Metal organic framework material with proton conductivity and preparation method and application thereof

Abstract

The invention belongs to the technical field of fuel cells, and discloses a metal organic framework material with proton conductivity and a preparation method and application thereof. Pyrazolo [3, 4-c] pyridine is used as a ligand, a binuclear cuprous cluster is used as a connection point, a two-dimensional layered structure is constructed through the ligand and the binuclear cuprous cluster, a cuprous multi-nitrogen heterocyclic metal organic framework is formed, the cuprous multi-nitrogen heterocyclic metal organic framework is oxidized, and the cuprous multi-nitrogen heterocyclic metal organic framework is obtained. Divalent copper ions and monovalent copper ions exist in the oxidized cuprous multi-nitrogen heterocyclic metal organic framework, and the metal organic framework material with proton conductivity is obtained. The proton conductivity of the metal organic framework material can be remarkably improved by adopting a metal post-synthesis modification oxidation technology, and the proton conductivity of the metal organic framework material is comparable with that of commercial Nafion, and an oxidized sample shows extremely high chemical stability; the problem of poor stability of a non-fluorinated hydrocarbon polymer proton exchange membrane and inorganic solid acid researched in the prior art is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and particularly relates to a metal-organic framework material with proton conductive properties, a preparation method thereof, and an application thereof. Background Art

[0002] Polymer electrolyte membrane fuel cells have been favored by people because of their advantages of low environmental pollution, high energy conversion efficiency, fast start-up at low temperature, and high reliability. Common polymer electrolyte membrane fuel cells are divided into two categories. One is proton exchange membrane fuel cells (PEMFCs) based on H + transport, and the other is anion exchange membrane fuel cells (AEMFCs) based on OH − transport. Among them, proton exchange membrane fuel cells have the advantages of low operating temperature, fast start-up, high specific power, simple structure, convenient operation, and easy commercialization, and thus have received extensive attention from researchers. As the core component of proton exchange membrane fuel cells, proton exchange membranes (PEMs) have always been one of the research hotspots in the fuel cell field. The proton exchange membrane (PEM) provides a channel for proton transport, enabling protons to pass through the membrane from the anode to the cathode and form a circuit with electron transfer in the external circuit to provide current to the external world.

[0003] Currently, the commercially available proton exchange membrane material is Nafion membrane. It is a perfluoroalkyl sulfonic acid polymer, in which the carbon-fluorine bond has a high bond energy (485 kJ·mol −1 ), a short bond length, and fluorine atoms rotate to cover and protect the C−C bond, which makes the Nafion membrane have good chemical stability and thermal stability. In addition, the sulfonic acid group has a strong acidity (pK a ~0.7), and combined with the inductive effect of adjacent F atoms, its acidity is further enhanced and can be completely ionized in water, so it can exhibit high proton conductivity (10 −1 S·cm~10 −2S·cm). Since the membrane needs to contain F atoms and introduce strongly acidic sulfonate groups, these factors make the manufacturing process of Nafion membranes complex, cause serious environmental pollution and high production costs, which is not conducive to large-scale commercial applications. In addition to Nafion, the most reported ones at present are non-fluorocarbon hydrogen polymer membranes (sulfonated polysulfone, polyimide, polystyrene, polyether ether ketone, polyphenylene sulfide) and acid-base blended polymer membranes (polyvinyl pyridine, polybenzimidazole). These polymers have the advantages of less environmental pollution during manufacturing, low price, and proton conductivity comparable to that of Nafion. However, they do not contain highly stable carbon-fluorine bonds, so they have poor environmental tolerance, poor chemical stability, and poor thermal stability, which is not conducive to long-term use.

[0004] Proton-conducting materials that have been studied more also include inorganic solid acids such as KH2PO4, CsHSO4, CsHPO4, etc. As a fuel cell electrolyte membrane, solid acids have the advantages that alcohols are not easily permeable, the proton conduction process is not restricted by the water content, and the operating temperature is high. However, there are still many problems to be solved when using solid acids as electrolyte membranes, including improving the proton conductivity of solid acids, improving their water resistance, and chemical stability. Summary of the Invention

[0005] The object of the present invention is to provide a metal-organic framework material with proton-conducting properties, its preparation method and application. The present invention uses pyrazolo[3,4-c]pyridine as a ligand and binuclear copper clusters as connection points to construct a two-dimensional layered structure through the ligand and binuclear copper clusters. In the binuclear copper clusters, Cu exists in the +1 valence state, which can form a thermodynamically stable structure with the soft-base pyrazole nitrogen and pyridine nitrogen in the ligand, making the metal-organic framework exhibit ultra-high chemical stability and thermal stability. By partially oxidizing the monovalent copper ions in the copper ions during oxidation to divalent copper ions, the hydrophilicity is enhanced, and a small amount of water molecules generated are used for proton conduction. The synergistic effect of the two enables the metal-organic framework material to have excellent proton conduction rate, significantly improves the proton conductivity of the metal-organic framework material, and solves the problem of poor stability of non-fluorocarbon hydrogen polymer proton exchange membranes and inorganic solid acids in previous studies.

[0006] In order to achieve the above object, the technical solution adopted in this application is as follows: One of the objects of the present invention is to provide a preparation method of a metal-organic framework material with proton-conducting properties, including the following steps: using pyrazolo[3,4-c]pyridine as a ligand and binuclear copper clusters as connection points to construct a two-dimensional layered structure through the ligand and binuclear copper clusters to form a copper polyazacyclic metal-organic framework, and oxidizing the copper polyazacyclic metal-organic framework so that divalent copper ions and monovalent copper ions exist in the oxidized copper polyazacyclic metal-organic framework to obtain a metal-organic framework material with proton-conducting properties.

[0007] Further, it includes the following steps: S1. Preparation of cuprous polyazacyclic metal-organic framework: Dissolve 1H-pyrazolo[3,4-c]pyridine and soluble copper salt in a mixed solvent, and carry out a solvothermal reaction to obtain the cuprous polyazacyclic metal-organic framework.

[0008] S2. Immerse the cuprous polyazacyclic metal-organic framework in a nitric acid solution or a potassium hydroxide solution for oxidation to obtain an oxidized cuprous polyazacyclic metal-organic framework material, so that divalent copper ions and monovalent copper ions exist in the oxidized cuprous polyazacyclic metal-organic framework, which is a metal-organic framework material with proton conductive performance.

[0009] Further, the molar volume ratio of 1H-pyrazolo[3,4-c]pyridine, soluble copper salt and mixed solvent is 1 mmol: 5 mmol - 6 mmol: 8 mL, the soluble copper salt is Cu(NO3)2·3H2O, and the mixed solvent is a mixture of ammonia water, N,N′-dimethylformamide and methanol with a volume ratio of 1: 5 - 7: 1.

[0010] Further, the temperature of the solvothermal reaction is 100 °C - 140 °C, and the time is 3 d - 5 d.

[0011] Further, the concentration of the nitric acid solution is 0.05 M - 0.25 M.

[0012] Further, the concentration of the potassium hydroxide solution is 0.01 M - 5 M.

[0013] Further, the soaking time is 3 d - 5 d.

[0014] The second object of the present invention is to provide a metal-organic framework material with proton conductive performance prepared by the above preparation method. The crystal system of the cuprous polyazacyclic metal-organic framework is monoclinic, and the space group is P2 1 / n , and the unit cell parameters are a = 5.4210(12) Å, b = 10.142(2) Å, c = 10.889(2) Å, α = 90°, β = 99.173(4)°, γ = 90°, V = 591.0(2) Å 3 .

[0015] The third object of the present invention is to provide the application of the above metal-organic framework material with proton conductive performance as a proton exchange membrane in a fuel cell.

[0016] Compared with the prior art, the beneficial effects of the present invention: In the present invention, pyrazolo[3,4-c]pyridine is used as a ligand, and a binuclear copper(I) cluster is used as a connection point. A two-dimensional layered structure constructed by the ligand and the binuclear copper(I) cluster forms a copper(I) polyazaheterocyclic metal-organic framework. In the binuclear copper(I) cluster, Cu exists in the +1 oxidation state, and can form a thermodynamically stable structure with the soft-base pyrazole nitrogen and pyridine nitrogen in the ligand, making the copper(I) polyazaheterocyclic metal-organic framework exhibit extremely high chemical stability and thermal stability. Then, the copper(I) polyazaheterocyclic metal-organic framework with high thermal stability and chemical stability is taken as the research object for oxidation, so that divalent copper ions and monovalent copper ions exist in the oxidized copper(I) polyazaheterocyclic metal-organic framework, enhancing the hydrophilicity, and a small amount of water molecules generated are used for proton conduction. The synergistic effect of the two makes the metal-organic framework material have excellent proton conduction rate and significantly improves the proton conductivity of the metal-organic framework material.

[0017] In one way of the preparation method provided by the present invention, nitric acid oxidation is used to partially oxidize monovalent copper ions in the material to divalent copper ions to enhance the hydrophilicity of the material; a small amount of water molecules generated during the oxidation of copper ions are used for proton conduction. The synergistic effect of the two makes the proton conduction rate of the oxidized material reach 10 −2 S / cm, which can be comparable to Nafion. In another way, potassium hydroxide oxidation is used to partially oxidize monovalent copper ions in the material to divalent copper ions to introduce hydroxide ions into the material as a conductive substance; a small amount of water molecules generated during the oxidation of copper ions are used for the rapid conduction of hydroxide ions. The synergistic effect of the two makes the hydroxide conduction rate of the oxidized material reach 10 −4 S / cm, which is 35.499 times higher than that of the original Cu-papy. At the same time, the oxidized material maintains the original crystalline characteristics and good stability. Only dilute nitric acid is used during the oxidation of the sample, so the environmental pollution is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the single crystal structure diagram of the metal-organic framework material prepared by the present invention, Figure 1 in which (a) is the coordination structure of copper(I) ions in Cu-papy, (b) is the structure of the binuclear copper cluster in Cu-papy, (c) is the two-dimensional coordination network structure formed by the papy ligand and the binuclear copper cluster, and (d) is the three-dimensional supramolecular network structure formed by C−H···π hydrogen bonds in Cu-papy.

[0019] Figure 2 is the structure diagram of the Cu-papy powder sample prepared by the present invention, Figure 2Among them, (a) is the X-ray diffraction pattern, (b) is the infrared spectrum, (c) is the high-resolution X-ray photoelectron spectrum in the Cu 2p region, and (d) is the thermogravimetric analysis curve and differential scanning calorimetry curve.

[0020] Figure 3 This is the stability diagram of the modified cuprous polyazacyclic metal-organic framework materials prepared in Examples 1 to 9 of the present invention. Figure 3 Among them, (a) is the PXRD pattern of nitric acid solution at different concentrations, and (b) is the PXRD pattern of potassium hydroxide solution at different concentrations.

[0021] Figure 4 This is the immersion stability diagram of the Cu-papy sample prepared in the present invention in different types of solvents. Figure 4 Among them, (a) is the PXRD pattern of different types of neutral solutions, and (b) is the PXRD pattern of different types of organic solvents.

[0022] Figure 5 This is the structural diagram of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Examples 1 to 4 of the present invention. Figure 5 Among them, (a) is the high-resolution XPS spectrum of Cu 2p, (b) is the FT-IR spectrum, and (c) is the TGA curve.

[0023] Figure 6 This is the proton conductivity of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Examples 1 to 4 of the present invention. Figure 6 Among them, (a) is the relative humidity (RH) dependence diagram of proton conductivity (σ) at 298 K, (b) is the relationship diagram between proton conductivity (σ) and temperature (T) in the temperature range of 298 K to 353 K and at 97% RH, (c) is the Arrhenius diagram in the temperature range of 298 K to 353 K and at 97% RH, (d) is the time-dependent proton conductivity diagram of Examples 1 to 3 at 298 K and 97% RH, and (e) is the relationship curve diagram between the ratio change of Cu II / Cu I and proton conductivity, and (f) includes the ratio curve diagram of Cu I and Cu II ratio curve diagram.

[0024] Figure 7 This is the proton conductivity improvement diagram of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Example 4 of the present invention.

[0025] Figure 8PXRD patterns of the modified oxidized cuprous polyazacyclic metal-organic frameworks prepared in Examples 1 to 4 of the present invention after proton conductivity tests Figure 8 In (a) is the PXRD pattern after the proton conductivity test, and in (b) is the PXRD pattern of the sample after 3 parallel proton conductivity tests in Example 4.

[0026] Figure 9 X-ray photoelectron spectroscopy of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Example 8 of the present invention Figure 9 In (a) is the high-resolution XPS spectrum of Cu 2p, and in (b) is the high-resolution XPS spectrum of O1s.

[0027] Figure 10 Hydroxide conductivity results of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Example 8 of the present invention Figure 10 In (a) is the hydroxide conductivity at different temperatures, and in (b) is the Arrhenius plot.

[0028] Figure 11 Hydroxide conductivity improvement diagram of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Example 8 of the present invention

[0029] Figure 12 Electrocatalytic reduction of CO2 curve of the cuprous polyazacyclic metal-organic framework of the present invention Detailed implementation mode

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the data in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the following embodiments of the present invention can be obtained through market purchases or prepared by existing methods.

[0032] On the one hand, the present invention provides a method for preparing a metal-organic framework material with proton-conducting properties, comprising the following steps: using pyrazolo[3,4-c]pyridine as a ligand and a binuclear copper cluster as a linker, forming a two-dimensional layered structure through the ligand and the binuclear copper cluster to form a copper polyazacyclic metal-organic framework, oxidizing the copper polyazacyclic metal-organic framework so that divalent copper ions and monovalent copper ions exist in the oxidized copper polyazacyclic metal-organic framework, to obtain a metal-organic framework material with proton-conducting properties.

[0033] The present invention uses pyrazolo[3,4-c]pyridine as a ligand and a binuclear copper cluster as a linker, forming a two-dimensional layered structure through the ligand and the binuclear copper cluster to form a copper polyazacyclic metal-organic framework. The Cu in the binuclear copper cluster exists in the +1 valence state, which can form a thermodynamically stable structure with the soft-base pyrazole nitrogen and pyridine nitrogen in the ligand, making the copper polyazacyclic metal-organic framework exhibit ultra-high chemical stability and thermal stability. Then, taking the copper polyazacyclic metal-organic framework with high thermal stability and chemical stability as the research object, oxidizing it so that divalent copper ions and monovalent copper ions exist in the oxidized copper polyazacyclic metal-organic framework, enhancing the hydrophilicity, and generating a small amount of water molecules to conduct protons. The synergistic effect of the two makes the metal-organic framework material have excellent proton conduction rate and significantly improves the proton-conducting properties of the metal-organic framework material.

[0034] In some specific embodiments, the method for preparing the above-mentioned metal-organic framework material with proton-conducting properties comprises the following steps: S1. Preparation of the copper polyazacyclic metal-organic framework: Dissolve 1H-pyrazolo[3,4-c]pyridine and a soluble copper salt in a mixed solvent, carry out a solvothermal reaction to obtain the copper polyazacyclic metal-organic framework.

[0035] S2. Immerse the copper polyazacyclic metal-organic framework in a nitric acid solution for oxidation so that divalent copper ions and monovalent copper ions exist in the oxidized copper polyazacyclic metal-organic framework, to obtain the oxidized copper polyazacyclic metal-organic framework material, which is the metal-organic framework material with proton-conducting properties.

[0036] Metal-organic framework materials are a new type of material that has emerged in recent years. They have the characteristics of crystal form, belong to hybrid materials, and also have the following advantages: (1) The regulation and optimization of the performance of the entire compound can be achieved through the modification and tailoring of the ligand structure at the molecular level; (2) The highly crystallized characteristics are conducive to accurately determining their structure and studying the structure-property relationship at the atomic level; (3) Good chemical stability and thermal stability provide the possibility for their further practical applications. These advantages provide the possibility for realizing the simplification of the material production process, the significant improvement of proton conduction performance, and the effective unity of chemical stability and crystalline structure. In this invention, a copper(I) multi-nitrogen heterocyclic metal-organic framework with high thermal stability and chemical stability is used as the research object. One way is to use nitric acid oxidation to partially oxidize the monovalent copper ions in the material to divalent copper ions to enhance the hydrophilicity of the material; use the small amount of water molecules generated during the oxidation of copper ions to conduct protons. The synergistic effect of the two makes the proton conduction rate of the oxidized material reach 10 −2 S·cm, which can be comparable to Nafion; Another way is to use potassium hydroxide oxidation to partially oxidize the monovalent copper ions in the material to divalent copper ions and introduce hydroxide ions into the material as conductive substances; use the small amount of water molecules generated during the oxidation of copper ions to rapidly conduct hydroxide ions. The synergistic effect of the two makes the hydroxide conduction rate of the oxidized material reach 10 −4 S / cm. At the same time, the oxidized material maintains the characteristics of crystal form and good stability. Only dilute nitric acid was used during the oxidation of the sample, so the environmental pollution is small. The original metal-organic framework material Cu-papy and the oxidized sample show extremely high chemical stability, which significantly improves the problem of poor stability of non-fluorocarbon hydrogen polymer proton exchange membranes and inorganic solid acids in previous studies.

[0037] In some embodiments, the molar volume ratio of 1H-pyrazolo[3,4-c]pyridine, soluble copper salt and mixed solvent is 1 mmol: 5 mmol to 6 mmol: 8 mL. The soluble copper salt is Cu(NO3)2·3H2O, and the mixed solvent is a mixture of ammonia water, N,N′-dimethylformamide and methanol in a volume ratio of 1:6:1.

[0038] In some embodiments, the temperature of the solvothermal reaction is 100 °C to 140 °C, and the time is 3 d to 5 d.

[0039] In some embodiments, the concentration of the nitric acid solution is 0.05 M to 0.25 M.

[0040] In the present invention, nitric acid oxidation is utilized to partially oxidize monovalent copper ions in the material to divalent copper ions to enhance the hydrophilicity of the material; a small amount of water molecules generated during the oxidation of copper ions are used for proton conduction. The synergistic effect of the two enables the proton conduction rate of the oxidized material to reach 10 −2 S / cm, which can be comparable to Nafion. Meanwhile, the oxidized material maintains its original crystalline characteristics and good stability. Only nitric acid is used during the oxidation of the sample, thus resulting in less environmental pollution. The original metal-organic framework material Cu-papy and the oxidized sample exhibit extremely high chemical stability, significantly improving the problem of poor stability of non-fluorocarbon hydrogen polymer proton exchange membranes and inorganic solid acids in previous studies.

[0041] In some embodiments, the concentration of potassium hydroxide is 0.01 M to 5 M.

[0042] In the present invention, potassium hydroxide oxidation is utilized to partially oxidize monovalent copper ions in the material to divalent copper ions to introduce hydroxide ions into the material as conductive substances; a small amount of water molecules generated during the oxidation of copper ions are used for the rapid conduction of hydroxide ions. The synergistic effect of the two enables the hydroxide conduction rate of the oxidized material to reach 10 −4 S / cm, which is 35.499 times higher than that of the original Cu-papy.

[0043] In some embodiments, the soaking time is 3 d to 5 d.

[0044] On the other hand, the present invention also provides a metal-organic framework material with proton conductive properties. It should be noted that a two-dimensional layered structure is constructed with pyrazolo[3,4-c]pyridine as the ligand and binuclear copper clusters as the connection points to form a copper polyazacyclic metal-organic framework. The unit structure molecular formula in the copper polyazacyclic metal-organic framework is C6H4N3Cu, and a three-dimensional supramolecular network structure is formed through C−H···π hydrogen bonds in C6H4N3Cu.

[0045] In some embodiments, the crystal system of the copper polyazacyclic metal-organic framework is monoclinic, and the space group is P2 1 / n , the unit cell parameters are a = 5.4210(12) Å, b = 10.142(2) Å, c = 10.889(2) Å, α = 90°, β = 99.173(4)°, γ = 90°, V = 591.0(2) Å 3 . The crystal structure of the metal-organic framework material is as shown in Figure 1As shown Figure 1 In (a) of Figure 1 is the coordination structure of cuprous ions in Cu-papy, (b) is the structure of binuclear copper clusters in Cu-papy, (c) is the two-dimensional coordination network structure formed by papy ligands and binuclear copper clusters, and (d) is the three-dimensional supramolecular network structure formed by C−H···π hydrogen bonds in Cu-papy. As Figure 1 shown by single-crystal X-ray diffraction in Figure 1 , each copper(I) ion in Cu-papy coordinates with two pyrazole nitrogen atoms and one pyridine nitrogen atom of the organic ligand (papy) to form a distorted planar triangular structure ( Figure 1 in (a) of Figure 1 ). The pyrazole nitrogen atoms in two ligands (papy) are connected to two copper(I) ions to form a binuclear copper(I) cluster ( Figure 1 in (b) of Figure 1 ). The uncoordinated pyridine nitrogen atom in each binuclear copper(I) cluster connects adjacent binuclear copper(I) clusters to form a two-dimensional layered structure ( Figure 1 in (c) of Figure 1 ). These two-dimensional layered structures further form a three-dimensional supramolecular network structure through C−H···π hydrogen bonds ( Figure 1 in (d) of Figure 1 )

[0046] In addition, the present invention also provides the application of the above-mentioned metal-organic framework material with proton conductive properties as a proton exchange membrane in fuel cells. It should be noted that since the metal-organic framework material with proton conductive properties provided by the present invention has high thermal stability, chemical stability and excellent proton conductivity, it can be used to prepare a proton exchange membrane. The metal-organic framework material can be blended with certain polymers to prepare a metal-organic framework-polymer composite proton exchange membrane for use in proton exchange membrane fuel cells.

[0047] The present invention also provides a cuprous polyazacyclic metal-organic framework prepared by the above preparation method and its application as a catalyst in the electrocatalytic reduction of carbon dioxide.

[0048] The following is further illustrated with specific examples.

[0049] Example 1 A preparation method of a metal-organic framework material with proton conductive properties, comprising the following steps: S1. Preparation of cuprous polyazacyclic metal-organic framework (Cu-papy): Dissolve 1H-pyrazolo[3,4-c]pyridine (Hpapy: 32 mg, 0.269 mmol) and Cu(NO3)2·3H2O (168 mg, 1.438 mmol) in a mixed solvent composed of 1 mL of ammonia water, 6 mL of DMF, and 1 mL of methanol, and place it in a stainless-steel autoclave. Carry out solvothermal reaction in an oven at 120 °C for 3 days. After the reaction is completed, cool it to room temperature, filter the sample, and air-dry it naturally to obtain the Cu-papy sample.

[0050] S2. Preparation of post-synthetic modified oxidized cuprous polyazacyclic metal-organic framework material: Immerse 200 mg of the Cu-papy sample in 10 mL of 0.05 M HNO3 solution for 3 days. After the immersion is completed, filter the sample and air-dry it naturally in the air to obtain the oxidized cuprous polyazacyclic metal-organic framework material, named Cu-papy-0.05 M HNO3.

[0051] Example 2 A preparation method of a metal-organic framework material with proton conduction performance, comprising the following steps: S1. Preparation of cuprous polyazacyclic metal-organic framework (Cu-papy): Dissolve Hpapy (32 mg, 0.269 mmol) and Cu(NO3)2·3H2O (168 mg, 1.438 mmol) in a mixed solvent composed of 1 mL of ammonia water, 6 mL of DMF, and 1 mL of methanol, and place it in a stainless-steel autoclave. Carry out solvothermal reaction in an oven at 120 °C for 3 days. After the reaction is completed, cool it to room temperature, filter the sample, and air-dry it naturally to obtain the Cu-papy sample.

[0052] S2. Preparation of post-synthetic modified oxidized cuprous polyazacyclic metal-organic framework material: Immerse 200 mg of the Cu-papy sample in 10 mL of 0.10 M HNO3 solution for 3 days. After the immersion is completed, filter the sample and air-dry it naturally in the air to obtain the oxidized cuprous polyazacyclic metal-organic framework material, named Cu-papy-0.10 M HNO3.

[0053] Example 3 A preparation method of a metal-organic framework material with proton conduction performance, comprising the following steps: S1. Preparation of copper(I) polyazacyclic metal-organic framework (Cu-papy): Dissolve Hpapy (32 mg, 0.269 mmol) and Cu(NO3)2·3H2O (168 mg, 1.438 mmol) in a mixed solvent composed of 1 mL of ammonia water, 6 mL of DMF, and 1 mL of methanol, and place it in a stainless-steel autoclave. Carry out solvothermal reaction in an oven at 120 °C for 3 days. After the reaction is completed, cool it to room temperature, filter the sample, and air-dry it naturally to obtain the Cu-papy sample.

[0054] S2. Preparation of post-synthetic modified oxidized copper(I) polyazacyclic metal-organic framework material: Immerse 200 mg of the Cu-papy sample in 10 mL of 0.15 M HNO3 solution for 3 days. After the immersion is completed, filter the sample and air-dry it naturally in the air to obtain the oxidized copper(I) polyazacyclic metal-organic framework material, named Cu-papy-0.15 M HNO3.

[0055] Example 4 A preparation method of a metal-organic framework material with proton conduction performance, comprising the following steps: S1. Preparation of copper(I) polyazacyclic metal-organic framework (Cu-papy): Dissolve Hpapy (32 mg, 0.269 mmol) and Cu(NO3)2·3H2O (168 mg, 1.438 mmol) in a mixed solvent composed of 1 mL of ammonia water, 6 mL of DMF, and 1 mL of methanol, and place it in a stainless-steel autoclave. Carry out solvothermal reaction in an oven at 120 °C for 3 days. After the reaction is completed, cool it to room temperature, filter the sample, and air-dry it naturally to obtain the Cu-papy sample.

[0056] S2. Preparation of post-synthetic modified oxidized copper(I) polyazacyclic metal-organic framework material: Immerse 200 mg of the Cu-papy sample in 10 mL of 0.25 M HNO3 solution for 3 days. After the immersion is completed, filter the sample and air-dry it naturally in the air to obtain the oxidized copper(I) polyazacyclic metal-organic framework material, named Cu-papy-0.25 M HNO3.

[0057] Example 5 A preparation method of a metal-organic framework material with proton conduction performance, comprising the following steps: S1. Preparation of Copper Polyazacyclic Metal-Organic Framework (Cu-papy): Dissolve Hpapy (32 mg, 0.269 mmol) and Cu(NO3)2·3H2O (168 mg, 1.438 mmol) in a mixed solvent composed of 1 mL of ammonia water, 6 mL of DMF, and 1 mL of methanol. Place the solution in a stainless-steel autoclave and carry out a solvothermal reaction in an oven at 120 °C for 3 days. After the reaction is completed, cool it to room temperature, filter the sample, and let it air-dry naturally to obtain the Cu-papy sample.

[0058] S2. Preparation of Post-Synthetic Modified Copper Polyazacyclic Metal-Organic Framework Material: Immerse 50 mg of the Cu-papy sample in 10 mL of a 0.01 M KOH solution for 3 days. After the immersion is completed, filter the sample and let it air-dry naturally in the air to obtain the modified copper polyazacyclic metal-organic framework material.

[0059] Example 6 A preparation method of a metal-organic framework material with proton conduction performance, comprising the following steps: S1. Preparation of Copper Polyazacyclic Metal-Organic Framework (Cu-papy): Dissolve Hpapy (32 mg, 0.269 mmol) and Cu(NO3)2·3H2O (168 mg, 1.438 mmol) in a mixed solvent composed of 1 mL of ammonia water, 6 mL of DMF, and 1 mL of methanol. Place the solution in a stainless-steel autoclave and carry out a solvothermal reaction in an oven at 120 °C for 3 days. After the reaction is completed, cool it to room temperature, filter the sample, and let it air-dry naturally to obtain the Cu-papy sample.

[0060] S2. Preparation of Post-Synthetic Modified Copper Polyazacyclic Metal-Organic Framework Material: Immerse 50 mg of the Cu-papy sample in 10 mL of a 1 M KOH solution for 3 days. After the immersion is completed, filter the sample and let it air-dry naturally in the air to obtain the modified copper polyazacyclic metal-organic framework material.

[0061] Example 7 A preparation method of a metal-organic framework material with proton conduction performance, comprising the following steps: S1. Preparation of cuprous polyazacyclic metal-organic framework (Cu-papy): Dissolve Hpapy (32 mg, 0.269 mmol) and Cu(NO3)2·3H2O (168 mg, 1.438 mmol) in a mixed solvent composed of 1 mL of ammonia water, 6 mL of DMF and 1 mL of methanol, and place it in a stainless steel autoclave. Carry out solvothermal reaction in an oven at 120 °C for 3 d. After the reaction is completed, cool it to room temperature, filter the sample and air-dry it naturally to obtain the Cu-papy sample.

[0062] S2. Preparation of post-synthetic modified cuprous polyazacyclic metal-organic framework material: Immerse 50 mg of the Cu-papy sample in 10 mL of a 2.5 M KOH solution for 3 d. After the immersion is completed, filter the sample and air-dry it in the air to obtain the modified cuprous polyazacyclic metal-organic framework material.

[0063] Example 8 A preparation method of a metal-organic framework material with proton conduction performance, comprising the following steps: S1. Preparation of cuprous polyazacyclic metal-organic framework (Cu-papy): Dissolve Hpapy (32 mg, 0.269 mmol) and Cu(NO3)2·3H2O (168 mg, 1.438 mmol) in a mixed solvent composed of 1 mL of ammonia water, 6 mL of DMF and 1 mL of methanol, and place it in a stainless steel autoclave. Carry out solvothermal reaction in an oven at 120 °C for 3 d. After the reaction is completed, cool it to room temperature, filter the sample and air-dry it naturally to obtain the Cu-papy sample.

[0064] S2. Preparation of synthetically modified cuprous polyazacyclic metal-organic framework material: Immerse 50 mg of the Cu-papy sample in 10 mL of a 5.0 M KOH solution for 3 d. After the immersion is completed, filter the sample and air-dry it in the air to obtain the modified cuprous polyazacyclic metal-organic framework material, named Cu-papy-5 M KOH.

[0065] Figure 2 It is the structural diagram of the Cu-papy sample prepared in the present invention. Figure 2 In (a) is the X-ray diffraction pattern, (b) is the infrared spectrum, (c) is the high-resolution X-ray photoelectron spectrum in the Cu 2p region, and (d) is the thermogravimetric analysis curve and differential scanning calorimetry curve. As Figure 2As shown in (a) therein, the X-ray diffraction pattern (PXRD pattern) shows that the diffraction peaks of the Cu-papy sample are highly consistent with the positions of the theoretical simulation peaks of the single crystal structure, indicating that it is a pure phase compound with high crystallinity and long-range order; the FT-IR spectrum shows that only the characteristic peaks of the organic ligand functional groups exist, without the characteristic peaks of water molecules, such as Figure 2 As shown in (b) therein, such as the C−H vibration peak (2850 cm −1 −1) and the C=N vibration peak (1620 cm −1 −1); as Figure 2 As shown in (c) therein, the XPS spectrum shows that Cu exists in the +1 valence state. Copper (I) ions belong to soft acids and can form thermodynamically stable structures with soft bases such as pyrazole nitrogen and pyridine nitrogen. Therefore, this metal-organic framework exhibits ultra-high chemical stability, which is beneficial to the application of the sample in the fields of proton, hydroxide conduction or electrocatalysis; as Figure 2 As shown in (d) therein, the thermogravimetric analysis (TGA) curve shows that the Cu-papy sample only shows weight loss behavior when the temperature is higher than 327 °C, indicating its high thermal stability. The differential scanning calorimetry (DSC) curve shows that there are no obvious endothermic and exothermic peaks in the Cu-papy sample when the temperature is less than 250 °C, indicating that there is no phase change process in the sample, which is consistent with the TGA data.

[0066] Figure 3 This is the stability diagram of the modified cuprous polyazaheterocyclic metal-organic framework materials prepared in Examples 1 to 9 of the present invention. Figure 3 In (a) therein is the PXRD pattern of nitric acid solution at different concentrations, and (b) is the PXRD pattern of potassium hydroxide solution at different concentrations. As Figure 3 As shown in (a) therein, after the Cu-papy is soaked in an acidic environment (0.01 M - 0.25 M) for 3 days, its PXRD pattern can still show characteristic diffraction peaks consistent with the theoretical simulation, indicating that the framework structure of the Cu-papy sample remains stable under acidic conditions; as Figure 3 As shown in (b) therein, after the sample is soaked in a basic environment (0.01 M - 5 M) for 3 days, its PXRD pattern can still show characteristic diffraction peaks consistent with the theoretical simulation, indicating that the framework structure of the sample remains stable under basic conditions.

[0067] 50 mg of the Cu-papy sample prepared in Example 1 was respectively soaked in 10 mL of PBS solution, 10 mL of 1 M KHCO3 solution, 10 mL of pure water, 10 ml of MeCN (acetonitrile), 10 mL of EtOH (ethanol), 10 mL of MeOH (methanol) and 10 mL of DMF (N,N′-dimethylformamide) for 7 days to detect the stability of the Cu-papy sample.

[0068] Figure 4 The stability diagram of the Cu-papy sample prepared for this invention when soaked in different types of solvents Figure 4 In (a) of , the PXRD patterns of different types of neutral solutions are shown, and in (d) of , the PXRD patterns of different types of organic solvents are shown. As Figure 4 shown, after the Cu-papy sample is soaked in neutral solutions such as PBS, KHCO3, and pure water for 1 week, its PXRD pattern can still show characteristic diffraction peaks consistent with the theoretical simulation, indicating that the framework structure of the sample remains highly stable under neutral conditions; after the Cu-papy sample is soaked in various organic solvents (MeCN, EtOH, MeOH, and DMF) for 1 week, its PXRD pattern can still show characteristic diffraction peaks consistent with the theoretical simulation, indicating that the framework structure of the sample remains highly stable in organic solvents.

[0069] Figure 5 The structure diagrams of the modified and oxidized cuprous polyazacyclic metal-organic frameworks prepared in Examples 1 to 4 of this invention Figure 5 In (a) of , the high-resolution XPS spectrum of Cu 2p is shown, in (b) is the FT-IR spectrum, and in (c) is the TGA curve. As Figure 5 shown in (a) of , for the Cu-papy sample soaked in HNO3, as the concentration of HNO3 increases from 0.01 M to 0.25 M, the chemical valence state of Cu is gradually oxidized from Cu(I) to Cu(II), and the ratio of Cu(II) / Cu(I) increases from 0.048 to 1.457; as Figure 5 shown in (b) of , compared with the original Cu-papy sample, in the FT-IR spectrum, characteristic vibration peaks of water molecules v (O−H) (3400 cm −1 ) and characteristic vibration peaks of nitrate v (NO3 − ) (1384 cm −1 ) appear, indicating that water molecules and nitrate exist in the oxidized sample. At the same time, as the concentration of the soaked nitric acid increases, the relative intensities of these two groups of characteristic peaks also gradually increase, indicating that the contents of water molecules and nitrate in the oxidized sample also gradually increase as the concentration of nitric acid increases; as Figure 5 shown in (c) of , the TGA curve shows that samples soaked in nitric acid all show varying degrees of weight loss before 120 °C, which corresponds to the loss of guest water molecules. After exceeding 194 °C, the oxidized samples will show obvious weight loss, which may be due to the degradation of the sample framework.

[0070] The elements and thermogravimetry of the modified and oxidized cuprous polyazacyclic metal-organic frameworks and Cu-papy prepared in Examples 1 to 4 were analyzed, as shown in Table 1.

[0071] Table 1 Comparison of Calculated and Measured Values of Elemental Analysis and Thermogravimetric Analysis of Modified Oxidized Cuprous Polyazacyclic Metal-Organic Frameworks As shown in Table 1, elemental analysis indicates that as the concentration of HNO3 increases from 0.05 M to 0.25 M, the carbon (C) content in the oxidized Cu-papy sample gradually decreases from 39.05% to 31.18%, and the nitrogen (N) content decreases from 23.13% to 21.78%. This result shows that as the concentration of HNO3 increases, the sample is gradually oxidized to form more oxygen-containing compounds (such as water molecules and nitrate ions). This is also consistent with the gradual increase in the oxygen element in the molecular formula of the samples from Cu-papy-0.05 M HNO3 to Cu-papy-0.25 M HNO3. Additionally, from the calculated molecular formula, it can be seen that the proportion of Cu II and Cu I in the oxidized sample increases significantly with the increase in the concentration of HNO3, indicating that high-concentration HNO3 promotes the oxidation transformation of Cu I to Cu II . From thermogravimetric analysis, it can be seen that the Cu-papy sample has no thermal weight loss (0%), but the thermal weight loss of the samples treated with HNO3 gradually increases, rising from 1.15% (0.05 M HNO3) to 5.47% (0.25 M HNO3), indicating that the content of guest water molecules also increases with the increase in the oxidation degree of Cu I . Finally, the theoretical and calculated values of the elemental composition and weight loss of the samples after HNO3 treatment show good agreement, indicating that the calculated chemical formula is correct and reasonable.

[0072] Figure 6 For the proton conductivity of the modified oxidized cuprous polyazacyclic metal-organic frameworks prepared in Examples 1 to 4 of the present invention, Figure 6 in (a) is the relative humidity (RH) dependence diagram of proton conductivity (σ) at 298 K, (b) is the relationship diagram between proton conductivity (σ) and temperature (T) in the temperature range of 298 K to 353 K and ~97% RH, (c) is the Arrhenius diagram in the temperature range of 298 K to 353 K and ~97% RH, (d) is the time-dependent proton conductivity diagram of Examples 1 to 3 at 298 K and ~97% RH, (e) is the relationship curve diagram between the ratio change of Cu II / Cu I and proton conductivity, (f) includes the ratio curve diagram of Cu I and Cu II . As Figure 6As shown in (a) therein, Examples 1 to 4 all showed humidity dependence, that is, the proton conductivity gradually increased with the increase in humidity; in addition, as Figure 6 shown in (b) therein, with the deepening of the oxidation degree, the proton conductivity of Examples 1 to 4 at the maximum humidity (~97%RH) showed a significant increase; as Figure 6 shown in (c) therein, for the samples of Examples 1 to 4 in their original and different treated states, the activation energy (E a ) of their proton conduction was 0.235 eV (Cu-papy), 0.247 eV (Example 1), 0.266 eV (Example 2), 0.253 eV (Example 3), and 0.265 eV (Example 4) respectively, which conformed to the Grotthuss mechanism of proton conduction; in addition, as Figure 6 shown in (d) and (e) therein, whether it was short-term (4 h) or long-term (96 h) testing, the proton conductivity of Example 4 remained almost unchanged, showing excellent stability and being suitable for long-term operation, indicating its potential for further practical applications. In addition, as Figure 6 seen from (f) therein, with the deepening of the oxidation degree, the proportion of Cu II in the whole Cu metal ions (including Cu I and Cu II ) increased from 0 in the original sample to 65.5% in the sample of Example 4, and its proton conductivity also increased significantly.

[0073] Figure 7 This is the proton conductivity improvement diagram of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Example 4 of the present invention. As Figure 7 shown, the proton conductivity of the original Cu-papy sample was only 1.033×10 −5 S·cm −1 under the conditions of ~97% RH and 80 °C, while the proton conductivity of the sample of Example 4 with the highest oxidation degree was as high as 2.699×10 −2 S·cm −1 under the same conditions. In contrast, as Figure 6 shown, it was 2612 times higher than that of Cu-papy, an increase of three orders of magnitude, which was due to the increase in hydrophilicity caused by the increase in its guest water molecules and framework ionic type.

[0074] Figure 8 This is the PXRD pattern of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Examples 1 to 4 of the present invention after proton conductivity testing, Figure 8 in which (a) is the PXRD pattern after proton conductivity testing, and (b) is the PXRD pattern of the sample after 3 parallel proton conductivity tests of Example 4. Among them,Figure 8 In (b), Cu-papy-0.25 M HNO3-a, Cu-papy-0.25 M HNO3-b, and Cu-papy-0.25 M HNO3-c are samples after three proton conductivity tests. As Figure 8 shown, after the proton conductivity test of Cu-papy and its nitric acid-treated samples, the positions of the diffraction peaks on their PXRD patterns are consistent with those of the original synthesized samples, indicating that the material maintains good structural stability during the proton conductivity test.

[0075] Figure 9 This is the X-ray photoelectron spectroscopy diagram of the modified and oxidized cuprous polyazacyclic metal-organic framework prepared in Example 8 of the present invention. Figure 9 In (a), it is the high-resolution XPS spectrum of Cu 2p, and in (b), it is the high-resolution XPS spectrum of O1s. As Figure 9 shown in (a), Cu I and Cu II appear in the Cu element. Calculation shows that the surface Cu II / Cu I element ratio is 29.93%, proving that the Cu element of the material is partially oxidized. As Figure 9 shown in (b), it shows two different components with binding energies of 531.2 eV and 532.8 eV, corresponding to hydroxide ions (OH − ), and adsorbed water molecules (H2O), respectively. The presence of hydroxide (OH − ) indicates that the cuprous polyazacyclic metal-organic framework material treated with 5 M KOH can be used as a material for conducting hydroxide. Therefore, the hydroxide conductivity of Cu-papy-5 M KOH under high humidity conditions (~97% RH) was systematically studied.

[0076] Figure 10 This is the hydroxide conductivity result of the modified and oxidized cuprous polyazacyclic metal-organic framework prepared in Example 8 of the present invention. Figure 10 In (a), it is the hydroxide conductivity at different temperatures, and in (b), it is the Arrhenius plot. As Figure 10 shown in (a), when the temperature increases from 298 K to 353 K, the hydroxide conductivity of Cu-papy-5 M KOH prepared in Example 9 increases from 1.109×10 −4 S cm −1 to 3.667×10 −4 S cm −1 , which is increased by 3.3 times. As Figure 10As shown in (b), the temperature-dependent hydroxide conductivity shows a good linear relationship with the reciprocal of temperature in the Arrhenius plot, verifying the reliability of the measured data. The calculated activation energy (E a ) is 0.221 eV, consistent with the Grotthuss mechanism, indicating that hydroxide migrates through a dynamic hydrogen bond network rather than through a vehicle diffusion mechanism.

[0077] Figure 11 This is the hydroxide conductivity improvement diagram of the modified oxidized cuprous polyazacyclic metal-organic framework prepared in Example 8 of the present invention. As Figure 11 shown, the hydroxide conductivity of Cu-papy-5 M KOH prepared in Example 8 is significantly better than that of the original sample Cu-papy (1.033×10 −5 S cm −1 ) under the same conditions (353 K and ~97% RH). The hydroxide conduction rate of Cu-papy-5 M KOH is 35.499 times higher than that of unmodified Cu-papy. This significant improvement is attributed to the synergistic effect of hydroxide introduced by partially oxidized copper and adsorbed water molecules.

[0078] In addition, the present invention also finds that the prepared metal-organic framework material can be used for the electrocatalytic performance of the CO2 reduction reaction. The ink used in the electrocatalysis is prepared by the following steps:

[0079] First, grind the cuprous polyazacyclic metal-organic framework sample prepared in Example 1 into fine powder with a mortar and pestle for about 30 min. Then, disperse 50 mg of the catalyst in 1 ml of DMF and ultrasonically treat it for 10 min to form a homogeneous ink. Finally, slowly coat the ink on a copper mesh (geometric area = 1.00 cm 2 ) and dry it overnight at room temperature. Electrochemical studies are carried out on an AUTOLAB PGSTAT 101 and MULTI AUTOLAB M101 (CH Instruments) system, using a copper mesh as the working electrode, an Ag / AgCl (3 M) electrode as the reference electrode, and a Pt wire as the counter electrode in a typical three-electrode cell. Use the following equation to calibrate all potentials to the reversible hydrogen electrode E RHE = E exp + E Ag / AgCl (3.0 M) + 0.059 pH = E exp + 0.21 + 0.059 pH, and normalize the current density to the effective geometric surface area.

[0080] Figure 12 This is the electrocatalytic reduction CO2 curve diagram of the cuprous polyazacyclic metal-organic framework of the present invention. AsFigure 12 As shown, the copper polyazacyclic metal-organic framework sample has a large cathodic current, about 140 mA·cm under N2 atmosphere conditions -2 , and about 170 mA·cm under CO2 atmosphere conditions -2 . The larger cathodic current under CO2 atmosphere conditions compared to that under N2 atmosphere conditions indicates that the compound Cu-papy has certain CO2 reduction activity and may be used as a catalyst for the CO2 reduction reaction.

[0081] It should be noted that when the present invention involves a numerical range, it should be understood that any value between the two endpoints of each numerical range and the two endpoints themselves can be selected. Since the step methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0082] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A preparation method of a metal-organic framework material with proton conductive properties, characterized in that, It includes the following steps: Using pyrazolo[3,4-c]pyridine as a ligand and a binuclear copper cluster as a connection point, a two-dimensional layered structure is constructed by the ligand and the binuclear copper cluster to form a copper polyazacyclic metal-organic framework. The copper polyazacyclic metal-organic framework is oxidized so that divalent copper ions and monovalent copper ions exist in the oxidized copper polyazacyclic metal-organic framework, obtaining a metal-organic framework material with proton conductive properties.

2. The preparation method of the metal-organic framework material with proton conductive property according to claim 1, characterized in that, It includes the following steps: Preparation of the copper polyazacyclic metal-organic framework: Dissolve 1H-pyrazolo[3,4-c]pyridine and a soluble copper salt in a mixed solvent, and carry out a solvothermal reaction to obtain the copper polyazacyclic metal-organic framework; Immerse the copper polyazacyclic metal-organic framework in a nitric acid solution or a potassium hydroxide solution for soaking and oxidation to obtain an oxidized copper polyazacyclic metal-organic framework material, so that divalent copper ions and monovalent copper ions exist in the oxidized copper polyazacyclic metal-organic framework, which is the metal-organic framework material with proton conductive properties.

3. The preparation method of the metal-organic framework material with proton conductive property according to claim 2, characterized in that, The molar volume ratio of 1H-pyrazolo[3,4-c]pyridine, the soluble copper salt and the mixed solvent is 1 mmol: 5 mmol to 6 mmol: 8 mL. The soluble copper salt is Cu(NO3)2·3H2O, and the mixed solvent is a mixture of ammonia water, N,N′-dimethylformamide and methanol in a volume ratio of 1: 5 to 7:

1.

4. The preparation method of the metal-organic framework material with proton conductive performance according to claim 2, characterized in that, The temperature of the solvothermal reaction is 100 °C to 140 °C, and the time is 3 d to 5 d.

5. The preparation method of the metal-organic framework material with proton conductive performance according to claim 2, characterized in that, The concentration of the nitric acid solution is 0.05 M to 0.25 M.

6. The preparation method of the metal-organic framework material with proton conductive performance according to claim 2, characterized in that, The concentration of potassium hydroxide is 0.01 M to 5 M.

7. The preparation method of the metal-organic framework material with proton conductive performance according to claim 2, characterized in that, The soaking time is 3 d to 5 d.

8. A metal-organic framework material with proton conductive properties, characterized in that, Prepared by using the preparation method described in any one of claims 1 to 7.

9. The metal-organic framework material with proton conductive property according to claim 8, characterized in that, The crystal system of the cuprous polyazacyclic metal-organic framework is monoclinic, and the space group is P2 1 / n , and the unit cell parameters are a = 5.4210(12) Å, b = 10.142(2) Å, c = 10.889(2) Å, α α = 90°, β β = 99.173(4)°, γ γ = 90°, V V = 591.0(2) Å 3 .

10. Application of the metal-organic framework material with proton conductive properties described in claim 8 as a proton exchange membrane in a fuel cell.

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