POM-based supramolecular nanostructure OER electro-catalytic material and preparation method thereof

Abstract

The invention discloses a POM-based supramolecular nanostructure OER electro-catalytic material and a preparation method thereof.The POM-based supramolecular nanostructure OER electro-catalytic material is characterized in that Na6K12 [H2Co8O4 (Nb6O19) 4]. 39H2O and transition metal atoms in the POM-based supramolecular nanostructure OER electro-catalytic material are alternately arranged to form a graphene-like bridging structure with the aperture of 2.7 nm, water-soluble POM is converted into a hydrophobic layered structure through cetyltrimethylammonium bromide modification, and the defined interlayer spacing of 3.5 nm is achieved; the OER electro-catalysis material with the POM-based supramolecular nanostructure is of a three-dimensional layered structure; according to the method, in the process of preparing the POM-based supramolecular nanostructure, cetyltrimethylammonium bromide (CTAB) converts water-soluble POM into a hydrophobic layered structure, transition metal can enhance electron transfer on a connected graphene-like structure, and POM-CTAB-Co shows faster reaction kinetics and higher electrochemical OER performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and in particular relates to a POM-based supramolecular nanostructured OER electrocatalytic material and a preparation method thereof. Background Art

[0002] The reserves of fossil fuels in the earth's crust are limited, and when burned, they produce carbon dioxide and toxic sulfides, which damage the ecological balance. Therefore, humans must find clean renewable energy to replace fossil fuels. Hydrogen energy is environmentally friendly and pollution-free, with high energy density. It is considered to be a good choice to replace traditional fossil fuels and solve energy problems. The method of producing hydrogen by electrolysis of water has the advantages of being pollution-free, having high product purity, being recyclable, and having a simple preparation process. It is considered to be one of the important means to achieve industrial large-scale hydrogen production. In the past few decades, research has focused on the development of low-cost and highly active non-precious metal electrocatalysts to overcome the limitations of the commercialization of precious metal-based catalysts. Cobalt-based oxides / hydroxides / oxyhydroxides are popular due to their adjustable valence states (Co 0 / Co 2+ / Co 3+ ) and controllable oxygen vacancy density. Despite these advantages, they still face inherent challenges such as low density of electrochemically active sites, poor electrical conductivity, and insufficient electrochemical interface compatibility between the active sites and the electrolyte, which together limit their practical applications. Therefore, it is crucial to develop new strategies to obtain high-performance cobalt-based electrocatalytic materials with universal applicability.

[0003] Polyoxometalates (POMs), also known as polyoxometalates, are generally composed of inorganic oxometalates of high-valent transition metals such as vanadium, niobium, tantalum, molybdenum, and tungsten, which undergo polycondensation and dehydration to form polynuclear metal clusters. Polymetallic niobates (PONbs), a class of niobate anions composed of niobium and oxygen atoms, possess well-defined structures capable of accommodating a large number of electrons and ions while maintaining structural stability, making them promising electrocatalytic OER materials. Furthermore, their structural tunability and modifiability allow the incorporation of a variety of metals, providing a unique opportunity to study the structure-performance relationship with atomic-level precision. However, the water solubility of pure inorganic niobates has limited their application in electrocatalysis, and converting water-soluble polyoxometalates into water-insoluble ones without compromising electrocatalytic performance remains a challenge. Supramolecular nanostructures, characterized by molecular assemblies stabilized by noncovalent interactions, have attracted considerable attention due to their unique properties that surpass the performance of individual molecular components. Polyoxymetalates (POMs) are ideal building blocks for constructing supramolecular nanostructures due to their structural diversity, subnanometer size, tunable properties, and ability to bind to organic or inorganic cations. However, precisely controlling POM building blocks and modulating the interactions between POMs and metal cations remain key challenges in the controlled synthesis of POM-based supramolecular structures. Summary of the Invention

[0004] To solve the above problems, the present invention proposes a POM-based supramolecular nanostructured OER electrocatalytic material and a preparation method thereof.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A POM-based supramolecular nanostructured OER electrocatalytic material, wherein Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O and transition metal atoms are alternately arranged to form a graphene-like bridge structure with a pore size of 2.7nm. Cetyltrimethylammonium bromide modification converts the water-soluble POM into a hydrophobic layered structure with a defined interlayer spacing of 3.5nm. The POM-based supramolecular nanostructured OER electrocatalytic material has a three-dimensional layered structure.

[0007] Preferably, in an anion exchange membrane water electrolyzer with the POM-based supramolecular nanostructured OER electrocatalytic material as anode and Pt / C as cathode, a 2Acm -2 current density.

[0008] A method for preparing a POM-based supramolecular nanostructured OER electrocatalytic material comprises the following steps:

[0009] S1, synthesis of niobate precursor K7HNb6O 19 ·13H2O;

[0010] S2, niobate precursor, cobalt chloride, disodium hydrogen phosphate, sodium phosphate, sodium peroxoborate and deionized water are weighed into a polytetrafluoroethylene kettle, stirred at room temperature for 0.5 h to mix the raw materials uniformly;

[0011] S3, the polytetrafluoroethylene kettle is placed in an oven for hydrothermal reaction;

[0012] S4, the polytetrafluoroethylene kettle after hydrothermal reaction is cooled, filtered and volatilized for 7 days to obtain Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O crystal;

[0013] S5, Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O crystal is dissolved in water, and cetyltrimethylammonium bromide is added, followed by the addition of cobalt acetate, and then left to stand; the product is washed by centrifugation with deionized water three times, and then washed with anhydrous ethanol once, and finally dried for 12 hours to obtain a POM-based supermolecular nanostructure OER electrocatalytic material.

[0014] Preferably, in step S2, the molar addition ratio of the niobate precursor, cobalt chloride, disodium hydrogen phosphate, sodium phosphate, sodium peroxoborate and deionized water is 30:6:1:3:7.

[0015] Preferably, in step S3, the reaction temperature of the hydrothermal reaction is 160°, and the reaction time is 4 days.

[0016] Preferably, in step S4, the polytetrafluoroethylene kettle after hydrothermal reaction is cooled to room temperature, impurities are filtered, and volatilized at 30℃ for 7 days.

[0017] Preferably, in step S5, the molar addition ratio of Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O crystal, water, cetyltrimethylammonium bromide and cobalt acetate is 1:2:3.

[0018] After adopting the above technical solution, the present invention has the following beneficial effects: the POM-based supramolecular nanostructure OER electrocatalytic material prepared by the present invention has a graphene-like layered framework structure with an interlayer spacing of 3.5nm and a pore size of 2.7nm, which can be used for OER electrocatalytic oxygen evolution and has the potential to be an advanced OER anode material. In the process of preparing the POM-based supramolecular nanostructure, hexadecyltrimethylammonium bromide (CTAB) converts the water-soluble POM into a hydrophobic layered structure. The transition metal can enhance the electron transfer in the connected graphene-like structure. POM-CTAB-Co shows faster reaction kinetics and higher electrochemical OER performance. Therefore, at 10mA cm -2 The anion exchange membrane water electrolyzer with POM-CTAB-Co as the anode and Pt / C as the cathode showed excellent performance, achieving a low overpotential of 292 mV at a current density of 2.247 V. -2 Calculations and a series of in situ results indicate that the high performance and fast kinetics of POM-CTAB-Co are primarily due to the cobalt on the clusters acting as the true active sites. Furthermore, the transition metal connecting the clusters can accelerate electron transport during electrocatalysis, thereby enhancing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the POM-based supramolecular nanostructured OER electrocatalytic material prepared in the present invention;

[0020] Figure 2 Transmission electron microscope morphology and mapping diagram of the POM-based supramolecular nanostructured OER electrocatalytic material prepared by the present invention;

[0021] Figure 3 The powder diffraction pattern of the POM-based supramolecular nanostructured OER electrocatalytic material prepared by the present invention;

[0022] Figure 4 This is the infrared spectrum of the POM-based supramolecular nanostructured OER electrocatalytic material prepared in the present invention;

[0023] Figure 5 This is the ultraviolet absorption spectrum of the POM-based supramolecular nanostructured OER electrocatalytic material prepared in the present invention;

[0024] Figure 6 This is the hydrogen nuclear magnetic resonance spectrum of the POM-based supramolecular nanostructured OER electrocatalytic material prepared in the present invention;

[0025] Figure 7 A comparison of linear sweep voltammetry curves of different POM-based supramolecular nanostructured OER electrocatalytic materials prepared in the present invention;

[0026] Figure 8 A performance comparison chart of anion exchange membrane water electrolyzer was constructed for the POM-CTAB-Co / IrO2 prepared by the present invention and commercial Pt / C as anode and cathode catalysts;

[0027] Figure 9 The stability diagram of an anion exchange membrane water electrolyzer at 80 °C 1 M KOH was constructed using POM-CTAB-Co / and commercial Pt / C as anode and cathode catalysts for the POM-based supramolecular nanostructure prepared in the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] like Figures 1 to 9 shown.

[0030] A method for preparing a POM-based supramolecular nanostructured OER electrocatalytic material (abbreviated as POM-CTAB-Co) comprises the following steps:

[0031] S1. Synthesis of niobate precursor K7HNb6O 19 13H2O, the synthesis method is based on the method provided in the document "Inorganic Chemistry" (1979, Vol. 18, pp. 93-103);

[0032] S2. Weigh the niobate precursor, cobalt chloride, disodium hydrogen phosphate, sodium phosphate, sodium perborate, and deionized water into a polytetrafluoroethylene kettle and stir at room temperature for 0.5 h to uniformly mix the raw materials;

[0033] In step S2, the molar addition ratio of the niobate precursor, cobalt chloride, disodium hydrogen phosphate, sodium phosphate, sodium perborate and deionized water is 30:6:1:3:7;

[0034] S3, placing the polytetrafluoroethylene kettle in an oven for hydrothermal reaction;

[0035] In step S3, the reaction temperature of the hydrothermal reaction is 160° and the reaction time is 4 days;

[0036] S4. Cool the polytetrafluoroethylene kettle after the hydrothermal reaction, filter and evaporate for 7 days to obtain Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O (POM for short) crystals;

[0037] In step S4, the polytetrafluoroethylene kettle after the hydrothermal reaction is cooled to room temperature, impurities are filtered, and volatilization is performed at 30℃ for 7 days;

[0038] S5, the Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O crystal is dissolved in water, and cetyltrimethylammonium bromide (CTAB) is added, followed by the addition of cobalt acetate, and then left to stand; the product is washed by centrifugation with deionized water three times, and then washed with anhydrous ethanol once, and finally dried for 12 hours to obtain a POM-based supermolecular nanostructured OER electrocatalytic material (POM-CTAB-Co);

[0039] In step S5, the Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O crystal, water, cetyltrimethylammonium bromide, and cobalt acetate are added in a molar ratio of 1:2:3.

[0040] In addition, in the preparation process, the transition metal Co can be replaced by Ni or Cu.

[0041] Characterization and performance testing of the material:

[0042] (1) Transmission electron microscopy characterization

[0043] 1 mg of POM-CTAB-Co is uniformly dispersed in ethanol and ultrasonicated for 30 minutes, then dropped on a copper grid, and the sample morphology and internal element distribution are determined by a Tecnai G2 F20 instrument under vacuum conditions. The obtained sample morphology and mapping diagram are as shown in Figure 2 .

[0044] (2) Powder diffraction characterization:

[0045] An appropriate amount of the POM-based supermolecular nanostructured OER electrocatalytic material prepared above is taken, and the powder diffraction pattern of the conductive material is measured at room temperature (as shown in Figure 3 ). By comparing the diffraction peaks simulated according to the MS data, it can be seen that the experimental determination result is in good agreement with the software fitting result, which indicates that the compound is consistent with the expected structure.

[0046] (3) Infrared spectroscopy characterization:

[0047] As shown in Figure 4 , the characteristic vibration bands of the compounds POM, POM-CTAB, POM-CTAB-Co, POM-CTAB-Ni, POM-CTAB-Cu POM include ν(Nb-Ot) at 864 cm -1 , ν(Nb-Ob) at 492 cm -1, and ν(Co-O) at 624 cm -1 and 1640cm -1 In addition, there are vibration bands of CTAB, such as ν(CH3) at 2920cm -1 , ν(CH2) at 2846cm -1 , and δ(CH2) at 1470cm -1 .

[0048] (4) NMR characterization:

[0049] like Figure 5 As shown, the compounds CTAB, POM-CTAB, POM-CTAB-Co, POM-CTAB-Ni, POM-CTAB-Cu POM 1 The chemical shifts of H are 1.2, 2.51, 3.02, and 3.37 ppm, which are consistent with the major shifts of CTAB and demonstrate the successful introduction of CTAB.

[0050] (5) UV absorption spectrum characterization:

[0051] like Figure 6 As shown in Figure 3, the broad absorption bands of compounds POM, POM-CTAB, POM-CTAB-Co, POM-CTAB-Ni, and POM-CTAB-Cu at 210 nm and 270 nm are mainly attributed to the charge transfer transition from O to Nb, and the broad absorption band of the compound at about 600 nm is attributed to the dd transition of Co.

[0052] (5) Electrocatalytic OER test:

[0053] Experimental method: 5 mg of each catalyst, 30 μL of 10% Nafion solution, and 300 μL of water / isopropanol (volume ratio 1:1) were mixed and ultrasonicated for 1 hour to prepare catalyst ink. The working electrode was prepared by dropping the catalyst ink onto a carbon-carbon electrode (CC). The catalyst loading on the CC was approximately 0.5 mg cm -2 .

[0054] Figure 7 Comparison of linear sweep voltammetry curves of different POM-based supramolecular nanostructures; Figure 8 A performance comparison chart of anion exchange membrane water electrolyzer using POM-CTAB-Co / IrO2 and commercial Pt / C as anode and cathode catalysts was constructed; Figure 9 Stability diagrams of anion exchange membrane water electrolyzers at 80°C and 1M KOH were constructed using POM-CTAB-Co / and commercial Pt / C as anode and cathode catalysts.

[0055] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A POM-based supramolecular nanostructured OER electrocatalytic material, characterized by: The POM-based supramolecular nanostructured OER electrocatalytic material contains Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O and transition metal atoms are alternately arranged to form a graphene-like bridge structure with a pore size of 2.7nm. Cetyltrimethylammonium bromide modification converts the water-soluble POM into a hydrophobic layered structure with a defined interlayer spacing of 3.5nm. The POM-based supramolecular nanostructured OER electrocatalytic material has a three-dimensional layered structure.

2. The POM-based supramolecular nanostructured OER electrocatalytic material according to claim 1, wherein: The POM-based supramolecular nanostructured OER electrocatalytic material was used as the anode and Pt / C as the cathode in an anion exchange membrane water electrolyzer, achieving a 2A cm-3 OER electrocatalytic efficiency of 2A cm-3 at a cell voltage of 2.247V. -2 current density.

3. A method for preparing the POM-based supramolecular nanostructured OER electrocatalytic material according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Synthesis of niobate precursor K7HNb6O 19 13H2O; S2. Weigh the niobate precursor, cobalt chloride, disodium hydrogen phosphate, sodium phosphate, sodium perborate, and deionized water into a polytetrafluoroethylene kettle and stir at room temperature for 0.5 h to uniformly mix the raw materials; S3, placing the polytetrafluoroethylene kettle in an oven for hydrothermal reaction; S4. Cool the polytetrafluoroethylene kettle after the hydrothermal reaction, filter and evaporate for 7 days to obtain Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O crystals; S5, Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O crystals were dissolved in water, and hexadecyltrimethylammonium bromide was added, followed by cobalt acetate, and the mixture was allowed to stand. The product was centrifugally washed three times with deionized water, washed once with anhydrous ethanol, and finally dried for 12 hours to obtain a POM-based supramolecular nanostructured OER electrocatalytic material.

4. The method for preparing a POM-based supramolecular nanostructured OER electrocatalytic material according to claim 3, characterized in that: In step S2, the molar addition ratio of the niobate precursor, cobalt chloride, disodium hydrogen phosphate, sodium phosphate, sodium perborate and deionized water is 30:6:1:3:

7.

5. The method for preparing a POM-based supramolecular nanostructured OER electrocatalytic material according to claim 3, characterized in that: In step S3, the reaction temperature of the hydrothermal reaction is 160° and the reaction time is 4 days.

6. The method for preparing a POM-based supramolecular nanostructured OER electrocatalytic material according to claim 3, characterized in that: In step S4, the polytetrafluoroethylene kettle after the hydrothermal reaction is cooled to room temperature, impurities are filtered, and volatilization is carried out at 30° C. for 7 days.

7. The method for preparing a POM-based supramolecular nanostructured OER electrocatalytic material according to claim 3, characterized in that: In step S5, the Na6K 12 [H2Co8O4(Nb6O 19 )4]·39H2O crystals, water, hexadecyltrimethylammonium bromide and cobalt acetate were added in a molar ratio of 1:2:3.

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