ZIFs / polyaniline multilevel structure composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of preparation and application of organic and inorganic composite materials, in particular to a ZIFs / polyaniline multilevel structure composite material and a preparation method and application thereof. The preparation method comprises the following steps: adding a metal compound into a solution containing a surfactant to obtain a metal salt solution A, adding an organic ligand into a solvent to obtain an organic ligand solution B, mixing the metal salt solution A and the organic ligand solution B, stirring for reaction, cooling, washing and drying to obtain a substrate metal ZIFs seed crystal, dispersing the substrate metal ZIFs seed crystal into the solvent, and performing ultrasonic treatment to obtain a suspension; and adding another metal compound and an organic ligand into the suspension, adjusting the pH value, carrying out hydrothermal reaction, cooling, washing and drying to obtain a multi-metal ZIFs material, adding the material into protonic acid, adding aniline and an oxidizing agent, carrying out stirring polymerization reaction in an ice bath, and carrying out strong coordination on polyaniline and metal sites on the ZIFs to obtain the composite material. The obtained composite material has excellent oxygen evolution performance in an electro-catalytic water decomposition oxygen evolution reaction.

Description

Technical Field

[0001] This invention relates to the field of organic-inorganic composite material preparation and application technology, specifically a ZIFs / polyaniline multi-level structure composite material and its preparation method and application. Background Technology

[0002] With global economic growth and population increase, the continuous consumption of fossil fuels (oil, coal, and natural gas) releases greenhouse gases such as carbon dioxide into the atmosphere, triggering a series of environmental problems. Protecting the environment and cherishing the planet, developing clean, sustainable, and renewable energy sources has become crucial. In recent years, researchers have made continuous technological innovations in the development of clean and renewable energy. Hydrogen energy is a promising new energy source with advantages such as high energy density, environmental friendliness, zero carbon emissions, and zero pollutants. Electrolysis of water is one of the simplest, lowest-cost, most efficient, and greenest methods for hydrogen production. The electricity required for this process can come from primary energy sources such as hydropower, solar energy, and wind power. Therefore, electrolysis of water is a highly attractive solution for achieving peak carbon emissions and carbon neutrality. Water electrolysis involves two half-reactions: the cathode hydrogen evolution reaction (HER) and the anode oxygen evolution reaction (OER). OER, the oxidation of water in the electrolyte solution to produce oxygen, occurs at the anode. OER (Organic Electrification) is an anodic four-electron transfer process that breaks hydrogen-oxygen bonds and forms oxygen double bonds. Kinetically, OER is very slow and requires a considerable overpotential to overcome a significant kinetic barrier. Therefore, OER has always been one of the key bottlenecks in the industrialization of hydrogen energy through water electrolysis.

[0003] Noble metals and their compounds are currently the only commercially viable OER electrocatalysts. However, their high cost and scarcity severely limit their widespread application in large-scale hydrogen production. Developing non-noble metal alternatives with both high OER electrocatalytic activity and lower cost has become a research hotspot in this field. Among these, transition metals are widely available and have a 3d valence electron structure. 6-8 4s 2 Unfilled d-electron orbitals have the ability to efficiently transfer and trap electrons, exhibiting excellent electrochemical performance. Transition metal compounds are considered to be among the most promising OER materials.

[0004] Zinc-ion interconnects (ZIFs) are a class of novel porous solid materials formed by the self-assembly of metal ions and organic ligands via coordination bonds. Due to their unique physicochemical properties, they have found wide applications in heterogeneous catalysis, gas adsorption, and separation. Compared to traditional inorganic materials, ZIFs possess ultra-high specific surface area and porosity, and their diverse structures, such as zero-dimensional nanoparticles, one-dimensional nanorods, and two-dimensional nanosheets, can be obtained by adjusting reaction conditions and preparation processes. Based on this, transition metal-based ZIFs are commonly used matrices for electrocatalytic materials. However, the metal nodes in ZIFs are mostly occupied by organic ligands, resulting in low electrical conductivity and catalytic activity. Therefore, it is urgent to address this issue using ligand modification, multi-metal site mixing, and heteroatom doping. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a ZIFs / polyaniline multi-level structure composite material, its preparation method, and its application. The multi-metal ZIFs / polyaniline composite material is prepared by using multi-metal ZIFs as a nucleating agent.

[0006] The present invention provides a method for preparing a ZIFs / polyaniline hierarchical composite material, which specifically includes the following steps: (1) A metal compound is added to a solution containing a surfactant and dissolved to obtain a metal salt solution A; an organic ligand is dissolved in a solvent to obtain an organic ligand solution B; metal salt solution A and organic ligand solution B are mixed and stirred at room temperature. After the reaction is completed, the mixture is cooled and centrifuged to separate the mixed solution obtained from the reaction. The supernatant is discarded and the lower precipitate is washed and dried to obtain the base metal ZIFs seed crystals. (2) The obtained base metal ZIFs seed crystals were uniformly dispersed in a solvent and ultrasonically sonicated to obtain a stable suspension. Another metal compound and organic ligand were added to the suspension, the pH was adjusted, and then the suspension was transferred to a stainless steel reactor with a polytetrafluoroethylene liner. The reactor was heated to carry out a hydrothermal reaction. After the reaction was completed, the mixture was cooled and centrifuged. The supernatant was discarded, the lower precipitate was washed and dried to obtain the multi-metal ZIFs material. (3) The obtained multi-metal ZIFs were used as nucleating agents and added to protic acid. Aniline and oxidant were added and ultrasonically dispersed evenly. Then, the mixture was stirred evenly in an ice bath. After the reaction was completed, the mixed solution was centrifuged and the upper clear liquid was discarded. The lower precipitate was washed until the washing liquid was neutral. After vacuum drying, multi-metal ZIFs / polyaniline composite material was obtained.

[0007] Preferably, the metal compound mentioned in step (1) and the other metal compound mentioned in step (2) are two of the following: Ni(NO3)2•6H2O, FeCl3•6H2O, Co(NO3)2•6H2O, MoCl3, CrCl3•6H2O, Zn(NO3)2•6H2O, and CuSO4•5H2O.

[0008] Preferably, the molar ratio of the metal element in the base metal ZIFs seed crystal in step (2) to the metal compound in step (2) is (1:0.2)-(1:0.5).

[0009] Preferably, the solution containing the surfactant in step (1) is a solution obtained by adding the surfactant to a solvent, wherein the surfactant is hexadecyltrimethylammonium bromide.

[0010] Preferably, the organic ligand in steps (1) and (2) is 2-methylimidazole.

[0011] Preferably, the solvent in steps (1) and (2) is one or more of deionized water, N,N-dimethylformamide (DMF), methanol, and ethanol.

[0012] Preferably, the total molar amount of the metal compound described in step (1) and the other metal compound described in step (2) is n1, and the total molar amount of the organic ligand described in step (1) and the organic ligand described in step (2) is n2, then the ratio of n1 to n2 is (1:2)-(1:5).

[0013] Preferably, the hydrothermal reaction temperature in step (2) is 25-150℃ and the time is 1-24h.

[0014] Preferably, the ultrasonic time in step (2) is half an hour; the pH is adjusted to 6.8-7.2 using ammonia.

[0015] Preferably, the protic acid in step (3) is one of hydrochloric acid, sulfuric acid, dodecylbenzenesulfonic acid, and acetic acid.

[0016] Preferably, the oxidant in step (3) is one of ammonium persulfate, potassium persulfate, hydrogen peroxide, and ferric chloride.

[0017] Preferably, the mass ratio of aniline to polymetallic ZIFs in step (3) is (1:1)-(1:2).

[0018] Preferably, the polymerization reaction time in step (3) is 5-24 hours.

[0019] Preferably, in step (3), the mixture is stirred evenly in an ice bath to induce a polymerization reaction, while polyaniline undergoes strong coordination with the metal sites on ZIFs.

[0020] The present invention also provides a ZIFs / polyaniline multi-level structure composite material obtained by the above preparation method and its application in the electrocatalytic water splitting oxygen evolution reaction.

[0021] Preferably, the application is in the electrocatalytic decomposition of water and oxygen evolution reaction in an alkaline electrolyte at room temperature.

[0022] Preferably, the application involves preparing a working electrode from a ZIFs / polyaniline multi-level structure composite material and performing an electrocatalytic oxygen evolution reaction in an alkaline electrolyte.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) The ZIFs / polyaniline multi-level structure composite material prepared by the present invention has multi-level structure characteristics. The innermost layer is a ZIFs structure of one metal, the middle layer is a ZIFs structure of another metal, and there is a transition layer between the two. The transition layer is a ZIFs structure with a topological structure formed by doping the two metals mentioned above. The outermost layer is a protonic acid-doped polyaniline layer with high electrical conductivity.

[0024] (2) Through the unique electronic synergistic effect of multiple metals, the addition of a second metal can increase the density of surface active sites and regulate the electronic structure of ZIFs, increase their interaction with oxygen intermediates, reduce the reaction energy barrier, and thus achieve efficient catalytic reaction.

[0025] (3) The present invention introduces a conductive polymer polyaniline to strongly coordinate with the metal sites on ZIFs, which can improve the conductivity of the catalyst. The hetero-elements in the conductive polymer can effectively regulate the electron density of the metal and improve the OER catalytic activity. Compared with the simple coating of the traditional carbon conductive layer, the conductive polymer can have a stronger coordination with the metal, which is more conducive to the transfer of electrons and accelerates the OER kinetics.

[0026] (4) In the preparation of composite materials, protic acid is added to the present invention to react with polyaniline to form imine cations. The charge is delocalized to the entire benzene ring and the conjugated skeleton of the quinone ring to form polyaniline conductive charge carriers. At the same time, the acid anion enters the molecular chain as a counter ion to balance the positive charge. The charge carriers can move freely, which greatly increases the conductivity of the catalyst. This acid-doped polyaniline is deposited on the surface of ZIFs, which improves the conductivity of ZIFs and reduces the charge transfer impedance.

[0027] (5) This invention synthesizes a high-performance composite catalyst based on multi-metal ZIFs under mild conditions, avoiding the high-temperature calcination process (which is not conducive to large-scale production and application) and solving the problem of complex electrocatalyst synthesis steps.

[0028] (6) The multi-metal ZIFs / polyaniline composite material provided by the present invention has an ultra-high specific surface area and abundant active sites, which greatly improves the electron transfer rate, can greatly improve the reaction efficiency and improve the catalytic performance, and has excellent catalytic performance in the electrocatalytic water splitting and oxygen evolution reaction.

[0029] (7) The multi-metal ZIFs / polyaniline composite material prepared by the present invention has excellent catalytic performance in the electrocatalytic water splitting and oxygen evolution reaction, has strong applicability, and has good practical application value. Attached Figure Description

[0030] Figure 1 The LSV curves are for testing the electrocatalytic hydrogen evolution performance of the ZIFs / polyaniline multi-level structure composite materials obtained in Examples 1-4.

[0031] Figure 2 Tafel curves are shown for the electrocatalytic hydrogen evolution performance test of the ZIFs / polyaniline hierarchical composite materials obtained in Examples 1-4.

[0032] Figure 3 The LSV curves are for testing the electrocatalytic oxygen evolution performance of the ZIFs / polyaniline multi-level structure composite materials obtained in Examples 1-4.

[0033] Figure 4 Tafel curves of the ZIFs / polyaniline hierarchical composite materials obtained in Examples 1-4 are used to test the electrocatalytic oxygen evolution performance.

[0034] Figure 5 The following are the CV curves at different scan rates for the electrocatalytic oxygen evolution performance test of the ZIFs / polyaniline hierarchical composite material obtained in Example 1. Figure 5 The directions indicated by the middle arrows correspond to 10mV / s, 20mV / s, 40mV / s, 60mV / s, and 80mV / s, respectively.

[0035] Figure 6 The following are the CV curves at different scan rates for the electrocatalytic oxygen evolution performance test of the ZIFs / polyaniline hierarchical composite material obtained in Example 2. Figure 6 The directions indicated by the middle arrows correspond to 20mV / s, 40mV / s, 60mV / s, and 80mV / s, respectively.

[0036] Figure 7The following are the CV curves at different scan rates for the electrocatalytic oxygen evolution performance test of the ZIFs / polyaniline hierarchical composite material obtained in Example 3. Figure 7 The directions indicated by the middle arrows correspond to 10mV / s, 20mV / s, 40mV / s, 60mV / s, and 80mV / s, respectively.

[0037] Figure 8 The following are the CV curves at different scan rates for the electrocatalytic oxygen evolution performance test of the ZIFs / polyaniline hierarchical composite material obtained in Example 4. Figure 8 The directions indicated by the middle arrows correspond to 10mV / s, 20mV / s, 40mV / s, 60mV / s, and 80mV / s, respectively.

[0038] Figure 9 The curves showing the change rate of current density versus the scan rate of the ZIFs / polyaniline multi-level composite materials obtained in Examples 1-4 for testing the electrocatalytic oxygen evolution performance. Detailed Implementation

[0039] To better understand the content of this invention, it will be further described below with reference to specific embodiments and accompanying drawings. The following embodiments are based on the technology of this invention and provide detailed implementation methods and operating steps, but the scope of protection of this invention is not limited to the following embodiments.

[0040] In step (1) of Examples 1-4, i.e., when preparing the base metal ZIFs seed crystals, the organic ligand 2-methylimidazole is in excess.

[0041] Example 1: (1) First, methanol and water with a volume ratio of 1:5 were mixed, and then 5 mg of hexadecyltrimethylammonium bromide was added to obtain 14 mL of mixed solution. Then, 2.9 g of Co(NO3)2•6H2O was dissolved in the above mixed solution to obtain metal salt solution A. Methanol and water with a volume ratio of 1:5 were mixed to obtain 70 mL of mixed solvent. Then, 4.14 g of organic ligand 2-methylimidazole was dissolved in the above mixed solvent to obtain organic ligand solution B. After mixing metal salt solution A and organic ligand solution B, the mixture was stirred at room temperature for 1 h. After the reaction was completed, the mixture was cooled naturally. The mixed solution obtained by the reaction was centrifuged and the supernatant was discarded. The lower precipitate was washed several times with ethanol and then dried in a vacuum oven at 80 °C for 24 h to obtain base metal ZIFs seed crystals. The molar ratio of cobalt to 2-methylimidazole in the base metal ZIFs seed crystals was 1:2. (2) Mix methanol and water in a volume ratio of 1:5 to obtain 15 mL of mixed solvent. Then, uniformly disperse 0.02 g of the base metal ZIFs seed crystals obtained in step (1) into the above mixed solvent. Sonicate for 30 min to obtain a stable suspension. Then, add 0.012 g of FeCl3•6H2O and 0.018 g of 2-methylimidazole to the above suspension respectively. Adjust the pH of the above suspension to 7 with ammonia water. Then, transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner. Heat to 80 °C and hydrothermally react for 3 h. After the reaction is completed, cool naturally. Centrifuge the mixed solution obtained from the reaction, discard the upper clear liquid, wash the lower precipitate several times with ethanol, and then vacuum dry in an oven at 80 °C for 24 h to obtain the multi-metal ZIFs material. (3) Take 0.01g of the polymetallic ZIFs obtained in step (2) and disperse it in 10mL of HCl solution with a concentration of 1mol / L. Then add 0.005g of aniline and 0.013g of ammonium persulfate in sequence and disperse it evenly by ultrasonication. Then stir it evenly in an ice bath for 5h to carry out the polymerization reaction. After the reaction is completed, centrifuge the mixed solution obtained, discard the supernatant, wash the lower precipitate with deionized water and ethanol until the washing liquid is neutral, and finally dry it under vacuum at 60℃ for 24h to obtain ZIFs / polyaniline multi-level structure composite material.

[0042] 5 mg of the ZIFs / polyaniline multi-level composite electrocatalyst powder obtained in Example 1 was placed in a small glass bottle. Then, 1 mL of a mixed solution of ethanol and deionized water and 50 µL of a 5 wt% Nafion solution were added. The volume ratio of ethanol to deionized water in the ethanol-deionized water mixture was 1:1. The bottle was then placed in an ultrasonic cleaner and ultrasonically cleaned for several hours to form a uniform catalyst ink. After ultrasonication, the obtained catalyst ink was dropped onto dilute hydrochloric acid-treated nickel foam. The nickel foam had a size of 1 × 1 cm. Specifically, 10 µL of catalyst ink was dropped onto the dilute hydrochloric acid-treated nickel foam each time using a pipette. The mixture was then dried at room temperature to obtain 5 mg of the desired catalyst ink. -2 Working electrode with catalyst loading. Its oxygen evolution reaction performance was tested in a 1 mol / L KOH electrolyte.

[0043] Example 2: (1) First, methanol and water with a volume ratio of 1:5 were mixed, and then 5 mg of hexadecyltrimethylammonium bromide was added to obtain 14 mL of mixed solution. Then, 2.9 g of Co(NO3)2•6H2O was dissolved in the above mixed solution to obtain metal salt solution A. Methanol and water with a volume ratio of 1:5 were mixed to obtain 70 mL of mixed solvent. Then, 2.07 g of organic ligand 2-methylimidazole was dissolved in the above mixed solvent to obtain organic ligand solution B. After mixing metal salt solution A and organic ligand solution B, the mixture was stirred at room temperature for 1 h. After the reaction was completed, the mixture was cooled naturally. The mixed solution obtained by the reaction was centrifuged and the supernatant was discarded. The lower precipitate was washed several times with ethanol and then dried in a vacuum oven at 80 °C for 24 h to obtain base metal ZIFs seed crystals. The molar ratio of cobalt to 2-methylimidazole in the base metal ZIFs seed crystals was 1:2. (2) Mix methanol and water in a volume ratio of 1:5 to obtain 15 mL of mixed solvent. Then, uniformly disperse 0.02 g of the base metal ZIFs seed crystals obtained in step (1) into the above mixed solvent. Sonicate for 30 min to obtain a stable suspension. Then, add 0.012 g FeCl3•6H2O and 0.009 g 2-methylimidazole to the above suspension respectively. Adjust the pH of the above suspension to 7 with ammonia water. Transfer the above suspension to a stainless steel reactor with a polytetrafluoroethylene liner. Heat to 80 °C and hydrothermally react for 3 h. After the reaction is completed, cool naturally. Centrifuge the mixed solution obtained from the reaction, discard the upper clear liquid, wash the lower precipitate several times with ethanol, and vacuum dry in an oven at 80 °C for 24 h to obtain the multi-metal ZIFs material. (3) Take 0.01g of the polymetallic ZIFs obtained in step (2) and disperse it in 10mL of HCl solution with a concentration of 1mol / L. Then add 0.005g of aniline and 0.013g of ammonium persulfate in sequence and disperse it evenly by ultrasonication. Then stir it evenly in an ice bath for 5h to carry out the polymerization reaction. After the reaction is completed, centrifuge the mixed solution obtained, discard the supernatant, wash the lower precipitate with deionized water and ethanol until the washing liquid is neutral, and finally dry it under vacuum at 60℃ for 24h to obtain ZIFs / polyaniline multi-level structure composite material.

[0044] 5 mg of the ZIFs / polyaniline multi-level composite electrocatalyst powder prepared in Example 2 was placed in a small glass bottle. Then, 1 mL of a mixed solution of ethanol and deionized water and 50 µL of a 5 wt% Nafion solution were added. The volume ratio of ethanol to deionized water in the ethanol-deionized water mixture was 1:1. The bottle was then placed in an ultrasonic cleaner and ultrasonically cleaned for several hours to form a uniform catalyst ink. After ultrasonication, the obtained catalyst ink was dropped onto dilute hydrochloric acid-treated nickel foam (1 × 1 cm). Specifically, 10 µL of catalyst ink was dropped onto the dilute hydrochloric acid-treated nickel foam each time using a pipette. The mixture was then dried at room temperature to obtain 5 mg of the desired catalyst ink. -2 Working electrode with catalyst loading. Its oxygen evolution reaction performance was tested in a 1 mol / L KOH electrolyte.

[0045] Example 3: (1) First, methanol and water with a volume ratio of 1:5 were mixed, and then 5 mg of hexadecyltrimethylammonium bromide was added to obtain 14 mL of mixed solution. Then, 2.9 g of Co(NO3)2•6H2O was dissolved in the above mixed solution to obtain metal salt solution A. Methanol and water with a volume ratio of 1:5 were mixed to obtain 70 mL of mixed solvent. Then, 4.14 g of organic ligand 2-methylimidazole was dissolved in the above mixed solvent to obtain organic ligand solution B. After mixing metal salt solution A and organic ligand solution B, the mixture was stirred at room temperature for 1 h. After the reaction was completed, the mixture was cooled naturally. The mixed solution obtained by the reaction was centrifuged and the supernatant was discarded. The lower precipitate was washed several times with ethanol and then dried in a vacuum oven at 80 °C for 24 h to obtain base metal ZIFs seed crystals. The molar ratio of cobalt to 2-methylimidazole in the base metal ZIFs seed crystals was 1:2. (2) Mix methanol and water in a volume ratio of 1:5 to obtain 15 mL of mixed solvent. Then, uniformly disperse 0.02 g of the base metal ZIFs seed crystals obtained in step (1) into the above mixed solvent. Sonicate for 30 min to obtain a stable suspension. Then, add 0.0048 g of FeCl3•6H2O and 0.0072 g of 2-methylimidazole to the above suspension respectively. Adjust the pH of the above suspension to 7 with ammonia water. Transfer the above suspension to a stainless steel reactor with a polytetrafluoroethylene liner. Heat to 80 °C and hydrothermally react for 3 h. After the reaction is completed, cool naturally. Centrifuge the mixed solution obtained from the reaction, discard the upper clear liquid, wash the lower precipitate several times with ethanol, and vacuum dry in an oven at 80 °C for 24 h to obtain the multi-metal ZIFs material. (3) Take 0.01g of the polymetallic ZIFs obtained in step (2) and disperse it in 10mL of HCl solution with a concentration of 1mol / L. Then add 0.005g of aniline and 0.013g of ammonium persulfate in sequence and disperse it evenly by ultrasonication. Then stir it evenly in an ice bath for 5h to carry out the polymerization reaction. After the reaction is completed, centrifuge the mixed solution obtained, discard the supernatant, wash the lower precipitate with deionized water and ethanol until the washing liquid is neutral, and finally dry it under vacuum at 60℃ for 24h to obtain ZIFs / polyaniline multi-level structure composite material.

[0046] 5 mg of the ZIFs / polyaniline multi-level composite electrocatalyst powder prepared in Example 3 was placed in a small glass bottle. Then, 1 mL of a mixed solution of ethanol and deionized water and 50 µL of a 5 wt% Nafion solution were added. The volume ratio of ethanol to deionized water in the ethanol-deionized water mixture was 1:1. The bottle was then placed in an ultrasonic cleaner and ultrasonically cleaned for several hours to form a uniform catalyst ink. After ultrasonication, the obtained catalyst ink was dropped onto dilute hydrochloric acid-treated nickel foam. The nickel foam had a size of 1 × 1 cm. Specifically, 10 µL of catalyst ink was dropped onto the dilute hydrochloric acid-treated nickel foam each time using a pipette. The mixture was then dried at room temperature to obtain 5 mg of the desired catalyst ink. -2 Working electrode with catalyst loading. Its oxygen evolution reaction performance was tested in a 1 mol / L KOH electrolyte.

[0047] Example 4: (1) First, methanol and water with a volume ratio of 1:5 were mixed, and then 5 mg of hexadecyltrimethylammonium bromide was added to obtain 14 mL of mixed solution. Then, 2.9 g of Co(NO3)2•6H2O was dissolved in the above mixed solution to obtain metal salt solution A. Methanol and water with a volume ratio of 1:5 were mixed to obtain 70 mL of mixed solvent. Then, 4.14 g of organic ligand 2-methylimidazole was dissolved in the above mixed solvent to obtain organic ligand solution B. After mixing metal salt solution A and organic ligand solution B, the mixture was stirred at room temperature for 1 h. After the reaction was completed, the mixture was cooled naturally. The mixed solution obtained by the reaction was centrifuged and the supernatant was discarded. The lower precipitate was washed several times with ethanol and then dried in a vacuum oven at 80 °C for 24 h to obtain base metal ZIFs seed crystals. The molar ratio of cobalt to 2-methylimidazole in the base metal ZIFs seed crystals was 1:2. (2) Mix methanol and water in a volume ratio of 1:5 to obtain 15 mL of mixed solvent. Then, uniformly disperse 0.02 g of the base metal ZIFs seed crystals obtained in step (1) into the above mixed solvent. Sonicate for 30 min to obtain a stable suspension. Then, add 0.012 g of FeCl3•6H2O and 0.018 g of 2-methylimidazole to the above suspension respectively. Adjust the pH of the above suspension to 7 with ammonia water. Transfer the above suspension to a stainless steel reactor with a polytetrafluoroethylene liner. Heat to 80 °C and hydrothermally react for 3 h. After the reaction is completed, cool naturally. Centrifuge the mixed solution obtained from the reaction, discard the upper clear liquid, wash the lower precipitate several times with ethanol, and vacuum dry in an oven at 80 °C for 24 h to obtain the multi-metal ZIFs material. (3) Take 0.01g of the polymetallic ZIFs obtained in step (2) and disperse it in 20mL of HCl solution with a concentration of 1mol / L. Then add 0.01g of aniline and 0.026g of ammonium persulfate and disperse it evenly by ultrasonication. Then stir it evenly in an ice bath for 5h to carry out the polymerization reaction. After the reaction is completed, centrifuge the mixed solution obtained, discard the supernatant, wash the lower precipitate with deionized water and ethanol until the washing liquid is neutral, and finally dry it under vacuum at 60℃ for 24h to obtain the ZIFs / polyaniline multi-level structure composite material.

[0048] 5 mg of the ZIFs / polyaniline multi-level composite electrocatalyst powder prepared in Example 4 was placed in a small glass bottle. Then, 1 mL of a mixed solution of ethanol and deionized water and 50 µL of a 5 wt% Nafion solution were added. The volume ratio of ethanol to deionized water in the ethanol-deionized water mixture was 1:1. The bottle was then placed in an ultrasonic cleaner and ultrasonically cleaned for several hours to form a uniform catalyst ink. After ultrasonication, the obtained catalyst ink was dropped onto dilute hydrochloric acid-treated nickel foam. The nickel foam had a size of 1 × 1 cm. Specifically, 10 µL of catalyst ink was dropped onto the dilute hydrochloric acid-treated nickel foam using a pipette each time. The mixture was then dried at room temperature to obtain 5 mg of the desired catalyst ink. -2 Working electrode with catalyst loading. Its oxygen evolution reaction performance was tested in a 1 mol / L KOH electrolyte.

[0049] Figure 1 The LSV curves of the ZIFs / polyaniline hierarchical composite materials obtained in Examples 1-4 are shown in the electrocatalytic hydrogen evolution performance test. Figure 1 It can be seen that the electrocatalysts prepared in Examples 1-4 have low hydrogen evolution overpotentials and current densities of 10 mA cm⁻¹. -2 The overpotentials were 310mV, 295mV, 285mV, and 272mV, respectively.

[0050] Figure 2 The Tafel curves for the electrocatalytic hydrogen evolution performance tests of the ZIFs / polyaniline hierarchical composite materials obtained in Examples 1-4 are shown below. Figure 2 The Tafel slopes of the electrocatalysts prepared in Examples 1-4 can be calculated, and are respectively 209 mVdec. -1 ,226mV dec -1 ,210mV dec -1 268mV dec -1 .

[0051] Figure 3 The LSV curves of the ZIFs / polyaniline hierarchical composite materials obtained in Examples 1-4 are shown in the electrocatalytic oxygen evolution performance test. Figure 1 It can be seen that the electrocatalysts prepared in Examples 1-4 have low oxygen evolution overpotentials at a current density of 10 mA cm⁻¹. -2 The overpotentials were 405mV, 393mV, 400mV, and 375mV, respectively.

[0052] Figure 4 The Tafel curves for the electrocatalytic oxygen evolution performance tests of the ZIFs / polyaniline hierarchical composite materials obtained in Examples 1-4 are shown below. Figure 2 The Tafel slopes of the electrocatalysts prepared in Examples 1-4 can be calculated, and are respectively 156 mVdec. -1 157mV dec -1 143mV dec -1 164mV dec -1 .

[0053] Figures 5-9 The figures show the CV curves and current density change rate versus scan rate curves of the ZIFs / polyaniline hierarchical composite materials obtained in Examples 1-4, respectively, for the electrocatalytic oxygen evolution performance test. Figure 9 The double-layer capacitance of the electrocatalysts prepared in Examples 1-4 can be calculated, and is 8.3 mF cm⁻¹. -2 6.3mF cm -2 8.6mF cm -2 13.7mF cm -2 .

[0054] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a ZIFs / polyaniline hierarchical composite material, characterized in that, Specifically, the following steps are included: (1) A metal compound is added to a solution containing a surfactant and dissolved to obtain a metal salt solution A; an organic ligand is dissolved in a solvent to obtain an organic ligand solution B; After mixing metal salt solution A and organic ligand solution B, the mixture was stirred at room temperature and then cooled. The resulting mixed solution was centrifuged, the supernatant was discarded, and the lower precipitate was washed and dried to obtain the base metal ZIFs seed crystals. (2) The obtained base metal ZIFs seed crystals were uniformly dispersed in a solvent and ultrasonically sonicated to obtain a stable suspension. Another metal compound and organic ligand were added to the suspension, the pH was adjusted, and then the suspension was transferred to a stainless steel reactor with a polytetrafluoroethylene liner. The reactor was heated to carry out a hydrothermal reaction. After the reaction was completed, the mixture was cooled and centrifuged. The supernatant was discarded, the lower precipitate was washed and dried to obtain the multi-metal ZIFs material. (3) The obtained multi-metal ZIFs were added to protic acid, aniline and oxidant were added and ultrasonically dispersed evenly. Then, the reaction was stirred evenly in an ice bath. After the reaction was completed, the mixed solution was centrifuged and the upper clear liquid was discarded. The lower precipitate was washed until the washing liquid was neutral. After vacuum drying, the multi-metal ZIFs / polyaniline composite material was obtained.

2. The method for preparing a ZIFs / polyaniline hierarchical composite material as described in claim 1, characterized in that, The metal compound mentioned in step (1) and the other metal compound mentioned in step (2) are two of the following: Ni(NO3)2•6H2O, FeCl3•6H2O, Co(NO3)2•6H2O, MoCl3, CrCl3•6H2O, Zn(NO3)2•6H2O, and CuSO4•5H2O.

3. The method for preparing a ZIFs / polyaniline hierarchical composite material as described in claim 1, characterized in that, The solution containing the surfactant in step (1) is a solution obtained by adding the surfactant to the solvent, wherein the surfactant is hexadecyltrimethylammonium bromide; the organic ligand in steps (1) and (2) is 2-methylimidazole; the solvent in steps (1) and (2) is one or more of deionized water, N,N-dimethylformamide, methanol, and ethanol.

4. The method for preparing a ZIFs / polyaniline hierarchical composite material as described in claim 1, characterized in that, In step (2), the ultrasonic time is half an hour, and the pH is adjusted to 6.8-7.2 using ammonia water.

5. The method for preparing a ZIFs / polyaniline hierarchical composite material as described in claim 1, characterized in that, The molar ratio of the metal in the base metal ZIFs seed crystal in step (2) to the metal compound in step (2) is (1:0.2)-(1:0.5); the total molar amount of one metal compound in step (1) and another metal compound in step (2) is n1, and the total molar amount of the organic ligand in step (1) and the organic ligand in step (2) is n2. Then the ratio of n1 to n2 is (1:2)-(1:5).

6. The method for preparing a ZIFs / polyaniline hierarchical composite material as described in claim 1, characterized in that, The mass ratio of aniline to polymetallic ZIFs in step (3) is (1:1)-(1:2).

7. The method for preparing a ZIFs / polyaniline hierarchical composite material as described in claim 1, characterized in that, In step (3), the protic acid is one of hydrochloric acid, sulfuric acid, dodecylbenzenesulfonic acid, or acetic acid; the oxidant is one of ammonium persulfate, potassium persulfate, hydrogen peroxide, or ferric chloride.

8. The method for preparing a ZIFs / polyaniline hierarchical composite material as described in claim 1, characterized in that, The hydrothermal reaction temperature in step (2) is 25-150℃ and the time is 1-24h; the polymerization reaction time in step (3) is 5-24h.

9. A ZIFs / polyaniline multi-level structure composite material obtained by any of the preparation methods described in claims 1-8.

10. The application of the ZIFs / polyaniline multi-level structure composite material as described in claim 9 in the electrocatalytic water splitting and oxygen evolution reaction.

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