Porous curved-surface hollow octadecahedron carbon nanobox material as well as preparation method and application thereof

Abstract

The invention discloses a porous curved-surface hollow octadecahedron carbon nanobox material and a preparation method and application thereof, the force balance of a ZIF-67 skeleton structure in heat treatment is adjusted by introducing quantum dots, and the polyhedral morphology of the material can be reserved, so that the material with rich microporous structures and large specific surface area is obtained; the exposure of rich catalytic active sites is facilitated, so that efficient electro-catalysis is realized. The catalyst prepared by the preparation method disclosed by the invention shows excellent bifunctional oxygen catalytic performance. Wherein the overpotential of the OER is only 130 mV when the OER is 10 mA / , and the half-wave potential of the ORR can also reach 0.86 V. According to the scheme, a new strategy is provided for designing a high-efficiency difunctional electrocatalyst, and the development of an air electrode catalyst in a metal-air battery is further promoted.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical oxygen reduction reaction, oxygen evolution reaction and zinc-air battery, specifically relating to a porous hollow octahedral carbon nanotube material, its preparation method and application. Background Technology

[0002] The energy crisis and environmental pollution have placed high demands on renewable and clean energy storage and conversion technologies, thus rechargeable zinc-air batteries have received continuous attention. However, their practical application is still limited by the lack of highly efficient oxygen evolution / oxygen reduction reactions (OER / ORR). This limitation stems from the slow kinetics of the four-electron multi-step reaction during redox reactions, resulting in high overpotentials for OER / ORR. Although traditional noble metal electrocatalysts (Ru, Ir, Pt, etc.) possess high electrochemical activity, they cannot guarantee the simultaneous maintenance of high catalytic activity for both ORR and OER in the same alkaline electrolyte. For example, Pt is a high-performance catalyst for ORR, but its performance for OER is not good enough. Conversely, and While precious metal catalysts exhibit high OER activity, their catalytic activity in other reactions is relatively weak. Therefore, developing non-precious metal electrocatalysts with both high ORR and OER activity presents a considerable challenge in overcoming the problems of high cost and limited activity of precious metal catalysts.

[0003] Related technological developments: Metal-organic frameworks (MOFs) have great potential as catalyst supports or catalysts themselves in catalysis due to their porosity and large specific surface area. ZIF-67, a cobalt-based MOF material, can be synthesized using a simple and environmentally friendly method. It possesses tunable pore size and a highly stable structure. Furthermore, studies have found that active sites tend to be dispersed on the curved surfaces of carbon nanospheres and carbon nanotubes. For example, by using… Fe-NC and Co-NC were prepared on a curved porous carbon structure by coating the MOF structure.

[0004] However, the above techniques do not solve the collapse problem of ZIF materials during pyrolysis. Furthermore, this method is relatively complex and requires acid treatment to remove the collapse. The coating may damage the active structure, causing the loss of active sites. Furthermore, it has a single function and has failed to catalyze OER and be used in zinc-air batteries. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the present invention provides a porous curved hollow octahedral carbon nanotube material, its preparation method and application.

[0006] The specific content is as follows: A method for preparing a porous curved hollow octahedral carbon nanotube material includes the following steps:

[0007] S1 Synthetic Block ;

[0008] S2 preparation quantum dots;

[0009] S3 Preparation of the porous curved hollow octahedral carbon nanotubes CNQD / CoNBs: Introduced during the synthesis of ZIF-67 Quantum dots are self-assembled using a surfactant-assisted method to form an octahedral precursor, which is then pyrolyzed in an N2 atmosphere; after pyrolysis, the porous curved hollow octahedral carbon nanotubes CNQD / CoNBs are formed.

[0010] Furthermore, the preparation process of S2 is as follows: First, concentrated sulfuric acid and concentrated nitric acid are used to... Etching into porous Then, hydrothermal treatment is performed in ammonia water to... The nanosheets are exfoliated into ultrathin nanosheets with a porous structure; finally, they are subjected to ultrasonic treatment in water to... Nanosheets were peeled off to obtain a monolayer. Quantum dots.

[0011] Furthermore, the specific preparation process of S1: synthesis of bulk form Heating 10 g of melamine to 600 °C at a rate of 10 °C / min and holding at that temperature for 2 hours, followed by cooling to room temperature at the same rate, yields a yellow block. product;

[0012] Furthermore, the specific preparation process of S2 is as follows: First, 1 g of... The powder was treated at room temperature for approximately 2 hours in a mixed solution of 20 mL each of concentrated sulfuric acid and concentrated nitric acid at room temperature. It was then diluted with 1 L of deionized water and washed several times. The resulting white product was porous. Secondly, 354 mg of the porous material obtained in the above steps was... The solution was dispersed in 30 mL of concentrated ammonia water and transferred to a 45 mL reactor liner. The mixture was then heated in a sealed autoclave at 150°C for 12 hours. The hydrothermal process resulted in a porous reactor. To be stripped into Porous nanosheets. The obtained product was dispersed in 100 mL of water and subjected to ultrasonic treatment for approximately 6 hours to obtain a mixture. Aqueous solution of quantum dots.

[0013] Further, the specific preparation process of S3 is as follows: 4.54 g of 2-methylimidazole is added to the final aqueous solution obtained from S2. 292 mg of... Dissolved in 10 mL of deionized water containing 5 mg of hexadecyltrimethylammonium bromide (CTAB), the solution was quickly poured into 100 mL of the above aqueous solution and stirred at room temperature for 20 minutes. After washing several times with ethanol, the product was collected by centrifugation and dried in an oven at 60 °C for 12 hours. The dried powder was then further ground to obtain the composite precursor. The prepared precursor was then... The material was heated to 800 °C at a heating rate of 10 °C / min under an atmosphere and pyrolyzed for 2 hours. Finally, the black solid product was collected and cooled to room temperature to obtain the final sample, namely the porous curved hollow octahedral carbon nanotube material.

[0014] This invention introduces Nanoquantum dots (CNQDs) modulate the thermal expansion (TEP) properties of zeolite imidazolium ester (ZIF) framework materials, effectively balancing the internal pressure generated during ZIF framework pyrolysis. This significantly reduces the thermal shrinkage rate of the final product, CNQD / CoNBs, achieving dimensional stability before and after pyrolysis and fundamentally inhibiting the collapse of the ZIF framework structure. This advantage ensures sufficient exposure of catalytically active sites, laying a core foundation for improving the oxygen catalytic performance of the material.

[0015] The air electrode material CNQD / CoNBs prepared based on the above-mentioned regulatory mechanism exhibits a curved, hollow cobalt-based octahedral carbon nanotube morphology. This unique structural design significantly increases the specific surface area of ​​the catalyst, enhances the mass transfer efficiency between the gas and liquid phases, and effectively accelerates the kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) while further optimizing the exposure of active sites. Therefore, CNQD / CoNBs demonstrate excellent OER / ORR bifunctional catalytic activity, providing a solid performance guarantee for its application in the air electrode field of zinc-air batteries.

[0016] This invention provides a porous curved hollow octahedral carbon nanotube material, which is prepared by the above method.

[0017] This invention provides an air electrode material for a zinc-air battery, which is made from the aforementioned porous curved hollow octahedral carbon nanotube material.

[0018] This invention provides a method for preparing an air electrode material for a zinc-air battery, the specific steps of which are as follows:

[0019] First, CNQD / CoNBs material and polyvinylidene fluoride binder were weighed at a mass ratio of 8:1, and N-methylpyrrolidone was used as the dispersion solvent. The mixture was placed in an agate mortar and ground for 15 min under the assistance of an infrared lamp to obtain a uniform and viscous electrode slurry. Second, the slurry was manually coated onto the surface of a hydrophobic carbon cloth (CC) current collector. The coated carbon cloth was then placed flat on a tempered glass substrate and dried in a vacuum drying oven at 110 ℃ for 8 h to obtain a CNQD / CoNBs-modified air electrode. Finally, using the CNQD / CoNBs-modified carbon cloth as the air electrode, 6 M KOH + 0.2 M... A zinc-air battery was assembled using a mixed solution as the electrolyte and a zinc sheet as the negative electrode, and its performance was tested. The test results showed that the zinc-air battery exhibited excellent discharge capacity and cycle charge-discharge stability.

[0020] Beneficial effects:

[0021] In this technical solution Quantum doping can minimize the size change of the prepared catalyst before and after pyrolysis, effectively preventing the aggregation of Co nanoparticles caused by the collapse of the ZIF framework structure. Furthermore, the curved and hollow octahedral structures significantly increase the specific surface area and the number of micropores, exposing more active sites and accelerating the reaction kinetics in the electrocatalytic process. Simultaneously, the prepared catalyst exhibits excellent performance. OER at 10 mA / The overpotential is only 130 mV, and the half-wave potential of ORR can reach 0.86 V. This scheme provides a new strategy for designing highly efficient bifunctional electrocatalysts.

[0022] Compared with existing technologies, this scheme introduces [a new method] during the synthesis of ZIF-67. Porous hollow carbon octahedrons (CNQD / CoNBs) were fabricated using quantum dots. Adjusting the force balance of the framework structure during heat treatment can preserve the polyhedral morphology of ZIF-67, thereby obtaining a material with abundant microporous structure and large specific surface area. This helps expose abundant catalytic active sites, thus achieving highly efficient electrocatalysis. During pyrolysis, the surface of CNQD / CoNBs will be graphitized into a carbon layer, and the interior of the carbon layer contains... Quantum dots, thus exhibiting different thermal expansion properties (TEP). Due to The low TEP of CNQD / CoNBs significantly reduces thermal shrinkage, resulting in only a slight decrease in dimensional change before and after pyrolysis, shrinking from 1200 nm to 900 nm, effectively preventing ZIF structure collapse. The stress on the edges and vertices of the polyhedron is greater than on the surface, leading to anisotropic shrinkage and causing surface bending. Curved surface topography can activate Co- particles that are difficult to obtain in non-curved surface particles. This partially increases the surface area of ​​the particles, thereby expanding the reaction interface and enhancing the reaction kinetics of OER and ORR. Attached Figure Description

[0023] Figure 1 Scanning electron microscope (SEM) images (a, c) and transmission electron microscope (TEM) images (b, d) of CNQD / CoNBs and ZIF-67.

[0024] Figure 2 Selected area electron diffraction (SAED) image (a) and high resolution transmission electron microscopy (HRTEM) image (b) of CNQD / CoNBs.

[0025] Figure 3 X-ray diffraction (XRD) patterns of ZIF-67, CNQD / CoNBs, uncalcined CNQD / CoNBs, and uncalcined ZIF-67;

[0026] Figure 4 For CNQD / CoNBs and ZIF-67 Adsorption-desorption isotherms and pore size distribution diagram;

[0027] Figure 5 (a) OER polarization curves in 1.0 M KOH solution and (b) the corresponding Tafel plots; (c) CNQD / CoNBs and Chronocurrent plot of the catalyst; (d) ORR polarization plot, (e) Tafel plot and (f) Chronoamperometric curves in saturated 0.1 M KOH solution;

[0028] Figure 6 For (a) CNQD / CoNBs and Pt / C+ LSV curves in 1.0 M KOH aqueous solution; (b) Open-circuit voltage curves; (c) CNQD / CoNBs and Pt / C+ Discharge polarization curves and corresponding power density curves. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] Example

[0031] 1. Material preparation method:

[0032] (1) Preparation: block Melamine was synthesized using a high-temperature polymerization method. Melamine was heated to 600 °C at a rate of 10 °C / min and held at that temperature for 2 hours, then cooled to room temperature at the same rate to obtain a yellow, blocky g-C3N4 product.

[0033] (2) Preparation Quantum dots: First, 1 g of The powder was treated at room temperature for approximately 2 hours in a mixed solution of 20 mL each of concentrated sulfuric acid and concentrated nitric acid at room temperature. It was then diluted with 1 L of deionized water and washed several times. The resulting white product was porous g-C3N4. Next, 354 mg of the porous product obtained in the above steps... The solution was dispersed in 30 mL of concentrated ammonia water and transferred to a 45 mL reactor liner. The mixture was then heated in a sealed autoclave at 150°C for 12 hours. The hydrothermal process resulted in a porous reactor. To be stripped into Porous nanosheets. The obtained product was dispersed in 100 mL of water and subjected to ultrasonic treatment for approximately 6 hours to obtain a mixture. Aqueous solution of quantum dots.

[0034] (3) Preparation of quantum dot-induced Co-based carbon nanotubes (CNQD / CoNBs): 4.54 g of 2-methylimidazole was added to the above aqueous solution. 292 mg of... The product was dissolved in 10 mL of deionized water containing 5 mg of hexadecyltrimethylammonium bromide (CTAB), and then rapidly poured into 100 mL of the above aqueous solution. The mixture was then stirred at room temperature for 20 minutes. After washing several times with ethanol, the product was collected by centrifugation and dried in an oven at 60 °C for 12 hours. The dried powder was then further ground to obtain the composite precursor. The prepared precursor was then used in… The sample was heated to 800 °C at a heating rate of 10 °C / min under a specific atmosphere and pyrolyzed for 2 hours. The resulting black solid product was collected and cooled to room temperature to obtain the final sample.

[0035] 2. Electrochemical testing:

[0036] (1) ORR testing was performed using a PINE dual potentiostat standard three-electrode cell in 0.1 M KOH aqueous solution. The counter electrode and working electrode each had an area of ​​0.196 mm. Carbon rods and glassy carbon electrodes were used. Before each use, the Hg / HgO reference electrode was calibrated relative to a reversible hydrogen electrode (RHE). 5 mg of catalyst was added to a mixture containing 5 μL of 5 wt.% Nafion solution (DuPont) and 250 μL of isopropanol and sonicated for 30 minutes to form a uniformly dispersed catalyst ink. Then, 5 μL of the catalyst ink was dropped onto the glassy carbon electrode and allowed to air dry. A noble metal control group was prepared using 20 wt.% Pt / C catalyst (Johnson Matthey). Chorometric galvanometry was performed while maintaining the potential at 0.7 V vs. RHE.

[0037] (2) OER tests were performed on a CHI 760E electrochemical workstation using a standard three-electrode cell structure. Hg / HgO, a graphite rod, and the prepared catalyst were used as the reference electrode, counter electrode, and working electrode, respectively. The catalyst loading was fixed at 3 mg / cm³. 2 All potentials were 90% IR corrected for electrolyte resistance and referenced to the reversible hydrogen electrode conversion potential. OER tests were performed in 1.0 M KOH aqueous solution, and polarization curves were measured at a scan rate of 10 mV / s.

[0038] Zinc-air battery test:

[0039] Zinc sheet was used as the negative electrode in the air battery. 10 mg of catalyst was dispersed in 1 mL of a mixture containing 40 μl Nafion and 960 μl isopropanol to form a uniformly distributed slurry. 200 μl of this slurry was dropped onto carbon paper as the air electrode. When the loading reached 2 mg, the effective area of ​​the carbon paper covering the catalyst was approximately 1... Then, the zinc sheet, nickel foam, and air electrode are assembled. After the mold is assembled, 6.0 M KOH electrolyte is injected.

[0040] from Figure 1 It can be seen that CNQD / CoNBs materials with a uniform size distribution of approximately 1200 nm have been synthesized. During the formation of ZIF-67, [the following is unclear and likely refers to a specific process or factor]. Quantum dots act as surfactants, inducing the 12 edges of a hexahedron ZIF to become 12 planes, transforming the hexahedron into a polyhedron with 18 planes. During pyrolysis, Complete decomposition results in a hollow interior for the octahedron. Simultaneously, the ammonia produced during decomposition reacts with the shell, creating a porous structure. This hollow and porous structure plays a crucial role in exposing active sites and transferring reactants and products. After pyrolysis, all the planes of the octahedron are compressed into curved surfaces, effectively preventing... Figure 1 The aggregation of Co nanoparticles caused by the collapse of the ZIF framework structure shown in d.

[0041] from Figure 2 As can be seen, a fringe spacing of 0.205 nm can be indexed onto the lattice fringes of Co(111), and the corresponding SAED image also shows clear diffraction rings of Co(111), which is consistent with... Figure 3 The XRD patterns match.

[0042] from Figure 3 It can be seen from the addition After quantum dot formation, the uncooked CNQD / CoNBs still maintained the same crystal phase as the uncooked ZIF-67, indicating that... The doping of quantum dots did not affect the formation of the ZIF-67 structure, but was instead encapsulated within ZIF-67, resulting in a significant increase in the size of ZIF-67. After pyrolysis, two distinct diffraction peaks of ZIF-67 and CNQD / CoNBs were observed at 44.2° and 51.3°, corresponding to the (111) and (200) crystal planes of the face-centered cubic phase metal Co, respectively.

[0043] from Figure 4 The data shows that the CNQD / CoNBs specific surface area is 296.6. It is greater than ZIF-67's 192.7. ,show Quantum dots have the ability to significantly increase specific surface area. Figure 4 The adsorption isotherm of medium β exhibits a typical IV isotherm with a significant hysteresis loop, indicating the presence of both micropores and mesopores, with micropores of 0.55 nm being predominant and much more abundant in CNQD / CoNBs than in ZIF-67. The abundant micropores likely originate from... The corrosion by gases during the thermal decomposition of quantum dots provides a larger surface area for the active sites. In addition to numerous micropores, mesoporous structures are also abundant. Literature reports that the active sites of oxygen reduction catalysts are mainly located in micropores, while mesoporous structures are… and A good mass transfer channel can improve catalytic efficiency.

[0044] from Figure 5 The prepared catalyst exhibits excellent bifunctional electrocatalytic performance. OER at 10 mA / The overpotential of CNQD / CoNBs was only 130 mV, and the Tafel slope was 140 mV. and more commercial It exhibits better long-term stability. Furthermore, the half-wave potential of the ORR can reach 0.86 V, and the Tafel slope is only 51 mV. It also exhibits superior cycle stability compared to Pt / C.

[0045] from Figure 6The result shows that the OER measured by CNQD / CoNBs is 10 mA / Potential and ORR half-wave potential The potential difference ΔE between them is only a minimum of 0.50 V, indicating that the material has good reversible oxygen reaction activity and can be used as the air electrode in zinc-air batteries. The assembled zinc-air battery has an open-circuit voltage that is basically stable at 1.49 V, and the power density can reach 210 mW / s. .

Claims

1. A method for preparing a porous curved hollow octahedral carbon nanotube material, characterized in that, The following steps are included: S1 Synthetic Block ; S2 preparation quantum dots; S3 Preparation of the porous curved hollow octahedral carbon nanotubes CNQD / CoNBs: Introduced during the synthesis of ZIF-67 Quantum dots are self-assembled using a surfactant-assisted method to form octahedral precursors, and then... Pyrolysis is performed in an atmosphere; after pyrolysis, the porous curved hollow octahedral carbon nanotubes CNQD / CoNBs are formed.

2. The method for preparing a porous curved hollow octahedral carbon nanotube material as described in claim 1, characterized in that, The preparation process of S2 is as follows: First, concentrated sulfuric acid and concentrated nitric acid are used to... Etching into porous Then, hydrothermal treatment is performed in ammonia water to... The nanosheets are exfoliated into ultrathin nanosheets with a porous structure; finally, they are subjected to ultrasonic treatment in water to... Nanosheets were peeled off to obtain a monolayer. Quantum dots.

3. The method for preparing a porous curved hollow octahedral carbon nanotube material as described in claim 1, characterized in that, The specific preparation process of S1: Synthesizing block form Heating 10 g of melamine to 600 °C at a rate of 10 °C / min and holding at that temperature for 2 hours, followed by cooling to room temperature at the same rate, yields a yellow block. product.

4. The method for preparing a porous curved hollow octahedral carbon nanotube material as described in claim 1, characterized in that, S2 preparation process: First, 1 g of... The powder was treated at room temperature for about 2 hours in a mixed solution of 20 mL each of concentrated sulfuric acid and concentrated nitric acid, then diluted with 1 L of deionized water and washed several times. The resulting white product was porous. Secondly, 354 mg of the porous material obtained in the above steps was used. Dispersed in 30 mL of concentrated ammonia water, and transferred to a 45 mL reactor liner, heated in a sealed autoclave at 150°C for 12 hours; the hydrothermal process is porous. To be stripped into Porous nanosheets; the obtained product was dispersed in 100 mL of water and subjected to ultrasonic treatment for about 6 hours to obtain a mixture. Aqueous solution of quantum dots.

5. The method for preparing a porous curved hollow octahedral carbon nanotube material as described in claim 4, characterized in that, The specific preparation process of S3 is as follows: 4.54 g of 2-methylimidazole is added to the final aqueous solution obtained from S2, and 292 mg of... Dissolve in 10 mL of deionized water containing 5 mg cetyltrimethylammonium bromide (CTAB), then quickly pour into the above 100 mL aqueous solution, and stir at room temperature for 20 minutes. After washing several times with ethanol, the product was collected by centrifugation and dried in an oven at 60 °C for 12 hours. Then, the dried powder was further ground to obtain a composite precursor. The prepared precursor was heated to 800 °C at a heating rate of 10 °C / min under N2 atmosphere and pyrolyzed for 2 hours. Finally, the black solid product was collected and cooled to room temperature to obtain the final sample, namely the porous curved hollow octahedral carbon nanotubes CNQD / CoNBs.

6. A porous curved hollow octahedral carbon nanotube material, characterized in that, It is prepared by any one of the methods described in claims 1-5.

7. An air electrode material for a zinc-air battery, characterized in that, It is made using the porous curved hollow octahedral carbon nanotube material described in claim 6.

8. The method for preparing the air electrode material of a zinc-air battery as described in claim 7, characterized in that, The specific operating steps are as follows: First, CNQD / CoNBs material and polyvinylidene fluoride binder were weighed at a mass ratio of 8:1, and N-methylpyrrolidone was used as the dispersion solvent. The mixture was placed in an agate mortar and ground for 15 min under the assistance of an infrared lamp to obtain a uniform and viscous electrode slurry. Second, the slurry was manually coated onto the surface of a hydrophobic carbon cloth (CC) current collector. The coated carbon cloth was then placed flat on a tempered glass substrate and dried in a vacuum drying oven at 110 ℃ for 8 h to obtain a CNQD / CoNBs-modified air electrode. Finally, using the CNQD / CoNBs-modified carbon cloth as the air electrode, 6 M KOH + 0.2 M... A mixed solution was used as the electrolyte, and a zinc sheet was used as the negative electrode. A zinc-air battery was assembled and its performance was measured. Test results show that the zinc-air battery exhibits excellent discharge capacity and cycle charge-discharge stability.

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