A method for preparing a praseodymium fluoride composite

Abstract

The application discloses a preparation method of praseodymium fluoride composite material and belongs to the technical field of electrocatalytic oxygen reduction reaction. The preparation method of the praseodymium fluoride composite material comprises the following steps: mixing praseodymium-loaded ZIF-8, ammonium fluoride and water, and then performing high-temperature carbonization after reaction to obtain the praseodymium fluoride composite material. The praseodymium fluoride composite material prepared by the application has excellent ORR performance and good stability under alkaline conditions, can be used as an excellent catalyst for electrocatalytic oxygen reduction reaction, and has certain application potential.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic oxygen reduction reaction technology, and in particular to a method for preparing a praseodymium fluoride composite material. Background Technology

[0002] Among various energy technology systems, cryogenic fuel cells have become a highly promising energy conversion technology due to their intrinsically high energy conversion efficiency and the core advantage of achieving zero greenhouse gas emissions when using hydrogen produced from renewable energy sources as fuel. Currently, the mainstream catalysts commonly used in cryogenic fuel cells are precious metal catalysts, which possess advantages such as high catalytic activity and good selectivity. However, precious metal catalysts are scarce, expensive, and prone to poisoning and deactivation, exhibiting poor stability, which seriously hinders the large-scale commercial application of cryogenic fuel cells.

[0003] For decades, researchers have been dedicated to developing efficient and stable non-noble metal oxygen reduction reaction (ORR) electrocatalysts. Among numerous candidate materials, atomically dispersed metal-nitrogen-carbon (MNC) materials are considered the most promising alternatives to platinum-based catalysts due to their well-defined active sites and precisely tunable electronic structures. To overcome the electronic and geometric symmetries of the active centers and thus enhance intrinsic catalytic activity, various efficient strategies have been developed, including coordination number regulation, heteroatom substitution, axial ligand modification, and second-shell engineering. The core structural feature of MNC catalysts is the formation of a stable coordination structure (MN) between metal atoms and the carbon matrix through nitrogen atoms. x The structure of the central metal (MNC) catalyst, which serves as the active center for ORR, is significantly different from traditional nano-metal catalysts, providing a flexible and broad platform for the design of high-performance ORR catalysts. On the one hand, ORR catalytic activity is highly dependent on the type of central metal; currently, 3d transition metal-based MNC catalysts, represented by Fe and Co, have demonstrated excellent catalytic performance. On the other hand, introducing heteroatoms such as B, O, S, and P can regulate the local charge distribution and the electronic state of the central metal, further enhancing ORR activity. Although atomically dispersed MNC catalysts, especially the Fe-NC system, have shown great potential in the ORR field, their practical application still faces a key bottleneck: Fe readily undergoes a Fenton reaction with the ORR byproduct H₂O₂, leading to rapid degradation of the catalyst structure and severely limiting its long-term stability. To address this, researchers have attempted to construct novel MNC catalysts using low-Fenton-activity metals such as Zn, Mn, Zr, and Sb; however, the overall performance of these materials is still far below the optimal level of Fe-NC, making it difficult to meet practical application requirements.

[0004] Compared to widely reported MNC systems containing traditional 3d and 4d transition metals, rare earth elements typically possess larger ionic radii, unique 4f and 5d electronic configurations, and stronger electron shielding effects, making them more likely to interact with surrounding atoms to form stable coordination structures, thereby enhancing their catalytic activity in oxygen reduction reactions (ORRs). In recent years, numerous studies have confirmed the considerable application potential of rare earth elements such as Y, Ce, Gd, and La in oxygen reduction reactions. However, the ORR performance of currently reported rare earth-based REM-NC catalysts is still significantly lower than that of the best Fe and Co-based MNC materials. The core reason for this can be attributed to the intrinsic physicochemical properties of rare earth elements: such as inert 4f electrons, more negative reduction potentials, larger ionic radii, and highly unsaturated coordination environments, making it difficult to efficiently construct atomically dispersed rare earth-based active site structures using traditional 3d metal MNC synthesis strategies. Therefore, there is an urgent need to find novel catalysts with superior activity to replace noble metal catalysts. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing praseodymium fluoride composite materials to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention: a method for preparing praseodymium fluoride composite material, comprising the following steps: The praseodymium-loaded ZIF-8, ammonium fluoride, and water were mixed and reacted, followed by high-temperature carbonization to obtain the praseodymium fluoride composite material.

[0007] This invention uses praseodymium-supported ZIF-8 and ammonium fluoride as main raw materials to obtain a rare earth-based REM-NC catalyst through high-temperature carbonization. It systematically solves the industry pain points of rare earth-based catalysts from three dimensions: "anti-agglomeration, activity enhancement, and structure preservation". It achieves efficient dispersion of rare earth-based active sites from the source, breaking through the loading bottleneck of traditional technology; it achieves an order-of-magnitude improvement in the intrinsic activity of rare earth active sites through precise control of coordination environment; and the mild process ensures the scalable preparation of the catalyst, while adapting to the application requirements of actual energy devices, overcoming the technical problems of existing technologies such as the difficulty in efficiently constructing atomically dispersed rare earth-based active site structures.

[0008] Preferably, the method for preparing the praseodymium-loaded ZIF-8 includes the following steps: A mixed solution containing praseodymium source, zinc source and surfactant was mixed with a solution of organic ligand, and then synthesized by coordination self-assembly to obtain the praseodymium-loaded ZIF-8.

[0009] Preferably, the organic ligand comprises 2-methylimidazole; The zinc source includes zinc nitrate; The praseodymium source includes praseodymium nitrate; The surfactant includes CTAB.

[0010] Preferably, the ratio of carbon, zinc source, praseodymium source and surfactant in the organic ligand is 60~100 mmol: 3~5 mmol: (0.1~0.5) mmol: 10 mg; Preferably, the coordination self-assembly synthesis includes stirring at room temperature for 10-14 hours.

[0011] Preferably, the mass ratio of the praseodymium-loaded ZIF-8 to ammonium fluoride is 1:(1~3).

[0012] Preferably, the high-temperature carbonization atmosphere is an inert atmosphere, the temperature is 850~1050℃, and the time is 2h.

[0013] The second technical solution of the present invention: a praseodymium fluoride composite material prepared by the above preparation method.

[0014] The third technical solution of the present invention: an application of the above-mentioned praseodymium fluoride composite material as an electrocatalytic oxygen reduction reaction catalyst.

[0015] The present invention discloses the following technical effects: (1) The praseodymium fluoride composite material prepared by the present invention has excellent ORR performance and good stability under alkaline conditions, and can be used as an excellent catalyst for electrocatalytic oxygen reduction reaction, with certain application potential.

[0016] (2) The preparation method of the present invention is simple and the preparation process is short, which greatly reduces the preparation cost and facilitates commercial promotion.

[0017] (3) The successful doping of fluorine in this invention effectively regulates the electronic structure of praseodymium, thereby improving the conductivity and ORR catalytic performance of the material. Attached Figure Description

[0018] 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.

[0019] Figure 1 X-ray powder diffraction patterns of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2. Figure 2Raman spectra of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2; Figure 3 The BET and average pore size diagrams of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2 are shown below. In the diagram, a is the BET diagram of the F@NC composite material, b is the BET diagram of the PrC2@NC composite material, c is the BET diagram of the PrF3@NC composite material, d is the average pore size diagram of the F@NC composite material, e is the average pore size diagram of the PrC2@NC composite material, and f is the average pore size diagram of the PrF3@NC composite material. Figure 4 The image shows the morphology characterization results of the PrF3@NC composite material prepared in Example 1. In the image, a and b are scanning electron microscope images, c and d are transmission electron microscope images, high-resolution transmission electron microscope images, and high-angle annular dark-field transmission electron microscope images, and e is the distribution map of each element. Figure 5 X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UVPS) spectra of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2. In the XPS, a is the full XPS spectrum, b is the Pr 3d spectrum of the PrC2@NC composite material, c is the Pr 3d spectrum of the PrF3@NC composite material, d is the F 1s spectrum of the PrF3@NC composite material, e is the F 1s spectrum of the F@NC composite material, and f is the UVPS spectrum. Figure 6 The electrochemical performance test results of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2 in 0.1M KOH are shown in the figures. a) cyclic voltammetry curves, b) linear sweep voltammetry polarization curves, c) half-wave potential and kinetic current density, d) Tafel slope plots, e) comparison of ORR activity of PrF3@NC (This work) with recently reported catalysts, and f) different catalysts... C dl Figure 1 shows the LSV curves and KL curves of PrF3@NC at different rotational speeds, g represents the H2O2 yield (%) and electron transfer number (n), and i represents the stability test results of PrF3@NC and 20wt.%Pt / C (20wt.% is the mass fraction of Pt) in 0.1 M KOH at a rotational speed of 1600 rpm. Figure 7The electrochemical performance test results of PrF3@NC (1F), PrF3@NC (2F), and PrF3@NC (3F) prepared in Examples 1-3 in 0.1M KOH are shown in the figure. In the figure, a is the cyclic voltammetry curve, b is the linear sweep voltammetry polarization curve, c is the Tafel slope diagram, and d is the H2O2 yield (%) and electron transfer number (n). Figure 8 The following table shows the hydrogen-oxygen fuel cell and its performance test results in Application Example 1. In this table, a is a schematic diagram of the fuel cell device; b shows the results under the following conditions: temperature 80°C, back pressure 250 kPa, relative humidity 100% (RH), and anode platinum loading of 0.2 mg / cm³. -2 Or 0.5 mg cm -2 The polarization curves and power density curves of PrF3@NC and Pt / C in a hydrogen-oxygen fuel cell are measured; c represents the values ​​obtained at 80℃, back pressure of 250 kPa, relative humidity of 100% (RH), and anode platinum loading of 0.2 mg / cm³. -2 Or 0.5 mg cm -2 The polarization curves and power density curves obtained by measuring PrF3@NC and Pt / C in a hydrogen-air fuel cell. Detailed Implementation

[0020] 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.

[0021] 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. Every smaller range between any stated value or intermediate value within a stated range, and 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.

[0022] 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.

[0023] 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 apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0024] 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.

[0025] 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.

[0026] In a first aspect, the present invention provides a method for preparing a praseodymium fluoride composite material, comprising the following steps: (1) Add praseodymium source and zinc source to water, sonicate, add surfactant, stir to dissolve, and obtain solution A; The organic ligand was added to water and stirred to dissolve, resulting in solution B. Solution A and solution B were mixed and stirred at room temperature (i.e., synthesized by coordination self-assembly). After the reaction was completed, the mixture was centrifuged and freeze-dried to obtain ZIF-8 loaded with praseodymium (i.e., the precursor). (2) Add ZIF-8 (i.e. precursor) loaded with praseodymium and ammonium fluoride to water, mix and dissolve, stir and react at room temperature, centrifuge and freeze dry after the reaction is completed, and finally grind the obtained product and place it in a tube furnace for high-temperature carbonization under argon protection atmosphere to obtain praseodymium fluoride composite material (abbreviated as PrF3@NC).

[0027] Preferably, in step (1), the organic ligand is 2-methylimidazole; the zinc source includes zinc nitrate hexahydrate; the praseodymium source includes praseodymium nitrate hexahydrate; and the surfactant includes CTAB. In solution A, the ratio of zinc source, praseodymium source, water, and surfactant is 3-5 mmol: (0.1-0.5) mmol: 100 mL: 10 mg; The ratio of carbon source to water in solution B is 60-100 mmol: 100 mL; The ratio of carbon source, zinc source, praseodymium source and surfactant is 80 mmol: 4 mmol: (0.1~0.3) mmol: 10 mg.

[0028] 2-Methylimidazole plays the following roles in the reaction process: (1) core organic ligand, which forms the structural basis of the three-dimensional zeolite framework of ZIF-8; (2) in-situ alkali source, which drives the coordination self-assembly and crystallization process; (3) crystal face and morphology regulator, which determines the crystal morphology, exposed crystal face and particle size of ZIF-8. The functions of surfactant CTAB are: (1) nucleation and growth of soft template confinement material; (2) dispersant and anti-agglomeration agent.

[0029] Preferably, in step (1), the stirring reaction at room temperature (i.e., the coordination self-assembly synthesis) takes 12 hours.

[0030] More preferably, in step (1), before freeze-drying after centrifugation, a step of washing the product is also included, specifically including washing three times alternately with deionized water and anhydrous ethanol.

[0031] Preferably, in step (2), the mass ratio of ZIF-8 loaded with praseodymium to ammonium fluoride is 1:(1~3).

[0032] Preferably, in step (2), the high-temperature carbonization temperature is 850~1050℃ and the time is 2h.

[0033] Preferably, in step (2), the stirring reaction time at room temperature is 10-14 hours.

[0034] More preferably, in step (2), the high-temperature carbonization temperature is 950°C and the time is 2 hours.

[0035] More preferably, in step (2), before freeze drying after centrifugation, a step of washing the product is also included, specifically including washing three times alternately with deionized water and anhydrous ethanol.

[0036] Ammonium fluoride, as a modifier, can introduce fluorine while modifying the precursor under stirring at room temperature. The ammonium fluoride (modifier) ​​used in this invention has the following advantages: (1) No thermal damage during stirring at room temperature, which completely avoids the problems of porous structure collapse, particle agglomeration, metal single-atom site sintering, and crystal destruction caused by high-temperature calcination fluorination and hydrothermal solvothermal fluorination. It can completely preserve the original morphology, particle size distribution, and hierarchical pore structure of ZIF precursor and pre-carbonized carbon material; (2) Simple and safe operation, low energy consumption, and strong experimental repeatability; (3) Excellent dispersibility in aqueous system, achieving molecular-level uniform doping / modification; (4) Precise and controllable doping / etching degree, easy to achieve performance-oriented optimization; (5) Simple post-processing, no impurity residue, and no interference with catalytic performance.

[0037] This invention prepares praseodymium fluoride composite materials (i.e., nitrogen-carbon composite materials loaded with praseodymium fluoride) through coordination self-assembly and aqueous phase mixing. The preparation method has the following advantages: (1) Simple and safe operation with extremely low energy consumption. (2) High safety: Compared with traditional methods, the operation is simpler and the steps are more concise. (3) The amount of fluorine doping and the bonding type of CF (covalent CF, half-ionic CF, etc.) can be precisely controlled by adjusting simple parameters such as ammonium fluoride concentration and stirring time. Figure 5At the same time, it can precisely control the degree of surface etching, achieving gradient control from "light surface modification" to "uniform bulk doping".

[0038] Example 1 A method for preparing praseodymium fluoride composite materials (using coordination self-assembly and aqueous phase mixing method): (1) Preparation of precursor: Take 4 mmol of zinc nitrate hexahydrate and 0.2 mmol of praseodymium nitrate hexahydrate and add them to a beaker containing 100 mL of deionized water. After sonicating for 10 min, add 10 mg of CTAB and stir to dissolve to obtain solution A. Add 80 mmol of 2-methylimidazole (nitrogen and carbon source) to 100 mL of water, stir to dissolve, and obtain solution B; Solution A and solution B were mixed and stirred at room temperature (25°C) for 12 h (i.e., coordination self-assembly synthesis). After the reaction was completed, the mixture was centrifuged, washed three times alternately with deionized water and anhydrous ethanol, and then freeze-dried to obtain ZIF-8 supported on praseodymium (i.e., the precursor).

[0039] (2) Preparation of fluoride: 300 mg of ZIF-8 loaded with praseodymium and 600 mg of ammonium fluoride were mixed and dissolved in 100 mL of deionized water. The mixture was stirred and reacted at room temperature for 12 h. After the reaction was completed, the mixture was centrifuged and washed three times alternately with deionized water and anhydrous ethanol. The mixture was then freeze-dried. Finally, the obtained product was ground and placed in a tube furnace for high-temperature carbonization under an argon protective atmosphere (temperature 950 °C, time 2 h) to obtain PrF3@NC composite material (i.e. praseodymium fluoride composite material, PrF3@NC(2F)).

[0040] Comparative Example 1 A method for preparing PrC2@NC composite material (using coordination self-assembly): (1) Preparation of precursor: Take 4 mmol of zinc nitrate hexahydrate and 0.2 mmol of praseodymium nitrate hexahydrate and add them to a beaker containing 100 mL of deionized water. After sonicating for 10 min, add 10 mg of CTAB and stir to dissolve to obtain solution A. Add 80 mmol of 2-methylimidazole to 100 mL of water, stir to dissolve, and obtain solution B; Solution A and solution B were mixed and stirred at room temperature (i.e., the coordination self-assembly method was used for synthesis). After the reaction was completed, the mixture was centrifuged, washed three times alternately with deionized water and anhydrous ethanol, and then freeze-dried to obtain ZIF-8 loaded with praseodymium (i.e., the precursor).

[0041] (2) ZIF-8 loaded with praseodymium was ground and placed in a tube furnace for high-temperature carbonization under an argon protective atmosphere (temperature 950℃, time 2h) to obtain PrC2@NC composite material.

[0042] Comparative Example 2 A method for preparing F@NC composite materials (using coordination self-assembly and aqueous phase mixing method): (1) Preparation of precursor: 4 mmol of zinc nitrate hexahydrate was added to a beaker containing 100 mL of deionized water, sonicated for 10 min, and then 10 mg of CTAB was added and stirred to dissolve, to obtain solution A; Add 80 mmol of 2-methylimidazole to 100 mL of water, stir to dissolve, and obtain solution B; Solution A and solution B were mixed and stirred at room temperature for 12 hours (i.e., coordination self-assembly synthesis). After the reaction was completed, the mixture was centrifuged, washed three times alternately with deionized water and anhydrous ethanol, and then freeze-dried to obtain the precursor.

[0043] (2) Preparation of fluoride: 300 mg of precursor and 600 mg of ammonium fluoride were mixed and dissolved in 100 mL of deionized water. The mixture was stirred and reacted at room temperature for 12 h. After the reaction was completed, the mixture was centrifuged and washed three times alternately with deionized water and anhydrous ethanol. The mixture was then freeze-dried. Finally, the obtained product was ground and placed in a tube furnace for high-temperature carbonization under an argon protective atmosphere (temperature 950 °C, time 2 h) to obtain F@NC composite material.

[0044] Example 2 Same as Example 1, except that the amount of ammonium fluoride used was 300 mg, and PrF3@NC composite material (i.e. praseodymium fluoride composite material, PrF3@NC(1F)) was prepared.

[0045] Example 3 Same as Example 1, except that the amount of ammonium fluoride used was 900 mg, and PrF3@NC composite material (i.e. praseodymium fluoride composite material, PrF3@NC (3F)) was prepared.

[0046] Example 1 The structure, composition, morphology, and electrical conductivity of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2 were characterized, and the results are shown in the figure. Figures 1-7 .

[0047] (1) The X-ray powder diffraction patterns of the PrF3@NC, PrC2@NC and F@NC composite materials prepared in Examples 1-3 are shown in the figure. Figure 1 .

[0048] from Figure 1As can be seen, the PrF3@NC composite material has obvious PrF3 (JCPDS: 46-1167) characteristic peaks, indicating that PrF3 was successfully synthesized. The PrC2@NC composite material has PrC2 (JCPDS: 29-1067) characteristic peaks, while F@NC only shows carbon peaks with disordered structure.

[0049] (2) The Raman spectra of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2 are shown in the figure. Figure 2 .

[0050] from Figure 2 It can be seen from this that at 1359cm -1 and 1587cm -1 The peaks at these locations correspond to the D-band and [other peaks] caused by defects, respectively. SP 2 The G-band caused by in-plane vibrations of carbon atoms, and the I-band of the PrF3@NC sample. D / I G The highest ratio indicates the most defects, which is beneficial for improving electrocatalytic activity.

[0051] (3) The BET and average pore size diagrams of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2 are shown in the figure. Figure 3 Where a is the BET diagram of F@NC composite material, b is the BET diagram of PrC2@NC composite material, c is the BET diagram of PrF3@NC composite material, d is the average pore size diagram of F@NC composite material, e is the average pore size diagram of PrC2@NC composite material, and f is the average pore size diagram of PrF3@NC composite material.

[0052] from Figure 3 As can be seen from the data, the BET surface area of ​​the PrF3@NC composite material prepared in Example 1 is between that of the PrC2@NC composite material and the F@NC composite material, but the average pore size is the smallest. The high mesoporous ratio can improve the charge storage and ion transport capacity of the material, providing a pathway for mass transfer within the catalyst layer.

[0053] (4) The morphology characterization results of the PrF3@NC composite material prepared in Example 1 are shown in the figure. Figure 4 In the figure, a and b are scanning electron microscope images, c and d are transmission electron microscope images, high-resolution transmission electron microscope images, and high-angle annular dark-field transmission electron microscope images, and e is the distribution map of each element.

[0054] from Figure 4As can be seen, the PrF3@NC composite material prepared in Example 1 has a clear dodecahedral morphology; PrF3 has unique lattice fringes (Figure d); C, N, F and Pr elements are uniformly distributed on the catalyst (Figure e).

[0055] (5) The X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy of the PrF3@NC composite material prepared in Example 1, the PrC2@NC composite material prepared in Comparative Example 1, and the F@NC composite material prepared in Comparative Example 2 are shown in the figure. Figure 5 In the spectrum, a is the full X-ray photoelectron spectroscopy (XPS) spectrum, b is the Pr 3d spectrum of PrC2@NC composite material, c is the Pr 3d spectrum of PrF3@NC composite material, d is the F 1s spectrum of PrF3@NC composite material, e is the F 1s spectrum of F@NC composite material, and f is the ultraviolet photoelectron spectrum.

[0056] from Figure 5 As can be seen from Figures b and c, PrF3@NC... 3+ / Pr 4+ The ratio was significantly higher than that of PrC2@NC, indicating that the introduction of fluorine can effectively regulate the electronic structure of Pr and promote Pr... 4+ To Pr 3+ The restoration. As can be seen from graphs d and e, the F1 value of PrF3@NC... s The characteristic peak binding energy is slightly lower than that of F@NC. This is because in PrF3@NC, fluorine forms a Pr-F covalent bond with Pr atoms, and the valence electrons of Pr shift to the 2' electrons of F. p Orbital transfer increases the electron cloud density of the F atom and decreases the binding energy.

[0057] from Figure 5 As can be seen from the f-plot, the Fermi level of PrF3@NC is closer to the vacuum level, and its work function is lower than that of PrC2@NC and F@NC. This indicates that the synergistic effect of fluorine and Pr can effectively increase the electron cloud density on the surface of PrF3@NC and enhance its electronic conductivity.

[0058] Example 2 Electrochemical testing: Test method: A CHI 760E electrochemical workstation was used to perform electrochemical measurements at room temperature in a 0.1 MkOH solution saturated with oxygen / nitrogen using a three-electrode system.

[0059] The working electrode was a glassy carbon rotating disk electrode (RDE, 5 mm in diameter) coated with catalyst ink, the reference electrode was saturated silver / silver chloride, and the counter electrode was a graphite rod. The catalyst ink was prepared by dispersing 1 mg of the composite material (PrF3@NC, PrC2@NC, or F@NC) prepared in Example 1 or Comparative Examples 1-2 in 200 µL of isopropanol, 50 µL of deionized water, and 5 µL of a 5% Nafion solution, followed by sonication for 60 min to obtain a homogeneous suspension (i.e., catalyst ink). Subsequently, 25 µL of the catalyst ink was drop-coated onto the RDE and allowed to air dry at room temperature, resulting in a loading of 0.51 mg / cm³. 2 The working electrode was used. The electrocatalytic activity of the reference Pt / C was tested using the same method. The measured potential was adjusted to that of the reversible hydrogen electrode (RHE) according to the formula: E (RHE) =E (Ag / AgCl) +0.059 pH +0.196 V, results are shown in [link to results]. Figure 6 In the figure, a is the cyclic voltammetry curve, b is the linear sweep voltammetry polarization curve, c is the half-wave potential and kinetic current density, d is the Tafel slope plot, e is the ORR activity comparison of PrF3@NC (This work) with recently reported catalysts, and f is the ORR activity of different catalysts. C dl Figure g shows the LSV curves and KL plots of PrF3@NC at different rotational rates, h shows the H2O2 yield (%) and electron transfer number (n), and i shows the stability test results of PrF3@NC and 20wt.% Pt / C in 0.1 M KOH at a rotational speed of 1600 rpm.

[0060] The preparation method of the reference Pt / C is as follows: The working electrode was a glassy carbon rotating disk electrode (RDE, 5 mm in diameter) coated with catalyst ink, the reference electrode was saturated silver / silver chloride, and the counter electrode was a graphite rod. Preparation of the catalyst ink: 2 mg of Pt / C (commercially available, Pt loading 20 wt.%) was added to a mixed solution consisting of 200 µL deionized water, 100 µL anhydrous ethanol, and 5 µL Nafion solution. The solution was sonicated for 60 min to obtain a homogeneous suspension (i.e., catalyst ink). Subsequently, the catalyst ink was drop-coated onto the RDE and allowed to air dry at room temperature to obtain a loading of 0.2 mg / cm². 2 The working electrode.

[0061] from Figure 6 As can be seen from the figure, PrF3@NC exhibits the most positive reduction peak potential, significantly superior to the control sample and commercial Pt / C (Figure a). The LSV curve shows that PrF3@NC has a half-wave potential of 0.92 V (Figure b). Not only does the target sample outperform commercial Pt / C in terms of half-wave potential (E...1 / 2 =0.85V) and all reference catalysts, and the reaction kinetic current density at 0.85V was also significantly higher than that of other samples (Figure c). The Tafel slope of PrF3@NC was 69.3 mV dec. -1 The concentrations were significantly lower than all control samples and commercial Pt / C, indicating an accelerated charge transfer kinetics during the ORR process (Figure d). PrF3@NC outperformed most previously reported non-noble metal catalysts in ORR performance (Figure e). Electrochemistry of Co-BFNC C dl The highest value was obtained, thus providing the largest ECSA after normalization (Figure f). PrF3@NC exhibited excellent linearity in the potential range of 0.5–0.65 V, indicating that the oxygen reduction reaction (ORR) follows first-order reaction kinetics (Figure g). Figure h further validated the reaction pathway of PrF3@NC, with its electron transfer number (n) consistently close to 4 in the potential range of 0.2–0.8 V, while the yield of H2O2 was consistently lower than that of commercial platinum-carbon (Pt / C). This indicates that it follows an ideal four-electron ORR pathway and efficiently converts O2 molecules to OH. - The i-figure demonstrates the excellent stability of the catalyst.

[0062] Example 3 Similar to Example 2, the only difference being that the composite material used in the catalyst ink was PrF3@NC (1F), PrF3@NC (2F), and PrF3@NC (3F) prepared in Examples 1-3; the electrochemical performance test results are shown in […]. Figure 7 a is the cyclic voltammetry curve, b is the linear sweep voltammetry polarization curve, c is the Tafel slope diagram, and d is the H2O2 yield (%) and electron transfer number (n).

[0063] Application Example 1 The anion exchange membrane used in the hydrogen-oxygen fuel cell test was Alkymer W-25. 14g of catalyst (PrF3@NC composite material or Pt / C from Example 1) was mixed with 2.5mL isopropanol and 5mL deionized water, then 300μL of Nafion (5wt%) was added, and the mixture was sonicated for 1h to obtain a slurry. The slurry was then sprayed onto a PTFE membrane and dried in a 60°C oven for 10min. The catalyst layer was then transferred onto the anion exchange membrane using a thermal transfer process at 120°C and 6MPa to form a catalyst-coated membrane (CCM). Subsequently, GDL (Freudenberg, P10023) was bonded to both the anode and cathode sides of the CCM to complete the MEA assembly. The experimental MEA catalyst cathode was 3.5 mg cm⁻¹. -2 The PrF3@NC catalyst, with an anode of 0.2 mg cm⁻¹ -2The catalyst was 20 wt% Pt / C. The control group cathode was 0.2 mg cm⁻¹. -2 A 20wt% Pt / C catalyst with an anode of 0.5 mg cm⁻¹ -2 The catalyst used was 20 wt% Pt / C. Fuel cell performance testing was conducted on the Qunyi HS-300 fuel cell test platform, with the MEA encapsulated in a substrate with an effective active area of ​​4 cm². 2 In a 2 cm × 2 cm test fixture, high-purity hydrogen was used as fuel and high-purity oxygen or air as oxidant. The gas pressure was 0.25 MPa, the test temperature was set to 80°C, and the relative humidity was 100% (RH). The relative humidity of the reaction gas was adjusted by slowly introducing saturated water vapor into the gas inlet. After the battery stabilized, the current density gradient was increased, and the battery polarization curve was recorded. The results are shown in […]. Figure 8 , Figure 8 In the diagram, 'a' represents a schematic of a fuel cell device; 'b' represents the conditions at 80°C, a back pressure of 250 kPa, a relative humidity of 100% (RH), and an anode platinum loading (referring to a loading of 20 wt% Pt / C) of 0.2 mg cm⁻¹. -2 Or 0.5 mg cm -2 The polarization curves and power density curves of PrF3@NC and Pt / C in a hydrogen-oxygen fuel cell are measured; c represents the values ​​obtained at 80℃, back pressure of 250 kPa, relative humidity of 100% (RH), and anode platinum loading of 0.2 mg / cm³. -2 Or 0.5 mg cm -2 The polarization curves and power density curves obtained by measuring PrF3@NC and Pt / C in a hydrogen-air fuel cell.

[0064] When testing the polarization and power density curves of PrF3@NC, the platinum loading at the anode was 0.2 mg / cm³. -2 When determining the polarization curves and power density curves of Pt / C, the platinum loading at the anode was 0.5 mg / cm³. -2 .

[0065] 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 method for preparing a praseodymium fluoride composite material, characterized in that, Includes the following steps: The praseodymium-loaded ZIF-8, ammonium fluoride, and water were mixed and reacted, followed by high-temperature carbonization to obtain the praseodymium fluoride composite material.

2. The preparation method according to claim 1, characterized in that, The method for preparing the praseodymium-loaded ZIF-8 includes the following steps: A mixed solution containing praseodymium source, zinc source and surfactant was mixed with a solution of organic ligand, and then synthesized by coordination self-assembly to obtain the praseodymium-loaded ZIF-8.

3. The preparation method according to claim 2, characterized in that, The organic ligand includes 2-methylimidazole; And / or, the zinc source includes zinc nitrate; And / or, the praseodymium source includes praseodymium nitrate; And / or, the surfactant includes CTAB.

4. The preparation method according to claim 2, characterized in that, The ratio of carbon, zinc source, praseodymium source and surfactant in the organic ligand is 60~100mmol:3~5mmol:(0.1~0.5)mmol:10mg.

5. The preparation method according to claim 2, characterized in that, The coordination self-assembly method synthesis involves stirring at room temperature for 10-14 hours.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the praseodymium-loaded ZIF-8 to ammonium fluoride is 1:(1~3).

7. The preparation method according to claim 1, characterized in that, The high-temperature carbonization atmosphere is an inert atmosphere, with a temperature of 850~1050℃ and a time of 2 hours.

8. A praseodymium fluoride composite material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the praseodymium fluoride composite material according to claim 8 as a catalyst for electrocatalytic oxygen reduction reaction.

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