Metal-organic framework-based oxygen evolution catalysts, methods of synthesis and use thereof

Abstract

The application discloses an oxygen evolution catalyst based on a metal organic framework as well as a synthesis method and application thereof. The oxygen evolution catalyst disclosed by the application comprises a metal organic framework and a pore structure modification unit inserted into the metal organic framework, the metal organic framework is formed by combination and coordination connection of a binary carboxylic acid-containing organic ligand A and a metal source reagent M1, and the pore structure modification unit is formed by combination and coordination connection of a triazole organic ligand B and a metal source reagent M2; wherein the binary carboxylic acid-containing organic ligand A is one or more of compounds shown in formula (I), and the triazole organic ligand B is one or more of compounds shown in formula (II).

Description

TECHNICAL FIELD

[0001] The present application relates to a metal-organic framework (MOF)-based oxygen evolution catalyst, a synthesis method thereof and an application thereof in an electrolytic water oxygen evolution reaction. BACKGROUND

[0002] Electrochemical water splitting is an effective way to produce high-purity hydrogen. However, in the anodic half-reaction, due to the multi-step proton / electron coupling, the oxygen evolution reaction (OER) requires a larger overpotential than the cathodic hydrogen evolution reaction (HER), which hinders the efficient conversion of energy. Among them, noble metal catalysts such as Ru and Ir oxides can significantly reduce the overpotential of OER, but their expensive price and scarce reserves seriously limit their large-scale industrial application. In contrast, MOFs materials are considered as a promising OER catalyst due to their structural flexibility and tunability. However, MOFs materials are usually prone to structural transformation in OER reactions, which makes it very challenging to accurately study the structure-property relationship.

[0003] Dynamic restructuring refers to the structural changes that occur on the surface of catalysts or materials. In catalytic reactions, dynamic restructuring can cause changes in the activity and selectivity of the catalyst, thereby affecting the efficiency and product distribution of the reaction. Dynamic restructuring usually occurs under high temperature, high pressure or specific reaction conditions, involving processes such as adsorption, dissociation, diffusion and recombination. These processes can cause surface atoms to rearrange, forming new crystal structures or surface phases. The mechanism and process of dynamic restructuring depend on factors such as the composition, morphology of the catalyst and reaction conditions. Dynamic restructuring has important effects on catalytic reactions. First, it can change the active site distribution and surface energy of the catalyst, thereby regulating the rate and selectivity of the reaction. Second, dynamic restructuring can change the interaction between the catalyst and the reactants, affecting the rate and energy barrier of adsorption, dissociation and diffusion, etc. In addition, dynamic restructuring can also regulate the stability and lifetime of the catalyst. Therefore, understanding and controlling dynamic restructuring is crucial for designing efficient catalysts and optimizing catalytic reactions.

[0004] In order to overcome the current development bottleneck of electrochemical performance, it is still urgent to effectively utilize the restructuring behavior of MOFs, optimize the catalyst structure design and realize the precise synthesis of high-efficiency catalysts. The present application aims to analyze the structural evolution and in-situ self-restructuring mechanism of MOFs to improve their intrinsic activity, and establish the relationship between the structural change mechanism of MOFs and the structure and performance in the OER process. This will provide specific guidance for structural regulation, thereby improving the performance and stability of the catalyst. SUMMARY

[0005] The application aims to reveal the structure-activity relationship of the catalyst surface through in-situ characterization by a dynamic reconstruction mechanism and kinetic process, so as to obtain an efficient electrocatalytic oxygen evolution catalyst. Meanwhile, the composition and coordination environment of the catalyst are regulated to control the surface reconstruction and optimize the efficiency and selectivity of the catalytic reaction.

[0006] The first aspect of the application discloses a metal organic framework-based oxygen evolution catalyst, which comprises a metal organic framework and a pore structure modification unit inserted into the metal organic framework, the metal organic framework is formed by coordination connection of a binary carboxylic acid-containing organic ligand A and a metal source reagent M1, and the pore structure modification unit is formed by coordination connection of a triazole organic ligand B and a metal source reagent M2; wherein the binary carboxylic acid-containing organic ligand A is one or more of the compounds shown in formula (I), and the triazole organic ligand B is one or more of the compounds shown in formula (II):

[0007]

[0008] wherein:

[0009] In formula (I), the combination of R1 / R2 / R3 / R4 is A1: H / H / H / H; A2: OH / H / H / H, A3: SH / H / H / H, A4: NH2 / H / H / H, A5: NO2 / H / H / H, A6: Br / H / Br / H, A7: OH / H / OH / H, A8: Cl / H / Cl / H, A9: F / F / F / F, A10: NHCHO / H / H / H, A11: Cl / H / H / H, A12: Br / H / H / H, A13: NH2 / H / NH2 / H, A14: Br / H / H / H or A15: Cl / H / H / H;

[0010] In formula (II), the combination of R5 / R6 is B1: H / H, B2: H / NH2, B3: H / NO2, B4: H / SH, B5: SH / CH3, B6: SH / NH2, B7: H / CH3, B8: H / CF3, B9: H / Br, B10: H / CN, B11: CH3 / CH3 or B12: NH2 / NH2.

[0011] In the application, M1 is a combination of metals or different metal ions capable of forming a trimer, and M2 is a combination of metals or different metal ions capable of forming a triazole dimer, [(M1)3O(A)3] formed by coordination connection of the binary carboxylic acid-containing organic ligand A and the metal source reagent M1 is a MIL-88B network MOF structure, and the triazole is a pore spacer ligand, and the pore structure modification unit [(M2)2(B)3X6] (X = H2O or Cl -) is a triazolate dimer network MOF structure, [(M2)2(B)3X6] is inserted into the MIL-88B network MOF structure. The metal source reagent M1 and the metal source reagent M2 can be the same or different.

[0012] Further, the metal source reagent M1 is a Fe salt, and the metal source reagent M2 is one or more of a Fe salt, a Fe salt, a Ni salt, a Co salt and a Mn salt.

[0013] Further, the metal source reagent M1 is FeCl3, and the metal source reagent M2 is one or more of FeCl2, FeCl3, Fe(NO3)2, Ni(NO3)2, Mn(OAc)2 and Co(OAc)2.

[0014] Further, the binary carboxylic acid-containing organic ligand A is 2-hydroxyterephthalic acid, and the triazolate organic ligand B is 1,2,4-triazolate or 3-amino-5-mercapto-1,2,4-triazolate.

[0015] The second aspect of the present application discloses a synthesis method of the aforementioned oxygen evolution catalyst, comprising the following steps:

[0016] Step (1): adding a binary carboxylic acid-containing organic ligand A, a triazolate organic ligand B, a metal source reagent M1 and a metal source reagent M2 into an organic solvent S to obtain a mixed solution a after dissolution;

[0017] Step (2): adding a synthesis reaction reagent Q into the mixed solution a to obtain a mixed solution b;

[0018] Step (3): hydrothermally reacting the mixed solution b at a temperature of 140-160°C for 24-72h, and then performing solid-liquid separation, washing and drying on the product.

[0019] Further, the mass ratio of the binary carboxylic acid-containing organic ligand A to the triazolate organic ligand B in step (1) is 1:1-1.2, and more preferably 1:1.

[0020] Further, the organic solvent S is N,N-dimethylformamide, and the amount of the organic solvent S is 10-15 times, and more preferably 15 times, the total mass of the binary carboxylic acid-containing organic ligand A and the triazolate-containing organic ligand B.

[0021] Further, the synthesis reaction reagent Q in step (2) is trifluoroacetic acid, and the mass ratio of the synthesis reaction reagent Q to the binary carboxylic acid-containing organic ligand A and the triazolate organic ligand B is A+B:Q=1:1.2-1.9.

[0022] Further, the synthesis method further comprises the following step (4): preparing a working electrode with the metal organic framework powder material obtained in step (3), and performing cyclic voltammetry in an alkaline environment to dynamically reconfigure the metal organic framework material. In the three-electrode system, a platinum sheet is used as a counter electrode, and mercury / mercury oxide is used as a reference electrode; the cyclic voltammetry (CV) is performed in a 1.0 mol / L potassium hydroxide solution under a voltage of 1.1-1.6 V vs. RHE.

[0023] Further, in step (3), an electrically conductive substrate can be added to the hydrothermal reaction container (for example, a Teflon stainless steel reaction container), so that the synthesized metal organic framework powder material is loaded / attached to the electrically conductive substrate to directly form an electrode. The electrically conductive substrate can be a nickel foam, carbon fiber paper, or a copper sheet, and the nickel foam is preferred.

[0024] The third aspect of the present application discloses the use of the aforementioned oxygen evolution catalyst in an electrolytic water oxygen evolution reaction.

[0025] Compared with the prior art, the technical scheme of the present application has the following advantages:

[0026] The oxygen evolution catalyst of the present application has a new framework structure of [(M1)3O(A)3][(M2)2(B)3X6], which includes a [(M1)3O(A)3] metal organic framework and a pore structure modification unit [(M2)2(B)3X6] inserted into the metal organic framework. The introduction of the pore structure modification unit [(M2)2(B)3X6] can stabilize the structure of the [(M1)3O(A)3] metal organic framework, and the [(M1)3O(A)3][(M2)2(B)3X6] with the new framework structure can form oxygen vacancy-rich, bond length-extended, and active site-adaptive under alkaline and applied voltage conditions to efficiently catalyze oxygen evolution, so that the catalyst undergoes reasonable dynamic reconfiguration, which affects its kinetic behavior and ensures long-term high-activity industrial stability, exceeding the catalytic activity and industrial stability of most reported anode catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Middle: a, b and c are XRD patterns of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6], respectively, d, e and f are XRD patterns of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after being placed in water for 1 day, respectively;

[0028] Figure 2a is [Fe3O(A2)3][Ni2(B1)3X6] and its FT-IR spectrum after being placed in water environment for 1 day, b is [Fe3O(A2)3] and its FT-IR spectrum after being placed in water environment for 1 day;

[0029] Figure 3 are N2 adsorption-desorption isotherms of [Fe3O(A2)3][Ni2(B1)3X6] and [Fe3O(A2)3];

[0030] Figure 4 a, b and c are SEM images of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6], respectively;

[0031] Figure 5 a and b are TEM and HRTEM images of [Fe3O(A2)3][Ni2(B1)3X6], respectively;

[0032] Figure 6 are Fe 2p XPS fine spectra of [Fe3O(A2)3][Ni2(B1)3X6] and [Fe3O(A2)3];

[0033] Figure 7 is Ni 2p XPS fine spectrum of [Fe3O(A2)3][Ni2(B1)3X6];

[0034] Figure 8 a are C1s XPS fine spectra of [Fe3O(A2)3][Ni2(B1)3X6] and [Fe3O(A2)3], b are O 1s XPS fine spectra of the two;

[0035] Figure 9 are VB-XPS fine spectra of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6];

[0036] Figure 10 are initial time electrocatalytic oxygen evolution performance diagrams of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6];

[0037] Figure 11Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively;

[0038] Figure 12 Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively;

[0039] Figure 13 Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively;

[0040] Figure 14 Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively;

[0041] Figure 15 Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively;

[0042] Figure 16 Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively;

[0043] Figure 17 Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively;

[0044] Figure 18 Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively;

[0045] Figure 19 Fig. 1 is a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] and a Raman spectrum of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] after 1M KOH treatment, wherein a and b are in-situ Raman spectra of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] for electrocatalytic oxygen evolution, respectively. DETAILED DESCRIPTION

[0046] The specific embodiments of the present application will be further described below. It should be noted that the description of the embodiments is used to help understand the present application, but does not constitute a limitation on the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0047] The materials, reagents and the like used in the following examples, such as the dicarboxylic acid-containing organic ligand A, the triazole organic ligand B, the metal source reagent M1, the metal source reagent M2, the solvent, the synthetic reaction reagent and the like used in the synthesis process are all commercially available products, and can be obtained from commercial channels if no special instructions are given.

[0048] The experimental methods used in the following implementation methods are conventional experimental methods if no special instructions are given.

[0049] The terms used in the following implementation methods and examples generally have the meanings commonly understood by those of ordinary skill in the art unless otherwise specified.

[0050] According to the method of rational design, the MIL-88B framework [M13O(A)3] is synthesized by using dicarboxylic acid containing various functional groups as ligand combined with metal. In order to realize high OER activity, the pore space separation strategy is adopted based on the MIL-88B framework as the parent structure, which involves inserting C3 symmetric triazole clusters into the MIL-88B type structure, and introducing high density metal site centers at the same time, so as to construct a new type of framework, named [M13O(A2)3][M22(B1)3X6]. In the MIL-88B framework, M1 is a metal or a combination of different metal ions capable of forming a trimer. In the triazole dimer, M2 is a metal or a combination of metals capable of forming a triazole dimer, and the triazole is a pore spacer ligand.

[0051] In the examples of the present application, A is one or more of the dicarboxylic acid-containing organic ligands represented by the following formula (I), and B is one or more of the triazole organic ligands represented by the following formula (II):

[0052]

[0053] In which:

[0054] In formula (I), the combination of R1 / R2 / R3 / R4 is A1: H / H / H / H; A2: OH / H / H / H, A3: SH / H / H / H, A4: NH2 / H / H / H, A5: NO2 / H / H / H, A6: Br / H / Br / H, A7: OH / H / OH / H, A8: Cl / H / Cl / H, A9: F / F / F / F, A10: NHCHO / H / H / H, A11: Cl / H / H / H, A12: Br / H / H / H, A13: NH2 / H / NH2 / H, A14: Br / H / H / H or A15: Cl / H / H / H;

[0055] The combination of R5 / R6 in formula (II) is B1: H / H, B2: H / NH2, B3: H / NO2, B4: H / SH, B5: SH / CH3, B6: SH / NH2, B7: H / CH3, B8: H / CF3, B9: H / Br, B10: H / CN, B11: CH3 / CH3, or B12: NH2 / NH2.

[0056] In the embodiments of the present application, the metal source reagent M1 and the metal source reagent M2 can be the same or different, and the actual amount used can be determined on the basis of the theoretical amount, and is preferably equal to or slightly greater than the theoretical amount. Hereinafter, the embodiments and comparative examples are described in detail.

[0057] Example 1

[0058] Synthesis of pore structure unit modified metal organic framework material [Fe3O(A2)3][Fe2(B1)3X6]

[0059] In a Teflon stainless steel reaction vessel, FeCl3·6H2O (411.3 mg, ~1.5 mmol), 2-hydroxyterephthalic acid (169.8 mg, ~0.9 mmol, A2 in formula (I)) and 1,2,4-triazole (62.2 mg, ~0.9 mmol) were first ultrasonically dissolved in 3.0 g of N,N-dimethylformamide (DMF), and then 320 mg of trifluoroacetic acid (TFA) was added. After magnetic stirring for 2 h, nickel foam (NF) was added as a conductive substrate, the Teflon stainless steel reaction vessel was sealed in a stainless steel autoclave, and placed in an oven at 150°C for 24 h. After cooling to room temperature, the solid-liquid separation was performed, and the synthesized [Fe3O(A2)3][Fe2(B1)3X6] was repeatedly washed with DMF and dried at 55°C for 12 hours.

[0060] Example 2

[0061] Synthesis of pore structure unit modified metal organic framework material [Fe3O(A2)3][Ni2(B1)3X6]

[0062] In a Teflon stainless steel reaction vessel, FeCl3-6H2O (251.5 mg, ~0.9 mmol), Ni(NO3)2-6H2O (204.8 mg, ~0.7 mmol), 2-hydroxyterephthalic acid (169.8 mg, ~0.9 mmol), and 1,2,4-triazole (62.2 mg, ~0.9 mmol) were ultrasonically dissolved in 3.0 g of N,N-dimethylformamide (DMF) and then 320 mg of trifluoroacetic acid (TFA) was added. After magnetic stirring for 2 h, nickel foam (NF) was added as a conductive substrate, and the Teflon stainless steel reaction vessel was sealed in a stainless steel autoclave and heated in an oven at 150 °C for 24 h. After cooling to room temperature, the solid-liquid separation was performed, and the synthesized [Fe3O(A2)3][Ni2(B1)3X6] was repeatedly washed with DMF and then dried at 55 °C for 12 h.

[0063] Example 3

[0064] Synthesis of metal-organic framework material [Fe3O(A)3][Ni2(B)3X6] modified with different special functional pore structure units

[0065] In a Teflon stainless steel reaction vessel, FeCl3-6H2O (251.5 mg, ~0.9 mmol), Ni(NO3)2-6H2O (204.8 mg, ~0.7 mmol), 0.9 mmol of one of the functional group-containing structures in the organic ligand (I) (terephthalic acid, 2-hydroxyterephthalic acid, 2-mercapto-terephthalic acid, 2-bromo-terephthalic acid, 2-chloro-terephthalic acid, 2-amino-terephthalic acid, 2-nitro-terephthalic acid, 2,5-dibromo-terephthalic acid, 2,5-dichloro-terephthalic acid, 2,5-dihydroxy-terephthalic acid, tetrafluoro-terephthalic acid, 2-formamido-terephthalic acid, or 2,5-diamino-terephthalic acid), and 0.9 mmol of one of the functional group-containing structures in the organic ligand (II) (1,2,4-triazole, 3-bromo-1,2,4-triazole, 3-amino-1,2,4-triazole, 3-nitro-1,2,4-triazole, 3-methyl-1,3,4-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, or 3,5-diamino-1,2,4-triazole) were ultrasonically dissolved in 3.0 g of N,N-dimethylformamide (DMF), and then 300 mg of trifluoroacetic acid (TFA) was added. After magnetic stirring for 2 h, a nickel foam (NF) was added as a conductive substrate, the Teflon stainless steel reaction vessel was sealed in a stainless steel autoclave, and heating was performed at 150°C for 24 h in an oven. After cooling to room temperature, solid-liquid separation was performed, and the synthesized [Fe3O(A)3][Ni2(B)3X6] was repeatedly washed with DMF and dried at 55°C for 12 h.

[0066] As a variation of the foregoing embodiment, a conductive substrate can not be added during synthesis, and the metal organic framework powder material is loaded onto a conductive substrate after synthesis. The conductive substrate can be nickel foam, carbon fiber paper, or a copper sheet, and is preferably nickel foam.

[0067] Comparative Example 1

[0068] Synthesis of metal organic framework material [Fe3O(A2)3]

[0069] In a Teflon-stainless steel reaction vessel, FeCl3-6H2O (251.5 mg, ~0.9 mmol) and 2-hydroxyterephthalic acid (169.8 mg, ~0.9 mmol) were first dissolved in 3.0 g of N,N-dimethylformamide (DMF) under sonication, followed by the addition of 320 mg of trifluoroacetic acid (TFA). After 2 h of magnetic stirring, foamed nickel (NF) was introduced as a conductive substrate, and the Teflon was sealed in a stainless steel autoclave, which was placed in an oven at 150 °C for 24 h. After cooling to room temperature, the synthesized [Fe3O(A2)3] was repeatedly washed with DMF and dried at 55 °C for 12 h.

[0070] Comparative Example 2

[0071] Synthesis of γ-NiFeOOH: 2 mmol of Ni(NO3)2-6H2O and 2 mmol of Fe(NO3)3-9H2O were dissolved in 45 mL of dimethylformamide (DMF). Then 0.9 mmol of NaOH in 6 mL of aqueous solution was added dropwise. After stirring at room temperature for 30 min, it was immersed in the homogeneous solution and heated at 120 °C for 6.5 h in a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. After cooling to room temperature, it was washed three times with deionized water and ethanol, and then dried at 80 °C to obtain γ-NiFeOOH.

[0072] Comparative Example 3

[0073] Synthesis of γ-FeOOH: 4 mmol of Fe(NO3)3-9H2O was dissolved in 45 mL of dimethylformamide (DMF). Then 0.9 mmol of NaOH in 6 mL of aqueous solution was added dropwise. After stirring at room temperature for 30 min, it was immersed in the homogeneous solution and heated at 120 °C for 6.5 h in a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. After cooling to room temperature, it was washed three times with deionized water and ethanol, and then dried at 80 °C to obtain γ-FeOOH.

[0074] Comparative Example 4

[0075] Synthesis of β-FeOOH: 1.350 g of FeCl3-6H2O was dissolved in 10 mL of deionized water, stirred for 10 min, and then the mixed solution was transferred to a 20 mL polytetrafluoroethylene-lined stainless steel autoclave and kept at 120 °C for 12 h. After the autoclave was naturally cooled, the product was collected by centrifugation, washed three times with deionized water and ethanol, and finally dried in a vacuum oven at room temperature for 6 h.

[0076] Comparative Example 5

[0077] Synthesis of β-FeOOH / Ni(OH)₂: 1.275 mmol of nickel nitrate hexahydrate and 3.75 mmol of urea were dissolved in 15 mL of deionized water, and 1 g of β-FeOOH was added. The solution was then transferred to a 20 mL PTFE-lined autoclave. The autoclave was heated to 100 °C and maintained for 3 hours. The resulting β-FeOOH / α-Ni(OH)₂ was washed several times with ethanol and deionized water, and then dried under vacuum at 60 °C overnight.

[0078] Structural characterization and performance testing of the materials in the examples and comparative examples

[0079] like Figure 1 As shown in a to 1c, the crystal phases of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6], and [Fe3O(A2)3][Ni2(B1)3X6] were studied by powder X-ray diffraction (PXRD). The experimental PXRD patterns of these metal-organic framework powders were consistent with the simulated diffraction patterns, indicating that the materials were successfully synthesized. Among them, the [Fe3O(A2)3] powder showed strong diffraction peaks at 7.34°, 8.84°, 10.05°, 12.45°, 16.08°, 16.84°, and 17.68°, which correspond to the (100), (101), (002), (102), (112), (103), and (202) crystal planes of the MIL-88B(Fe) structure (CCDC:2088535), respectively, indicating its excellent crystallinity. It is worth noting that, due to the insertion of [Ni2(B1)3X6] and [Fe2(B1)3X6] fragments into the MIL-88B(Fe) structure, the XRD diffraction peaks of [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] show significant differences in position and intensity compared to [Fe3O(A2)3].

[0080] To further verify the insertion of the [Ni2(B1)3X6] and [Fe2(B1)3X6] fragments (collectively referred to as the [M22(B1)3X6] fragment) into the MIL-88B(Fe) structure and to evaluate the extent of [M22(B1)3X6] fragment introduction and water stability, the synthesized powder sample was immersed in water and stirred for one day. Figure 1 As shown in Figure d, the newly formed XRD peaks of the [Fe3O(A2)3] sample after immersion in water for one day are at 9.16°, 9.46°, 10.7°, 16.6°, and 18.2°, which belong to the (002), (100), (101), (103), and (200) crystal planes (CCDC: 1485530) of MIL-88B(Fe) in H2O, respectively, further confirming the "breathing" effect of the crystal lattice. It is worth noting that, as Figure 1As shown in e and 1f, when the [M22(B1)3X6] fragment is inserted into the [Fe3O(A2)3] structure, the crystal no longer shows shrinkage, indicating that the [M22(B1)3X6] fragment has been successfully inserted into the [Fe3O(A2)3] structure, forming the [Fe3O(A2)3][M22(B1)3X6] structure.

[0081] In addition, such as Figure 2 As shown, no significant changes were observed in the Fourier transform infrared (FT-IR) spectra of the [Fe3O(A2)3] framework and the [M22(B1)3X6] modified [Fe3O(A2)3][M22(B1)3X6] before and after the water stability test, indicating that although the [Fe3O(A2)3] framework contracted, it maintained the same spatial coordination.

[0082] Figure 3 The N2 adsorption-desorption isotherm reveals that the BET specific surface area of ​​[Fe3O(A2)3][Ni2(B1)3X6] is 34.9 m². 2 / g, higher than the specific surface area of ​​[Fe3O(A2)3] (8.2m²). 2 Both metal-organic framework catalysts exhibited a distinct adsorption hysteresis loop, a typical feature of type III isotherms, indicating their microporous properties. The measured pore sizes of [Fe3O(A2)3][Ni2(B1)3X6] and [Fe3O(A2)3] were mainly concentrated at 0.68 nm and 1.59 nm, respectively, which is highly consistent with their crystal structures.

[0083] Furthermore, such as Figure 4 The morphology of the [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6], and [Fe3O(A2)3][Ni2(B1)3X6] samples was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). [Fe3O(A2)3] exhibited a uniform hexagonal bipyramidal morphology. Figure 4 a) The average diameter is approximately 3.5 μm, and the average length is approximately 9.5 μm. When the [Fe2(B2)3X6] fragment is inserted into the [Fe3O(A2)3] structure, the morphology remains hexagonal bipyramidal. Figure 4 (b) However, the average size is significantly reduced (average diameter is approximately 1.6 μm, average length is approximately 5.5 μm). In contrast, when the [Ni2(B2)3X6] fragment is inserted into the [Fe3O(A2)3] structure, the [[Fe3O(A2)3][Ni2(B1)3X6] crystal self-assembles into a hexagonal prism ( Figure 4 c).

[0084] Figure 5TEM images show that [Fe3O(A2)3][Ni2(B1)3X6] is a hexagonal prism with an average length of approximately 2.1 ± 0.5 μm and a thickness of approximately 220 nm, clearly visible in both TEM and high-resolution TEM (HRTEM) images. Elemental mapping by TEM and energy-dispersive X-ray spectroscopy (EDS) indicates that Fe, Ni, Cl, C, N, and O are uniformly distributed within the [Fe3O(A2)3][Ni2(B1)3X6] hexagonal prism, with a Fe:Ni ratio close to 1:1.

[0085] Furthermore, high-resolution Fe 2p X-ray photoelectron spectroscopy (XPS) analysis of the catalyst [Fe3O(A2)3][Ni2(B1)3X6] revealed that it could be decomposed into components representing Fe2P. 3+ Characteristic peaks of (712.2 and 725.6 eV) and their corresponding vibration satellite peaks (717.5 and 729.7 eV) Figure 6 Compared to [Fe3O(A2)3], the Fe 2p in [Fe3O(A2)3][Ni2(B1)3X6] shifts towards a lower binding energy direction (Fe 2p in [Fe3O(A2)3]...). 1 / 2 The valence value is 712.26 eV, while it is 712.04 eV in [Fe3O(A2)3][Ni2(B1)3X6], indicating a decrease in valence state, which is consistent with the XAS results. Figure 7 As shown, the Ni 2pXPS spectrum in the [Fe3O(A2)3][Ni2(B1)3X6] catalyst exhibits a double peak at 712.1 and 724.1 eV, which is attributed to Ni 2+ Compared to [Fe3O(A2)3], XPS analysis revealed the presence of N and Cl in the catalyst [Fe3O(A2)3][Ni2(B1)3X6], indicating the successful introduction of pore-modifying units. High-resolution C1s XPS spectroscopy also confirmed the composition of [Fe3O(A2)3][Ni2(B1)3X6]: the aromatic rings in these MOFs are C=C / CC (284.7 eV), CO / CN (286.4 eV), and carboxyl groups (C=O, 288.8 eV). Figure 8 ).

[0086] A comprehensive understanding of the Fermi level (E) of electrocatalysts F Information on occupied and unoccupied states near the [M22(B1)3X6] ion, including the hybridization of transition metal 3d and O2p, is crucial for elucidating the relationship between the electronic structure of a catalyst and its catalytic activity. Therefore, valence band XPS (VB-XPS) studies were conducted to investigate changes in the density of occupied and unoccupied states (DOS) near the Fermi level before and after the introduction of the [M22(B1)3X6] ion. Figure 9 ).fromFigure 9 It can be seen that the occupied states in the valence band after the introduction of [M22(B1)3X6] move towards the Fermi level. The valence band of [Fe3O(A2)3][Ni2(B1)3X6] (1.27 eV) moves to the low binding energy direction compared with pure [Fe3O(A2)3] (2.26 eV), indicating that the introduction of [Ni2(B1)3X6] effectively changes the electronic structure and promotes the charge transfer process in OER.

[0087] Figure 10 The initial electrocatalytic oxygen evolution performance of [Fe3O(A2)3], [Fe3O(A2)3][Fe2(B1)3X6] and [Fe3O(A2)3][Ni2(B1)3X6] is shown in the figure. In the initial cycle, the [Fe3O(A2)3][Ni2(B1)3X6] catalyst exhibits an overpotential of 226.8 mV and a Tafel slope of 49.8 mV / dec at a current density of 10 mA / cm 2 , which is lower than the overpotential and Tafel slope of [Fe3O(A2)3] (251.1 mV, 58.4 mV / dec), [Fe3O(A2)3][Fe2(B1)3X6] (234.7 mV, 53.2 mV / dec) and IrO2 (335.8 mV, 98.6 mV / dec) catalysts (Figures a and b in the Figure 10 ). The double-layer capacitance (C dl ) value of the [Fe3O(A2)3][Ni2(B1)3X6] catalyst is estimated to be 2.87 mF / cm 2 , which is slightly higher than that of the [Fe3O(A2)3] catalyst (2.19 mF / cm 2 ) (Figure c in the Figure 10 ). In addition, the turnover frequency (TOF) of the [Fe3O(A2)3][Ni2(B1)3X6] catalyst is as high as 0.633 s -1 under a constant overpotential of 300 mV, which is higher than that of several other catalysts (Figure d in the Figure 10 ).

[0088] In addition, in-situ electrochemical Raman spectroscopy was also studied to explore the active mechanism of metal-organic frameworks in the oxygen evolution reaction (OER). Before applying the oxidation potential, [Fe3O(A2)3] shows a Raman peak at 683.9 cm-1 in the electrolyte, which is attributed to the Fe-O vibration mode ( Figure 11 ). As Figure 12As shown in Figure 2a, in the in-situ Raman spectra of [Fe3O(A2)3], the characteristic peak of Fe-O disappeared when the initial voltage was applied; when the voltage was further increased to 1.24 V vs. RHE, two characteristic peaks at 669.2 cm-1and 493 cm-1appeared, which was related to FeOOH; when the voltage was further increased to 1.84 V vs. RHE, the characteristic peak at 669.2 cm-1moved significantly to a higher wavenumber, which was attributed to the change of Fe-O bond length.

[0089] As shown in Figure 2b, in the in-situ Raman spectra of [Fe3O(A2)3][Fe2(B1)3X6], after the voltage was applied, the characteristic peak at 683 cm-1moved slightly to a higher wavenumber (1.24 V vs. RHE), while the characteristic peak at 723 cm-1gradually decreased. When the voltage was further increased to 1.44 V vs. RHE, the characteristic peak at 723 cm-1moved to a lower wavenumber, which indicated that the [Fe2(B1)3X6] unit underwent a reconstruction process to form FeOOH. Figure 11 As shown in Figure 2c, in [Fe3O(A2)3][Ni2(B1)3X6] in electrolyte, two distinct characteristic Raman peaks at 531 cm-1and 683 cm-1were observed, which were attributed to the vibration modes of Ni-O and Fe-O, respectively.

[0090] Figure 12 As shown in Figure 2d, when the voltage was increased to 1.04 V vs. RHE, the intensity of the characteristic Fe-O peak decreased and moved to a higher wavenumber (686 cm-1). When the voltage was further increased to 1.24 V vs. RHE, the characteristic Fe-O peak moved to a lower wavenumber (674 cm-1), which indicated that the Fe center underwent a transformation to form FeOOH. When the voltage continued to increase to 1.74 V, the growth of a pair of new peaks at 475 cm-1(δ(Ni III-O )) and 551 cm-1(ν(Ni III-O )) was attributed to the e g bond vibration and A 1g stretching vibration bond of NiOOH, respectively, which indicated that the catalyst underwent structural reconstruction during the OER process. All the results indicated that the reconstruction rate of [Fe3O(A2)3] (Fe-O: carboxylate oxygen coordination) structural unit was faster than that of the inserted [M22(B1)3X6] unit (Fe / Ni-N coordinated by triazole), and the reconstruction rate of [Fe2(B1)3X6] unit was faster than that of [Ni2(B1)3X6] unit, finally forming FeOOH and NiOOH, respectively.

[0091] ​Raman and X-ray photoelectron spectroscopy (XPS) analyses show that MOF structures undergo reconstruction under the influence of electrolyte and potential operation, which involves phase transition, valence state, and valence band adjustment. To reveal the relationship between structural changes, dynamic behavior, and OER performance of MOF reconstruction in real time, the present invention performs continuous cyclic voltammetry (CV) cycles in the range of 1.1-1.6 V vs. RHE. The electrochemically active surface area (ECSA) and OER activity of [Fe3O(A2)3] and [Fe3O(A2)3][Ni2(B1)3X6] electrodes change with the number of CV cycles. Notably, the overpotential of [Fe3O(A2)3][Ni2(B1)3X6] reaches a minimum value at the 200th cycle, reaching 263.1 mV at 100 mA / cm 2 , which is 16.8 mV lower than that in the first cycle. Figure 13 ).

[0092] Due to the structural reconstruction of MOFs, as well as oxygen vacancies, bond length extension, and activation of oxygen on active sites, the energy barrier and kinetics of MOF catalytic reactions change significantly during the oxygen evolution reaction (OER), triggering changes in intrinsic OER activity. Compared with the synthesized FeOOH catalyst, the FeOOH species generated by MOF self-reconstruction exhibits better OER catalytic activity and lower time constant ( Figure 14 ) under the same conditions. In situ Raman analysis combined with X-ray absorption spectroscopy, electron paramagnetic resonance (EPR), and Raman data at different cycles shows that the [Fe3O(A2)3] coordination structure rapidly restructures to FeOOH during the OER process due to the presence of OH- and applied voltage. Compared with the M-N structure coordinated by nitrogen azoles, the Fe-O bond coordinated by carboxylic acid structures has a faster reconstruction speed. In addition, the reconstruction process of [M22(B1)3X6] is relatively slow. Initially, the water molecules and Cl- coordination in both complexes are affected by OH-, leading to changes in part of the coordination. In the [M22(B1)3X6] series, the Fe-N bond coordination of [Fe2(B1)3X6] eventually restructures faster than the Ni-N bond coordination of [Ni2(B1)3X6].

[0093] Dynamic behavior is one of the key factors affecting electrocatalytic stability. As can be seen in Figure 15 , the potential remains stable for 120 h at a current density of 500 mA / cm 2 , and [Fe3O(A2)3][Ni2(B1)3X6] exhibits significantly better catalytic stability than the original [Fe3O(A2)3]. For [Fe3O(A2)3][Ni2(B1)3X6], the potential remains stable for 120 h at a current density of 500 mA / cm 2At that time, the overpotential increased by only 9 mV, while the overpotential of [Fe3O(A2)3] increased significantly by 33 mV. Furthermore, further X-ray diffraction (XRD) analysis indicated that the material structure changed after the OER stability test. Scanning electron microscopy (SEM) images showed that the [Fe3O(A2)3][Ni2(B1)3X6] catalyst retained its hexagonal prism structure after the OER stability test, but the catalyst surface became rougher. Figure 16 Although [Fe3O(A2)3] remained stable for 120 hours, its original form completely collapsed. Figure 17 This is because [Fe3O(A2)3][Ni2(B1)3X6] contains a non-planar binuclear triazole cluster, with two metal ions arranged along the channel direction, making its size quite compact and ensuring that it will not collapse during the reconstruction process.

[0094] To investigate the application prospects of [Fe3O(A2)3][Ni2(B1)3X6] as a cathode material under practical industrial conditions, an electrolytic cell was constructed based on an anion exchange membrane electrolyzer (AEMWE). Surprisingly, the [Fe3O(A2)3][Ni2(B1)3X6] catalyst showed promising performance at 1,000 and 2,000 mA / cm². 2 The battery voltages for the two methods were 1.9V and 2.3V, respectively, while the battery voltages for the IrO2-based methods were 2.5V and 3.0V, respectively. Figure 18 To further verify its potential for practical applications near industrial scale, this invention was tested at 1,000 mA / cm². 2 The electrolytic cell underwent a long-term stability test for nearly 200 hours. Figure 19 Therefore, the synthesized [Fe3O(A2)3][Ni2(B1)3X6] catalyst underwent reasonable dynamic reconstruction due to structural factors, which affected its kinetic behavior and ensured long-term high activity and industrial stability, exceeding the catalytic activity and industrial stability of most reported anode catalysts.

[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. An oxygen evolution catalyst based on a metal-organic framework, characterized in that: The oxygen evolution catalyst comprises a metal-organic framework and a pore structure modification unit inserted into the metal-organic framework. The metal-organic framework is formed by the coordination linkage of an organic ligand A containing a dicarboxylic acid with a metal source reagent M1, and the pore structure modification unit is formed by the coordination linkage of a triazole organic ligand B with a metal source reagent M2. The organic ligand A containing the dicarboxylic acid is one or more of the compounds shown in formula (I), and the triazole organic ligand B is one or more of the compounds shown in formula (II). in: In formula (Ⅰ), the combination of R1 / R2 / R3 / R4 is A1: H / H / H / H; A2: OH / H / H / H, A3: SH / H / H / H, A4: NH2 / H / H / H, A5: NO2 / H / H / H, A6: Br / H / Br / H, A7: OH / H / OH / H, A8: Cl / H / Cl / H, A9: F / F / F / F, A10: NHCHO / H / H / H, A11: Cl / H / H / H, A12: Br / H / H / H, A13: NH2 / H / NH2 / H, A14: Br / H / H / H or A15: Cl / H / H / H; In formula (II), the combinations of R5 / R6 are B1: H / H, B2: H / NH2, B3: H / NO2, B4: H / SH, B5: SH / CH3, B6: SH / NH2, B7: H / CH3, B8: H / CF3, B9: H / Br, B10: H / CN, B11: CH3 / CH3 or B12: NH2 / NH2.

2. The oxygen evolution catalyst according to claim 1, characterized in that: The metal source reagent M1 is a trivalent Fe salt, and the metal source reagent M2 is one or more of Fe(II), trivalent Fe, Ni, Co, and Mn salts.

3. The oxygen evolution catalyst according to claim 2, characterized in that: The metal source reagent M1 is FeCl3, and the metal source reagent M2 is one or more of FeCl2, FeCl3, Fe(NO3)2, Ni(NO3)2, Mn(OAc)2 and Co(OAc)2.

4. The oxygen evolution catalyst according to claim 1, characterized in that: The organic ligand A containing a dicarboxylic acid is 2-hydroxyterephthalic acid, and the triazole organic ligand B is 1,2,4-triazole or 3-amino-5-mercapto-1,2,4-triazole.

5. The method for synthesizing the oxygen evolution catalyst according to any one of claims 1-4, characterized in that... Includes the following steps: Step (1): Add organic ligand A containing dicarboxylic acid, organic ligand B containing triazole, metal source reagent M1 and metal source reagent M2 to organic solvent S, and dissolve to obtain mixed solution a; Step (2): Add the synthesis reagent Q to the mixed solution a to obtain the mixed solution b; Step (3): The mixed solution b is subjected to hydrothermal reaction at a temperature of 140-160℃ for 24-72h, and the product is subjected to solid-liquid separation, washing and drying.

6. The synthesis method according to claim 5, characterized in that: The molar ratio of the organic ligand A containing dicarboxylic acid to the triazole organic ligand B in step (1) is 1:1 to 1.

2.

7. The synthesis method according to claim 5, characterized in that: In step (3), a conductive substrate is added to the hydrothermal reaction vessel.

8. The synthesis method according to claim 5, characterized in that: The organic solvent S is N,N-dimethylformamide.

9. The synthesis method according to claim 5, characterized in that: The synthesis reagent Q in step (2) is trifluoroacetic acid, and the mass ratio of the synthesis reagent Q to the organic ligand A of the dicarboxylic acid and the organic ligand B of the triazole is A+B:Q = 1:1.2~1.

9.

10. The application of the oxygen evolution catalyst according to any one of claims 1-4 in the oxygen evolution reaction of water electrolysis.

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