A nitrogen-doped carbon composite material modified with Fe@Fe2O3, its preparation method and application

Abstract

This invention discloses a Fe@Fe2O3-modified nitrogen-doped carbon composite material, its preparation method, and its applications, belonging to the technical field of nitrogen-doped carbon composite materials. It consists of a nitrogen-doped carbon matrix and Fe@Fe2O3 particles uniformly dispersed in the matrix. The Fe@Fe2O3 particles have a core-void-shell structure, are polyhedral nanoparticles, with Fe particles inside the Fe2O3 particles and void layers between them. The core-void-shell structured Fe@Fe2O3 is prepared using a stepwise atmosphere-controlled strategy, first by high-temperature calcination under an inert atmosphere, followed by mild oxidation in air, and then interface separation induced by lattice expansion stress. The nitrogen-doped carbon matrix is ​​obtained by carbonization of L-lysine hydrochloride; the porous structure is obtained by the action of sodium chloride. This composite material, used as a positive electrode catalyst in zinc-air batteries, exhibits a cycle life exceeding that of commercial platinum-carbon and ruthenium dioxide; and as an anode catalyst in AEM water electrolysis, the electrolyzer can operate stably for 1000 hours.

Description

Technical Field

[0001] This invention belongs to the field of nitrogen-doped carbon composite material technology, specifically relating to a nitrogen-doped carbon composite material modified with Fe@Fe2O3, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Zinc-air batteries (ZAB) and alkaline anion exchange membrane (AEM) water electrolysis technologies are key technologies for clean energy conversion and storage. However, the slow kinetics of oxygen reduction (ORR) at the cathode and oxygen evolution (OER) at the anode severely limit the overall efficiency. Currently used precious metal catalysts (such as Pt / C and IrO2) are expensive and prone to dissolution and deactivation under alkaline operating conditions, making them unsuitable for large-scale applications.

[0004] To address this issue, non-noble metal-based catalysts, such as nitrogen-doped carbon (NC) supported iron-based materials, have attracted widespread attention. However, single-component materials struggle to simultaneously achieve high ORR and OER activities and suffer from insufficient stability (easily detached or dissolved). While catalysts with core-shell and interstitial structures (such as Fe@oxides) can synergistically enhance bifunctional performance, their precise synthesis during carbonization is challenging: metal precursors tend to agglomerate at high temperatures, making it difficult to achieve topologically oriented growth with uniform particle size on NCs; and the formation of nano-interstitials (e.g., through the Kirkendall effect or etching) often relies on complex liquid-phase steps, making it impossible to precisely control interstitial size and interface state during solid-phase reactions. Therefore, developing a simple and controllable solid-phase synthesis strategy to construct structurally stable, site-rich interstitial core-shell catalysts has become a critical technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a nitrogen-doped carbon composite material modified with Fe@Fe2O3, its preparation method, and its application. The composite material provided by the present invention is used as a positive electrode catalyst in a liquid rechargeable zinc-air battery, with a cycle life exceeding that of commercial platinum-carbon and ruthenium dioxide; it is also used as an anode catalyst in AEM water electrolysis, enabling the electrolyzer to operate stably for 1000 hours.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a nitrogen-doped carbon composite material modified with Fe@Fe2O3, comprising a nitrogen-doped carbon matrix and Fe@Fe2O3 particles dispersed in the nitrogen-doped carbon matrix; The Fe@Fe2O3 particles consist of an iron core and an iron oxide shell, with a void layer between the iron core and the iron oxide shell.

[0007] In some embodiments of the present invention, the particle size of the Fe@Fe2O3 particles is 20~100 nm.

[0008] In some embodiments of the present invention, the thickness of the void layer is 5~20 nm.

[0009] In some embodiments of the present invention, the nitrogen-doped carbon matrix is ​​a layered porous carbon structure.

[0010] In some embodiments of the present invention, the relative atomic content of the Fe@Fe2O3 particles is 5-30 at.%.

[0011] A second aspect of the present invention provides a method for preparing the Fe@Fe2O3 modified nitrogen-doped carbon composite material described in the first aspect, comprising: The ferric salt and carbon source are dissolved in water, a self-sacrificing template is added, dried, calcined in a reducing atmosphere, cooled to 50-80℃ and oxidized in air to remove the self-sacrificing template, thus obtaining the product.

[0012] In some embodiments of the present invention, the trivalent iron salt includes any one or more of ferric nitrate, ferric chloride, and ferric sulfate.

[0013] In some embodiments of the present invention, the carbon source is any one or more of urea, thiourea, melamine and L-lysine hydrochloride.

[0014] In some embodiments of the present invention, the self-sacrificing template is sodium chloride.

[0015] In some embodiments of the present invention, the molar ratio of the trivalent iron salt, carbon source, and self-sacrificing template is (0.1-1):(5-6):(170-175).

[0016] In some embodiments of the present invention, the calcination is performed at 700-900°C for 2-4 hours.

[0017] In some embodiments of the present invention, the oxidation in air is performed by allowing the air to stand for 0.5-4 hours.

[0018] In some embodiments of the present invention, the method for removing the self-sacrificing template includes washing to remove the self-sacrificing template, followed by vacuum freeze-drying to obtain a nitrogen-doped carbon composite material modified with Fe@Fe2O3.

[0019] A third aspect of the present invention provides an application of the Fe@Fe2O3 modified nitrogen-doped carbon composite material described in the first aspect in a zinc-air battery; The Fe@Fe2O3 modified nitrogen-doped carbon composite material is used as the positive electrode catalyst for zinc-air batteries.

[0020] A fourth aspect of the present invention provides a zinc-air battery comprising a zinc metal electrode, an air electrode, and an electrolyte, wherein the catalyst in the air electrode is a nitrogen-doped carbon composite material modified with Fe@Fe2O3 as described in the first aspect.

[0021] A fifth aspect of the present invention provides an application of the Fe@Fe2O3 modified nitrogen-doped carbon composite material described in the first aspect in AEM water electrolysis; The Fe@Fe2O3 modified nitrogen-doped carbon composite material was used as an anode catalyst for AEM water electrolysis.

[0022] The beneficial effects of this invention are as follows: This invention provides a nitrogen-doped carbon composite material modified with Fe@Fe2O3. The nitrogen-doped carbon matrix is ​​a loose, lamellar, porous carbon structure, with Fe@Fe2O3 particles uniformly embedded within the porous carbon and tightly bonded to the nitrogen-doped carbon matrix. The Fe@Fe2O3 particles are polyhedral Fe@Fe2O3 particles with a core-void-shell structure, where elemental iron is contained within ferric oxide, with a void layer between them. The metal core activates oxygen molecules in the oxygen exchanger reaction (ORR), the oxide shell optimizes OER intermediates, and the voids buffer volumetric strain. It possesses high active sites and a stable metal composite structure, exhibiting high oxygen catalytic activity and excellent zinc-air battery performance as an electrocatalyst. When used as a positive electrode catalyst in a liquid rechargeable zinc-air battery, the composite material provided by this invention exhibits a cycle life exceeding that of commercial platinum-carbon and ruthenium dioxide; when used as an anode catalyst in AEM water electrolysis, the electrolyzer can operate stably for 1000 hours.

[0023] This invention also provides a method for preparing Fe@Fe2O3 modified nitrogen-doped carbon composite materials. Utilizing a distribution atmosphere control strategy, the method involves first high-temperature calcination in a reducing atmosphere, followed by mild oxidation in air. Through lattice expansion stress-induced interfacial separation, core-void-shell structured Fe@Fe2O3 polyhedral nanoparticles are formed. This achieves one-step, precise, and controllable preparation of Fe@Fe2O3 polyhedral nanoparticles with a core-void-shell structure in a nitrogen-doped carbon matrix. The Fe@Fe2O3 polyhedral nanoparticles are uniformly dispersed in the NC matrix, synergistically enhancing the activity and stability of the bifunctional catalyst. The preparation method of this invention is simple and easily scalable. Furthermore, the structure is precisely controllable, overcoming the stringent dependence on precursor morphology and reaction conditions of traditional methods (such as the Kirkendall effect), and achieving effective control over core-shell size and interfacial dimensions. This method enhances structural and interfacial stability; the resulting core-shell particles are firmly embedded and dispersed in the nitrogen-doped carbon matrix, avoiding agglomeration, detachment, or dissolution of active particles, and greatly improving the overall stability of the catalyst. This method also synergistically optimizes catalytic performance, and the prepared composite material exhibits excellent bifunctional catalytic activity and long-term durability in both zinc-air batteries and AEM water electrolysis devices. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 The following are scanning electron microscope (SEM) images of the Fe@Fe2O3 / NC-1 sample obtained in Example 1 of this invention: where the scale bar of (a) is 5 μm and the scale bar of (b) is 200 nm.

[0026] Figure 2 The following are SEM images of the Fe@Fe2O3 / NC-3 sample obtained in Example 3 of this invention: (a) has a scale bar of 5 μm, and (b) has a scale bar of 100 nm.

[0027] Figure 3 The following are SEM images of the Fe@Fe2O3 / NC-5 sample obtained in Example 5 of this invention: (a) has a scale bar of 5 μm, and (b) has a scale bar of 500 nm.

[0028] Figure 4 The following are SEM images of the NC sample obtained in Comparative Example 1 of this invention: (a) has a scale bar of 10 μm and (b) has a scale bar of 500 nm.

[0029] Figure 5The images show the morphology of the Fe@Fe2O3 / NC-3 sample obtained in Example 3 of this invention; where (a) is a transmission electron microscope (TEM) image, (b) is a high-resolution transmission electron microscope (HR-TEM) image of the NC region with a scale bar of 10 nm, (c) is an HR-TEM image of the white box area in (b) with a scale bar of 2 nm, (d) is an HR-TEM image of the Fe@Fe2O3 region, (e) is a fast Fourier transform (FFT) image of the Fe@Fe2O3 region, and (f) is a high-angle annular dark field image (HADDF) and elemental distribution map.

[0030] Figure 6 The images show the X-ray diffraction (XRD) patterns of the samples obtained in Examples 1, 3, 5 and Comparative Example 1 of this invention.

[0031] Figure 7 Images of the Fe@Fe2O3 / NC-3 sample obtained in Example 3 of this invention are shown; where (a) is the full X-ray photoelectron spectroscopy (XPS) spectrum, (b) is a bar chart of element content, (c) is C1s, (d) is N 1s, (e) is O 1s, and (f) is Fe 2p.

[0032] Figure 8 The oxygen reduction reaction (ORR) of the samples obtained in Examples 1-5 and Comparative Example 1 of this invention, as well as commercial Pt / C, is shown; wherein, (a) is the linear sweep voltammetry (LSV) curve, and (b) is the half-wave potential ( E 1 / 2 (c) is a bar chart, and (d) is the Tafel Slope.

[0033] Figure 9 The oxygen evolution reaction (OER) of the samples obtained in Examples 1-5 and Comparative Example 1 of this invention, as well as commercial RuO2, is shown; where (a) is the LSV curve, and (b) is the current density at 10 mA / cm². 2 Overpotential at time ( E j=10 (c) is a bar chart, where (c) is the Tafel slope.

[0034] Figure 10 The chronocurrent stability of ORR for the Fe@Fe2O3 / NC-3 sample obtained in Example 3 of this invention and for commercial Pt / C is shown.

[0035] Figure 11The following are the performance test results of Fe@Fe2O3 / NC-3 sample, Pt / C, and RuO2 in a liquid rechargeable zinc-air battery in Experimental Example 2 of this invention; wherein, (a) is a schematic diagram of the structure of the liquid rechargeable zinc-air battery catalyzed by Fe@Fe2O3 / NC-3 sample, Pt / C, and RuO2 obtained in Example 3, (b) is an open-circuit voltage photograph, (c) is an open-circuit voltage curve, (d) is a discharge polarization curve and power density, and (e) is a 10 mA cm⁻¹ power density curve. -2 The discharge curves and battery capacity are shown in Figure 1. (f) shows the rate performance at different current densities, and (g) shows a comparison of long-term cyclic charge-discharge curves.

[0036] Figure 12 The results of the performance test of Fe@Fe2O3 / NC-3 as an anode catalyst in AEM electrolysis of water in Experimental Example 3 of the present invention are shown. Among them, (a) is the comparison of the initial activation voltage of AEM electrolysis of water with Fe@Fe2O3 / NC-3 sample or RuO2 as anode and Pt / C as cathode obtained in Example 3, and (b) is the long-term stability test result of Fe@Fe2O3 / NC-3 as anode. Detailed Implementation

[0037] In view of the difficulty in the directional construction of interstitial core-shell structures in NC matrix in the prior art, this invention proposes a nitrogen-doped carbon composite material modified with Fe@Fe2O3, its preparation method and application.

[0038] This invention provides a nitrogen-doped carbon composite material modified with Fe@Fe2O3, comprising a nitrogen-doped carbon matrix and Fe@Fe2O3 particles dispersed in the nitrogen-doped carbon matrix; The Fe@Fe2O3 particles consist of an iron core and an iron oxide shell, with a void layer between the iron core and the iron oxide shell.

[0039] This invention solves the challenges of activity, stability, and synergistic dual-function design through an ingenious "core-gap-shell" structure. The iron core and iron oxide shell are optimized for ORR and OER, respectively, while the void layer ensures structural stability. The nitrogen-doped carbon matrix provides multiple functions, including dispersion, conductivity, and protection. This makes the Fe@Fe2O3-modified nitrogen-doped carbon composite material suitable not only for zinc-air batteries with high cycle life requirements but also for the harsh AEM water electrolysis anolyte reaction in high-potential, strongly alkaline environments.

[0040] Specifically: (1) The iron core, as a good electronic conductor, possesses electron-rich properties that optimize the adsorption and activation of oxygen molecules (O2), significantly enhancing the activity of the oxygen reduction reaction (ORR). The ferric oxide shell enhances the adsorption and activation of oxygen intermediates (such as OH-). -It has suitable adsorption energy and can efficiently catalyze the oxygen evolution reaction (OER).

[0041] (2) The core-shell structure integrates the ORR active site (core) and the OER active site (shell) at the nanoscale, realizing bifunctional and efficient catalysis of a single catalyst. The void layer between the core and shell provides a buffer space for the volume change of the iron core during the electrochemical reaction, effectively alleviating the stress and strain caused by repeated charging and discharging, and preventing the active material from being pulverized and detached.

[0042] (3) Nitrogen-doped carbon materials not only uniformly disperse the core-shell particles and prevent their agglomeration, but more importantly, they provide stable mechanical support and confinement protection for the entire structure. Their good conductivity also promotes rapid electron transport. The matrix can also effectively isolate the alkaline electrolyte from direct erosion of the metal core, greatly improving the long-term stability of the catalyst.

[0043] (4) The rich interface formed by the core-shell structure and the nitrogen-doped carbon matrix can optimize the charge distribution and reduce the reaction energy barrier.

[0044] In this invention, the particle size of the Fe@Fe2O3 particles is 20~100 nm. The particle size can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc., or it can be any range consisting of two values.

[0045] Within this particle size range, Fe@Fe2O3 particles possess a high specific surface area and abundant active sites, providing ample reaction sites for ORR and OER, thus contributing to improved catalytic activity. Furthermore, this particle size range ensures excellent dispersibility and stability, guaranteeing uniform dispersion in the nitrogen-doped carbon matrix, preventing agglomeration, and effectively anchoring and protecting the NC matrix, preventing particle detachment or loss during the reaction process, thereby ensuring long-term stability. This size range is sufficient to allow the mechanism of "lattice expansion stress-induced interface separation" to occur effectively. The particles have sufficient volume to generate and accommodate the void layer formed by oxidation, while maintaining structural integrity, forming a clear and stable "core-gap-shell" structure. Particles of this size can form a continuous and efficient conductive network in the NC matrix, ensuring rapid electron transport. Simultaneously, it does not significantly hinder the transport of electrolytes and gases, maintaining excellent reaction kinetics.

[0046] Understandably, if the particle size of Fe@Fe2O3 particles is too small (<20 nm), there are problems with thermodynamic instability and difficulty in forming the "core-shell" structure. Nanoparticles with excessively small sizes have extremely high surface energy, making them prone to migration and aggregation during high-temperature calcination. This leads to larger particles, uneven distribution, loss of the nanoscale effect, and a reduction in the number of active sites. Furthermore, at such a small scale, the void layer between the core and shell may be difficult to form or maintain effectively through "lattice expansion stress," making the entire core-shell structure prone to collapse or fusion during oxidation and cycling, resulting in structural failure.

[0047] If the particle size of Fe@Fe2O3 particles is too large (>100 nm), the specific surface area of ​​the particles decreases significantly, resulting in reduced mass transfer and weak bonding with the matrix. Larger particles have a smaller total specific surface area, drastically reducing the number of exposed active sites, which is detrimental to the contact between reactants and catalyst, directly leading to a decrease in intrinsic catalytic activity. Large particles also hinder electrolyte penetration and oxygen / product diffusion, increasing mass transfer resistance and reducing reaction kinetics. Furthermore, excessively large particles undergo more significant volume changes during charge and discharge, making them more prone to detachment from the nitrogen-doped carbon matrix, leading to deactivation. Simultaneously, large particles may also disrupt the continuity of the carbon matrix, affecting electron conduction.

[0048] In this invention, the thickness of the void layer is 5~20 nm. The thickness can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm, etc., or it can be any range consisting of two values.

[0049] This thickness range allows for an optimized balance of multiple performance characteristics. First, Fe@Fe2O3 particles within this thickness range exhibit optimal buffering capacity. The porosity layer at this thickness effectively accommodates the significant volume difference between the iron core and the iron oxide shell (iron oxidizes to Fe2O3, expanding in volume by approximately 2 times), fully releasing stress during electrochemical cycling and preventing shell cracking and core exposure. Second, this thickness range ensures efficient electron transport. The thickness is sufficient to act as a buffer without completely isolating electron conduction. Electrons can be transported through tunneling or through the nitrogen-doped carbon matrix in close contact, ensuring a sufficient electron supply to catalytically active sites (especially the oxide shell) and maintaining high intrinsic catalytic activity. Third, this thickness range maintains the structural integrity of the Fe@Fe2O3 particles. The porosity layer at this scale, combined with the core-shell particles, maintains a robust overall structure, firmly encapsulated by the carbon matrix, preventing breakage or detachment and ensuring the material's mechanical stability. Finally, this thickness range maximizes interfacial effects. At this thickness, the electronic interactions between the metal core and the oxide shell (such as electron injection and built-in electric field) remain significant, which can optimize the surface electronic structure, reduce the reaction energy barrier, and synergistically enhance ORR and OER activities.

[0050] If the pores are too thin (<5 nm), the buffer is insufficient and cannot provide enough space to accommodate the volume changes generated during the OER process and charging process, which makes the iron oxide shell easy to crack, and the iron core inside directly contacts the electrolyte and dissolves and becomes inactive; the interface effect is weak, and the core and shell are too close, so their unique electronic interaction and stress effect cannot be fully manifested, which limits the improvement of catalytic activity by the interface effect.

[0051] If the porosity is too thick (>20 nm), electron conduction is hindered, severely impeding the transfer of electrons from the highly conductive metal core to the oxide shell, significantly reducing charge transport efficiency and thus leading to a decrease in catalytic activity (especially OER activity); structural stability deteriorates, as an excessively thick porosity layer makes the core-shell structure "loose," reducing the overall mechanical strength of the particle. During ultrasonication, stirring, or long-term electrochemical cycling, the shell is more likely to detach from the core or shift within the carbon matrix, leading to catalyst deactivation; the density of active sites decreases, as an excessively thick porosity layer crowds out the space of the active material (core and shell), effectively reducing the number of active sites per unit mass or unit volume.

[0052] In some embodiments of the present invention, the nitrogen-doped carbon matrix is ​​a layered porous carbon structure.

[0053] In this invention, the relative atomic content of the Fe@Fe2O3 particles is 5-30 at.%.

[0054] It is understood that the relative atomic content of the Fe@Fe2O3 particles refers to the total relative atomic content of elemental iron and metal and oxygen in Fe2O3 in the nitrogen-doped carbon composite material modified by Fe@Fe2O3, that is, the total relative atomic content of elemental iron and Fe2O3.

[0055] The present invention also provides a method for preparing the above-mentioned Fe@Fe2O3 modified nitrogen-doped carbon composite material, comprising: The ferric salt and carbon source are dissolved in water, a self-sacrificing template is added, dried, calcined in a reducing atmosphere, cooled to 50-80℃ and oxidized in air to remove the self-sacrificing template, thus obtaining the product.

[0056] This invention involves dissolving and mixing Fe source, carbon source, and self-sacrificing template, calcining at high temperature under a reducing atmosphere, and then oxidizing in air at 50-80℃ to obtain a nitrogen-doped carbon composite material modified with Fe@Fe2O3 polyhedral particles having a core-void-shell structure.

[0057] This invention employs a simple solid-phase mixing and one-step high-temperature heat treatment, avoiding complex liquid-phase synthesis, template removal, or etching steps. The process is concise, highly repeatable, and lays the foundation for large-scale production. Through high-temperature calcination in a reducing atmosphere, metallic iron (Fe) encapsulated by nitrogen-doped carbon is preferentially formed. 0 The iron oxide nanocrystals are then subjected to mild oxidation in air at a low temperature (50-80℃). The internal stress generated by the lattice expansion during the transformation of metallic iron to ferric oxide actively induces core-shell interface separation, thereby spontaneously and precisely forming a uniformly sized void layer. This method overcomes the stringent dependence on precursor morphology and reaction conditions of traditional methods (such as the Kirkendall effect), achieving effective control over core-shell size and void size. This in-situ self-formation process ensures a tight chemical bond between the iron oxide shell and the metallic iron core, while the void layer effectively buffers volume changes during charge and discharge. The resulting core-shell particles are firmly embedded and dispersed in a nitrogen-doped carbon matrix, preventing agglomeration, detachment, or dissolution of active particles and greatly improving the overall stability of the catalyst. This method successfully integrates a high ORR-active iron core with a high OER-active iron oxide shell into a single particle, and ensures excellent electronic conductivity through the nitrogen-doped carbon matrix. The prepared composite material exhibits excellent bifunctional catalytic activity and long-term durability in zinc-air batteries and AEM water electrolysis devices.

[0058] In this invention, the trivalent iron salt includes, but is not limited to, any one or more of ferric nitrate, ferric chloride, and ferric sulfate.

[0059] In this invention, the carbon source is any one or more of urea, thiourea, melamine, and L-lysine hydrochloride.

[0060] Because the yield of carbon materials after pyrolysis of L-lysine hydrochloride is relatively high; and because L-lysine hydrochloride and sodium chloride (NaCl) are dissolved and dried together, L-lysine hydrochloride can better adhere to the surface of NaCl crystals, and calcination can yield a porous structure. Therefore, the preferred carbon source is L-lysine hydrochloride.

[0061] In this invention, the self-sacrificing template is sodium chloride. Sodium chloride is inexpensive, readily available, highly soluble, and easily mixed and dispersed with the precursor; it recrystallizes easily after drying to form a nano-cubic template; it imparts a porous structure to the carbon material obtained by high-temperature calcination; and it can be easily removed by washing with water.

[0062] In this invention, the molar ratio of the trivalent iron salt, carbon source, and self-sacrificing template is (0.1-1):(5-6):(170-175).

[0063] In this invention, the calcination is carried out at 700-900℃ for 2-4 hours.

[0064] In this invention, oxidation in air is defined as standing in air for 0.5-4 hours, allowing the sample to cool down naturally.

[0065] In this invention, the removal of the self-sacrificing template includes washing to remove the self-sacrificing template, followed by vacuum freeze-drying to obtain a nitrogen-doped carbon composite material modified with Fe@Fe2O3.

[0066] The present invention also provides an application of the above-mentioned Fe@Fe2O3 modified nitrogen-doped carbon composite material in a zinc-air battery; The Fe@Fe2O3 modified nitrogen-doped carbon composite material is used as the positive electrode catalyst for zinc-air batteries.

[0067] The present invention also provides a zinc-air battery, comprising a zinc electrode, a membrane separator, an air electrode and an electrolyte, wherein the catalyst in the air electrode is the above-mentioned Fe@Fe2O3 modified nitrogen-doped carbon composite material.

[0068] The present invention also provides an application of the above-mentioned Fe@Fe2O3 modified nitrogen-doped carbon composite material in AEM water electrolysis; The Fe@Fe2O3 modified nitrogen-doped carbon composite material was used as an anode catalyst for AEM water electrolysis.

[0069] Verification has shown that the Fe@Fe2O3 / NC composite material prepared in this invention possesses high active sites and a stable metal composite structure, exhibiting high oxygen catalytic activity and excellent zinc-air battery performance as an electrocatalyst. (1) Regarding the catalytic activity of oxygen reduction, the half-wave potential of the oxygen reduction reaction polarization curve of Fe@Fe2O3 / NC-3 was 0.88 V, which was 70 mV higher than that of the NC control sample and 20 mV higher than that of commercial platinum carbon (Pt / C). After continuous catalysis for 43,000 s, the voltage decay was only 7%, which was better than the half-wave potential decay of Pt / C (52%). Its oxygen evolution reaction polarization curve was at 10 mA cm⁻¹ -2 The potential below is 1.72 V, reducing the OER overpotential to 490 mV (10 mA / cm). 2 It is 90 mV lower than NC and only 130 mV higher than commercial ruthenium dioxide (RuO2).

[0070] (2) Regarding battery performance, as the positive electrode electrocatalyst of a liquid rechargeable zinc-air battery, at 10 mA cm⁻¹ -2 The battery capacity of 755 mAh g⁻¹ Zn obtained by low discharge is higher than that of the Pt / C catalyzed liquid zinc-air battery (684 mAh g⁻¹ Zn). During long-term charge-discharge cycles, it can stably cycle for more than 500 cycles, which is better than the 200 cycles of Pt / C.

[0071] (3) Regarding the performance of AEM water electrolysis, Fe@Fe2O3 / NC-3, as the anode catalyst for AEM water electrolysis, after activation for 1800 min, had a voltage of 1.67 V, which is lower than that of Pt / C+RuO2 (1.68 V); subsequently, at 0.5 A / cm 2 After operating at the current density for 1000 hours, the electrolytic cell exhibited high stability and showed no signs of degradation.

[0072] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0073] Example 1 This embodiment prepares a nitrogen-doped carbon composite material modified with Fe@Fe2O3. The specific steps are as follows: First, 0.031 g of ferric chloride hexahydrate (FeCl3·6H2O) and 1 g of L-lysine hydrochloride were added to 40 mL of deionized water and stirred until completely dissolved. Then, 10 g of NaCl was added and stirred until completely dissolved. The resulting mixture was placed in a beaker in an 80°C water bath and stirred continuously until completely dry. The dried mixture was then placed in a tube furnace and calcined at 800°C for 3 hours under an argon / hydrogen mixed atmosphere. When the furnace temperature dropped to 50°C, the sample was removed and exposed to air for mild oxidation (approximately 2 hours), followed by natural cooling. Then, the product was washed with a large amount of deionized water by vacuum filtration to remove the abundant NaCl crystals, and subsequently freeze-dried under vacuum to obtain the Fe@Fe2O3 / NC-1 sample.

[0074] Example 2 This embodiment prepared a nitrogen-doped carbon composite material modified with Fe@Fe2O3. The difference from Example 1 is that the amount of FeCl3·6H2O added was 0.062 g. The remaining steps were completely consistent with those of Example 1, resulting in the Fe@Fe2O3 / NC-2 sample.

[0075] Example 3 This embodiment prepared a nitrogen-doped carbon composite material modified with Fe@Fe2O3. The difference from Example 1 is that the amount of FeCl3·6H2O added was 0.125 g. The remaining steps were completely consistent with those of Example 1, resulting in the Fe@Fe2O3 / NC-3 sample.

[0076] Example 4 This embodiment prepared a nitrogen-doped carbon composite material modified with Fe@Fe2O3. The difference from Example 1 is that the amount of FeCl3·6H2O added was 0.19 g. The remaining steps were completely consistent with those of Example 1, resulting in the Fe@Fe2O3 / NC-4 sample.

[0077] Example 5 This embodiment prepared a nitrogen-doped carbon composite material modified with Fe@Fe2O3. The difference from Example 1 is that the amount of FeCl3·6H2O added was 0.25 g. The remaining steps were completely consistent with those of Example 1, resulting in the Fe@Fe2O3 / NC-5 sample.

[0078] Comparative Example 1 This comparative example prepared a nitrogen-doped carbon composite material, the difference from Example 1 being that FeCl3·6H2O was not added. The remaining steps were completely consistent with Example 1, yielding an NC sample.

[0079] Performance verification Figure 4 The image shows a SEM image of the NC prepared in Comparative Example 1. Figure 4 As can be seen, due to the template effect of NaCl crystals, the prepared NC has a loose porous carbon structure. Furthermore, there are no obvious metal nanoparticles present in the porous carbon matrix.

[0080] Figure 1 This is a SEM image of the Fe@Fe2O3 / NC-1 sample prepared in Example 1 of this invention. Figure 1 As can be seen, the microstructure of the prepared sample was slightly altered due to the addition of Fe salt, exhibiting a noticeable granular texture. Magnified SEM images reveal the presence of distinct small metal particles, but the cores of these particles are not tightly bound to the carbon substrate.

[0081] Figure 2 This is a SEM image of the Fe@Fe2O3 / NC-3 sample prepared in Example 3 of this invention. Figure 2 As can be seen, the microstructure of the prepared sample changed slightly with the increase of Fe salt, and the lamellar structure gradually became more obvious, which may be due to the interference of Fe. The magnified SEM images show that most of the small metal particles are embedded inside the porous carbon and are tightly bound to the carbon substrate.

[0082] Figure 3 This is a SEM image of the Fe@Fe2O3 / NC-5 sample prepared in Example 5 of this invention. From... Figure 3 As can be seen, with the further increase of Fe salt, a large amount of Fe interferes with the carbon substrate, making the lamellar structure of the prepared sample's microstructure more obvious. The magnified SEM images show that the metal particles become very abundant, clearly embedded in the carbon layers, and exhibit aggregation.

[0083] Figure 5 Figure (a) is a TEM image of the Fe@Fe2O3 / NC-3 sample prepared in Example 3 of the present invention; (b) and (c) are HR-TEM images of the NC region; (d) and (e) are HR-TEM images and corresponding FFT images of the Fe@Fe2O3 region; and (f) is a HADDF image and elemental distribution map.

[0084] pass Figure 5 As shown in Figure (a), Fe@Fe2O3 / NC-3 is composed of irregularly porous carbon, and the metal nanoparticles (20~100 nm) are uniformly dispersed in the porous carbon matrix. Through... Figure 5 The high-magnification TEM (HR-TEM) image in (b) shows that the porous carbon in Fe@Fe2O3 / NC-3 exhibits a typical layered carbon structure with a carbon interlayer spacing of 0.34 nm, corresponding to the C(002) crystal plane of graphitic carbon. Figure 5 (Figure c) Figure 5The magnified image (d) of the metal nanoparticles reveals a distinct core-void-shell structure, with intervoid spacing of approximately 5–20 nm. Figure 5 Analysis of the lattice fringes of the polyhedral nanoparticles in Figure (e) reveals that the core has a lattice spacing of 0.252 nm, corresponding to the Fe(110) crystal plane, while the shell has a lattice spacing of 0.252 nm, corresponding to the Fe2O3(311) crystal plane. This confirms that the metal nanoparticles are interstitial core-shell Fe@Fe2O3 polyhedra. Figure 5 The elemental distribution in Figure (f) clearly shows the presence of four elements: C, N, O, and Fe. N and C are distributed in the same way, forming N-doped C. O is only distributed in the Fe shell, which is consistent with the HR-TEM results.

[0085] Figure 6 The XRD patterns of the samples prepared in the embodiments and comparative examples of this invention are shown. The XRD patterns show that NC exhibits a relatively broad C(002) peak only at 16°. With the increase of Fe precursor (Fe@Fe2O3 / NC-...), the XRD pattern shows... x The carbon peaks significantly decreased, while sharp metallic diffraction peaks appeared. The peaks at 30.2°, 35.6°, 43.3°, and 62.9° were assigned to the (220), (311), (400), and (440) crystal planes of Fe2O3 (PDF#39-1346, α-Fe2O3, rhombohedral structure), respectively, while the peaks at 44.7° and 65.0° corresponded to the (110) / (200) crystal plane of elemental Fe (PDF#06-0696, α-Fe, body-centered cubic bcc structure). It is worth noting that from NC to Fe@Fe2O3 / NC-5, the intensity of the Fe characteristic peaks continued to increase. This is mainly due to the increased crystallinity caused by the increase in the number of Fe particles, and the superposition of diffraction signals caused by particle agglomeration.

[0086] Figure 7 XPS data for the Fe@Fe2O3 / NC-3 sample prepared in Example 3 of this invention. Figure 7 Figure (a) shows the XPS full spectrum of Fe@Fe2O3 / NC-3, confirming that the material contains C (81.8 at%), N (2.6 at%), O (8.3 at%), and Fe (7.3 at%). For details of the relative atomic contents of the elements, please refer to [link to relevant documentation]. Figure 7 Figure (b) shows that fine spectral analysis reveals that C 1s ( Figure 7The peaks in Figure (c) show 284.8 eV (CC / C=C), 286.2 eV (CN), 287.5 eV (CO / C=O), and 290.0 eV (π-π*), with the CN peak clearly confirming successful N doping into the carbon framework. There are five deconvolution peaks in the N 1s curve, located at 398.2, 399.1, 399.9, 401.0, and 404.4 eV, which are respectively attributed to Pyridinc-N, Metal-N, Pyrrolic-N, Graphitic-N, and Oxidized-N. Figure 7 (d) Figure). O 1s ( Figure 7 Figure (e) shows that 530.0 eV (MO bond) dominates, supporting the conclusion that surface oxygen is mainly hosted in metal oxides. 531.4 eV (CO / NO) and 533.0 eV (adsorbed -OH) indicate that oxygen is partially bonded to carbon groups or adsorbed on the surface, explaining the contradiction that the O atom content (8.3%) is higher than that of Fe (7.3%). Fe 2p ( Figure 7 (Figure f) 710.7 / 724.4 eV (Fe 3+ ), 713.5 / 727.3 eV (Fe 2+ The 718.7 / 732.6 eV (satellite peaks) indicate that the surface iron is in the form of Fe. 3+ The primary elemental Fe core was not detected due to the limited depth of XPS detection, consistent with the "metal core-oxide shell" structural characteristics. The nitrogen atoms doped in the NC (pyridine nitrogen, graphitic nitrogen, etc.) are not only effective reactive sites (especially significantly promoting ORR), but also effectively modulate its electronic structure through interactions with the metal component, such as electron transfer or the formation of MNC bonds, further enhancing intrinsic activity. The MNC sites themselves are also important catalytic active centers for ORR.

[0087] Experimental Example 1 To evaluate the oxygen catalytic performance of the material, an ORR / OER test was performed using a standard three-electrode system. The preparation process of the slurry and electrode head is shown below: Two mg of catalyst (the Fe@Fe2O3-modified nitrogen-doped carbon composite material obtained in Examples 1-5) was mixed with two mg of acetylene black and ultrasonically dispersed in a mixture of 20 μL Nafion, 380 μL ethanol, and 100 μL deionized water for 30 minutes, yielding a loading of 0.32 mg cm⁻¹. -2 The ink is dropped onto the glassy carbon working electrode, while the graphite rod and Hg / HgO serve as the counter electrode and reference electrode, respectively.

[0088] Figure 8 The ORR performance of the prepared sample. Figure 8Figure (a) shows the LSV curve, where Fe@Fe2O3 / NC-3 reaches 5.26 mA cm⁻¹ at 0.20 V in 0.1 M KOH. -2 The diffusion-limiting current density. Figure 8 Figure (b) is E 1 / 2 The bar chart shows that the half-wave potential of Fe@Fe2O3 / NC-3 is as high as 0.88 V, significantly exceeding that of NC (0.81 V), Fe@Fe2O3 / NC-1 (0.82 V), Fe@Fe2O3 / NC-2 (0.86 V), Fe@Fe2O3 / NC-4 (0.85 V), and Fe@Fe2O3 / NC-5 (0.82 V), and even surpassing that of commercial Pt / C (0.86 V), indicating its excellent intrinsic ORR activity. Kinetic analysis shows ( Figure 8 (Figure c) shows that the Tafel slope of Fe@Fe2O3 / NC-3 is only 72 mV dec. -1 This is the lowest 86 mV dec for Pt / C in the examples and comparative examples, and below that of Pt / C. -1 This indicates a faster charge transfer rate and a more favorable O2 dissociation pathway. In summary, Fe@Fe2O3 / NC-3 exhibits superior overall ORR performance.

[0089] Figure 9 The OER performance of the prepared samples was measured. The OER performance was tested in 0.1 M KOH under the same system. Figure 9 Figure (a) shows the LSV curve. The performance changes of OER and ORR show similar trends: initially improving and then deteriorating. Specifically, from... Figure 9 As shown in Figure (b), Fe@Fe2O3 / NC-3 at 10 mA cm⁻¹ -2 The overpotential is as low as 1.72 V, which is superior to the NC sample. E j=10 =1.81V), Fe@Fe2O3 / NC-1 sample ( E j=10 =1.80 V), Fe@Fe2O3 / NC-2 sample ( E j=10 =1.75 V), Fe@Fe2O3 / NC-4 sample ( E j=10 =1.75 V), Fe@Fe2O3 / NC-5 sample ( E j=10 =1.84 V), and is closest to the commercial RuO2 benchmark ( E j=10 =1.59V). Additionally, from Figure 9As shown in Figure (c), the Tafel slope of the Fe@Fe2O3 / NC-3 sample is only 134 mV dec. -1 Approaching the commercial RuO2 benchmark (1.59 V, 111 mV dec) -1 However, there is still room for optimization.

[0090] Figure 10 The ORR performance of Fe@Fe2O3 / NC-3 samples and commercial Pt / C is presented. In stability tests, the voltage decay of the Fe@Fe2O3 / NC-3 sample was only 7% after 43,000 s under constant current ORR conditions, which is less than 1 / 7 of the decay rate of Pt / C (52%). This ultrastability is attributed to: the core-shell structure of Fe@Fe2O3 inhibiting Fe dissolution; the N-doped carbon support protecting metal particles from detachment; and the Fe-N coordination bond enhancing interfacial stability.

[0091] Experiment Example 2 To evaluate the performance of the materials in a liquid rechargeable zinc-air battery, liquid zinc-air batteries were assembled using a zinc plate as the negative electrode and carbon paper with added catalyst as the air electrode. The electrolyte consisted of 6 mol L... -1 KOH and 0.2 mol L - 1 The catalyst slurry was composed of a mixed solution of Zn(CH3COO)2. It was prepared by dispersing 1 mg of catalyst (Fe@Fe2O3 / NC-3 obtained in Example 3), 1 mg of acetylene black, and 10 μL of 5wt% Nafion in 260 μL of ethanol, and then uniformly drop-feeding it onto carbon paper. The catalyst loading was 1 mg cm⁻¹. -2 .

[0092] Figure 11 Performance testing of Fe@Fe2O3 / NC-3 samples, Pt / C, and RuO2 in liquid rechargeable zinc-air batteries.

[0093] in, Figure 11 Figure (a) illustrates the working principle of a rechargeable zinc-air battery. Figure 11 As shown in Figures (b) and (c), the Fe@Fe2O3 / NC-3-based battery successfully lit the LED lamp and exhibited a stable open-circuit voltage of 1.425 V. The discharge polarization curve further confirms this. Figure 11 In the middle (d), Fe@Fe2O3 / NC-3 at 350 mA·cm -2 219 mW·cm was obtained at the current density -2 Peak power density. Constant current discharge test (10 mA·cm⁻¹) -2 The results showed that the discharge specific capacity of the Fe@Fe2O3 / NC-3 sample reached 755 mAh·g.-1 684 mAh·g, surpassing Pt / C catalysts -1 ( Figure 11 (Figure e). Furthermore, at 5-50 mA·cm -2 Under different current densities, the discharge voltage plateau of the Fe@Fe2O3 / NC-3 sample remained stable, and the voltage recovery rate was also very good, demonstrating excellent rate performance. Figure 11 (Figure f) . At 10 mA·cm -2 In constant current cycling tests, the Fe@Fe2O3 / NC-3 based zinc-air battery achieved over 500 stable cycles, with the charge-discharge voltage difference consistently maintained at 0.76-0.83 V. This performance is significantly superior to the Pt / C+RuO2 combination (…). Figure 11 (See Figure g). These results fully validate the feasibility and stability of Fe@Fe2O3 / NC-3 as a high-performance bifunctional catalyst in zinc-air batteries.

[0094] Experimental Example 3 To further evaluate the feasibility of the catalyst in practical commercial applications, a slurry was prepared by ultrasonically (ice-water bath, 40 kHz) for 60 min in a 1:1 (v / v) ethanol-isopropanol solvent mixture with 0.4 g Fe@Fe2O3 / NC-3 (anodic catalyst) or 0.25 g Pt / C (cathode catalyst) and 0.8 mL FAA-3-SOLUTE-10 anionic polymerization solution. Based on an integrated continuous liquid supply system and relying on a high-precision peristaltic pump fluid control system, fluid pulsation was significantly suppressed through multi-channel synergy and adaptive flow compensation mechanisms, effectively overcoming flow fluctuations caused by tubing elastic deformation and temperature drift. The system employed high-frequency ultrasonic atomization technology and an argon protective atmosphere, combined with substrate gradient temperature control, to uniformly spray the catalyst slurry onto the pretreated anion exchange membrane surface at a rate of 5 mL / min. On the other side, a Pt / C cathode catalyst layer was deposited using the same ultrasonic spraying method for the hydrogen evolution reaction. Subsequently, the catalytically modified membrane electrode assembly was stacked with the gas diffusion layer, and subjected to high temperature and pressure in a hot press. Through a staged depressurization and pressure holding cooling process, the catalytic layer and the membrane were tightly bonded, significantly reducing the interfacial transport resistance and enhancing the membrane's anti-peel strength. Finally, the membrane electrode assembly was assembled with bipolar plates to form a complete high-performance anion exchange membrane (AEM) electrolyzer unit.

[0095] Figure 12 Performance testing of Fe@Fe2O3 / NC-3 as an anode catalyst in AEM water electrolysis (cathode is Pt / C catalyst).

[0096] from Figure 12As shown in Figure (a), Fe@Fe2O3 / NC-3, as the anode catalyst for AEM water electrolysis, achieved an activation voltage of 1.67 V after 1800 min of activation, which is lower than that of Pt / C+RuO2 (1.68 V). Next, at 0.5 A / cm... 2 In a 1000-hour long-term stability test at current density, Pt / C+ Fe@Fe2O3 / NC-3 exhibited high stability and showed no degradation. Figure 12 Figure (b) above demonstrates that the Fe@Fe2O3 / NC-3 sample exhibits high activity and long-term stability in AEM water electrolysis.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A Fe@Fe2O3 modified nitrogen-doped carbon composite material, characterized in that, It includes a nitrogen-doped carbon matrix and Fe@Fe2O3 particles dispersed in the nitrogen-doped carbon matrix; The Fe@Fe2O3 particles consist of an iron core and an iron oxide shell, with a void layer between the iron core and the iron oxide shell. The Fe@Fe2O3 particles have a particle size of 20~100 nm; The thickness of the void layer is 5~20 nm. 2.The Fe@Fe2O3 modified nitrogen-doped carbon composite material of claim 1, wherein, The nitrogen-doped carbon matrix has a layered porous carbon structure. 3.The Fe@Fe2O3 modified nitrogen-doped carbon composite material of claim 1, wherein, The relative atomic content of the Fe@Fe2O3 particles is 5-30 at.%.

4. A method for preparing the Fe@Fe2O3 modified nitrogen-doped carbon composite material according to any one of claims 1-3, characterized in that, include: The ferric salt and carbon source are dissolved in water, a self-sacrificing template is added, dried, calcined in a reducing atmosphere, cooled to 50-80℃ and oxidized in air to remove the self-sacrificing template, thus obtaining the product. The carbon source is any one or more of urea, thiourea, melamine, and L-lysine hydrochloride.

5. The method for preparing the Fe@Fe2O3 modified nitrogen-doped carbon composite material as described in claim 4, characterized in that, The ferric salts include any one or more of ferric nitrate, ferric chloride, and ferric sulfate; The self-sacrificing template is sodium chloride.

6. The method for preparing the Fe@Fe2O3 modified nitrogen-doped carbon composite material as described in claim 4, characterized in that, The molar ratio of the trivalent iron salt, carbon source, and self-sacrificing template is (0.1-1):(5-6):(170-175).

7. The method for preparing the Fe@Fe2O3 modified nitrogen-doped carbon composite material as described in claim 4, characterized in that, The calcination is carried out at 700-900℃ for 2-4 hours; The oxidation in air is described as being left to stand in air for 0.5-4 hours; The method for removing the self-sacrificing template includes washing to remove the self-sacrificing template, followed by vacuum freeze-drying to obtain a nitrogen-doped carbon composite material modified with Fe@Fe2O3.

8. The application of the Fe@Fe2O3 modified nitrogen-doped carbon composite material according to any one of claims 1-3 in a zinc-air battery; The Fe@Fe2O3 modified nitrogen-doped carbon composite material is used as the positive electrode catalyst for zinc-air batteries.

9. A zinc-air battery, comprising a zinc electrode, an air electrode, and an electrolyte, characterized in that, The catalyst in the air electrode is the nitrogen-doped carbon composite material modified with Fe@Fe2O3 as described in any one of claims 1-3.

10. The application of the Fe@Fe2O3 modified nitrogen-doped carbon composite material according to any one of claims 1-3 in AEM water electrolysis; The Fe@Fe2O3 modified nitrogen-doped carbon composite material was used as an anode catalyst for AEM water electrolysis.

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