Anode catalyst-metal organic framework material for electrolyzing alkaline water as well as preparation method and application of anode catalyst-metal organic framework material

Abstract

The invention discloses an anode catalyst for electrolyzing alkaline water, namely a metal organic framework material as well as a preparation method and application thereof. According to the method, 2, 5-dihydroxy terephthalic acid and 2-hydroxy terephthalic acid are taken as organic connectors, nickel acetate and ferrous chloride are taken as metal centers, and solvothermal reaction is carried out in methanol. Metal coordination defects are caused by side group deletion, and meanwhile, a metal-organic framework is maintained not to be obviously changed, so that more active sites are exposed. The OER performance eta 1000 of the material in a three-electrode system and a seawater electrolyte with the pH value of 14 is 280-350 mV, and the stability is 60-500 h. The seawater corrosion resistance and the ultrahigh electrolytic stability are realized. According to the method, efficient seawater electrolysis can be achieved, seawater resource utilization is achieved, and the application prospect is wide.

Description

Technical Field

[0001] The present invention belongs to the field of energy, and particularly relates to a metal-organic framework material used as an anode catalyst for electrolyzing alkaline water, a preparation method thereof, and an application thereof. Background Art

[0002] With the growing global demand for clean energy, natural water energy, as a potential renewable energy source, has gradually attracted attention. Among them, the technology of electrolyzing alkaline water to produce hydrogen is considered to be a highly potential energy conversion method due to its rich raw materials and environmental friendliness. During the process of electrolyzing alkaline water to produce hydrogen, the performance of the anode oxygen evolution catalyst directly affects the efficiency and energy consumption of the electrolyzer.

[0003] Currently, the commonly used anode oxygen evolution catalysts mainly include noble metals, oxides, and composite materials, etc., but they have problems such as high cost, poor stability, and limited catalytic activity.

[0004] The Chinese patent application document with the publication number CN111905827A discloses a preparation method of a nickel-based heterogeneous composite material and its application in catalyzing methanol oxidation. Specifically, a Ni-MOF is newly synthesized by a hydrothermal method, and at the same time, Fe3O4 / NiOOH is introduced to construct a heterogeneous composite material, which is used as the positive electrode catalyst material for methanol oxidation, and its application in methanol oxidation is explored. This patent uses the organic ligands 2,5-dihydroxyterephthalic acid and 1,4-bis(imidazole)butane and nickel sulfate to perform self-assembly in a mixed solution of N,N-dimethylformamide, deionized water, and KOH to obtain a porous metal-organic framework material. The synthesized material is assembled into a three-electrode system for testing methanol oxidation. The advantages of this patent are: the synthesis process of this metal-organic framework material is simple, and the crystallization purity is high; and the structure is novel, and the porosity is large; the incorporation of Fe3O4 / NiOOH has the advantages of low temperature, safety, and no harmful solvents. However, the stability and catalytic activity of this material are poor, so it still needs to be further improved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to solve the problems of poor stability and low catalytic activity existing in the existing anode oxygen evolution catalysts.

[0006] The present invention solves the above technical problems by the following technical means:

[0007] The first aspect of the present invention provides a preparation method of a NiFe-based metal-organic framework material, comprising the following steps:

[0008] Using 2,5-dihydroxyterephthalic acid (DHTP) and 2-hydroxyterephthalic acid (HTP) as organic linkers, and nickel salts and iron salts as the sources of metal centers, performing a solvothermal reaction in an alcohol solution to obtain a NiFe-based metal-organic framework material.

[0009] Preferably, the molar ratio of the 2,5-dihydroxyterephthalic acid (DHTP) to the 2-hydroxyterephthalic acid (HTP) is (1-4):(1-3).

[0010] Preferably, the nickel salt can be any one of nickel acetate, nickel nitrate, nickel chloride, nickel sulfate, and nickel phosphate, and the iron salt can be any one of ferrous acetate, ferric nitrate, ferrous chloride, ferrous sulfate, and ferrous phosphate.

[0011] Preferably, the molar ratio of the nickel salt to the iron salt is (0.5-3):(1-3).

[0012] Preferably, the alcohol solution can be one of methanol and ethanol, and ethanol is preferably used as the reaction solvent after further optimization.

[0013] Preferably, the temperature of the solvothermal reaction is 120-200 °C, and more preferably 175 °C.

[0014] Preferably, the time of the solvothermal reaction is 6-15 h, and more preferably 12 h.

[0015] In the second aspect of the present invention, an NiFe-based metal-organic framework material prepared by the above preparation method is provided.

[0016] In the third aspect of the present invention, the application of the above NiFe-based metal-organic framework material as an anode catalyst in alkaline water electrolysis is provided.

[0017] Preferably, the above NiFe-based metal-organic framework material is placed in a three-electrode electrolytic cell, seawater with a pH of 14 is used as the electrolyte, and a voltage is applied. The overpotential at a current density of 1 A cm -2 is 280-350 mV, and the stability is 60-500 h.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. In the present invention, 2,5-dihydroxyterephthalic acid and 2-hydroxyterephthalic acid are used as organic linkers, and nickel acetate and ferrous chloride are used as metal centers. A solvothermal reaction is carried out in an alcohol solution to synthesize a metal-organic framework material. The main performance gain comes from the introduction of a missing side-chain hydroxyl ligand (2-hydroxyterephthalic acid), which can create more undercoordinated metal centers, that is, reaction sites, on the basis of maintaining the metal-organic framework structure unchanged.

[0020] 2. The OER performance η of the material in a three-electrode system and an alkaline water electrolyte with a pH of 14 1000= 280 - 350 mV, with a stability of 60 - 500 h, having the characteristics of alkali water corrosion resistance and ultra-high electrolytic stability. This method can achieve efficient alkaline water electrolysis, realize the resource utilization of natural water, and has broad application prospects. Brief Description of the Drawings

[0021] Figure 1 Scanning electron microscope images of the materials prepared in Examples 1 - 4 of the present invention;

[0022] Figure 2 XRD spectra of the materials prepared in Examples 1 - 4 of the present invention;

[0023] Figure 3 Performance test comparison diagrams of the materials prepared in Examples 1 - 4 of the present invention;

[0024] In the figures, a - d respectively refer to Examples 1 - 4. Detailed Embodiments

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] The test materials and reagents used in the following embodiments can be obtained from commercial sources without special instructions.

[0027] For those not specifying specific technologies or conditions in the embodiments, they can all be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. Without special instructions, the quantitative tests in the following embodiments are all set with more than three repeated experiments, and the results are averaged.

[0028] Configuration of the electrolyte: Use a KOH solution to precipitate metal ions in natural seawater and adjust the pH to 14.

[0029] Example 1:

[0030] A preparation method of a NiFe-based metal-organic framework material, comprising the following steps:

[0031] Using 2,5-dihydroxyterephthalic acid (DHTP) and 2-hydroxyterephthalic acid (HTP) with a molar ratio of 1:1 as organic linkers, and nickel acetate and ferrous chloride with a molar ratio of 0.5:1 as metal centers, carrying out a solvothermal reaction at 175 °C for 6 h in methanol (50 mL) to obtain a NiFe-based metal-organic framework material.

[0032] The successful preparation of the material was confirmed by scanning electron microscopy and XRD characterization. The characterization diagrams and performance test results are shown in Figures 1-2 as follows.

[0033] Application of the material:

[0034] The metal-organic framework material prepared in this example was placed in a three-electrode electrolytic cell (the synthesized metal-based MOF was loaded on nickel foam as the working electrode, Hg / HgO as the reference electrode, and a carbon rod as the counter electrode to form a three-electrode system). Using seawater with a pH of 14 as the electrolyte and applying a voltage for testing, the results showed that: η 1000 = 340 mV, and the stability was 60 h.

[0035] (The level of catalytic activity is judged by the overpotential to reach 1000 mA cm -2 . The lower the overpotential, the higher the performance.)

[0036] Example 2:

[0037] A preparation method of a NiFe-based metal-organic framework material, comprising the following steps:

[0038] Using 2,5-dihydroxyterephthalic acid (DHTP) and 2-hydroxyterephthalic acid (HTP) with a molar ratio of 2:1 as the organic linker, and nickel acetate and ferrous chloride with a molar ratio of 1:1 as the metal center, carrying out a solvothermal reaction at 175 °C in methanol (50 mL) for 9 h to obtain the NiFe-based metal-organic framework material.

[0039] Application of the material: The method steps are the same as those in Example 1. The results showed that: η 1000 = 300 mV, and the stability was 230 h.

[0040] Example 3:

[0041] A preparation method of a NiFe-based metal-organic framework material, comprising the following steps:

[0042] Using 2,5-dihydroxyterephthalic acid (DHTP) and 2-hydroxyterephthalic acid (HTP) with a molar ratio of 3:1 as the organic linker, and nickel acetate and ferrous chloride with a molar ratio of 2:1 as the metal center, carrying out a solvothermal reaction at 175 °C in methanol (50 mL) for 12 h to obtain the NiFe-based metal-organic framework material.

[0043] Application of the material: The method steps are the same as those in Example 1. The results showed that: η 1000 = 281 mV, and the stability was 500 h.

[0044] Example 4:

[0045] A preparation method of NiFe-based metal-organic framework material, comprising the following steps:

[0046] Using 2,5-dihydroxyterephthalic acid (DHTP) and 2-hydroxyterephthalic acid (HTP) with a molar ratio of 4:1 as organic linkers, and nickel acetate and ferrous chloride with a molar ratio of 3:1 as metal centers, carrying out a solvothermal reaction at 175 °C in methanol (50 mL) for 15 h to obtain the NiFe-based metal-organic framework material.

[0047] Application of the material: The method steps are the same as those in Example 1, and the results show that: η 1000 = 290 mV, and the stability is 310 h.

[0048] Summary of the application effects of the NiFe-based metal-organic framework materials prepared in Examples 1-4 in electrolyzing alkaline seawater:

[0049] Taking Examples 1-4 as examples, the effects of the parameters of the NiFe-based metal-organic framework material (ligand ratio, metal ratio, solvothermal time) on the performance of electrolyzing seawater (η 1000 , stability) are shown in the following table:

[0050] Table 1: Effects of NiFe-based metal-organic framework materials on electrolyzing alkaline seawater under different parameters

[0051]

[0052] Example 5:

[0053] The difference between this example and Example 1 is that: the molar ratio of 2,5-dihydroxyterephthalic acid (DHTP) and 2-hydroxyterephthalic acid (HTP) is 4:3; the molar ratio of nickel acetate and ferrous chloride is 1:2, the temperature of the solvothermal reaction is 200 °C, and the time is 6 h, and the rest is the same as Example 1.

[0054] Example 6:

[0055] The difference between this example and Example 1 is that: the molar ratio of 2,5-dihydroxyterephthalic acid (DHTP) and 2-hydroxyterephthalic acid (HTP) is 2:1.5; the molar ratio of nickel acetate and ferrous chloride is 3:3, the temperature of the solvothermal reaction is 120 °C, and the time is 15 h, and the rest is the same as Example 1.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a NiFe-based metal-organic framework material, characterized in that: The following steps are involved: Using 2,5-dihydroxyterephthalic acid and 2-hydroxyterephthalic acid as organic linkers, nickel salt and iron salt as sources of metal centers, a solvothermal reaction was carried out in an alcohol solution to obtain NiFe-based metal-organic framework materials.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the 2,5-dihydroxyterephthalic acid to the 2-hydroxyterephthalic acid is (1-4): (1-3).

3. The preparation method according to claim 1, characterized in that: The molar ratio of the nickel salt to the iron salt is (0.5-3):(1-3).

4. The preparation method according to claim 1, characterized in that: The nickel salt is any one of nickel acetate, nickel nitrate, nickel chloride, nickel sulfate and nickel phosphate; the iron salt is any one of ferrous acetate, ferrous nitrate, ferrous chloride, ferrous sulfate and ferrous phosphate.

5. The preparation method according to claim 1, characterized in that: The alcohol solution is one of methanol and ethanol.

6. The preparation method according to claim 1, characterized in that: The temperature of the solvent thermal reaction is 120-200°C.

7. The preparation method according to claim 1, characterized in that: The solvent thermal reaction time is 6 to 15 hours.

8. The NiFe-based metal-organic framework material obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the NiFe-based metal-organic framework material according to claim 8 as an anode catalyst in electrolysis of alkaline water.

10. The use according to claim 9, characterized in that: The NiFe-based metal-organic framework material was placed in a three-electrode electrolytic cell, seawater with a pH of 14 was used as the electrolyte and a voltage was applied.

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