Application of benzoquinonyl covalent organic framework material as bifunctional photocatalyst in photo-assisted lithium-air battery

Abstract

The invention discloses application of a benzoquinone-based covalent organic framework material as a bifunctional photocatalyst in a photo-assisted lithium-air battery, and the benzoquinone-based covalent organic framework material is prepared by taking cyclohexanehexone octahydrate and 2, 3, 5, 6-tetraaminocyclohexane-2, 5-diene-1, 4-diketone as raw materials, ethylene glycol as a solvent and acetic acid as a catalyst through a hydrothermal reaction. And carrying out Schiff base reaction under the protection of nitrogen atmosphere. The benzoquinonyl covalent organic framework material has a large number of donor and acceptor units, has a wide visible light absorption range, can be used as a photo-assisted lithium-air battery bifunctional photocatalyst, greatly inhibits photon-generated carrier recombination, reduces the over-potential of a photo-assisted lithium-air battery, remarkably improves the battery assembly efficiency, and has a wide application prospect. And a new direction is provided for selection of photocatalysts in the field of lithium-air batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-air battery technology, specifically relating to the application of a benzoquinone-based covalent organic framework material as a bifunctional photocatalyst in light-assisted lithium-air batteries. Background Technology

[0002] To meet the demands for high-energy-density, long-life, safe, and cost-effective energy conversion and storage devices, photo-assisted lithium-air batteries have received significant attention and experienced exciting development over the past decade. However, the high decomposition kinetics and insufficient conductivity of their discharge products (Li₂O₂, Li₂CO₃, etc.) lead to large charge / discharge overpotentials, slow reaction kinetics, poor cycle performance, and numerous side reactions, severely hindering their further development and practical application. To address these challenges, developing more efficient photocatalysts to effectively promote the cathode reaction in photo-assisted lithium-air batteries is crucial. Covalent organic frameworks (COFs) are a class of crystalline porous polymer materials assembled from lightweight organic structural units through strong covalent bonds. They exhibit excellent photoelectric active structures and can serve as channels for photon capture and charge carrier transport. However, due to the poor conductivity of COFs themselves, the reaction kinetics are slow, resulting in poor rate performance of the prepared lithium-air batteries. Summary of the Invention

[0003] The purpose of this invention is to provide an application of benzoquinone-based covalent organic framework materials as bifunctional photocatalysts in light-assisted lithium-air batteries.

[0004] The above-mentioned benzoquinone-based covalent organic framework material was prepared by the following method: Step 1: Sonicately mix cyclohexane hexaone octahydrate and 2,3,5,6-tetraaminocyclohexane-2,5-diene-1,4-dione in a mixture of ethylene glycol and 3 mol / L aqueous acetic acid solution; Step 2: After ultrasonic mixing in Step 1, the solution is subjected to freezing-vacuuming-thawing operations, which are repeated 3 times. Then, nitrogen gas is introduced for protection. Step 3: The nitrogen-protected solution from Step 2 is heated at 110–130 °C for 90–100 h. The resulting solution is filtered, and the solid product is subjected to Soxhlet extraction using acetone as a washing agent. Subsequently, it is vacuum dried at 50–70 °C to obtain the benzoquinone-based covalent organic framework material. The purpose of the Soxhlet extraction is to remove unreacted residual reactants and byproducts.

[0005] In step 1 above, the preferred mass ratio of the cyclohexanehexanone octhydrate to 2,3,5,6-tetraaminocyclohex-2,5-diene-1,4-dione is 1.0 to 1.5:1.

[0006] In step 1 above, the volume ratio of ethylene glycol to 3 mol / L acetic acid aqueous solution in the mixture is preferably 1:1.

[0007] In step 2 above, the ultrasonically mixed solution from step 1 is rapidly frozen in liquid nitrogen at -180 to -200 °C, then evacuated, and then thawed in water to complete the freezing-evacuation-thawing operation. The freezing-evacuation-thawing operation is repeated 3 times, and then nitrogen gas is introduced for protection.

[0008] The beneficial effects of this invention are as follows: 1. This invention uses cyclohexanehexaone octahedrate and 2,3,5,6-tetraaminocyclohexane-2,5-diene-1,4-dione as raw materials, ethylene glycol as solvent, and acetic acid as catalyst, and carries out a Schiff base reaction under high temperature and nitrogen atmosphere protection to finally obtain a benzoquinone-based covalent organic framework material. The benzoquinone-based covalent organic framework material of this invention, as a bifunctional photocatalyst for lithium-air batteries, exhibits ultra-high performance in photo-assisted lithium-air battery applications. Photo-assisted lithium-air batteries assembled with the benzoquinone-based covalent organic framework material as a bifunctional photocatalyst possess excellent performance with high round-trip efficiency, high rate performance, and good cycle stability, mainly attributed to the large number of donor and acceptor units in the benzoquinone-based covalent organic framework material, which can effectively suppress the recombination of photogenerated carriers.

[0009] 2. The method for preparing benzoquinone-based covalent organic framework materials in this invention is simple and has low production cost. Benzoquinone-based covalent organic framework materials can be prepared using a simple Schiff base reaction. Furthermore, this invention is the first to apply benzoquinone-based covalent organic framework materials to photo-assisted lithium-air batteries, providing a new direction for the selection of catalysts in the field of lithium-air batteries. Attached Figure Description

[0010] Figure 1 These are infrared comparison spectra of four COFs materials.

[0011] Figure 2 These are Raman comparison spectra of four COFs materials.

[0012] Figure 3 This is a field emission scan image of COF-2.

[0013] Figure 4 These are XPS comparison spectra of C 1s for four COFs materials.

[0014] Figure 5 These are the surface potentials and line scan surface potentials of four COFs materials.

[0015] Figure 6 These are the charge-discharge performance test spectra of lithium-air batteries assembled with four COFs materials under both light and non-light conditions.

[0016] Figure 7 This is a comparison chart of the overpotential and round-trip efficiency of lithium-air batteries assembled with four COFs materials under both light and non-light conditions. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to these embodiments. Example 1

[0018] Preparation of benzoquinone-based covalent organic framework materials Step 1: Add 1.25 g of cyclohexanehexanone octahydrate and 1 g of 2,3,5,6-tetraaminocyclohexane-2,5-diene-1,4-dione salt to a flask, and add 130 mL of a mixture of ethylene glycol and 3 mol / L acetic acid aqueous solution in a volume ratio of 1:1. Sonicate for 1 h at a power of 60 W.

[0019] Step 2: Place the flask containing the ultrasonically mixed solution from Step 1 in liquid nitrogen at -190 °C to rapidly freeze the solution. Then connect the flask to a circulating water vacuum pump to remove the air from the flask. Next, place the flask in warm water to allow it to thaw normally. The pressure difference between the liquid and the vacuum chamber inside the flask will remove the air dissolved in the mixed liquid, thus completing one freezing-vacuuming-thawing operation. Repeat the freezing-vacuuming-thawing operation three times to ensure that there is no air in the flask and solution to avoid affecting the next solvothermal reaction. Finally, fill the flask with nitrogen gas for protection.

[0020] Step 3: Place the flask containing the nitrogen-protected solution from Step 2 in an oil bath and heat at 120 °C for 96 h. After the reaction, filter the solution and wash the resulting solid product in a Soxhlet extractor containing acetone for 12 h. Finally, dry the product in a vacuum drying oven at 60 °C for 12 h to obtain the benzoquinone-based covalent organic framework material, denoted as COF-2.

[0021] Comparative Example 1 Preparation of phenyl covalent organic framework materials In step 1 of Example 1 above, 2,3,5,6-tetraaminocyclohexane-2,5-diene-1,4-dione was replaced with 1.7g of 1,2,4,5-phenyltetramine tetrahydrochloride. The other steps were the same as in Example 1, and a phenyl covalent organic framework material was obtained, denoted as COF-1.

[0022] Comparative Example 2 Preparation of hydroxyl covalent organic framework materials Step 1: Add 620 mg of cyclohexanehexanone octahydrate and 1.12 g of 4-bromo-o-phenylenediamine to a flask, add 60 mL of glacial acetic acid, and sonicate for 1 h at 60 W.

[0023] Step 2: Perform three freezing-vacuuming-thawing operations on the flask containing the ultrasonically mixed solution from Step 1, following the procedure in Step 2 of Example 1, to ensure that there is no air in the flask and solution, and then fill it with nitrogen for protection.

[0024] Step 3: Place the flask containing the nitrogen-protected solution from Step 2 in an oil bath and heat at 100 °C for 24 h. After the reaction is complete, filter the solution and wash the resulting solid product in a Soxhlet extractor containing acetone for 12 h. Finally, dry the product in a vacuum drying oven at 60 °C for 12 h to obtain a yellow-green precursor.

[0025] Step 4: Add 200 mg of the yellow-green precursor obtained in Step 3 and 102 mg of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride to a flask, along with 30.5 mg CuI, 267 mg K2CO3 and 60 mL N,N-dimethylformamide, and sonicate at 60 W for 1 h.

[0026] Step 5: Perform three freezing-vacuuming-thawing operations on the flask containing the ultrasonically mixed solution from Step 4, following the procedure in Step 2 of Example 1, to ensure that there is no air in the flask and solution, and then fill it with nitrogen for protection.

[0027] Step 6: Place the flask containing the nitrogen-protected solution from Step 5 in an oil bath and heat at 140 °C for 24 h. After the reaction is complete, filter the solution and wash the resulting solid product in a Soxhlet extractor containing acetone for 24 h. Finally, dry the product in a vacuum drying oven at 60 °C for 12 h to obtain the hydroxyl covalent organic framework material, denoted as COF-3.

[0028] Comparative Example 3 In step 4 of Comparative Example 2 above, 2,5-diamino-1,4-dihydroxybenzene dihydrochloride was replaced with 100.5 mg of 2,6-diaminoanthraquinone, and the other steps were the same as in Comparative Example 2, to obtain an anthraquinone-based covalent organic framework material, denoted as COF-4.

[0029] The four COFs materials obtained in Example 1 and Comparative Examples 1-3 were characterized using infrared spectroscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and an electrochemical workstation. The results are shown in the figure. Figures 1-7 .

[0030] Depend on Figure 1 As can be seen, the material obtained in Example 1 shows that the corresponding COF-2 is located at 1635 cm⁻¹. -1 C=O and 1564 cm -1 The characteristic stretching vibration peak in infrared radiation corresponding to C=N. (From...) Figure 2 As can be seen, the obtained material shows that the corresponding COF-2 is located at 1510 cm⁻¹. -1 The corresponding Raman characteristic peaks for C=N can be used to calculate the I of COF-2. D / I G It is 0.83. (By...) Figure 3 As can be seen, COF-2 exhibits a highly crystalline, granular aggregate morphology. (From...) Figure 4 The X-ray photoelectron spectroscopy results show that the C 1s absorption peak of the obtained material indicates that COF-2 exhibits a significant C=O bond compared to other COF materials. These characterization results prove that COF-2 was successfully prepared. Figure 5 The surface potentials and line scan surface potentials of the four COFs materials show that COF-2 has the largest potential of 61.7 mV compared to the other three COFs, which indicates that the photogenerated electrons in COF-2 can be separated and migrate more effectively.

[0031] Depend on Figures 1-2 It is evident that when the reactant raw materials are changed, the infrared and Raman spectra do not change significantly, proving that the prepared COFs materials belong to the same type of organic compounds. Figure 4 The X-ray photoelectron spectroscopy results show that the four COFs materials correspond to different characteristic peaks, proving that changes in raw materials can affect the content of various chemical bonds in the synthesized COFs. Figure 5 The surface potentials and line scan surface potentials of the four COFs materials show that changes in reactant raw materials can affect the voltage difference of the materials.

[0032] Application Example 1 Application of the benzoquinone-based covalent organic framework material (COF-2) prepared in Example 1 as a bifunctional photocatalyst in a light-assisted Li-Air battery Using nickel foam as a substrate, COF-2, acetylene black, and PVDF were mixed in a mass ratio of 8:1:1 and dispersed in N,N-dimethylformamide (DMF). The mixture was ultrasonicated for 1 h to achieve uniform dispersion and a liquid state, then uniformly dripped onto the nickel foam and vacuum dried at 100 °C for 12 h to obtain a COF-2-loaded electrode sheet. The electrode sheet was transferred to an argon-atmosphere glove box where the moisture and oxygen content were both below 0.1 ppm. A CR2032 coin cell (with a porous cathode) was assembled using a lithium sheet as the negative electrode, the COF-2-loaded electrode sheet as the photoelectrode, glass fiber (GF / A) as the separator, and a 1.0 mol / L LiTFSI tetraethylene glycol dimethyl ether solution as the electrolyte for testing of a photo-assisted lithium-air battery system. COF-1, COF-3, and COF-4 were used as control experiments. Finally, all battery systems were tested on an electrochemical workstation. GEL S500 / 350 Xe-4 xenon lamps were used as the lighting source.

[0033] Depend on Figure 6 and Figure 7 As can be seen, the COF-2 of Example 1 exhibits excellent lithium-air battery performance, specifically at 200 mA g. -1 At a given current density, the COF-2 photo-assisted lithium-air battery, using COF-2 as the photoelectrode, exhibits an ultra-high discharge voltage of 3.34 V and an ultra-low overpotential of 0.08 V, enabling it to achieve a round-trip efficiency of up to 98%. Its performance is far superior to that of the COF-1 photo-assisted lithium-air battery with a discharge voltage of 3.09 V and an overpotential of 0.17 V, the COF-3 photo-assisted lithium-air battery with a discharge voltage of 2.81 V and an overpotential of 0.32 V, and the COF-4 photo-assisted lithium-air battery with a discharge voltage of 2.84 V and an overpotential of 0.49 V.

Claims

1. Use of benzoquinone-based covalent organic frameworks as bifunctional photocatalysts in photo-assisted lithium-air batteries, characterized in that The benzoquinone-based covalent organic framework material is prepared by the following method: Step 1: ultrasonic mixing of cyclohexanehexone octahydrate and 2,3,5,6-tetraaminocyclohexa-2,5-diene-1,4-dione in a mixed solution of ethylene glycol and 3 mol / L aqueous acetic acid solution; Step 2: freeze-vacuum-thaw operation is performed on the solution after ultrasonic mixing in step 1, and after 3 cycles of operation, nitrogen is filled for protection; Step 3: after heating the nitrogen-protected solution in step 2 at 110-130 °C for 90-100 h, filtration is performed, and Soxhlet extraction is performed on the solid product using acetone as a washing agent, followed by vacuum drying at 50-70 °C to obtain the benzoquinone-based covalent organic framework material.

2. Use of the benzoquinol-based covalent organic framework material according to claim 1 as a bifunctional photocatalyst in a photo-assisted lithium-air battery, characterized in that: In step 1, the mass ratio of the cyclohexanehexone octahydrate and 2,3,5,6-tetraaminocyclohexa-2,5-diene-1,4-dione is 1.0-1.5:

1.

3. Use of the benzoquinone-based covalent organic framework material according to claim 1 as a bifunctional photocatalyst in a photo-assisted lithium-air battery, characterized in that: In step 1, the volume ratio of ethylene glycol and 3 mol / L aqueous acetic acid solution in the mixed solution is 1:

1.

4. Use of the benzoquinol-based covalent organic framework material according to claim 1 as a bifunctional photocatalyst in a photo-assisted lithium-air battery, characterized in that: In step 2, the solution after ultrasonic mixing in step 1 is rapidly frozen in liquid nitrogen at -180 to -200 °C, vacuumed, and thawed in water in sequence to complete the freeze-vacuum-thaw operation; the foregoing freeze-vacuum-thaw operation is repeated 3 times, and then nitrogen is filled for protection.

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