Medium-entropy metal organic framework power generation material and preparation method and application thereof

Abstract

The invention belongs to the technical field of friction nano power generation material preparation, discloses a medium-entropy metal organic framework (MOF) power generation material as well as a preparation method and application thereof, and solves the technical problems that a nano friction generator prepared from a metal MOF material is small in current signal, difficult to synthesize and difficult to apply on a large scale. According to the invention, terephthalic acid and 4, 4 '-dipyridyl are used as organic ligands, and the organic ligands and transition metal centers of nickel, cobalt and iron are coordinated synergistically to form the medium-entropy MOF coordination polymer. The prepared CoNiFe-MOF has the advantages of being stable in structure, low in cost, easy to synthesize, excellent in friction power generation property and high in output signal. The stable alternating current signal output under the working frequency of 5 Hz can reach 85 microamperes, the voltage signal is 400 V or above, the stability is good, the stable output state can be kept within 10000 s, and the stable alternating current power supply is suitable for future commercial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of triboelectric nanogenerator materials, and particularly relates to the preparation of a metal-organic framework (MOF) material. Background Art

[0002] In recent years, the technology of triboelectric nanogenerators has developed rapidly. It has been found that many composite materials, electrospun fibers, and surface-treated materials prepared by different processes have considerable output signals in the working principle of vertical contact-separation triboelectric nanogenerators. However, there are still problems such as complex preparation processes. For example, the synthesis of traditional composite materials (such as electrospun materials and surface-treated materials) requires multiple-step reactions, high temperature and high pressure, or special equipment, resulting in high costs and difficulty in large-scale production; single functionality, existing materials mostly rely on single metals or simple binary systems, lacking the synergistic effect of multiple components, which limits the charge generation and transport efficiency of materials in triboelectricity; low output signal and poor stability, the current / voltage output of most materials is limited by low specific surface area and charge storage capacity, and it is easy to cause performance degradation due to structural collapse or interface failure during long-term cycling; low recyclability, traditional MOF materials are prone to structural damage during post-treatment (such as calcination and activation), resulting in irreversible decline in triboelectric performance, and it is difficult to meet the actual application requirements. These problems seriously hinder the further development and application of triboelectric nanogenerators.

[0003] Compared with traditional materials, metal-organic frameworks (MOFs) materials have controllability in size, structure, and function, with high porosity and rich pore structures. The cavity pore size can be adjusted, which can effectively increase the contact area between the material and the friction surface. In recent years, it has become an ideal carrier for many applications such as gas sensors, biosensors, drug delivery, fuel storage, catalysis, and adsorption. Among them, medium-entropy materials refer to materials containing two to four metal elements and having a mixing entropy in the range of 1-1.5r. They are usually easy to synthesize, and the reaction conditions are relatively simple, suitable for large-scale industrial production. Medium-entropy MOF materials have the unique cocktail effect of medium-high entropy materials compared with traditional multi-component MOF-derived materials. Traditional multi-component MOF materials often cause structural damage after post-treatment, while medium-entropy MOF materials can form a stable single-phase structure. Therefore, synthesizing new metal-organic framework materials and developing them into triboelectric materials with high performance, low cost, and good repeatability has important practical application significance. Summary of the Invention

[0004] Aiming at the technical problems that the current signal of the nanogenerator prepared from metal-organic framework (MOF) materials is small and difficult to synthesize, making it difficult to be applied on a large scale, the present invention proposes a medium-entropy metal-organic framework power generation material, its preparation method and application. Using terephthalic acid and 4,4'-bipyridine as organic ligands, they are coordinated with transition metal nickel, cobalt, and iron metal centers through synergistic coordination to form a medium-entropy MOF coordination polymer. Utilize the strong interaction between the ligand and the metal and the synergistic effect between the metals to form a stable medium-entropy MOF structure. It has high triboelectric performance, stable structure, low cost and is easy to synthesize.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] A preparation method of a medium-entropy metal-organic framework power generation material, the steps are as follows:

[0007] (1) Dissolve nickel salt, iron salt and cobalt salt in deionized water to obtain solution A. Various easily soluble inorganic salts can be used for the metal salts (nickel salt, iron salt and cobalt salt), such as hydrochloride, nitrate, sulfate, etc. Ni(d 8 ), Co(d 7 ), Fe(d 6 ) have similar coordination environments. The mixing of the three introduces electronic diversity, forms a local electron gradient through the "cocktail effect", reduces the triboelectric interface barrier, and enhances the contact electrification effect. The equimolar ratio of the three metals forms a stable single-phase structure, avoiding the phase separation problem that occurs in multi-component MOFs due to different solubilities and affinities. Its high-entropy effect inhibits grain boundary migration, ensuring the mechanical durability of the material during the friction process.

[0008] (2) Add terephthalic acid and 4,4'-bipyridine (4,4’-bipy) to an alkaline aqueous solution to obtain solution B. Terephthalic acid serves as a rigid carboxylic acid ligand. The carboxylic acid groups anchor the metal centers, ensuring the mechanical stability of the MOF. It forms a stable three-dimensional framework with metal centers (Ni, Co, Fe) through strong coordination bonds. Its conjugated structure is conducive to electron delocalization, enhancing the charge transport efficiency. Moreover, the rigid structure and strong metal coordination bonds endow the MOF with high thermal and chemical stability, forming a highly stable three-dimensional framework. In contrast, the carboxyl groups of phthalic acid in the ortho position are difficult to form a long-range ordered framework, and the monodentate coordination of benzoic acid is difficult to form a high-dimensional framework. 4,4'-bipyridine consists of two pyridine rings directly connected by carbon atoms, with two nitrogen atoms in the para position, having higher symmetry and directionality. Compared with 2,2’-bipyridine (V-shaped flexible linker) or ethylenediamine (flexible chain), 4,4'-bipyridine maintains a fixed geometric configuration during coordination, reducing structural distortion and being more likely to form an ordered extended framework. Using terephthalic acid and 4,4'-bipyridine as bidentate ligands, the two pyridine nitrogen atoms bridging metal ions tend to form one-dimensional chain-like or high-dimensional structures. Compared with imidazole-based (such as 2-methylimidazole) which often generates zeolite-type (ZIFs) structures, through the lone pair electrons of the pyridine ring coordinating with the metal center, additional axial coordination bonds (such as M-N bonds) are formed, enhancing the cross-linking density between metals. At the same time, the π-conjugated system can establish the π-π stacking ability between layers to construct a continuous electron transport path, optimizing the interlayer electron channels of the MOF and promoting the rapid longitudinal migration of frictional charges. Through the synergistic coordination of terephthalic acid and 4,4'-bipyridine, a "coordination system" that combines rigidity and flexibility is achieved, regulating the surface chemical properties of the MOF and optimizing the frictional interface.

[0009] (3) Mix solution A and solution B and stir for a period of time, then filter and dry to obtain CoNiFe(-BDC)-MOF, which is the medium-entropy metal-organic framework power generation material.

[0010] In the above step (1), the molar ratio of nickel salt, iron salt to cobalt salt is 1 - 1.25:1 - 1.25:1 - 1.25; the concentration of nickel salt in solution A is 0.028 - 0.038 mol / L.

[0011] In the above step (2), the molar ratio of terephthalic acid to 4,4'-bipyridine is 1:(0.5 - 2), the concentration of terephthalic acid in solution B is 0.04 - 0.08 mol / L; the base in the alkaline aqueous solution is a strong base.

[0012] Furthermore, the above strong base is potassium hydroxide or sodium hydroxide, and the molar ratio of the strong base to terephthalic acid is (1.5 - 3):1, aiming to completely deprotonate the terephthalic acid in the solution.

[0013] In the above step (3), the volume ratio of solution A to solution B is 1:(1.5 - 2.5); the mixing and stirring time is 10 - 30 min.

[0014] The medium-entropy metal-organic framework material prepared by the above preparation method.

[0015] The application of the above medium-entropy metal-organic framework power generation material in a triboelectric nanogenerator.

[0016] A triboelectric nanogenerator is prepared as follows:

[0017] S1. Use a mortar to fully grind the medium-entropy metal-organic framework power generation material for more than 30 min into a powder with a micron size (1 - 4 μm) without obvious particles. Cut a 5 cm × 5 cm copper tape, tear off the release paper, coat the powder on the adhesive surface, and use an ear syringe to blow the surface of the sample to evenly disperse the sample on the copper sheet. Finally, fix the copper wire on the other side of the copper sheet through silver epoxy resin as the electrode material for triboelectric power generation, and attach an insulating tape to the back of the copper sheet as a protective layer to obtain a sample electrode.

[0018] S2. Mix a certain amount of acetone, N,N-dimethylacetamide, and polyvinylidene fluoride powder in an eggplant-shaped flask, and heat and stir at 60 °C to dissolve to form a polyvinylidene fluoride solution. At a rotation speed of 2500 r / min of a KW 4A bench-type straightening machine, use a dropper to spin-coat the prepared polyvinylidene fluoride solution on the PI film for 120 seconds, and place it in an 80 °C oven for drying. Then adhere the copper sheet to the back of the PI film coated with polyvinylidene fluoride, fix the copper wire on the copper sheet through conductive silver epoxy resin, and attach an insulating tape to the outer layer as a protective layer to complete the preparation of the counter electrode for triboelectric power generation.

[0019] S3. Assemble a triboelectric nanogenerator using the vertical separation-contact power generation method.

[0020] The beneficial effects produced by the present invention are:

[0021] (1) Low cost, simple and fast synthesis. The present invention uses common transition metal inorganic salts as raw materials, uses terephthalic acid and 4,4'-bipyridine as an organic bidentate ligand combination, and uses a simple stirring method to safely, simply, and quickly prepare a medium-entropy metal-organic framework at room temperature, which is expected to be further implemented in large-scale industrial production.

[0022] (2) In the present invention, Ni(d 8 )、Co(d 7 )、Fe(d 6) They have similar coordination environments. The mixing of the three introduces electronic diversity, forming a local electron gradient through the "cocktail effect", reducing the friction interface barrier, and enhancing the contact electrification effect. The equimolar ratio of the three metals forms a single-phase structure, and its high-entropy effect inhibits grain boundary migration, ensuring the mechanical durability of the material during the friction process. Secondly, by using terephthalic acid and 4,4'-bipyridine as dual ligands, the hydrophobic benzene ring of terephthalic acid reduces the interference of environmental humidity on the triboelectric properties, while the polar pyridine group of 4,4'-bipyridine enhances the interfacial adsorption force between the material and the counter electrode (such as PVDF), reducing the contact resistance. And in terms of structure, the two complement each other in terms of rigidity and flexibility. While terephthalic acid provides appropriate rigidity to the MOF, 4,4'-bipyridine can provide higher freedom and better flexibility due to the relative presence of its nitrogen atoms. Through the above two aspects, the prepared medium-entropy metal-organic framework material has high triboelectric performance with a short-circuit current signal, and explores the influence and application of MOF materials in the field of triboelectric power generation from the perspective of entropy increase effect, expanding more new energy collection methods.

[0023] (3) The medium-entropy metal-organic framework CoNiFe(-BDC)-MOF of the present invention has excellent triboelectric properties and strong output signals. After stabilizing at a working frequency of 5 Hz, the alternating current signal can reach 80 - 90 μA, and the voltage signal is between 400 - 500 V, with good stability and can maintain a relatively stable output state within 10,000 s. The cost of raw materials is relatively low, which is suitable for future commercial applications. Brief Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 The molecular formulas of the ligands terephthalic acid (PTA) and 4,4'-bipyridine (4,4’-bipy).

[0026] Figure 2 The X-ray diffraction patterns (a) and infrared spectra (b) of the metal-organic framework materials prepared in Example 1 of the present invention and Comparative Examples 2 - 4.

[0027] Figure 3 The high-resolution transmission electron microscope photograph of the medium-entropy metal-organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention.

[0028] Figure 4X-ray photoelectron spectroscopy (XPS) of the medium-entropy metal-organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention, the full spectrum and the high-resolution spectra of each element.

[0029] Figure 5 Scanning electron microscope photos of the metal-organic frameworks prepared in Example 1 and Comparative Examples 1-5.

[0030] Figure 6 For the N of the metal-organic frameworks prepared in Example 1 and Comparative Examples 1-5 2 Adsorption-desorption curve.

[0031] Figure 7 Short-circuit current test diagram of the self-powered unit of the medium-entropy metal-organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention under the working condition of 5 Hz.

[0032] Figure 8 Short-circuit current performance of triboelectric nanogenerators assembled with different metal framework materials under the working condition of 5 Hz; among them, (a) are the metal-organic frameworks prepared in Example 1 and Comparative Examples 1-2; (b) are the metal-organic frameworks prepared in Example 1, Comparative Example 3 and Comparative Example 4.

[0033] Figure 9 Short-circuit current cycling stability of the triboelectric nanogenerator of the medium-entropy metal-organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention under the working condition of 5 Hz.

[0034] Figure 10 Open-circuit voltage diagram of the triboelectric nanogenerator of the medium-entropy metal-organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention under the working condition of 5 Hz.

[0035] Figure 11 Performance of the CoNiFe(-BDC)-MOF-TENG triboelectric nanogenerator at different working frequencies; among them, (a) is the open-circuit voltage; (b) is the short-circuit current.

[0036] Figure 12 Open-circuit voltage cycling stability of the triboelectric nanogenerator of the medium-entropy metal-organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention under the working condition of 5 Hz.

[0037] Figure 13 Power diagram of CoNiFe(-BDC)-MOF-TENG at a working frequency of 5 Hz.

[0038] Figure 14It is a diagram showing that CoNiFe(-BDC)-MOF-TENG lights up 1200 LED lights at a working frequency of 5 Hz. Detailed implementation mode

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings 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.

[0040] Example 1

[0041] The preparation method of the medium-entropy metal-organic framework power generation material in this embodiment is as follows:

[0042] (1) Disperse 78.52 mg (0.33 mmol) of cobalt chloride into 10 mL of deionized water under stirring. After stirring and dispersing evenly, add 78.44 mg (0.33 mmol) of nickel chloride. After stirring evenly, add 89.20 mg (0.33 mmol) of iron chloride, and ultrasonically disperse evenly to obtain a uniform solution A;

[0043] (2) Add 80 mg (2 mmol) of sodium hydroxide to 20 mL of deionized water under stirring to obtain a clear solution. Add 166.13 mg (1 mmol) of terephthalic acid (structural formula as Figure 1 shown), and ultrasonically mix evenly to obtain a uniform solution. Add 156.18 mg (1 mmol) of 4,4'-bipyridine (structural formula as Figure 1 shown), and ultrasonically mix evenly to obtain a uniform solution B;

[0044] (3) Add solution A to solution B, mix and stir for 10 minutes, then use a filter paper for suction filtration, and wash twice with deionized water and absolute ethanol respectively for purification to remove impurities. Place it in an oven and dry at 60 °C for more than 6 hours to obtain the medium-entropy metal-organic framework power generation material, named CoNiFe(-BDC)-MOF or NiCoFe(-BDC)-MOF.

[0045] Example 2

[0046] The preparation method of the medium-entropy metal-organic framework power generation material in this embodiment is as follows:

[0047] (1) 78.52 mg (0.33 mmol) of cobalt chloride was dispersed in 10 mL of stirred deionized water. After stirring to disperse evenly, 78.44 mg (0.33 mmol) of nickel chloride was added. After stirring evenly, 89.20 mg (0.33 mmol) of iron chloride was added, and ultrasonic dispersion was carried out to obtain a homogeneous solution A.

[0048] (2) 80 mg (2 mmol) of sodium hydroxide was added to 20 mL of stirred deionized water to obtain a clear solution. 166.13 mg (1 mmol) of terephthalic acid was added, and ultrasonic homogenization was carried out to obtain a homogeneous solution. 312.36 mg (2 mmol) of 4,4'-bipyridine was added, and ultrasonic homogenization was carried out to obtain a homogeneous solution B.

[0049] (3) Solution A was added to solution B, and after mixing and stirring for 2 h, suction filtration was carried out using filter paper, and purification treatment was carried out. It was washed twice with deionized water and absolute ethanol respectively, and then placed in an oven and dried at 60 °C for more than 6 hours to obtain a medium-entropy metal-organic framework power generation material, named CoNiFe(-BDC)-MOF or NiCoFe(-BDC)-MOF.

[0050] Example 3

[0051] The preparation method of the medium-entropy metal-organic framework power generation material in this example is as follows:

[0052] (1) 78.52 mg (0.33 mmol) of cobalt chloride was dispersed in 10 mL of stirred deionized water. After stirring to disperse evenly, 78.44 mg (0.33 mmol) of nickel chloride was added. After stirring evenly, 89.20 mg (0.33 mmol) of iron chloride was added, and ultrasonic dispersion was carried out to obtain a homogeneous solution A.

[0053] (2) 80 mg (2 mmol) of sodium hydroxide was added to 20 mL of stirred deionized water to obtain a clear solution. 166.13 mg (1 mmol) of terephthalic acid was added, and ultrasonic homogenization was carried out to obtain a homogeneous solution. 78.09 mg (0.5 mmol) of 4,4'-bipyridine was added, and ultrasonic homogenization was carried out to obtain a homogeneous solution B.

[0054] (3) Solution A was added to solution B, and after mixing and stirring for 30 minutes, suction filtration was carried out using filter paper, and purification treatment was carried out. It was washed twice with deionized water and absolute ethanol respectively, and then placed in an oven and dried at 60 °C for more than 6 hours to obtain a medium-entropy metal-organic framework power generation material, named CoNiFe(-BDC)-MOF or NiCoFe(-BDC)-MOF.

[0055] Example 4

[0056] The preparation method of the medium-entropy metal-organic framework power generation material in this embodiment is as follows:

[0057] (1) Disperse 83.27 mg (0.35 mmol) of cobalt chloride into 10 mL of stirred deionized water. After stirring and dispersing evenly, add 66.55 mg (0.28 mmol) of nickel chloride. After stirring evenly, add 94.60 mg (0.35 mmol) of iron chloride, and ultrasonically disperse evenly to obtain a homogeneous solution A;

[0058] (2) Add 120 mg (3 mmol) of sodium hydroxide to 25 mL of stirred deionized water to obtain a clear solution. Add 332.26 mg (2 mmol) of terephthalic acid, and ultrasonically mix evenly to obtain a homogeneous solution. Add 156.18 mg (1 mmol) of 4,4'-bipyridine, and ultrasonically mix evenly to obtain a homogeneous solution B;

[0059] (3) Add solution A to solution B, mix and stir for 30 minutes, then use filter paper for suction filtration, and wash twice with deionized water and absolute ethanol respectively for purification to remove impurities. Place it in an oven and dry at 60 °C for more than 6 hours to obtain the medium-entropy metal-organic framework power generation material, named CoNiFe(-BDC)-MOF or NiCoFe(-BDC)-MOF.

[0060] Example 5

[0061] The preparation method of the medium-entropy metal-organic framework power generation material in this embodiment is as follows:

[0062] (1) Disperse 71.38 mg (0.30 mmol) of cobalt chloride into 10 mL of stirred deionized water. After stirring and dispersing evenly, add 90.32 mg (0.38 mmol) of nickel chloride. After stirring evenly, add 127.04 mg (0.47 mmol) of iron chloride, and ultrasonically disperse evenly to obtain a homogeneous solution A;

[0063] (2) Add 72 mg (1.8 mmol) of sodium hydroxide to 15 mL of stirred deionized water to obtain a clear solution. Add 99.68 mg (0.6 mmol) of terephthalic acid, and ultrasonically mix evenly to obtain a homogeneous solution. Add 156.18 mg (1 mmol) of 4,4'-bipyridine, and ultrasonically mix evenly to obtain a homogeneous solution B;

[0064] (3) Add solution A to solution B, mix and stir for 20 minutes, then use filter paper for suction filtration. Wash twice with deionized water and anhydrous ethanol respectively for purification to remove impurities, and place in an oven to dry at 60 °C for more than 6 hours to obtain the medium-entropy metal-organic framework power generation material, named CoNiFe(-BDC)-MOF or NiCoFe(-BDC)-MOF.

[0065] Comparative Example 1

[0066] The preparation method of the metal-organic framework (Ni-MOF) power generation material in this comparative example is as follows:

[0067] (1) Disperse 237.69 mg (1 mmol) of nickel chloride into 10 mL of deionized water under stirring. After stirring and dispersing evenly, perform ultrasonic dispersion to obtain a homogeneous solution A;

[0068] (2) Add 80 mg (2 mmol) of sodium hydroxide to 20 mL of deionized water under stirring to obtain a clear solution. Add 166.13 mg (1 mmol) of terephthalic acid, perform ultrasonic homogenization to obtain a homogeneous solution. Add 156.18 mg (1 mmol) of 4,4'-bipyridine, perform ultrasonic homogenization to obtain a homogeneous solution B;

[0069] (3) Add solution A to solution B, mix and stir for 10 min, then use filter paper for suction filtration, and perform purification treatment. Wash twice with deionized water and anhydrous ethanol respectively, and place in an oven to dry at 60 °C for more than 6 hours to obtain the medium-entropy metal-organic framework power generation material, named Ni-MOF.

[0070] Comparative Example 2

[0071] The preparation method of the medium-entropy metal-organic framework (NiFe-MOF) power generation material in this comparative example is as follows:

[0072] (1) Disperse 118.85 mg (0.5 mmol) of nickel chloride into 10 ml of deionized water under stirring. After stirring and dispersing evenly, add 145.02 mg (0.5 mmol) of cobalt chloride, and perform ultrasonic dispersion to obtain a homogeneous solution A;

[0073] (2) Add 80 mg (2 mmol) of sodium hydroxide to 20 mL of deionized water under stirring to obtain a clear solution. Add 166.13 mg (1 mmol) of terephthalic acid, perform ultrasonic homogenization to obtain a homogeneous solution. Add 156.18 mg (1 mmol) of 4,4'-bipyridine, perform ultrasonic homogenization to obtain a homogeneous solution B;

[0074] (3) Add solution A to solution B, mix and stir for 10 min, then use filter paper for suction filtration, and perform purification treatment. Wash twice with deionized water and anhydrous ethanol respectively, and place in an oven to dry at 60 °C for more than 6 hours to obtain the medium-entropy metal-organic framework power generation material, named NiFe-MOF.

[0075] Comparative Example 3

[0076] The preparation method of the medium-entropy metal-organic framework power generation material in this comparative example is as follows:

[0077] (1) Disperse 78.52 mg (0.33 mmol) of cobalt chloride into 10 mL of stirred deionized water. After stirring and dispersing evenly, add 78.44 mg (0.33 mmol) of nickel chloride. After stirring evenly, add 89.20 mg (0.33 mmol) of iron chloride, and ultrasonically disperse evenly to obtain a homogeneous solution A;

[0078] (2) Add 80 mg (2 mmol) of sodium hydroxide to 20 mL of stirred deionized water to obtain a clear solution. Add 181.14 mg (1 mmol) of 2-aminoterephthalic acid, and ultrasonically disperse evenly to obtain a homogeneous solution B;

[0079] (3) Add solution A to solution B, mix and stir for 10 minutes, then use filter paper for suction filtration, and perform purification treatment. Wash twice with deionized water and anhydrous ethanol respectively, and place in an oven to dry at 60 °C for more than 6 hours to obtain the medium-entropy metal-organic framework power generation material, named CoNiFe(-NH 2 )-MOF.

[0080] Comparative Example 4

[0081] The preparation method of the medium-entropy metal-organic framework power generation material in this comparative example is as follows:

[0082] (1) Disperse 78.52 mg (0.33 mmol) of cobalt chloride into 10 mL of stirred deionized water. After stirring and dispersing evenly, add 78.44 mg (0.33 mmol) of nickel chloride. After stirring evenly, add 89.20 mg (0.33 mmol) of iron chloride, and ultrasonically disperse evenly to obtain a homogeneous solution A;

[0083] (2) Add 80 mg (2 mmol) of sodium hydroxide to 20 mL of stirred deionized water to obtain a clear solution. Add 112.17 mg (1 mmol) of triethylenediamine, and ultrasonically disperse evenly to obtain a homogeneous solution B;

[0084] (3) Add solution A to solution B, mix and stir for 10 minutes, then filter with filter paper, and perform purification treatment. Wash twice with deionized water and absolute ethanol respectively, and dry in an oven at 60 °C for more than 6 hours to obtain the medium-entropy metal-organic framework power generation material, named CoNiFe(-TEDA)-MOF.

[0085] Example of implementation effect

[0086] Physically characterize the materials prepared in Example 1 and Comparative Examples 1-4 by XRD, FT-IR, SEM, HRTEM, XPS, and BET.

[0087] Figure 2 X-ray diffraction pattern (a) and infrared spectrum (b) of the metal-organic framework materials prepared in Example 1 and Comparative Examples 1-2 of the present invention. As can be seen from Figure 2 a, the characteristic peaks of the sample CoNiFe(-BDC)-MOF in Example 1 are consistent with those of the control group samples. Infrared spectrum (FT-IR)( Figure 2 b) shows that the characteristic peaks of the sample CoNiFe(-BDC)-MOF in Example 1 are consistent with those of the control group samples.

[0088] Figure 3 High-resolution transmission electron microscope photograph of the medium-entropy metal-organic framework NiCoFe(-BDC)-MOF (CoNiFe(-BDC)-MOF) prepared in Example 1 of the present invention. It can be seen that the particle size of the NiCoFe(-BDC)-MOF prepared in the present invention is 15-30 nm, presenting an amorphous structure.

[0089] Figure 4 X-ray photoelectron spectrum (XPS) of the medium-entropy metal-organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention. As can be seen from the figure, the high-signal spectra of each element in the full spectrum indicate that each element of the prepared material exists uniformly and stably in the material, and the valence state distribution of each element is in the high-resolution spectrum.

[0090] Figure 5 Scanning electron microscope photographs of the metal-organic frameworks prepared in Example 1 and Comparative Examples 1-4. It can be seen that the single-metal, double-metal, and triple-metal MOFs all present an irregular flaky structure with a size of 80-150 nm, while the morphology prepared with diaminoterephthalic acid and triethylenediamine as ligands presents a uniform crystalline state and an uneven blocky state.

[0091] Figure 6 N 2 adsorption-desorption curve of the metal-organic frameworks prepared in Example 1 and Comparative Examples 1-2. It can be seen that the curve is not completely closed, which is the reason for the small BET of the MOF material.

[0092] Application Example

[0093] The materials prepared in Example 1 and Comparative Examples 1-4 of the present invention were applied to a triboelectric nanogenerator, and the specific preparation method is as follows.

[0094] (1) Preparation of sample electrode material

[0095] Use a mortar to fully grind the sample for more than 30 minutes into a powder of micron size (1-4 μm) without obvious particles, and coat it on a copper sheet of 5 cm × 5 cm. Use an ear bulb to blow the surface of the sample to evenly disperse the sample on the copper sheet. Finally, fix the copper wire on the other side of the copper sheet through silver epoxy resin as the electrode material for triboelectric power generation, and apply insulating tape on the back of the copper sheet as a protective layer.

[0096] (2) Preparation of counter electrode material

[0097] Put 12.5 g of acetone, 8.5 g of N,N-dimethylacetamide and 3.75 g of polyvinylidene fluoride powder in a 100 mL flask, and heat and stir at 60 °C for 30 minutes to dissolve and form a polyvinylidene fluoride solution. At a rotation speed of 2500 r / min of a KW-4A bench straightening machine, use a dropper to spin-coat the prepared polyvinylidene fluoride solution on a PI film. The spin-coating time is 120 seconds, and it is placed in an 80 °C oven for drying. Then, adhere a copper sheet to the back of the PI film coated with polyvinylidene fluoride, and fix the copper wire on the copper sheet with conductive silver epoxy resin. Apply insulating tape on the outer layer as a protective layer to complete the preparation of the counter electrode for triboelectric power generation.

[0098] (3) Assembly

[0099] Use the electrode material prepared in step (1) as the positive electrode sheet and the electrode material prepared in step (2) as the negative electrode sheet. Place the material surfaces parallel to each other, and the insulating tape surfaces as the protective layers face outward. A triboelectric nanogenerator is formed by using the vertical separation-contact power generation method.

[0100] Conduct relevant triboelectric performance tests on the prepared triboelectric nanogenerator:

[0101] (1) Short-circuit current test

[0102] Under room temperature environment, use a voice coil motor of model SUTP from Wanzida Motor Manufacturing Co., Ltd. to simulate mechanical energy at different frequencies of 1 Hz, 2 Hz, 4 Hz, 5 Hz, 6 Hz, and 8 Hz. Then connect the two copper wires in the triboelectric nanogenerator to both ends of a low-noise current amplifier of model SR570 produced by Stanford Research System Company to collect short-circuit current signals. The charge density σ per unit area is obtained by integrating the curve of time and current under the working condition of 5 Hz. Calculated

[0103] Figure 7 This is the short - circuit current test of the self - powered unit within 10 seconds when the medium - entropy metal - organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention operates at 5 Hz. The current signal ranges from - 55 to 85 μA.

[0104] Figure 8 It is the short - circuit current performance of triboelectric nanogenerators assembled with different metal - framework materials when operating at 5 Hz; among them, Figure 8 a is the comparison chart of the short - circuit current performance of triboelectric nanogenerators assembled with the metal - organic frameworks prepared in Example 1, Comparative Example 1, and Comparative Example 2 as raw materials. It can be seen that at a working frequency of 5 Hz, the short - circuit current signal of Ni - MOF ranges from - 45 μA to 82 μA, the short - circuit current signal of NiFe - MOF ranges from - 30 μA to 45 μA, and the short - circuit current signal of CoNiFe(-BDC)-MOF ranges from - 60 μA to 90 μA; Figure 8 b is the comparison chart of the short - circuit current performance of triboelectric nanogenerators assembled with the metal - organic frameworks prepared in Example 1, Comparative Example 3, and Comparative Example 4 as raw materials. It can be seen that at a working frequency of 5 Hz, the short - circuit current signal of CoNiFe(-NH 2 )-MOF ranges from - 25 μA to 70 μA, and the short - circuit current signal of CoNiFe(-TEDA)-MOF ranges from - 22 μA to 60 μA.

[0105] (2) Short - circuit current cycling stability test

[0106] At room temperature, a voice - coil motor of model SUTP from WANZIDA Motor Manufacturing Co., Ltd. is used to simulate mechanical energy at a frequency of 5 Hz. Then, the two copper wires in the triboelectric nanogenerator are respectively connected to both ends of a low - noise current amplifier of model SR570 produced by Stanford Research System Company to collect the short - circuit current signal. The short - circuit current cycling stability at a working frequency of 5 Hz is as Figure 9 shown. Figure 9 This is the short - circuit current cycling stability of the triboelectric nanogenerator with the medium - entropy metal - organic framework CoNiFe(-BDC)-MOF prepared in Example 1 of the present invention for 10000 seconds when operating at 5 Hz. The current signal ranges from - 60 μA to 90 μA.

[0107] (3) Open - circuit voltage test

[0108] At room temperature, a voice coil motor of model SUTP manufactured by Wanzida Motor Manufacturing Co., Ltd. was used to simulate mechanical energy at different frequencies of 1 Hz, 2 Hz, 4 Hz, 5 Hz, 6 Hz, and 8 Hz. Then, two copper wires in the triboelectric nanogenerator were respectively connected to both ends of a high-power digital source meter of model 2657A produced by Tektronix, Inc. to collect the open-circuit voltage signal.

[0109] Figure 10 The open-circuit voltage diagram of the triboelectric nanogenerator prepared in Example 1 of the present invention with the medium-entropy metal-organic framework CoNiFe(-BDC)-MOF under the working condition of 5 Hz shows that the open-circuit voltage is stable above 500 V within 10 s.

[0110] Figure 11 It is a comparison diagram of the short-circuit current and open-circuit voltage of the CoNiFe(-BDC)-MOF-TENG triboelectric nanogenerator at different working frequencies. From Figure 11 a, it can be seen that the open-circuit voltage at a working frequency of 1 Hz is 350 V, the open-circuit voltage at a working frequency of 2 Hz is 420 V, the open-circuit voltage at a working frequency of 4 Hz is 460 V, the open-circuit voltage at a working frequency of 5 Hz is 500 V, the open-circuit voltage at a working frequency of 6 Hz is 540 V, and the open-circuit voltage at a working frequency of 8 Hz is 580 V; from Figure 11 b, it can be seen that the short-circuit current at a working frequency of 1 Hz ranges from -10 μA to 50 μA, the short-circuit current at a working frequency of 2 Hz ranges from -20 μA to 70 μA, the short-circuit current at a working frequency of 4 Hz ranges from -40 μA to 78 μA, the short-circuit current at a working frequency of 5 Hz ranges from -58 μA to 85 μA, the short-circuit current at a working frequency of 6 Hz ranges from -64 μA to 86 μA, and the short-circuit current at a working frequency of 8 Hz ranges from -80 μA to 87 μA.

[0111] (4) Open-circuit voltage cycling stability

[0112] At room temperature, a voice coil motor of model SUTP manufactured by Wanzida Motor Manufacturing Co., Ltd. was used to simulate mechanical energy at a frequency of 5 Hz. Then, two copper wires in the triboelectric nanogenerator were respectively connected to both ends of a high-power digital source meter of model 2657A produced by Tektronix, Inc. to collect the open-circuit voltage signal. The open-circuit voltage stability at a working frequency of 5 Hz is as shown in Figure 12 the figure. It can be seen from the figure that the open-circuit voltage of the triboelectric nanogenerator prepared with CoNiFe(-BDC)-MOF is stable above 400 V for more than 50,000 working cycles (i.e., 10,000 s).

[0113] (5) Power density test

[0114] First, the well-ground NiCoFe(-BDC)-MOF powder was coated on a copper sheet of 5 cm × 6 cm. Then, a copper sheet of 5 cm × 6 cm was adhered to the counter electrode as the conductive layer, and the copper wires were fixed on the copper sheet with conductive silver epoxy resin. At room temperature, a voice coil motor of model SUTP manufactured by Wanzhida Motor Manufacturing Co., Ltd. was used to simulate mechanical energy at a frequency of 5 Hz. Then, the two copper wires were respectively connected to both ends of a low-noise current amplifier of model SR570 produced by Stanford Research System to collect short-circuit current signals. By externally connecting a load resistor with different resistance values from 10 2 to 10 8 Ω, the current I was measured, and the power was calculated through P = I 2 R, where I represents the short-circuit current and R represents the corresponding resistance. Figure 13 is the power diagram of CoNiFe(-BDC)-MOF-TENG at a working frequency of 5 Hz. It can be seen that for the triboelectric nanogenerator, the change of current signals with different resistance values from 10 2 to 10 8 Ω was measured. When a resistor of 100 Ω was connected, the current value was 76 μA. Then, as the resistance value of the connected resistor increased, the current gradually decreased. Until the resistance value of the connected resistor reached 10 6 Ω, due to ohmic loss, the current decreased significantly. When the resistance value reached 10 8 Ω, the current value was only 14 μA. In Figure 13 , the power situation of the triboelectric nanogenerator was shown. As different resistance values were connected, the change of its power was opposite to the change of current, which was caused by the influence of the external load resistance on the short-circuit current and the corresponding output power. The output power P was calculated through the formula P = I 2 R. Then, when the external load resistance reached 10 6 , the electric power began to increase. When the load resistance was about 40 MΩ, the maximum power reached 1.79 mW.

[0115] Figure 14 is the diagram of CoNiFe(-BDC)-MOF-TENG lighting 1200 LED lights at a working frequency of 5 Hz. It can be seen that the triboelectric nanogenerator can light LED lights simultaneously, indicating that the instantaneous voltage can reach a relatively high value, meeting certain application requirements.

[0116] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a medium-entropy metal-organic framework power generation material, characterized in that: Here are the steps: (1) dissolving nickel salt, iron salt and cobalt salt in deionized water to obtain a uniform solution A; (2) adding terephthalic acid and 4,4'-bipyridine to an alkaline aqueous solution, stirring or ultrasonicating to obtain a solution B; (3) Pour solution A into solution B, mix well, filter and dry.

2. The method for preparing the medium-entropy metal-organic framework power generation material according to claim 1, characterized in that: In the step (1), the molar ratio of the nickel salt, the iron salt and the cobalt salt is 1-1.25:1-1.25:1-1.25; the concentration of the nickel salt in solution A is 0.028-0.038 mol / L.

3. The method for preparing the medium-entropy metal-organic framework power generation material according to claim 1 or 2, characterized in that: In step (1), the nickel salt is nickel chloride, nickel nitrate or nickel sulfate; the iron salt is iron chloride, iron nitrate or iron sulfate; and the cobalt salt is cobalt chloride, cobalt nitrate or cobalt sulfate.

4. The method for preparing the medium-entropy metal-organic framework power generation material according to claim 3, characterized in that: In the step (2), the molar ratio of terephthalic acid to 4,4'-bipyridine is 1:(0.5-2), the concentration of terephthalic acid in solution B is 0.04-0.08 mol / L; and the base in the alkaline aqueous solution is a strong base.

5. The method for preparing the medium-entropy metal-organic framework power generation material according to claim 4, characterized in that: The strong base is potassium hydroxide or sodium hydroxide, and the molar ratio of the strong base to terephthalic acid is (1.5-3):

1.

6. The method for preparing the medium-entropy metal-organic framework power generation material according to claim 4, characterized in that: In the step (3), the volume ratio of solution A to solution B is 1:(1.5-2.5); and the stirring time is 10-30 min.

7. A medium-entropy metal-organic framework power generation material prepared by the preparation method according to claim 1.

8. Use of the medium-entropy metal-organic framework power generation material according to claim 7 in a friction nanogenerator.

9. A friction nanogenerator, characterized in that: The preparation steps are as follows: S1. Grind the medium entropy metal organic framework power generation material according to claim 7 to 1-4 μm, and apply it on a copper sheet; fix the copper wire on the other side of the copper sheet by silver epoxy resin to obtain a sample electrode; S2. The polyvinylidene fluoride solution is applied to the PI film and dried; then, a copper sheet is adhered to the back of the polyvinylidene fluoride PI film, and a copper wire is fixed to the copper sheet to obtain a counter electrode; S3. The counter electrode and sample electrode are assembled into a friction nanogenerator using a vertical separation-contact power generation method.

10. The triboelectric nanogenerator according to claim 9, characterized in that: The solvents in the polyvinylidene fluoride solution in step S3 are acetone and N,N-dimethylacetamide.

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