Metal organic framework catalyst containing metal nodes with different coordination modes as well as synthesis method and application of metal organic framework catalyst

Abstract

The invention discloses a metal organic framework catalyst containing metal nodes with different coordination modes as well as a synthesis method and application of the metal organic framework catalyst. The synthesis method of the metal organic framework catalyst comprises the following steps that S1, a triazole organic ligand L and M1 and M2 metal source reagents are subjected to a hydrothermal reaction to obtain a parent framework, the parent framework has octahedral sites and tetrahedral sites, M1 metal nodes occupy the centers of the octahedral sites, and M2 metal nodes occupy the centers of the tetrahedral sites; and S2, performing coordination substitution on M2-Cl at tetrahedral sites by using an aldehyde group auxiliary modification ligand H to form M2-O. The metal organic framework catalyst disclosed by the invention is based on an M-TZ framework constructed by a triazole organic ligand and metal M, has the characteristics of clear structure, adjustable pore channels, flexible electronic structure and the like, and can form an active phase rich in oxygen vacancies, optimized in bond length and adaptive to active sites through dynamic reconstruction under alkaline and external voltage conditions; the oxygen evolution reaction activity and stability are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework catalysts; more specifically, it relates to a metal-organic framework catalyst containing metal nodes with different coordination modes, its synthesis method, and its application in the oxygen evolution reaction of water electrolysis. Background Technology

[0002] In the search for efficient and sustainable energy conversion technologies, the oxygen evolution reaction (OER) has attracted much attention due to its central role in water splitting, which offers enormous potential for clean energy production. However, current electrochemical processes face numerous challenges, such as sluggish OER kinetics, which necessitates the use of expensive noble metal catalysts; furthermore, the lack of active sites significantly hinders its practical application.

[0003] Metal-organic frameworks (MOFs) are considered among the most effective electrocatalysts due to their independent active sites and tunable porous structures. However, the complex transformations of MOFs during oxygen evolution reaction (OER) pose significant challenges to accurately elucidating their catalytic mechanisms. In OER, catalyst self-reconstruction is crucial for the further development of energy conversion technologies. In recent years, numerous studies have employed advanced experimental and theoretical calculation methods to explore how to better understand the dynamic reconstruction process on the catalyst surface during electrocatalytic OER, but some fundamental questions remain unresolved: (i) How to achieve spatial control of reconstruction sites? (ii) Can electronic modulation guide the selective activation of specific metal centers? The dynamic properties of a catalyst are as important as its catalytic activity, as dynamic changes in catalysts are often closely related to real-time changes in their performance, which are usually attributed to dynamic structural changes on the catalyst surface. During OER, MOFs undergo complex dynamic transformations, which can lead to enhanced, weakened, or unchanged catalytic activity. Therefore, strategic regulation of structural reconstruction through reconstruction strategies to improve OER activity is crucial. However, current research on the intrinsic relationship between catalyst surface reconstruction, reaction mechanisms, and electrocatalytic behavior after self-reconstruction remains insufficient.

[0004] To overcome the current bottlenecks in electrochemical performance development, effectively utilizing the remodeling behavior of MOFs, optimizing catalyst structure design, and achieving the precise synthesis of highly efficient catalysts remain urgent tasks. This invention aims to elucidate the structural evolution and in-situ self-remodeling mechanisms of MOFs to improve their intrinsic activity, and to establish the mechanism of MOF structural changes and the relationship between structure and performance during OER (Optical Emission Reduction). This will provide specific guidance for structural regulation, thereby improving the performance and stability of catalysts. Summary of the Invention

[0005] This invention aims to reveal the structure-activity relationship on the catalyst surface through in-situ characterization using dynamic reconstruction mechanisms and kinetic processes, thereby obtaining a highly efficient electrocatalytic oxygen evolution catalyst. Simultaneously, by regulating the composition and structural coordination environment of the catalyst, surface reconstruction can be controlled, optimizing the efficiency and selectivity of the catalytic reaction.

[0006] The first aspect of this invention discloses a method for synthesizing metal-organic framework catalysts containing metal nodes with different coordination modes, comprising the following steps:

[0007] S1, the triazole organic ligand L is subjected to a hydrothermal reaction with metal source reagents M1 and M2 to obtain... The parent frame has the structure shown in formula (I), including the octahedron shown in formula (II). The site and the tetrahedron shown in formula (III) Site, M1 metal node occupies octahedron At the site center, the M2 metal node occupies a tetrahedron. Site center:

[0008]

[0009] S2, using aldehyde-assisted modified ligand H for directional coordination to replace the tetrahedron. M2-Cl at the site forms M2-O, thus obtaining the metal-organic framework catalyst containing metal nodes with different coordination modes.

[0010] Further, the triazole organic ligand L is any one or more of 1,2,4-triazole, 3-amino-1,2,4-triazole, 3-bromo-1,2,4-triazole, 3-amino-1,2,4-triazole, 3-nitro-1,2,4-triazole, 3-methyl-1,2,4-triazole, 3-cyano-1,2,4-triazole, 3,5-dimethyl-1,2,4-triazole, 3-bromo-4H-1,2,4-triazole, 1H-1,2,4-triazole-3-thiol, 3,5-diamino-1,2,4-triazole, and 1H-1,2,4-triazole-3-thiol.

[0011] Preferably, the triazole organic ligand L is 1,2,4-triazole.

[0012] Furthermore, the aldehyde-assisted ligand H is ferrocene formaldehyde or benzaldehyde, which directionally coordinates to substitute the tetrahedral ligand. M2-Cl at the site subsequently forms the structure shown in formula (Ⅳ) or formula (Ⅴ):

[0013]

[0014] Furthermore, the M1 metal source reagent is one or more of Ni salt and Co salt, and the M2 metal source reagent is Co salt.

[0015] Furthermore, the M1 metal source reagent is one or more of CoCl2·6H2O and NiCl2·6H2O, and the M2 metal source reagent is CoCl2·6H2O.

[0016] Further, step S1 includes:

[0017] S11, dissolve the triazole organic ligand L in water to obtain a mixed solution A;

[0018] S12, add metal source reagents M1 and M2 to water, and after dissolving, obtain mixed solution B;

[0019] S13, Mix solution A and solution B to obtain solution C;

[0020] S14, the mixed solution C is hydrothermally reacted at a temperature of 170-190℃ for 20-72h, and the product is subjected to solid-liquid separation, washing and drying to obtain a powdered parent framework F.

[0021] Furthermore, when M1 and M2 are different metal source reagents, the molar ratio of M1 to M2 in step S12 is 1:1 to 1.12, more preferably 1:1.

[0022] Further, step S2 includes:

[0023] S21, the obtained parent framework F is dispersed in a mixed solution of water and ethanol to obtain a mixed solution D;

[0024] S22, aldehyde-assisted ligand H was gradually added to the mixed solution D, and the pH was adjusted to 10-12 with potassium hydroxide;

[0025] S23, the mixed solution obtained in step S22 is subjected to hydrothermal reaction at a temperature of 50-70℃ for 10-24h, and the product is subjected to solid-liquid separation, washing and drying.

[0026] Furthermore, in steps S11 and S12, the molar ratio of triazole organic ligand L to metal source reagent M (the total of metal source reagents M1 and M2) can be 2 to 3:1 (preferably 2.15:1).

[0027] Furthermore, in steps S21 and S22, the mass ratio of the parent framework F to the aldehyde-assisted modified ligand H is 1 to 1.8:1 (preferably 1.5:1).

[0028] Furthermore, in step S14 or S21, a conductive substrate can be added inside the hydrothermal reaction vessel (e.g., a Teflon stainless steel reaction vessel) to load / attach the synthesized metal-organic framework powder material onto the conductive substrate to directly form an electrode. The conductive substrate can be nickel foam, carbon fiber paper, or copper sheet, with nickel foam being preferred.

[0029] The second aspect of the present invention discloses metal-organic framework catalysts containing metal nodes with different coordination modes obtained by the aforementioned synthesis method.

[0030] The third aspect of the present invention discloses the application of the aforementioned metal-organic framework catalyst in the oxygen evolution reaction of water electrolysis.

[0031] The metal-organic framework catalyst of this invention is based on an M-TZ framework constructed from triazole organic ligands and metals, featuring a well-defined structure, tunable pores, and flexible electronic structure. Under alkaline conditions and applied voltage, this framework can be dynamically reconstructed to form an active phase rich in oxygen vacancies, with optimized bond lengths and adaptive active sites, significantly improving the activity and stability of the oxygen evolution reaction (OER). Furthermore, the synthesis method is simple, uses inexpensive raw materials, and is environmentally friendly, making it suitable for large-scale preparation and showing broad application prospects in the field of energy conversion. Attached Figure Description

[0032] Figure 1 In the image, a and b are the XRD patterns of NiCo-TZ and NiCo-TZ(Fc), respectively.

[0033] Figure 2 In the image, a, b, and c are SEM images of NiCo-TZ; e, f, and g are SEM images of NiCo-TZ(Ph); h, i, and j are SEM images of NiCo-TZ(Fc).

[0034] Figure 3 In the image, a and c are the TEM and HRTEM spectra of NiCo-TZ, respectively; b and d are the TEM and HRTEM spectra of NiCo-TZ(Fc), respectively.

[0035] Figure 4 In the figure, a and b are transmission electron microscopy / energy dispersive X-ray spectroscopy (TEM / EDS) images of NiCo-TZ and NiCo-TZ(Fc) and their corresponding elemental contents (insets) (copper peaks are from TEM copper grids);

[0036] Figure 5 FT-IR spectra of the organic ligand ferrocene formaldehyde and two MOFs (NiCo-TZ and NiCo-TZ(Fc));

[0037] Figure 6Raman spectra of the organic ligands 1,2,4-triazole (1,2,4-TZ), NiCo-TZ, NiCo-TZ(Ph) and NiCo-TZ(Fc);

[0038] Figure 7 XPS full spectra of NiCo-TZ and NiCo-TZ(Fc);

[0039] Figure 8 Fine VB-XPS spectra of NiCo-TZ and NiCo-TZ(Fc);

[0040] Figure 9 Image a shows the Ni K-edge X-ray absorption near-edge structure (XANES) spectra of NiCo-TZ, NiCo-TZ(Fc), and Ni reference samples (including Ni oxides and Ni metal foils). Image b shows the Ni K-edge EXAFS spectra of NiCo-TZ, NiCo-TZ(Fc), and their reference compounds: (The image shows the range of k...) k 2 The R-space spectrum obtained by Fourier transforming the weighted K-space spectrum;

[0041] Figure 10 Image a shows the CoK-edge X-ray absorption near-edge structure (XANES) spectra of NiCo-TZ, NiCo-TZ(Fc), and Co reference samples (including Co oxides and Co metal foils). Image b shows the Ni K-edge EXAFS spectra of NiCo-TZ, NiCo-TZ(Fc), and their reference compounds: (The image shows the range of k...) k 2 The R-space spectrum obtained by Fourier transforming the weighted K-space spectrum;

[0042] Figure 11 The middle section compares the experimental Ni K-edge X-ray absorption near-edge structure (XANES) spectrum of Ni(TZ)6Co(TZ)3Cl with the density functional theory (DFT) simulated spectrum (inset: DFT model). The inset shows the comparison between the experimental k-space spectrum of Ni(TZ)6Co(TZ)3Cl and the DFT simulated extended X-ray absorption fine structure Fourier transform (FT-EXAFS) spectrum.

[0043] Figure 12 The middle section shows a comparison between the experimental Co K-edge X-ray absorption near-edge structure (XANES) spectrum of Ni(TZ)6Co(TZ)3Cl and the density functional theory (DFT) simulated spectrum (inset: DFT model). The inset shows a comparison between the experimental k-space spectrum of Ni(TZ)6Co(TZ)3Cl and the DFT simulated extended X-ray absorption fine structure Fourier transform (FT-EXAFS) spectrum.

[0044] Figure 13Comparison of experimental k-space spectrum and DFT simulated FT-EXAFS spectrum of Ni(TZ)6Co(TZ)3Cl(Fc);

[0045] Figure 14 In Figure a, the initial electrocatalytic oxygen evolution performance of NiCo-TZ, NiCo-TZ(Ph), and NiCo-TZ(Fc) is shown; and in Figure b, the Tafel slope of the electrocatalytic oxygen evolution of NiCo-TZ, NiCo-TZ(Ph), and NiCo-TZ(Fc) is shown.

[0046] Figure 15 Turnover frequency diagrams for NiCo-TZ, NiCo-TZ(Ph), and NiCo-TZ(Fc);

[0047] Figure 16 Electrochemical impedance spectroscopy (EIS) spectra of NiCo-TZ, NiCo-TZ(Ph), and NiCo-TZ(Fc);

[0048] Figure 17 In the image, a and b are the in-situ Raman spectra of NiCo-TZ and NiCo-TZ(Fc) in 1 mol / L KOH electrolyte for electrocatalytic oxygen evolution as a function of voltage.

[0049] Figure 18 The in-situ Raman spectrum of NiCo-TZ(Ph) in 1 mol / L KOH electrolyte for electrocatalytic oxygen evolution as a function of voltage.

[0050] Figure 19 In the figure, a and b are the in-situ Raman spectra of Co-TZ and NiCo-TZ in 1M KOH electrolyte for electrocatalytic oxygen evolution at 1.64V vs. RHE as the reaction time increases.

[0051] Figure 20 In the figure, a and b are the in-situ Raman spectra of NiCo-TZ(Ph) and NiCo-TZ(Fc) in 1 mol / L KOH electrolyte for electrocatalytic oxygen evolution as a function of reaction time at 1.64 V vs. RHE.

[0052] Figure 21 The in-situ Raman spectrum of the organic ligand Fc-CHO in 1 mol / L KOH electrolyte for electrocatalytic oxygen evolution as a function of reaction time at 1.64 V vs. RHE.

[0053] Figure 22 For NiCo-TZ and NiCo-TZ(Fc) in the oxygen evolution reaction, the frequency range is 10. -2 -10 5 In-situ electrochemical impedance spectroscopy (EIS) Bode plot at Hz;

[0054] Figure 23 The figure shows the electrocatalytic oxygen evolution stability of NiCo-TZ and NiCo-TZ(Fc). Detailed Implementation

[0055] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0056] The materials and reagents used in the following examples, such as the triazole organic ligand L, the aldehyde-assisted modification ligand H, the M1 metal source reagent, the M2 metal source reagent, and the solvents used in the synthesis process, are all commercially available products and can be obtained commercially unless otherwise specified.

[0057] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional experimental methods. Furthermore, the terminology used in the following embodiments and examples, unless otherwise specified, generally has the meanings commonly understood by those skilled in the art.

[0058] According to the rational design method, this invention uses a triazole organic ligand L to coordinate with metal source reagents M1 and M2 (where M1 and M2 can be the same or different) to form the structure shown in formula (Ⅰ). The parent framework has an octahedron as shown in (II). The site and the tetrahedron shown in formula (III) Site:

[0059]

[0060] Among them, M1 is capable of occupying an octahedron. The transition metal at the site center, M2, is capable of occupying a tetrahedron. Transition metal at the site center.

[0061] To achieve high OER activity, this invention uses an aldehyde-assisted modified ligand H for directional coordination instead of... tetrahedron in the parent framework A novel metal-organic framework, named M1M2-TZ(H), was constructed by octahedralizing M2-Cl at the site. In the M1M2-TZ(H) framework, M1 occupies an octahedral position. At the site center, M2 occupies a tetrahedron. At the site center, aldehyde-assisted ligand H-substituted coordination tetrahedron M2-Cl at the site forms M2-O.

[0062] In this invention, the aldehyde-assisted modification ligand H can be ferrocene formaldehyde or benzaldehyde, which is directionally coordinated to substitute for tetrahedral ligands. M2-Cl at the site subsequently forms the structure shown in formula (Ⅳ) or formula (Ⅴ):

[0063]

[0064] In this invention, the triazole organic ligand L can be any one or more of 1,2,4-triazole, 3-amino-1,2,4-triazole, 3-bromo-1,2,4-triazole, 3-amino-1,2,4-triazole, 3-nitro-1,2,4-triazole, 3-methyl-1,2,4-triazole, 3-cyano-1,2,4-triazole, 3,5-dimethyl-1,2,4-triazole, 3-bromo-4H-1,2,4-triazole, 1H-1,2,4-triazole-3-thiol, 3,5-diamino-1,2,4-triazole, and 1H-1,2,4-triazole-3-thiol, with 1,2,4-triazole being preferred.

[0065] In this invention, the M1 metal source reagent can be nickel chloride hexahydrate or cobalt chloride hexahydrate, and the M2 metal source reagent can be cobalt chloride hexahydrate.

[0066] The following is a detailed description with reference to embodiments and comparative examples.

[0067] Example 1

[0068] Phenyl-oriented modification (where nickel occupies octahedral sites and cobalt occupies tetrahedral sites) Synthesis of NiCo-TZ(Ph) metal-organic framework material

[0069] In a Teflon stainless steel reaction vessel, CoCl₂·6H₂O (642.4 mg, 2.7 mmol) and NiCl₂·6H₂O (641.8 mg, 2.7 mmol) were dissolved in 5.0 mL of deionized water. A solution of 1,2,4-triazole (169.8 mg, 11.6 mmol) dissolved in 5.0 mL of deionized water by sonication was added to the above metal solution. The Teflon was sealed in a stainless steel autoclave and heated in an oven at 180 °C for 24 h. After cooling to room temperature, the product was collected by centrifugation and washed with fresh deionized water. Finally, the sample was dried overnight at 40 °C to obtain the parent framework NiCo-TZ with the structure shown in formula (VI).

[0070]

[0071] The NiCo-TZ parent framework has octahedral sites as shown in formula (VII) and tetrahedral sites as shown in formula (VIII).

[0072]

[0073] Subsequently, 270 mg of the dried NiCo-TZ material was uniformly dispersed in a mixed solution consisting of 30 mL of deionized water and 5 mL of ethanol. Then, 0.84 mmol of benzaldehyde (Ph-CHO) and 50 mg of potassium hydroxide (KOH) were gradually added to this mixed solution. The mixture was then sonicated for 15 minutes. Finally, the mixed solution was transferred to a hydrothermal reactor, heated to 60 °C, and maintained at this temperature for 12 h to allow the reaction to proceed, causing the Co-Cl in the tetrahedral sites of benzaldehyde (Ph-CHO) to form Co-O (the tetrahedral site structure after coordination substitution can be seen in formula (V)). After cooling to room temperature, the product was collected by centrifugation and then washed three times each with fresh deionized water and ethanol to remove any remaining unreacted organic ligands. The NiCo-TZ (Ph) sample was then dried overnight at 40 °C.

[0074] Example 2

[0075] Phenyl-oriented modification (where nickel occupies octahedral sites and cobalt occupies tetrahedral sites) Synthesis of NiCo-TZ(Fc) metal-organic framework material

[0076] In a Teflon stainless steel reaction vessel, CoCl₂·6H₂O (642.4 mg, 2.7 mmol) and NiCl₂·6H₂O (641.8 mg, 2.7 mmol) were dissolved in 5.0 mL of deionized water. A solution of 1,2,4-triazole (169.8 mg, 11.6 mmol) dissolved in 5.0 mL of deionized water by sonication was added to the above metal solution. The Teflon was sealed in a stainless steel autoclave and heated in an oven at 180 °C for 24 h. After cooling to room temperature, the product was collected by centrifugation and washed with fresh deionized water. Finally, the sample was dried overnight at 40 °C.

[0077] Subsequently, 270 mg of the dried NiCo-TZ material was uniformly dispersed in a mixed solution consisting of 30 mL of deionized water and 5 mL of ethanol. Then, 0.84 mmol of ferrocene formaldehyde (Fc-CHO) and 50 mg of potassium hydroxide (KOH) were gradually added to this mixed solution. The mixture was then sonicated for 15 minutes. Finally, the mixed solution was transferred to a hydrothermal reactor, heated to 60 °C, and maintained at this temperature for 12 h to allow the reaction to proceed, causing the Co-Cl in the tetrahedral sites of ferrocene formaldehyde (Fc-CHO) to form Co-O (the tetrahedral site structure after coordination substitution can be seen in formula (IV)). After cooling to room temperature, the product was collected by centrifugation and then washed three times each with fresh deionized water and ethanol to remove any remaining unreacted organic ligands. The NiCo-TZ (Fc) sample was then dried overnight at 40 °C.

[0078] As a variation of the foregoing embodiments, a conductive substrate can be added during the synthesis process to load the metal-organic framework powder material onto it, or the metal-organic framework powder material can be loaded onto the conductive substrate after synthesis. The conductive substrate can be nickel foam, carbon fiber paper, or copper sheet, with nickel foam being preferred.

[0079] Comparative Example 1

[0080] Synthesis of Co-TZ, a metal-organic framework material

[0081] In a Teflon stainless steel reaction vessel, CoCl₂·6H₂O (1,290.0 mg, ~5.4 mmol) was first dissolved in 5.0 mL of deionized water. A solution of 1,2,4-triazole (169.8 mg, 11.6 mmol) dissolved in 5.0 mL of deionized water by sonication was added to the metal solution. The Teflon was sealed in a stainless steel autoclave and heated in an oven at 180 °C for 24 h. After cooling to room temperature, the product was collected by centrifugation and washed with fresh deionized water. Finally, the sample was dried overnight at 40 °C.

[0082] Structural characterization and performance testing of the materials in the examples and comparative examples

[0083] Based on the design concept of this invention, the embodiments are exemplified by M. 2+ A metal-organic framework (MOF) material, [M2(trz)3Cl] (abbreviated as M-TZ), exhibiting both water and strong basic stability was synthesized via an environmentally friendly hydrothermal method using metal ions and the inexpensive commercial ligand 1,2,4-triazole (1,2,4-TZ). Due to the strong coordination between the nitrogen ligand and the transition metal, triazole MOFs typically exhibit excellent stability in both aqueous and alkaline environments.

[0084] To establish the correlation between electronic structure modulation and macroscopic material properties, the crystal structure stability of NiCo-TZ before and after ferrocene (Fc) functionalization was investigated by powder X-ray diffraction (PXRD). The experimental PXRD patterns of NiCo-TZ and NiCo-TZ(Fc) were consistent with the simulated patterns. Figure 1 The high degree of agreement between the two materials confirms their phase purity and structural integrity. Strong diffraction peaks were observed in the NiCo-TZ powder at 10.29°, 12.94°, 15.71°, 17.80°, 20.60°, 23.85°, and 35.96°, corresponding to the (002), (101), (111), (020), (022), (122), and (026) crystal planes of the MOF structure, indicating excellent crystallinity. Notably, the XRD diffraction peak positions and intensities of NiCo-TZ(Fc) did not change significantly after the introduction of the Fc group. Clear, strong Bragg reflection spots were observed in both NiCo-TZ and NiCo-TZ(Fc), indicating their distinct single-crystal characteristics.

[0085] The synthesized NiCo-TZ compound was a fine purple powder, as shown in the scanning electron microscope (SEM) image. Figure 2 (ac) shows that the compound exhibits a rod-like morphology with a length range of approximately 4-12 μm. When some Cl in NiCo-TZ... - When substituted with -Ph (phenyl) or -Fc (ferrocene), it retains its rod-like morphology, but its size is reduced. Figure 2 ej).

[0086] Selected area electron diffraction (SAED) patterns of NiCo-TZ and NiCo-TZ(Fc) are consistent with simulation results along the zone axis of the crystal structure

[110] . Figure 3 Furthermore, the observed color changes may be attributed to alterations in the local coordination environment of the metal. Elemental mapping analysis using transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDS) showed that Fe, Ni, Co, Cl, C, N, and O elements were uniformly distributed in the NiCo-TZ(Fc) hexagonal prism structure; and the ratio of metallic M to Cl in the NiCo-TZ(Fc) material was approximately 5.46:1, with an Fe content of 1.92%. Figure 4 ).

[0087] Furthermore, NiCo-TZ and Cl- substituted with ferrocene or phenyl groups are also included. - and OH -The modified materials NiCo-TZ(Ph) and NiCo-TZ(Fc) were characterized by Fourier transform infrared (FT-IR) and Raman spectroscopy. Raman spectroscopy results showed that the characteristic Raman peaks of NiCo-TZ(Fc) / NiCo-TZ(Ph) were not significantly different from those of NiCo-TZ. Figure 6 However, in the FT-IR spectrum, compared to NiCo-TZ, NiCo-TZ(Fc) shows better performance in the 456-525 cm⁻¹ range. -1 756.0cm -1 844.6cm -1 996.7cm -1 and 3090cm -1 New characteristic vibrational peaks appeared at this location, and these peaks were attributed to the vibrational peaks of the ferrocene group. Figure 5 Notably, the characteristic -CHO peak was not observed in NiCo-TZ(Fc), indicating that in the reaction involving ferrocene formaldehyde, some metal-chlorine coordination in the material has been transformed into metal-oxygen coordination. X-ray photoelectron spectroscopy (XPS) analysis showed that Ni, Co, Cl, C, and O elements were present in both NiCo-TZ and NiCo-TZ(Fc) samples, and NiCo-TZ(Fc) additionally contained Fe element. Figure 7 Subsequently, valence band spectroscopy (VB-XPS) based on X-ray photoelectron spectroscopy was used to study the delocalization of the frontier orbit and the Fermi level (E) before and after the introduction of ferrocene. F The density of states (DOS) changes in occupied and unoccupied states near the occupied state. Figure 8 As can be seen, the occupied states in the valence band (VB) shift towards the Fermi level. Compared to NiCo-TZ (binding energy 2.12 eV), the valence band of NiCo-TZ(Fc) (binding energy 1.11 eV) shifts towards lower binding energies, indicating that the introduction of Fc can effectively change the electronic structure. Figure 8 ).

[0088] To gain a deeper understanding of the fine structure and chemical state of the synthesized NiCo-TZ and NiCo-TZ(Fc), X-ray absorption spectroscopy (XAS) was used to measure the K-edge of Co and Ni, including X-ray absorption near-edge structure (XANES) analysis and extended X-ray absorption fine structure (EXAFS) analysis. Figure 9As shown in Figure a, the XANES spectra of NiCo-TZ and NiCo-TZ(Fc) are similar to those of Ni(OH)₂, indicating that nickel ions remain in a divalent state. The leading-edge peak observed at approximately 8333 eV corresponds to the 1s→3d transition of Ni, indicating a distortion of the symmetry at the central nickel site. Based on linear fitting of the nickel K-edge transition energy (at the 50% level) in the XANES of NiCo-TZ, NiCo-TZ(Fc), and nickel reference samples including nickel oxide and nickel foil, the oxidation states of nickel in NiCo-TZ and NiCo-TZ(Fc) are estimated to be +1.81 and +1.92, respectively. In R space, the nickel K-edge EXAFS spectrum (k... 2 The weighted Fourier transform (FT) reveals the existence of a... The first shell is centered on the first shell, while the first shell of NiCo-TZ(Fc) is located at approximately... place ( Figure 9 b). Compared to NiCo-TZ, the shift in the main peak of NiCo-TZ(Fc) is due to the partial substitution of chloride ions (Cl-) by ferrocene structural units. - This leads to an increase in the Ni-N bond length. After specific modification with the auxiliary ligand ferrocene formaldehyde (Fc-CHO), significant differences in Co K-edge XAS spectra were observed in both k-space and R-space. Figure 10 The modified Ni K-edge XAS spectrum did not show significant changes in k-space. Figure 10 In a, compared to NiCo-TZ, NiCo-TZ(Fc) exhibits a higher leading-edge peak intensity, indicating a decrease in the symmetry of cobalt sites due to local spatial distortion caused by edges and pores. These findings suggest that targeted modification with Fc-CHO significantly alters the local structure of cobalt at the active sites.

[0089] To further verify this conclusion, theoretical simulations were performed on NiCo-TZ and NiCo-TZ(Fc) catalysts based on optimized structural models derived from density functional theory (DFT) calculations, in order to reproduce their corresponding extended X-ray absorption fine structure (EXAFS) spectra. Figure 11-13 The results showed that, In the theoretically simulated EXAFS spectrum (where nickel occupies octahedral sites and cobalt occupies tetrahedral sites), the fingerprint features of the leading edge and edge structures are in high agreement with the experimental spectra. Figure 11 and Figure 12 However, after targeted modification with ferrocene (Fc) groups, the experimentally obtained Co K-edge spectra were different from those obtained from other experiments. The theoretical simulation results showed significant deviations, while the Ni K-edge spectrum remained essentially unchanged. Subsequently, a theoretical model of NiCo-TZ(Fc) was constructed, which showed that the simulated EXAFS spectrum of tetrahedral coordinated Co(TZ)3Cl(Fc) was highly consistent with the experimental spectrum. These findings indicate that NiCo-TZ and NiCo-TZ(Fc) primarily possess two different active center coordination environments: octahedral coordinated Ni(TZ)6 and tetrahedral coordinated Co(TZ)3Cl. Based on the structural model derived from DFT simulations, we fitted the EXAFS spectra of Co K-edge and Ni K-edge structures, and the results showed a good fit.

[0090] The prepared electrocatalyst was loaded onto nickel foam as the working electrode, and its oxygen evolution reaction performance was evaluated in a 1.0 mol / L KOH electrolyte. Linear sweep voltammetry (LSV) curves showed that NiCo-TZ(Fc) exhibited good performance in the oxygen evolution reaction at 10 mA cm⁻¹. -2 The overpotential at the given current density is 213.8 mV. Figure 14 a) This is significantly lower than that of NiCo-TZ(Ph), NiCo-TZ, and commercially available iridium dioxide. Furthermore, NiCo-TZ(Fc) achieves an overpotential of only 353.7 mV to 500 mA cm⁻¹. -2 High current density. NiCo-TZ(Fc) has a lower Tafel slope of 66.7 mV dec. -1 This indicates that its OER reaction kinetics are faster ( Figure 14 b). Based on the electrochemical impedance spectroscopy results, the charge transfer resistance (R) of NiCo-TZ(Fc) is... ct The impedance is 0.86 Ω, significantly lower than that of NiCo-TZ(Ph) (1.5 Ω) and NiCo-TZ (13.7 Ω). Furthermore, NiCo-TZ(Fc) achieves a transition frequency (TOF) of 1.47 s at an overpotential of 350 mV. -1 It is 8 times that of NiCo-TZ, and even surpasses the performance of benchmark noble metal catalysts (18.3 times that of IrO2). Figure 15 Therefore, the reaction trend indicates that NiCo-TZ(Fc) has the best OER performance.

[0091] In the electrocatalytic process of the oxygen evolution reaction, the typical phase transition process from metal-organic frameworks (MOFs) to metal hydroxyl oxides (MOOHs) was observed using in-situ Raman spectroscopy. Figure 17 and 18 In air and in 1.0 mol / L KOH electrolyte, without applied voltage, NiCo-TZ and NiCo-TZ(Fc) at 167.4 cm⁻¹ -1 196.5cm -1 278.6cm-1 316.8cm -1 1168.9cm -1 and 1293.6cm -1 Multiple characteristic Raman peaks of MOF structures were observed. After applying voltage, the characteristic peaks of NiCo-TZ did not change significantly; when the voltage was further increased to 2.44V vs. RHE, the characteristic peaks of NiCo-TZ and NiCo-TZ(Ph) remained significant, and no new significant peaks were observed during this period. Figure 17 and 18 In comparison, such as Figure 17 As shown in b, at a potential of 1.44 V vs. RHE, NiCo-TZ(Fc) exhibits two characteristic peaks (472 cm⁻¹) corresponding to nickel hydroxyl oxide. -1 :δ(Ni III -O) and 552cm -1 :ν(Ni III Subsequently, when the voltage was increased to 1.64V relative to the reversible hydrogen electrode vs. RHE, the structural characteristic peaks of NiCo-TZ(Fc) weakened, while the characteristic peaks of hydroxyl oxides gradually strengthened.

[0092] Furthermore, we compared the reconstruction behavior of NiCo-TZ(Ph) and NiCo-TZ(Fc) to analyze the influence of ligand modification on reconstruction kinetics. In-situ Raman spectroscopy results showed that NiCo-TZ(Ph) required 30 minutes of reaction at 1.64 V vs. RHE to generate the characteristic peak of NiOOH, while NiCo-TZ(Fc) completed reconstruction in only 5 minutes at the same potential, and no significant structural changes were detected in the ferrocene (Fc) group. Figure 19-21 To elucidate the active sites (tetrahedral T) in MOFs. d With octahedron O h The spatial selectivity of the reconstruction was investigated using in-situ Raman spectroscopy at 1.64 V vs. RHE, to track the dynamic reconstruction process at different time points. Figure 19-21 Containing only Co and simultaneously possessing O. h and T d Co-TZ in a coordinated environment served as a control. After continuous operation at 1.64V vs. RHE for 30 minutes, its MOF characteristic peak disappeared, accompanied by a Co-reconstructed species characteristic peak (494.2 cm⁻¹). -1 601.8cm -1 and 689.1cm -1 The presence of (19a) indicates that Co-TZ has undergone reconstruction. However, X-ray absorption spectroscopy (XAS) analysis in the bimetallic NiCo-TZ node confirms that Ni... 2+ Occupy Oh The site forms a rigid framework, while Co 2+ Then selectively occupy T d Site. Notably, in the bimetallic node NiCo-TZ The introduction of the chain significantly altered the reconstruction pathway: at the same potential, a reaction time of up to 60 minutes was required before the characteristic peak of NiOOH (472 cm⁻¹) could be observed. -1 :δ(Ni III -O) and 552cm -1 :ν(Ni III -O)), and no characteristic peaks were found that were the same as those in the Co-TZ reconstruction. This comparison indicates that O h The site, due to its unique electronic structure, dominates the dynamic reconstruction process. Notably, under the same reaction time, the NiOOH signal intensity of NiCo-TZ(Fc) is 33.4 times higher than that of the original NiCo-TZ, highlighting the role of ferrocene functionalization in accelerating the O2O2 reaction. h It plays a key role in site reconstruction and enhancing catalytic activity.

[0093] In addition, in-situ electrochemical impedance spectroscopy (EIS) and Raman spectroscopy were used to monitor the reaction kinetics at the interface during the OER process in real time. Figure 22 Bode plots of the two samples show that NiCo-TZ(Fc) exhibits a faster transition rate (marked by arrows in the figure). As the potential increases, the Bode plot shifts towards the lower frequency region, indicating an electro-oxidation reaction. Upon further increasing the potential, the shoulder peak shifts towards the higher frequency region, and the phase angle decreases, which is related to the redox reaction at the electrode / electrolyte interface. Compared to NiCo-TZ, NiCo-TZ(Fc) has a lower potential and a faster phase angle change, indicating a superior reaction kinetic rate after activation.

[0094] To further investigate the stability of the NiCo-TZ(Fc) catalyst, chronopotential bonding (CP) tests were performed. Figure 23 As shown, at 100mA cm -2 At current densities as high as 1,000 mA cm⁻¹, the potential of NiCo-TZ(Fc) remained almost constant for over 1800 hours, demonstrating excellent long-term oxygen evolution reaction stability. Notably, even at current densities as high as 1,000 mA cm⁻¹, the potential remained almost constant. -2 At current densities of [specific values], the catalyst maintains stability for over 200 hours, highlighting its reliability in practical applications. This stability stems from the rigid O [structure / structure]. h Site framework and electronic modulation T d Synergistic effects between sites.

[0095] The above-described embodiments merely illustrate preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. The technical features of the embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, but any combinations that do not contradict each other should be considered within the scope of this specification. For those skilled in the art, several modifications and variations can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the claims.

Claims

1. A method for synthesizing metal-organic framework catalysts containing metal nodes with different coordination modes, characterized in that... Includes the following steps: S1, the triazole organic ligand L is subjected to a hydrothermal reaction with metal source reagents M1 and M2 to obtain... The parent frame has the structure shown in formula (I), including the octahedron shown in formula (II). The site and the tetrahedron shown in formula (III) Site, M1 metal node occupies octahedron At the site center, the M2 metal node occupies a tetrahedron. Site center: S2, using aldehyde-assisted modified ligand H for directional coordination to replace the tetrahedron. M2-Cl at the site forms M2-O, thus obtaining the metal-organic framework catalyst containing metal nodes with different coordination modes.

2. The synthesis method according to claim 1, characterized in that: The triazole organic ligand L is any one or more of 1,2,4-triazole, 3-amino-1,2,4-triazole, 3-bromo-1,2,4-triazole, 3-amino-1,2,4-triazole, 3-nitro-1,2,4-triazole, 3-methyl-1,2,4-triazole, 3-cyano-1,2,4-triazole, 3,5-dimethyl-1,2,4-triazole, 3-bromo-4H-1,2,4-triazole, 1H-1,2,4-triazole-3-thiol, 3,5-diamino-1,2,4-triazole, and 1H-1,2,4-triazole-3-thiol.

3. The synthesis method according to claim 2, characterized in that: The triazole organic ligand L is 1,2,4-triazole.

4. The synthesis method according to claim 1, characterized in that: The aldehyde-assisted ligand H is ferrocene formaldehyde or benzaldehyde, which directionally coordinates to substitute the tetrahedral M2. Td M2-Cl at the site subsequently forms the structure shown in formula (Ⅳ) or formula (Ⅴ):

5. The synthesis method according to claim 1, characterized in that: The M1 metal source reagent is one or more of Ni salt and Co salt, and the M2 metal source reagent is a Co salt.

6. The synthesis method according to claim 5, characterized in that: The M1 metal source reagent is one or more of CoCl2·6H2O and NiCl2·6H2O, and the M2 metal source reagent is CoCl2·6H2O.

7. The synthesis method according to claim 1, characterized in that... Step S1 includes: S11, dissolve the triazole organic ligand L in water to obtain a mixed solution A; S12, add metal source reagents M1 and M2 to water, and after dissolving, obtain mixed solution B; S13, Mix solution A and solution B to obtain solution C; S14, the mixed solution C is hydrothermally reacted at a temperature of 170-190℃ for 20-72h, and the product is subjected to solid-liquid separation, washing and drying to obtain a powdered parent framework F.

8. The synthesis method according to claim 7, characterized in that... Step S2 includes: S21, the obtained parent framework F is dispersed in a mixed solution of water and ethanol to obtain a mixed solution D; S22, aldehyde-assisted ligand H was gradually added to the mixed solution D, and the pH was adjusted to 10-12 with potassium hydroxide; S23, the mixed solution obtained in step S22 is subjected to hydrothermal reaction at a temperature of 50-70℃ for 10-24h, and the product is subjected to solid-liquid separation, washing and drying.

9. A metal-organic framework catalyst containing metal nodes with different coordination modes, characterized in that: The metal-organic framework catalyst is obtained by the synthesis method described in any one of claims 1-8.

10. The application of the metal-organic framework catalyst of claim 9 in the oxygen evolution reaction of water electrolysis.

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