that of Fe3C and Co. SAc A comparative analysis was conducted using Fe3C and commercially available Pt / C reference materials. All electrochemical potentials were referenced to a reversible hydrogen electrode. The results are as follows: Figure 5 As shown. The results of the cyclic voltammetry method are as follows: Figure 5 As shown in Figure a, Co SAc / V Fe -Fe3C exhibits the most positive reduction peak, indicating its excellent oxygen reduction activity. The redox polarization curves are shown below. Figure 5 As shown in Figure b, its excellent oxygen reduction activity is further verified: the onset potential reaches 1.022V, and the half-wave potential (E) 1 / 2 The value is 0.91V, surpassing commercial Pt / C and other comparative catalysts. Tafel slope analysis, such as... Figure 5 As shown in Figure c, Co is further revealed SAc / V Fe -Fe3C exhibits excellent oxygen reduction kinetics, with a Tafel slope (67 mV dec) -1 The value was significantly lower than that of Pt / C (77 mVdec). -1 ), Co SAc / -Fe3C (72mV dec) -1 ) and Fe3C (94mV dec -1 The lower Tafel slope indicates enhanced O2 adsorption / activation kinetics, exhibiting the fastest reaction rate among the tested catalysts. Furthermore, measurements were performed over a speed range of 400–2500 rpm to evaluate the oxygen reduction reaction kinetics, with results as follows: Figure 5 As shown in d. For Co SAc / V Fe For the Fe3C catalyst, the linear sweep voltammetry curves obtained at different rotational speeds all exhibited relatively flat current plateaus below 0.7 V. This characteristic plateau indicates that the oxygen reduction reaction proceeds via a four-electron transfer pathway. In 0.1 M KOH solution, Co... SAc / V Fe The Fe3C catalyst maintained excellent stability after 3000 CV cycles, as shown in the results. Figure 5 As shown in e, Co SAc / V Fe -Fe3C exhibits better stability than Pt / C. Furthermore, the generation of hydrogen peroxide during the oxygen reduction reaction was quantitatively analyzed using a rotating ring-disk electrode measurement technique. Co SAc / V Fe The Fe3C catalyst consistently exhibits low hydrogen peroxide yield within a potential range of 0.2–0.7 V, while possessing a high electron transfer number, approaching a 4-electron pathway, demonstrating near-ideal electronic oxygen reduction reaction characteristics. The results are as follows... Figure 5 As shown in f.

[0063] To evaluate its performance in practical applications, a zinc-air battery (ZAB) was assembled using a zinc anode and an air cathode, as shown in the following structure. Figure 6 As shown in Figure a. Compared to the control cell using Pt / C+RuO2, the Co-containing cell of Example 1... SAc / V Fe Zinc-air batteries prepared with Fe3C catalysts exhibit higher discharge current density and narrower charge-discharge voltage gaps, such as... Figure 6 As shown in b. Furthermore, based on Co... SAc / V Fe -Fe3C zinc-air batteries achieve up to 183.5mW cm⁻¹ -2 The discharge power density significantly surpasses that of Pt / C+RuO2 batteries (121.7 mW / cm²). -2 ),like Figure 6 As shown in c. And as Figure 6 The physical image shown in d is based on Co from Example 1. SAc / V FeThe successful power supply of a zinc-air battery using Fe3C to a mobile phone further validates the practical application potential of this catalyst. The battery exhibits excellent electrochemical stability, maintaining a stable open-circuit potential of 1.486V for 28 hours. Figure 6 As shown in Figure e. It is worth noting that this system operates at 2-20 mA cm⁻¹. -2 No significant performance degradation was observed over a wide current density range, such as Figure 6 As shown in Figure f. Long-term cycle testing further confirms its excellent durability; after 680 hours of continuous charge-discharge cycles, its performance showed no significant degradation, as shown in Figure f. Figure 6 As shown in g. Co SAc / V Fe The superior ORR activity and zinc-air battery performance of the Fe3C catalyst are mainly attributed to the doping of single atoms of the transition metal cobalt, which modulates the electronic structure of iron carbide with defect states. This electronic reconstruction significantly alters the adsorption behavior of reaction intermediates, thereby greatly improving the overall electrocatalytic performance.

[0064] In summary, this invention provides a ferrocarbide electrocatalytic material with single-atom anchored defect states, its preparation method, and its applications. The catalyst obtained by this invention exhibits excellent oxygen reduction activity, with an onset potential of 1.022 V and a half-wave potential (E1 / 2) of 0.91 V, both exceeding those of commercial Pt / C and other comparative catalysts. The faster the reaction rate, the higher its Tafel slope (67 mVdec). - ¹) Significantly lower than Pt / C (77 mV dec) - ¹), Co SAc / -Fe3C (72mV dec) - ¹) and Fe3C (94mV dec - ¹). It exhibits excellent long-term stability, maintaining superior stability even after 3000 CV cycles. Furthermore, in practical applications, its discharge power density significantly surpasses that of Pt / C+RuO2 batteries (121.7 mW / cm²). -2 It is expected to be applied in practical applications.

[0065] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing an iron carbide electrocatalytic material with single-atom anchored defect states, characterized in that, Includes the following steps: S1. Iron salt and organic precursors containing carbon and nitrogen are calcined for the first time under an inert atmosphere to form Fe3C composite material in which iron carbide nanoparticles are embedded in nitrogen-doped carbon nanotubes. S2. The Fe3C composite material obtained in S1 is immersed and etched in an acidic solution to remove some iron atoms from the iron carbide nanoparticles and introduce iron vacancies into the iron carbide nanoparticles, so that the iron carbide nanoparticles become defective iron carbide materials containing iron vacancies. S3. The defective iron carbide material containing iron vacancies is stirred and reacted with zinc salt and imidazole ligands to encapsulate the defective iron carbide material containing iron vacancies with a metal-organic framework material. S4. The product obtained in S3 and the cobalt source are placed in a vapor deposition apparatus and calcined for the second time under an inert atmosphere, so that the cobalt source volatilizes and deposits onto the iron vacancies of the defective iron carbide material containing iron vacancies, and the cobalt atoms are anchored to the iron vacancies, thus obtaining the electrocatalytic material of iron carbide with single-atom anchored defective state.

2. The method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states according to claim 1, characterized in that, The iron salt in S1 is at least one of anhydrous ferric chloride, ferric nitrate, and ferric acetate. The organic precursor containing carbon and nitrogen is at least one of dicyandiamine, melamine, and urea.

3. The method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states according to claim 1, characterized in that, In S1, the first calcination temperature is 850-950℃, the time is 1-3 hours, and the heating rate is 3-10℃ / min.

4. The method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states according to claim 1, characterized in that, In S2, the acidic solution is at least one of hydrochloric acid, sulfuric acid, and nitric acid, with a concentration of 1 to 6 mol / L; the immersion etching temperature is 25°C, and the time is 3 hours.

5. The method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states according to claim 1, characterized in that, In S3, the zinc salt is zinc nitrate hexahydrate or zinc acetate; the imidazole ligand is one of dimethylimidazolium, imidazole, or 4-methylimidazolium; the stirring reaction is carried out at a temperature of 25°C for 12 hours.

6. The method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states according to claim 1, characterized in that, The reaction of defective iron carbide material containing iron vacancies with zinc salt and imidazole ligands by stirring includes: dissolving the defective iron carbide material containing iron vacancies and zinc salt in methanol to obtain solution A; The imidazole ligand is then dissolved in methanol to obtain solution B; Solution B was poured into solution A, stirred and soaked for more than 12 hours, then centrifuged and washed to collect the precipitate, and finally dried at 60°C to obtain a defect-state iron carbide composite material encapsulated by a metal-organic framework.

7. The method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states according to claim 1, characterized in that, In S4, the cobalt source is at least one of cobalt nitrate hexahydrate, cobalt acetate, and cobalt acetylacetonate.

8. The method for preparing a ferrocarbide electrocatalytic material with single-atom anchored defect states according to claim 1, characterized in that, In S4, the second calcination temperature is 850–950℃, the time is 1–3 hours, and the heating rate is 3–10℃ / min.

9. A type of iron carbide electrocatalytic material with single-atom anchored defect states, characterized in that, Prepared by the preparation method described in any one of claims 1-8.

10. The application of the iron carbide electrocatalytic material with single-atom anchored defect states as described in claim 9 in a metal-air battery.

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