Method for preparing nanometer net-shaped oxygen-vacancy-rich high-entropy spinel SOFC cathode material based on microwave method

Abstract

The invention discloses a method for preparing a nanometer net-shaped oxygen-vacancy-rich high-entropy spinel SOFC (Solid Oxide Fuel Cell) cathode material based on a microwave method, and relates to the field of solid oxide fuel cells. The preparation method comprises the following steps: taking metal nitrates corresponding to equimolar Ni < 2 + >, Fe < 2 + > / Fe < 3 + >, Cr < 3 + >, Mg < 2 + > and Zn < 2 + > as precursors, mixing the precursors with glycine in deionized water, and stirring at 80-100 DEG C until gel is formed; and carrying out self-combustion on the gel at 150-200 DEG C to obtain precursor powder, and carrying out microwave heat treatment on the precursor powder to obtain the nano reticular oxygen-vacancy-enriched high-entropy spinel (Ni < 0.2 > Fe < 0.2 > Cr < 0.2 > Zn < 0.2 > Mg < 0.2 >) 3O4. The material shows excellent medium-temperature performance at 600-800 DEG C in an SOFC symmetric battery, the high-entropy design solves the problem of high-temperature phase stability of a traditional cathode, and an ion transmission path is optimized; the triple effects of rapid crystallization, grain refinement and defect engineering of microwave heat treatment provide a new thought for performance optimization of the medium-temperature SOFC.

Description

Technical Field

[0001] This invention relates to the field of solid oxide fuel cell technology, and in particular to a method for preparing nano-network oxygen-rich vacancy high-entropy spinel SOFC cathode material based on microwave method. Background Technology

[0002] With the continuous growth of energy demand and increasingly stringent environmental protection requirements, traditional fossil fuel energy conversion technologies face severe challenges. Solid oxide fuel cells (SOFCs), with their significant advantages of high efficiency and low emissions, have become a promising new energy conversion technology. However, the development of SOFCs is still limited by the performance of cathode materials: traditional cathode materials exhibit slow oxygen reduction reaction (ORR) kinetics under medium and low temperature conditions, severely impacting the overall performance of the battery; simultaneously, their stability is insufficient during long-term use at high temperatures, and their chemical compatibility with the electrolyte needs further improvement. These issues restrict the practical application and widespread adoption of SOFCs.

[0003] The emergence of high-entropy oxides offers a new approach to solving the aforementioned problems. High-entropy oxides are typically composed of five or more elements in equimolar or near-equimolar ratios, exhibiting a unique multi-principal component composition. This high-entropy effect effectively suppresses the segregation and precipitation of single elements, thereby significantly improving the thermal and chemical stability of the material and enabling it to maintain good structural integrity under the high-temperature operating environment of SOFCs. Furthermore, the multi-principal component design of high-entropy oxides helps optimize the electronic and band structures of the material, thereby enhancing its electrochemical performance, such as improving the catalytic activity of the oxygen reduction reaction, reducing the polarization resistance of the cathode, and improving the overall performance of the SOFC. Simultaneously, the diversity and designability of high-entropy oxides provide a wider range of choices for optimizing the performance of SOFC cathode materials. By rationally selecting and controlling the constituent elements, precise control of material performance can be achieved to meet different operating conditions and application requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing nano-network oxygen-rich vacancy high-entropy spinel SOFC cathode materials based on microwave method, so as to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention: provides a nano-network oxygen-rich vacancy high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The preparation method of 3O4 includes the following steps:

[0007] (1) Take equimolar amounts of Ni 2+ Salt, Fe salt, Cr 3+ Salt, Mg 2+ Salt and Zn 2+ Salt, as a metal precursor, is mixed with a combustion accelerant in deionized water and stirred at 80-100°C until a gel is formed.

[0008] (2) The gel is placed at 150-200°C for self-combustion to form precursor powder;

[0009] (3) The precursor powder is heat-treated under microwave conditions to obtain the nano-network oxygen-rich vacancy high-entropy spinel (Ni). 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4;

[0010] Wherein, the Fe salt is Fe 2+ Salt and / or Fe 3+ Salt;

[0011] The Ni 2+ Salt, Fe salt, Cr 3+ Salt, Mg 2+ Salt and Zn 2+ The salt is a nitrate.

[0012] As a further preferred embodiment of the present invention, the combustion aid includes one or more of glycine, glucose, urea and citric acid.

[0013] As a further preferred embodiment of the present invention, the heat treatment temperature in step (3) is 500-900℃ and the power is 1000-2500W.

[0014] As a further preferred embodiment of the present invention, the heat treatment time in step (3) is 10-60 min.

[0015] As a further preferred embodiment of the present invention, the ratio of the total molar amount of metal ions in the metal precursor to the molar amount of the combustion improver is 1:(1-2).

[0016] As a further preferred embodiment of the present invention, step (3) further includes the step of raising the temperature from room temperature to the temperature of the heat treatment.

[0017] As a further preferred embodiment of the present invention, the heating rate is 20-100°C / min when heating from room temperature to the temperature of the heat treatment.

[0018] The second technical solution of this invention: Provides the above-mentioned preparation method to prepare nano-network oxygen-vacancy-rich high-entropy spinel (Ni 0.2 Fe0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4.

[0019] The third technical solution of this invention: providing the above-mentioned nano-network oxygen-rich vacancy high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 Application of 3O4 as a cathode material for solid oxide fuel cells.

[0020] Fourth technical solution of the present invention: Provides a solid oxide fuel cell, employing the aforementioned nano-network oxygen-rich vacancy high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 3O4 was used as the cathode material.

[0021] In this invention, five metallic elements—Ni, Fe, Cr, Mg, and Zn—are selected because their similar ionic radii and electronic structures readily facilitate the formation of single-phase spinel high-entropy oxides (HEOs). Within the spinel structure, multivalent nickel-iron elements exhibit certain catalytic activity. Simultaneously, Cr... 3+ Zinc tends to occupy B sites to maintain charge balance. This doping strategy not only optimizes the crystal structure of the material but also improves its oxidation resistance. Zinc doping plays a crucial role in optimizing the spinel crystal structure. 2+ The presence of Mg can enhance the thermal and chemical stability of materials. 2+ This can increase the oxygen vacancy concentration inside the material, thereby improving its conductivity and catalytic activity for the oxygen reduction reaction (ORR). Therefore, developing high-entropy oxides as SOFC cathode materials is of great significance and is expected to promote the further development and application of SOFC technology.

[0022] The present invention discloses the following technical effects:

[0023] This invention utilizes a combination of a simple solution combustion method and a microwave method to prepare nano-network oxygen-rich, high-entropy spinel (Ni). 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The 3O4 material exhibits excellent performance in the mid-temperature range (600-800℃) when used as a cathode material for solid oxide fuel cells. Compared to conventional heat treatment, the microwave heat treatment of this invention can produce finer grains. Furthermore, microwaves can effectively control oxygen vacancies, which is more conducive to the formation of oxygen vacancy defects.

[0024] The high-entropy spinel (Ni) prepared by this invention 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 3O4 exhibits excellent mid-temperature performance (600-800℃) in SOFC symmetric cells. High-entropy design not only solves the phase stability problem of traditional cathode materials at high temperatures, reduces interfacial polarization and optimizes ion transport paths, but also provides a new approach to optimizing the performance of mid- and low-temperature SOFCs through the triple effect of "rapid crystallization-grain refinement-defect engineering" introduced by microwave heat treatment. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 High-entropy spinel (Ni) prepared under different conditions in Examples 1 and 2-8 of this invention 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 XRD pattern of 3O4 material;

[0027] Figure 2 The high-entropy spinel (Ni) prepared in Examples 1-2 of this invention 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 Scanning electron microscope image and particle size distribution of 3O4 material; where a is the high-entropy spinel (Ni3O4) prepared in Example 2. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The microstructure of the 3O4 material (labeled as MW), b is the high-entropy spinel (Ni) prepared in Example 1. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The microstructure of the 3O4 material (labeled CH), c is the high-entropy spinel (Ni) prepared in Example 2. 0.2 Fe 0.2 Cr 0.2 Zn0.2 Mg 0.2 The particle size distribution of the 3O4 material (labeled as MW), where d represents the high-entropy spinel (Ni3O4) prepared in Example 1. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 Particle size distribution of 3O4 material (labeled CH).

[0028] Figure 3 The high-entropy spinel (Ni) prepared in Examples 1-7 of this invention 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 ESR spectrum of 3O4 material.

[0029] Figure 4 The high-entropy spinel (Ni) prepared in Examples 1-2 of this invention 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 XPS spectra of 3O4 materials: a) O 1s, b) Ni 2p, c) Fe 2p, d) Cr 2p, e) Zn 2p, f) Mg 1s.

[0030] Figure 5 The high-entropy spinel (Ni) prepared in Examples 1-2 of this invention 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 EIS spectrum of 3O4 material. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0034] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0035] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0036] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0037] The reagents used in the embodiments of this invention are as follows: ferric nitrate (Fe(NO3)3·9H2O, AR grade), magnesium nitrate (Mg(NO3)2·4H2O, AR grade), chromium nitrate (Cr(NO3)3·6H2O, AR grade), nickel nitrate (Ni(NO3)2·6H2O, AR grade), zinc nitrate (Zn(NO3)2·6H2O2, AR grade), glycine (AR grade), isopropanol (AR grade), ethylene glycol (AR grade), and glycerol (AR grade).

[0038] Example 1

[0039] (1) Take 0.1 mol of nickel nitrate, ferric nitrate, chromium nitrate, magnesium nitrate and zinc nitrate respectively, and dissolve them completely in 30 ml of deionized water. Stir for 10 min to ensure they are fully dissolved.

[0040] (2) Take 0.5 mol of glycine (as a complexing agent and combustion aid), dissolve it in 30 ml of deionized water, and stir for 10 min to ensure it is fully dissolved;

[0041] (3) Mix the two solutions from steps (1) and (2) (Ni) 2+ Fe 3+ Cr 3+ Mg 2+ and Zn 2+The total molar amount of glycine is in the ratio of 1:1. The mixture is stirred and dried at 90°C until a gel-like substance is formed.

[0042] (4) Place the gelatinous substance in a 200°C oven and let it self-combust to obtain a fluffy and porous precursor.

[0043] (5) After grinding and pulverizing the precursor, it is placed in a resistance furnace and heated to 900℃ at a heating rate of 10℃ / min, and then held at that temperature for 30min to obtain high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4 material, marked as 900℃-30CH.

[0044] Example 2

[0045] The only difference from Example 1 is that the heat treatment method in step (5) is different:

[0046] (5) After grinding the precursor, the sample was placed in a microwave tube furnace, heated to 900℃ at a microwave power of 2500W and a heating rate of 50℃ / min, and held for 30min to obtain high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4 material, marked as 900℃-30MW.

[0047] Example 3

[0048] The only difference from Example 2 is that the heat treatment temperature in step (5) is different:

[0049] (5) After grinding the precursor, the sample was placed in a microwave tube furnace and heated to 600°C at a microwave power of 2500W and a heating rate of 50°C / min, and held for 30 min to obtain high-entropy spinel (Ni). 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4 material, marked as 600℃-30MW.

[0050] Example 4

[0051] The only difference from Example 2 is that the heat treatment temperature in step (5) is different:

[0052] (5) After grinding the precursor, the sample was placed in a microwave tube furnace and heated to 700°C at a microwave power of 2500W and a heating rate of 50°C / min, and held for 30 min to obtain high-entropy spinel (Ni). 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4 material, marked as 700℃-30MW.

[0053] Example 5

[0054] The only difference from Example 2 is that the heat treatment temperature in step (5) is different:

[0055] (5) After grinding the precursor, the sample was placed in a microwave tube furnace and heated to 800°C at a microwave power of 2500W and a heating rate of 50°C / min, and held for 30 min to obtain high-entropy spinel (Ni). 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4 material, marked as 800℃-30MW.

[0056] Example 6

[0057] The only difference from Example 2 is that the heat treatment time in step (5) is different:

[0058] (5) After grinding the precursor, the sample was placed in a microwave tube furnace and heated to 900°C at a microwave power of 2500W and a heating rate of 50°C / min, and held for 10 min to obtain high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4 material, marked as 900℃-10MW.

[0059] Example 7

[0060] The only difference from Example 2 is that the heat treatment time in step (5) is different:

[0061] (5) After grinding the precursor, the sample was placed in a microwave tube furnace and heated to 900°C at a microwave power of 2500W and a heating rate of 50°C / min, and held for 20 min to obtain high-entropy spinel (Ni). 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4 material, marked as 900℃-20MW.

[0062] Example 8

[0063] The high-entropy spinel (900℃-30MW) obtained in Example 2 was ground and pulverized, then placed in a resistance furnace and heated to 1200℃ at a heating rate of 10℃ / min, and held at that temperature for 120min to obtain high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4 material, marked as 1200℃.

[0064] The microstructure of the samples was analyzed using a scanning electron microscope (Talos F200S). X-ray diffraction (D8 Advance) was used to analyze the structural phases of the material, with a scanning range of 10°–80°. X-ray photoelectron spectroscopy (Thermofisher K-Alpha) was used to analyze the valence states of elements and detect the oxygen vacancy content. Oxygen vacancy analysis of the high-entropy spinel was performed using an electron spin resonance spectrometer (JEOL JES X320). Electrochemical analysis was conducted using an electrochemical workstation (VersaSTAT 4, Princeton Applied Research) at a range of 0.1–10⁻⁶. 5 The AC impedance response at different temperatures was tested within the Hz frequency range to analyze the polarization impedance of the cathode material.

[0065] Figure 1 These are high-entropy spinel (Ni) prepared under different conditions in Examples 1-8. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The XRD pattern of Ni3O4 material shows obvious diffraction peaks, and the positions of these peaks are basically consistent at different temperatures. This indicates that the products obtained under different preparation conditions have the same crystal structure, all being spinel phases with high purity. Furthermore, the diffraction peak intensity continuously increases with increasing temperature, clearly reflecting the enhanced crystallinity of high-entropy materials with increasing temperature. XRD patterns from microwave heat treatment and conventional heat treatment show that the diffraction peak positions of the two groups of samples are basically the same, indicating that the crystal structure of the products is consistent. The difference in peak intensity may be due to the different heating mechanisms of microwave and conventional heating. Meanwhile, (Ni3O4) material heat-treated at 900℃... 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2NiO4 was heat-treated again at 1200℃ (i.e., the material prepared in Example 8), and it was found that its XRD phase did not decompose, proving that (NiO4) 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 3O4 exhibits a certain degree of stability at high temperatures.

[0066] The synthesis of (Ni) was observed using field emission scanning electron microscopy. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 Microstructure of 3O4 material. Figure 2 The high-entropy spinel (Ni) prepared in Examples 1-2 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 Scanning electron microscope image and particle size distribution of 3O4 material. Wherein, a represents the high-entropy spinel (Ni3O4) prepared in Example 2. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The microstructure of the 3O4 material (labeled as MW), b is the high-entropy spinel (Ni) prepared in Example 1. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The microstructure of the 3O4 material (labeled CH), c is the high-entropy spinel (Ni) prepared in Example 2. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The particle size distribution of the 3O4 material (labeled as MW), where d represents the high-entropy spinel (Ni3O4) prepared in Example 1. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 Particle size distribution of 3O4 material (labeled CH). From Figure 2As can be seen from a and b, the material synthesized in Example 2 forms a network structure through the interconnection of grains. This nanostructure-formed porous network not only possesses good thermal stability and durability but may also provide more active sites on the material surface, enhancing the material's electrochemical performance. For the cathode materials prepared by the two different methods, it is evident that the material produced by microwave heat treatment has a finer particle size. The particle size distribution, measured and statistically analyzed using Nano Measure software, is shown below. Figure 2 As shown in Figures c and d, further calculations revealed that the average particle sizes of the materials synthesized by microwave heat treatment and conventional heat treatment were 42.43 nm and 72.00 nm, respectively, further demonstrating that the materials produced by microwave heat treatment have finer particle sizes.

[0067] The introduction of oxygen vacancies in spinel oxides can alter their electronic structure, increasing the number of unpaired electrons and thus improving electrical conductivity and catalytic activity in the oxygen reduction reaction (ORR). In ESR (Enhanced Sequencing Ratio) detection of oxygen vacancies, the g-factor is typically around 2.00. This is primarily because the presence of oxygen vacancies leads to the formation of unpaired electrons, whose spin magnetic moments are similar to those of free electrons. The g-factor of free electrons is approximately 2.0023, and the g-factor of oxygen vacancies is close to this value, thus appearing as a signal with a g-factor of approximately 2.00 in the ESR spectrum. This signal is a typical characteristic of oxygen vacancies and can be used to determine their presence in materials. Using ESR pairs (Ni... 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The oxygen vacancies in 3O4 were detected, and the results are as follows: Figure 3 As shown, through oxygen vacancy testing at different temperatures, high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The g-factor of 3O4 is 2.018, close to the material's oxygen vacancy g = 2.00, proving that (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 Oxygen vacancies exist in 3O4. Simultaneously, (Ni) was found... 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The peak intensity of 3O4 increases with increasing temperature, indicating that there may be more unpaired electrons at 900℃. This increase in unpaired electrons may be related to (Ni) 0.2 Fe0.2 Cr 0.2 Zn 0.2 Mg 0.2 This is related to the increased concentration of oxygen vacancy defects in 3O4. Meanwhile, at 900℃, the ESR intensity of conventional heat treatment is much lower than that of microwave heat treatment, proving that microwave heat treatment is beneficial for the formation of oxygen vacancies.

[0068] To reveal the metallic valence states of elements in SOFC cathode materials, X-ray photoelectron spectroscopy (XPS) was used to study the high-entropy spinel (Ni)... 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The elements were characterized using 3O4, with XPS spectra of all elements calibrated using the C1s (284.80 eV) peak. From the analysis of (Ni... 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 XPS characterization using 3O4 can observe ( Figure 4 af), high entropy (Ni) 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 XPS broadband spectroscopy of the 3O4 material confirmed the presence of Fe, Ni, Cr, Zn, Mg, and O elements, among which (Ni) 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 In 3O4, Fe and Ni metal cations exhibit a mixture of divalent and trivalent states, while Cr metal cations appear as a mixture of trivalent and hexavalent states, indicating the diversity of chemical valence states within high-entropy spinel. The spin orbital peak positions of different valence states of elements in the material after microwave heat treatment deviate slightly from those after conventional heat treatment, generally showing a slight increase in electron binding energy. This may be due to the increased oxidation state of elements on the material surface caused by microwave heat treatment, or the rapid heating characteristic of microwaves leading to intense chemical reactions on the material surface, thereby altering the electronic structure of the elements. Furthermore, higher valence states of metal cations in spinel oxides are more favorable for redox reactions. In fact, the distribution and valence states of metal elements on the material surface exhibit complex diversity. This diversity creates a multi-metal coexistence environment on the surface of high-entropy oxides, where strong synergistic effects can occur between the various metal elements. This synergistic effect may help improve the structural and thermal stability of the material, which is crucial for cathode materials operating long-term in SOFCs.

[0069] For SOFC cathode materials, oxygen species are crucial for the cathode ORR process. Figure 4 a represents the O1s spectra of the materials under different heat treatments. Fitting analysis revealed that the O1s spectrum splits into three peaks, with binding energies of 530.04 eV, 531.91 eV, and 533.19 eV corresponding to lattice oxygen (O₂) at these energies. lat ), adsorbed oxygen (O ads ) and hydroxyl oxygen (O oh ), where the ratio of adsorbed oxygen to lattice oxygen (O ads / O lat This can characterize the oxygen vacancy content of spinel materials. By comparing the three peaks of the splitting of two spectra in microwave heat treatment and conventional resistance furnace heat treatment, it can be found that the adsorbed oxygen (O2) generated by the splitting of the O1s spectrum in microwave heat-treated materials is different. ads The peak intensity of oxygen vacancy (O₂) in the high-entropy spinel material is significantly higher than that in conventionally heat-treated materials, while the peak intensities of lattice oxygen and hydroxyl oxygen in both materials are almost identical. Therefore, it can be concluded that microwave heat treatment can greatly enrich the oxygen vacancy content (O₂) on the surface of high-entropy spinel materials. ads / O lat =0.98(MS)>O ads / O lat =0.4(CH)), which enables the material to obtain better cathode performance.

[0070] In electrochemical testing, electrochemical impedance spectroscopy (EIS) is currently the mainstream method for evaluating the performance of cathode materials. Using EIS, high-entropy spinel (Ni) can be further detected and evaluated. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The redox activity of Ni3O4 as a SOFC cathode material in air at 600℃-800℃. Example 2: Ni3O4 prepared by microwave heat treatment. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The polarization resistance of the 3O4 material at different temperatures of 650℃, 700℃, 750℃, and 800℃ is 1.17 Ωcm. 2 0.52Ωcm 2 0.18Ωcm 2 0.11Ωcm 2 . Figure 5 b compared the (Ni) prepared by the microwave heat treatment method in Example 2. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg0.2 )3O4 material (labeled as MW), Ni 3O4 material prepared by conventional heat treatment method in Example 1 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The impedance spectra of 3O4 material (labeled CH) at the same temperature (750℃) show that the polarization impedance under microwave heat treatment is 0.18 Ω·cm. 2 It is significantly lower than the polarization resistance of the material after conventional heat treatment, which is 0.34 Ω·cm. 2 Clearly, materials treated with microwaves at the same temperature exhibit lower polarization resistance, demonstrating a significant advantage.

[0071] In summary, based on the multi-component synergistic effect of high-entropy materials, nano-high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 3O4 forms a single cubic spinel solid solution structure. Multiple metals co-enter the lattice within the high-entropy spinel, resulting in surface reconstruction. The metals exist in complex valence states, especially a large amount of Fe. 2+ :Fe 3+ Ni 2+ :Ni 3+ and Cr 3+ :Cr 6+ The presence of ion pairs promotes an increase in oxygen vacancy content. This unique "multivalent cation-oxygen vacancy-lattice distortion" synergistic structure significantly promotes the oxygen adsorption, desorption, and conduction processes involved in cathode ORR. The introduction of a microwave field significantly modulates the microstructure evolution of the material. This microstructure optimization increases the density of oxygen adsorption sites on the material surface, significantly enhancing the oxygen molecule activation efficiency during the ORR process. The high-entropy spinel (Ni) obtained by the microwave treatment method of this invention... 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 3O4 exhibits excellent mid-temperature performance (600-800℃) in SOFC symmetric cells. Electrochemical impedance spectroscopy (EIS) shows that the polarization impedance under microwave heat treatment is 0.18 Ω·cm. 2 It is significantly lower than the polarization resistance of the material after conventional heat treatment, which is 0.34 Ω·cm. 2 High-entropy design not only solves the phase stability problem of traditional cathode materials at high temperatures, reduces interfacial polarization and optimizes ion transport paths, but also provides a new approach to optimizing the performance of medium- and low-temperature SOFCs through the triple effect of "rapid crystallization-grain refinement-defect engineering" introduced by microwave heat treatment.

[0072] This invention employs a solution combustion method to prepare a high-entropy spinel precursor, and utilizes microwave heat treatment to construct oxygen vacancies, thereby obtaining a nano-network of oxygen-vacancy-rich high-entropy spinel (Ni). 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4, the method has the following significant characteristics: (1) Compared with conventional heat treatment, the (Ni) prepared by the present invention has the following significant characteristics: 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 (1) The oxygen vacancy concentration of Ni3O4 is significantly increased; (2) Compared with conventional heat treatment, the oxygen vacancy concentration of Ni3O4 prepared by this invention is significantly increased. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 (3) The grain size of NiO4 is significantly reduced, by about 60%; (4) Compared with conventional heat treatment, the microwave heat treatment of NiO4 prepared in this invention significantly reduces the grain size of NiO4. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The heat treatment time for NiO4 can be reduced by approximately 50%. (NiO4 prepared by different methods...) 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 NiO4, used as a cathode material in solid oxide fuel cells, demonstrates effective performance in symmetrical cell AC impedance testing using the microwave method of this invention. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The cathode polarization resistance of 3O4 is as low as 0.18 Ω·cm at 750℃. 2 Compared to Ni prepared by conventional heat treatment 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The polarization resistance of the 3O4 cathode was reduced by 53%. This invention provides a new and efficient method for optimizing the performance of intermediate-temperature SOFC cathode materials.

[0073] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A nano-network oxygen-rich vacancy high-entropy spinel (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 The method for preparing 3O4 is characterized by, Includes the following steps: (1) Take equimolar amounts of Ni 2+ Salt, Fe salt, Cr 3+ Salt, Mg 2+ Salt and Zn 2+ Salt, as a metal precursor, is mixed with a combustion accelerant in water and stirred at 80-100°C until a gel is formed. (2) The gel is placed at 150-200°C for self-combustion to form precursor powder; (3) The precursor powder is heat-treated under microwave conditions to obtain the nano-network oxygen-rich vacancy high-entropy spinel (Ni). 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4;。 Wherein, the Fe salt is Fe 2+ Salt and / or Fe 3+ Salt; The Ni 2+ Salt, Fe salt, Cr 3+ Salt, Mg 2+ Salt and Zn 2+ The salt is a nitrate.

2. The preparation method according to claim 1, characterized in that, The combustion aid includes one or more of glycine, glucose, urea and citric acid; the heat treatment temperature in step (3) is 500-900℃ and the power is 1000-2500W.

3. The preparation method according to claim 2, characterized in that, The heat treatment time in step (3) is 10-60 min.

4. The preparation method according to claim 1, characterized in that, The ratio of the total molar amount of metal ions in the metal precursor to the molar amount of the combustion improver is 1:(1-2).

5. The preparation method according to claim 2, characterized in that, Step (3) also includes the step of heating from room temperature to the temperature of the heat treatment.

6. The preparation method according to claim 5, characterized in that, When heating from room temperature to the temperature of the heat treatment, the heating rate is 20-100℃ / min.

7. Nanostructured oxygen-rich, high-entropy spinel (Ni) prepared by the preparation method according to any one of claims 1-6. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 )3O4.

8. The nano-network oxygen-vacancy-rich high-entropy spinel (Ni) as described in claim 7 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 Application of 3O4 as a cathode material for solid oxide fuel cells.

9. A solid oxide fuel cell, characterized in that, The nano-network oxygen-vacancy-rich high-entropy spinel (Ni) described in claim 7 is used. 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 3O4 is used as the cathode material.

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