Preparation method of low-cost and high-efficiency waste durian peel-based biochar nano composite electrode material

Abstract

The invention discloses a supercapacitor electrode material based on durian peel charcoal and tannic acid modified Co-MOF and a preparation method and application thereof. According to the method, waste durian peel is taken as a raw material, porous biochar (DR) is prepared through pyrolysis, Co-MOF is induced to uniformly grow on the surface of the biochar under the hydrothermal condition by utilizing the interface regulation and control effect of tannic acid (TA), a Co-MOF-TA-DR precursor is formed, and the final electrode material is obtained through high-temperature heat treatment. The tannic acid effectively optimizes the morphology and dispersity of the Co-MOF and enhances the binding force of the Co-MOF and the biochar, so that the structural stability and electrochemical activity of the material are improved. The specific capacitance of the obtained composite material reaches 788 F.g at the current density of 1 A.g, the capacitance retention rate exceeds 80% after 3000 cycles at the current density of 10 A.g, and the composite material has high specific capacitance and excellent cycle stability. The method is low in raw material cost, simple in process, environment-friendly and suitable for large-scale production, and a feasible path is provided for agricultural waste recycling and high-performance supercapacitor electrode development.

Description

Technical Field

[0001] This invention relates to the fields of electrochemical energy storage materials and waste resource utilization technology, and in particular to a method for preparing high-performance supercapacitor electrode materials by using agricultural waste durian peel as raw material, preparing porous biochar through pyrolysis, and inducing cobalt-based metal-organic frameworks (Co-MOFs) to grow directionally on its surface using tannic acid interface modification technology, as well as the electrode materials prepared by this method and their applications in supercapacitors. Background Technology

[0002] As the global energy structure shifts towards cleaner and lower-carbon energy, the development and utilization of renewable energy sources such as wind and solar power are becoming increasingly widespread. However, these energy sources are intermittent and fluctuating, necessitating efficient and stable energy storage systems to achieve smooth power output and dispatch. Supercapacitors, as a novel energy storage device, have demonstrated enormous application potential in fields such as rail transportation, smart grids, new energy vehicles, and portable electronic devices due to their advantages of high power density, rapid charge and discharge capabilities, long cycle life, and high safety. Electrode materials are the core components determining the performance of supercapacitors. Currently, commonly used electrode materials mainly include carbon-based materials (such as activated carbon, carbon nanotubes, and graphene), metal oxides (such as RuO2 and MnO2), and conductive polymers. Among them, metal-organic frameworks (MOFs) have attracted much attention in the field of electrochemical energy storage in recent years due to their ultra-high specific surface area, tunable pore structure, and abundant metal active sites. However, most MOF materials have poor intrinsic conductivity and their structures are prone to collapse during electrochemical cycling, resulting in poor rate performance and cycle stability, limiting their practical applications.

[0003] To overcome the aforementioned shortcomings, researchers often combine MOFs with highly conductive carbon materials to construct MOF / carbon composites. Biochar, due to its wide availability, low cost, good conductivity, chemical stability, and abundant porous structure, has become an ideal growth carrier for MOFs. Agricultural waste (such as rice husks, straw, and fruit peels) is an important raw material for biochar production, and its resource utilization offers both environmental and economic benefits. Durian, a tropical fruit, has a peel that accounts for about 60-70% of its weight, which is usually discarded as waste, causing resource waste and potential environmental pollution. Durian peel is rich in cellulose, hemicellulose, and lignin, and after pyrolysis, it can form porous carbon materials rich in mesopores and macropores, possessing good conductivity and ion transport capabilities, making it suitable as an electrode material or carrier for supercapacitors. On the other hand, achieving uniform and robust growth of MOFs on the carbon carrier surface is a key technical challenge in constructing high-performance MOF / carbon composites. Tannic acid (TA) is a natural polyphenol compound widely found in plants. Its molecular structure contains a large number of catechol and carboxylic acid groups, giving it a strong coordination ability with various metal ions. Recent studies have shown that tannic acid can serve as an excellent interface modifier. Through its abundant functional groups, it interacts with metal ions and the surface of carbon materials, effectively regulating the nucleation and growth process of MOF crystals, improving the dispersibility of MOF particles, and enhancing the interfacial bonding between MOF and the carbon matrix, thereby improving the mechanical stability and electrochemical performance of composite materials.

[0004] Based on this, this invention proposes a method for preparing porous biochar from waste durian peels via pyrolysis, and then inducing the uniform growth of Co-MOF on the biochar surface under hydrothermal conditions by utilizing the interfacial modification effect of tannic acid. Following high-temperature heat treatment, a structurally stable and high-performance Co-MOF-TA@DR supercapacitor electrode material is finally obtained. This method not only achieves high-value utilization of agricultural waste but also effectively improves the comprehensive electrochemical performance of the composite electrode material through ingenious interfacial engineering strategies, providing a new material and approach for developing low-cost, high-performance supercapacitors. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing supercapacitor electrode materials that is characterized by readily available raw materials, simple processing, low cost, environmental friendliness, and suitability for large-scale production. Another objective of this invention is to provide a supercapacitor electrode material prepared by the above method that exhibits high specific capacitance, excellent rate performance, and long-cycle stability. A further objective of this invention is to provide the application of the above electrode material in supercapacitors.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing supercapacitor electrode materials based on waste durian peel through tannic acid interface modification and growth of Co-MOF includes the following steps: (1) Pretreatment of durian peel: The collected fresh durian peels are repeatedly rinsed with running water to remove surface dirt and impurities. The washed durian peels are cut into thin slices of uniform thickness (e.g., 1-3 mm) and placed in an oven at 50-70°C for 10-14 hours to completely remove moisture, resulting in dried durian peel fragments. Preferably, the drying conditions are 60°C for 12 hours.

[0007] (2) Preparation of porous biochar: The dried durian peel fragments obtained in step (1) were placed in a tube furnace and subjected to the first stage of pyrolysis (pre-carbonization) under an inert protective atmosphere (such as argon or nitrogen). The pyrolysis was carried out at 2-10℃·min. -1 The temperature is increased to 350-450℃ at a heating rate and held at this temperature for 1-3 hours, followed by natural cooling to room temperature to obtain pre-carbonized biochar. This process mainly removes volatiles and forms a preliminary carbon skeleton. Preferably, the heating rate is 5℃·min. -1 Heat to 400℃ and keep warm for 2 hours.

[0008] The pre-carbonized biochar and chemical activators (such as KOH, NaOH, ZnCl2, etc.) are thoroughly ground and mixed at a certain mass ratio (e.g., 1:1-3:1). The mixture is then transferred to a tube furnace for a second-stage high-temperature activation under an inert atmosphere. The activation temperature range is 800-1000℃, and the activation time is 1-3 hours. During the high-temperature activation, the activator reacts with the carbon, creating numerous pores and significantly increasing the specific surface area and porosity of the material. After the reaction, the mixture is naturally cooled to room temperature. The activated product is first soaked in dilute acid (e.g., 1 M HCl) to neutralize excess alkali and remove metallic impurities, then repeatedly washed with deionized water and anhydrous ethanol until the filtrate is neutral. Finally, it is dried at 50-80℃ for 6-12 hours to obtain high specific surface area durian peel-based porous biochar (denoted as DR). Preferably, the activator is KOH, with a mass ratio of 2:1 to the pre-carbonized biochar, and the activation condition is activation at 900℃ for 2 hours.

[0009] (3) Preparation of Co-MOF-TA@DR precursor: Co-MOF (taking Co-MOF-74 as an example) was synthesized by a one-pot solvothermal method, and composite with biochar and tannic acid modification were achieved simultaneously. First, cobalt salt (such as cobalt nitrate hexahydrate) was dissolved in a mixed solvent composed of N,N-dimethylformamide (DMF), anhydrous ethanol and deionized water in a certain volume ratio, and magnetically stirred until completely dissolved to form a homogeneous solution. Then, an organic ligand (such as 2,5-dihydroxyterephthalic acid) was added to the above solution, and stirring was continued to ensure that it was fully dissolved and mixed. Next, a predetermined amount of tannic acid (TA) and durian peel biochar (DR) prepared in step (2) were added, ultrasonically dispersed and continuously stirred to form a uniform suspension. The amount of tannic acid added is usually 5%-50% of the mass of cobalt salt, and the mass ratio of biochar to cobalt salt can be adjusted in the range of 1:10 to 10:1.

[0010] The pre-carbonized biochar and chemical activators (such as KOH, NaOH, ZnCl2, etc.) are thoroughly ground and mixed at a certain mass ratio (e.g., 1:1-3:1). The mixture is then transferred to a tube furnace for a second-stage high-temperature activation under an inert atmosphere. The activation temperature range is 800-1000℃, and the activation time is 1-3 hours. During the high-temperature activation, the activator reacts with the carbon, creating numerous pores and significantly increasing the specific surface area and porosity of the material. After the reaction, the mixture is naturally cooled to room temperature. The activated product is first soaked in dilute acid (e.g., 1 M HCl) to neutralize excess alkali and remove metallic impurities, then repeatedly washed with deionized water and anhydrous ethanol until the filtrate is neutral. Finally, it is dried at 50-80℃ for 6-12 hours to obtain high specific surface area durian peel-based porous biochar (denoted as DR). Preferably, the activator is KOH, with a mass ratio of 2:1 to the pre-carbonized biochar, and the activation condition is activation at 900℃ for 2 hours.

[0011] (4) Preparation of Co-MOF-TA@DR precursor: Co-MOF (taking Co-MOF-74 as an example) was synthesized by a one-pot solvothermal method, and composite with biochar and tannic acid modification were achieved simultaneously. First, cobalt salt (such as cobalt nitrate hexahydrate) was dissolved in a mixed solvent composed of N,N-dimethylformamide (DMF), anhydrous ethanol and deionized water in a certain volume ratio, and magnetically stirred until completely dissolved to form a homogeneous solution. Then, an organic ligand (such as 2,5-dihydroxyterephthalic acid) was added to the above solution, and stirring was continued to ensure that it was fully dissolved and mixed. Next, a predetermined amount of tannic acid (TA) and durian peel biochar (DR) prepared in step (2) were added, ultrasonically dispersed and continuously stirred to form a uniform suspension. The amount of tannic acid added is usually 5%-50% of the mass of cobalt salt, and the mass ratio of biochar to cobalt salt can be adjusted in the range of 1:10 to 10:1.

[0012] The above-mentioned mixed suspension was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene (PTFE), sealed, and placed in an oven for hydrothermal reaction. The reaction temperature was controlled at 100-150℃, and the reaction time was 12-36 hours. After the reaction, the reactor was allowed to cool naturally to room temperature. The reactor was opened, the precipitate was collected, and washed several times with DMF and anhydrous ethanol by centrifugation to remove unreacted raw materials and solvents. Finally, the washed product was vacuum dried at 60-80℃ for 6-12 hours to obtain the Co-MOF-TA@DR composite precursor. Preferably, the hydrothermal reaction conditions were 120℃ for 24 hours.

[0013] (5) High-temperature heat treatment: The Co-MOF-TA@DR precursor powder obtained in step (3) is evenly spread in a ceramic boat and then placed in a tube furnace. Under an inert protective atmosphere (such as argon), the temperature is increased to 2-10℃·min. -1 The temperature is programmed to reach a set temperature (700-1000℃) and held at that temperature for 1-3 hours. This high-temperature heat treatment process transforms the Co-MOF portion in the precursor into a metal oxide / carbon or metal / carbon composite with higher conductivity, while further optimizing the crystal and pore structures of the material, enhancing its graphitization degree and conductivity. After heat treatment, the material is naturally cooled to room temperature under an inert atmosphere to obtain the final Co-MOF-TA@DR composite material. The preferred heat treatment conditions are a heating rate of 5 ℃·min. -1 Heat to 900℃ and keep warm for 2 hours.

[0014] The beneficial effects of this invention are:

[0015] 1. Significant benefits in resource utilization and environmental protection: Using waste durian peels as the main raw material, it realizes the high-value utilization of agricultural waste, turns waste into treasure, reduces raw material costs, and conforms to the concept of green and sustainable development.

[0016] 2. Interface Engineering Optimizes Material Structure: Tannic acid is innovatively introduced as an interface modifier. The polyphenol and carboxyl functional groups in the tannic acid molecule can, on the one hand, interact with Co... 2+ Coordination regulates the nucleation rate and growth orientation of Co-MOF, enabling it to grow uniformly and densely on the biochar surface and preventing particle aggregation. On the other hand, tannic acid can firmly bind to the biochar surface through π-π stacking, hydrogen bonding and other interactions, thereby "anchoring" the Co-MOF crystals, significantly enhancing the interfacial bonding force between MOF and carbon support, and improving the structural stability of the composite material.

[0017] 3. Excellent electrochemical performance: The prepared Co-MOF-TA@DR composite material combines the high conductivity and good mechanical strength of biochar, the high specific surface area and abundant active sites of Co-MOF, and the interface optimization effect brought about by tannic acid modification. Electrochemical tests show that this material, as a supercapacitor electrode, exhibits excellent electrochemical performance at 1 A•g -1 The specific capacitance at current density is as high as 788 F•g -1 Even at 10 A•g -1 After 3000 charge-discharge cycles at high current density, the capacitance retention rate still exceeds 80%, demonstrating excellent rate performance and ultra-long cycle life.

[0018] 4. The preparation process is simple and controllable, and suitable for large-scale production: The entire preparation process mainly includes three steps: pyrolysis, hydrothermal treatment and heat treatment. The equipment used is conventional, the reaction conditions are mild, the parameters are easy to control, the process flow is simple, there is no complicated post-processing, and it has the potential for large-scale production.

[0019] In summary, this invention provides a high-performance, low-cost, and environmentally friendly supercapacitor electrode material and its efficient preparation method, which has important practical significance for promoting the commercial application of supercapacitors and the resource utilization of agricultural waste. Attached Figure Description

[0020] Figure 1 These are scanning electron microscope (SEM) images of the Co-MOF-TA@DR composite material prepared in Example 1, showing the polyhedral morphology and rich porous structure of the material.

[0021] Figure 2 The X-ray diffraction (XRD) pattern of the Co-MOF-TA@DR composite material prepared in Example 1 demonstrates that the material exhibits good crystallinity and graphitization characteristics after heat treatment.

[0022] Figure 3 The Co-MOF-TA@DR composite material prepared in Example 1 was tested at different scanning rates (10-50 mV·s). -1 The cyclic voltammetry (CV) curves under these conditions show good capacitive behavior and fast ion response.

[0023] Figure 4 This is a comparison of the galvanostatic charge-discharge (GCD) curves of Co-MOF-TA@DR composite materials prepared at different heat treatment temperatures (700℃, 800℃, 900℃) under the same current density.

[0024] Figure 5 This is a comparison of the GCD curves of Co-MOF-TA@DR composite materials prepared with different cobalt salt to biochar mass ratios at the same current density.

[0025] Figure 6 The GCD curves of the Co-MOF-TA@DR composite material prepared in Example 1 at different current densities demonstrate its excellent rate performance.

[0026] Figure 7 The images show the electrochemical impedance spectroscopy (EIS) Nyquist plot and equivalent circuit fitting diagram of the Co-MOF-TA@DR composite material prepared in Example 1, which demonstrate its low charge transfer resistance.

[0027] Figure 8 Co-MOF-TA@DR composites prepared at different heat treatment temperatures at 1 A·g -1 Bar chart comparing specific capacitance under current density.

[0028] Figure 9 Co-MOF-TA@DR composite materials prepared at different cobalt salt to biochar mass ratios at 1 A·g -1 Bar chart comparing specific capacitance under current density.

[0029] Figure 10 The Co-MOF-TA@DR composite material prepared in Example 1 was tested at 10 A·g. -1 Capacitance retention curve during 3000 cycles at current density. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention. Furthermore, it should be understood that after reading the disclosure of this invention, those skilled in the art can make various modifications or alterations to the invention, and these equivalent forms also fall within the scope of protection defined by this invention.

[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0032] Example 1: Preparation of Co-MOF-TA@DR composite material (1) Pretreatment of durian peel: Take 500g of fresh durian peel and rinse it repeatedly with running tap water 4-5 times to remove dirt and residual fruit pulp. Cut the washed durian peel into thin slices about 2mm thick. Spread the slices evenly on a tray and place them in a forced-air drying oven. Dry them at 60℃ for 12 hours to obtain dried durian peel fragments.

[0033] (2) Preparation of porous biochar: Weigh approximately 20g of dried durian peel fragments and place them evenly in a square porcelain boat. Place the porcelain boat in the constant temperature zone of a tube furnace. Introduce high-purity argon gas (flow rate 200 mL·min). -1 As a protective gas, purge for 30 minutes to remove air from the furnace. Then purge at 5°C / min. -1 The temperature was programmed to rise to 400°C and held at 400°C for 2 hours for pre-carbonization. It was then allowed to cool naturally to room temperature to obtain black pre-carbonized biochar, weighing approximately 6g.

[0034] Pre-carbonized biochar and potassium hydroxide (KOH) were weighed at a mass ratio of 1:2 (i.e., 6g biochar to 12g KOH) and thoroughly ground and mixed in an agate mortar for 30 minutes. The mixture was then transferred to a porcelain boat and placed back into a tube furnace. Under argon protection, the furnace was directly heated at 5℃·min. -1 The temperature was raised to 900℃ and activated at 900℃ for 2 hours. After activation, the product was cooled to room temperature under an argon atmosphere. The activated product was removed and first soaked and stirred in 1 M dilute hydrochloric acid solution for 6 hours to neutralize residual KOH and remove soluble metal salts. Then, it was repeatedly washed with a large amount of deionized water until the pH of the filtrate was close to 7. Finally, it was washed twice with anhydrous ethanol. The washed solid product was dried overnight in an oven at 80℃ to obtain durian peel-based porous biochar (DR), with a mass of approximately 2.5 g.

[0035] (3) Preparation of Co-MOF-TA@DR precursor: Weigh 0.5 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) into a 100 mL beaker, add a mixed solvent consisting of 30 mL of N,N-dimethylformamide (DMF), 1.8 mL of anhydrous ethanol and 1.8 mL of deionized water. Stir magnetically for 30 minutes until the cobalt salt is completely dissolved, resulting in a clear pink solution. Add 0.1 g of 2,5-dihydroxyterephthalic acid (H2DHBDC) to the solution and continue stirring for 30 minutes; the solution color will slightly darken.

[0036] Weigh 0.05 g of tannic acid (TA, equivalent to 10% of the mass of cobalt salt) and 0.1 g of biochar DR prepared in step (2) (mass ratio of cobalt salt to 1:5), and add them to the above solution. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 30 minutes, then continue to stir magnetically for 2 hours to obtain a uniform dark brown suspension.

[0037] The entire suspension was transferred to a 100 mL PTFE-lined high-pressure reactor and sealed. The reactor was placed in a forced-air drying oven and reacted at 120 °C for 24 hours. After the reaction, the oven was closed, and the reactor was allowed to cool naturally to room temperature. Upon opening the reactor, a large amount of precipitate was observed at the bottom. The precipitate was collected by centrifugation and washed three times each with DMF and anhydrous ethanol. The washed product was transferred to a petri dish and dried in a 60 °C vacuum drying oven for 12 hours to obtain a dark brown Co-MOF-TA@DR precursor powder.

[0038] (4) High-temperature heat treatment: Weigh approximately 0.5g of the above precursor powder and spread it evenly on the bottom of a small porcelain boat. Place the porcelain boat into a tube furnace. Introduce argon gas (flow rate 150 mL·min). -1 Purge for 20 minutes. Then purge at 5°C / min. -1 The temperature was programmed to rise to 900℃ and held at 900℃ for 2 hours for heat treatment. The entire heat treatment process was conducted under argon protection. After the heat treatment, the material was allowed to cool naturally to room temperature in an argon atmosphere. The ceramic boat was then removed, yielding the final black powdery Co-MOF-TA@DR composite material, denoted as Co-MOF-TA@DR-900.

[0039] Comparative Example 1: Preparation of Co-MOF@DR composite material without tannic acid modification The steps are basically the same as in Example 1, except that tannic acid (TA) is not added in step (3), and other conditions remain unchanged. The resulting material is denoted as Co-MOF@DR-900.

[0040] Comparative Example 2: Preparation of Co-MOF-TA materials without biochar support The steps are basically the same as in Example 1, except that biochar DR is not added in step (3), and other conditions remain unchanged. The resulting material is denoted as Co-MOF-TA-900.

[0041] Example 2: Preparation of Co-MOF-TA@DR composite materials with different cobalt salt to biochar mass ratios Referring to the steps of Example 1, only the mass ratio of cobalt salt (Co(NO3)2·6H2O) to biochar (DR) in step (3) was changed to 5:1, 5:3, 5:5, 3:5, and 1:5, respectively, while other conditions remained unchanged, to prepare a series of Co-MOF-TA@DR-900 composite materials with different compositions.

[0042] Example 3: Preparation of Co-MOF-TA@DR composite materials at different heat treatment temperatures Referring to the steps of Example 1, only the heat treatment temperature in step (4) is changed to 700℃ and 800℃ respectively, the holding time remains 2 hours, and the heating rate remains 5℃·min. -1 Co-MOF-TA@DR-700 and Co-MOF-TA@DR-800 composite materials were prepared.

[0043] The Co-MOF-TA@DR material obtained in this embodiment was subjected to phase identification and microstructure and structural characterization: the prepared material was identified by powder X-ray diffraction and X-ray photoelectron spectroscopy, and the obtained material was characterized by scanning electron microscopy.

[0044] Figure 1 This is a scanning electron microscope (SEM) image of Co-MOF-TA@DR. The image shows that the material exhibits a regular polyhedral morphology with abundant porous structures on its surface. This indicates that the free H+ released by tannic acid during the interface modification process etches the precursor, promoting the formation of a well-developed porous structure within it, thereby exposing more metal active sites and enhancing the material's electrochemical performance.

[0045] Figure 2 This is the XRD pattern of the Co-MOF-TA@DR nanocomposite material. It indicates that the material exhibits a good degree of graphitization after heat treatment.

[0046] This embodiment demonstrates a method for preparing supercapacitor electrode materials by growing Co-MOF through tannic acid interface modification based on waste biomass, and the application of this material as a supercapacitor electrode material.

[0047] The active material described in this invention is abbreviated as Co-MOF-TA@DR. A three-electrode system is used to test electrode performance individually, wherein the counter electrode is a platinum sheet electrode, the reference electrode is an Hg / HgO electrode, and the prepared positive electrode and activated carbon electrode can be used as working electrodes. During electrochemical testing, the green line connects to the working electrode, the red line connects to the counter electrode, and the white line connects to the reference electrode.

[0048] Preparation of the negative electrode material of this invention: Activated carbon, acetylene black, and PVDF are mixed in a mass ratio of 8:1:1, and an appropriate amount of anhydrous ethanol is added dropwise and mixed evenly. A piece of pre-treated nickel foam is prepared, and the uniformly mixed slurry is evenly coated onto the nickel foam. The coated nickel foam is then placed in a vacuum drying oven at 60 °C and dried for 12 h, with a loading of 4 mg·cm³. -2 .

[0049] All electrochemical performance tests described in this invention were performed with an electrolyte concentration of 6 mol·L⁻¹. -1 KOH solution.

[0050] The catalyst described in this invention requires CV activation for 3 cycles before electrochemical testing.

[0051] All tests described in this invention are conducted at room temperature to prevent large temperature variations from affecting electrochemical performance.

[0052] The catalyst obtained in this embodiment was subjected to cyclic voltammetry and galvanostatic charge-discharge (GCD) curve testing: an electrochemical workstation manufactured by Pine Corporation, USA, was used at 10⁻⁵ mV·s. -1 Cyclic voltammetry experiments were conducted within the scan rate range, with a test voltage of 0-0.5 V. During the test, a 50 mV·s band was used. -1 After activating the device with a current density for three cycles, cyclic voltammetry was performed. Linear cyclic voltammetry was also conducted using a Pine electrochemical workstation, with a voltage scan range of 0–0.5 V and a scan rate of 50 mV·s. -1 Rotational speed testing can yield constant current charge-discharge (GCD) curves under different current densities.

[0053] Electrochemical impedance spectroscopy and cycling tests are also important indicators of catalyst performance, at 5 A·g -1 Under high current density conditions, it can still maintain 80% of the initial specific capacitance after 3000 consecutive charge-discharge cycles. This cycle retention rate is significantly better than that of previously reported transition metal sulfide-based electrode materials.

[0054] Figure 3 This is a cyclic voltammetric curve of the Co-MOF-TA@DR nanocomposite; it shows that the Co-MOF-TA@DR composite material exhibits cyclic voltammetric characteristics in the range of 10-50 mV·s. -1 The evolution of cyclic voltammetry (CV) curves within the scan rate range was studied, and test results showed that even at 50 mV·s... -1 Even at high scan rates, the CV curves still maintain stable morphology, confirming that the material has excellent electrochemical reversibility and fast charge storage kinetics.

[0055] Figure 4 This section presents the galvanostatic charge-discharge curves of Co-MOF-TA@DR nanocomposites at different activation temperatures. It systematically demonstrates the galvanostatic charge-discharge curves and corresponding specific capacitance performance changes of the Co-MOF-TA@DR composites under different calcination temperatures (700 ℃, 800 ℃, and 900 ℃). Electrochemical test data show that calcination temperature, as a key preparation parameter, significantly affects the electrochemical energy storage behavior by controlling the integrity of the crystal structure and the evolution of the composition. When the calcination temperature reaches 900 ℃, the material exhibits the best electrochemical performance, achieving a specific capacitance of 1 A·g⁻¹. -1 The specific capacitance reaches 736 F·g at current density -1 .

[0056] Figure 5 The figures show the galvanostatic charge-discharge curves of Co-MOF-TA@DR nanocomposites with different mass ratios. Based on the determination that 900℃ is the optimal calcination temperature, this study further systematically investigated the influence mechanism of mass ratio on the electrochemical performance of Co-MOF-TA@DR composite materials. Figure 5 The galvanostatic charge-discharge (GCD) curves of Co-MOF-TA@DR prepared under five different mass ratios (5:1, 5:3, 5:5, 3:5, and 1:5) are presented. When the mass ratio of cobalt salt to biochar is 5:1, the composite material exhibits the best electrochemical energy storage performance, reaching 1 A·g⁻¹. -1 The specific capacitance at current density is as high as 788 F·g -1 .

[0057] Figure 6 These are galvanostatic charge-discharge curves of Co-MOF-TA@DR nanocomposites at different current densities. The Co-MOF-TA@DR-900 composite material at 1 A·g -1 It exhibits 788 F·g at current density -1 High specific capacitance, when the current density is increased to 5 A·g -1 It still maintains 750 F·g -1 The high specific capacity indicates that the material possesses an efficient charge transport mechanism and good reversibility of reaction.

[0058] Figure 7 The image shows the EIS spectra of the Co-MOF-TA@DR nanocomposite material, which demonstrates the electrochemical impedance spectroscopy (EIS) test results and the analysis of its equivalent circuit model. The Nyquist spectrum exhibits typical frequency response characteristics: in the high-frequency region, it presents a compressed semicircle feature intersecting the real axis. The diameter of the semicircle is fitted by the equivalent circuit, and the charge transfer resistance (Rct) is 0.37 Ω, which effectively promotes the charge exchange kinetics at the electrode / electrolyte interface.

[0059] Figure 8 This is a bar chart of the specific capacitance of Co-MOF-TA@DR nanocomposite materials at different temperatures. At 900℃, the specific capacitance of the Co-MOF-TA@D-900 composite material at 1 A·g -1 It exhibits 736 F·g at current density -1 The high specific capacitance and excellent rate performance indicate that the material has an efficient charge transport mechanism and good reversibility of reaction.

[0060] Figure 9This is a bar chart of the specific capacitance of Co-MOF-TA@DR nanocomposites with different mass ratios. When the mass ratio is 5:1, the specific capacitance of the Co-MOF-TA@D-900 composite material at 1 A·g -1 It exhibits 788 F·g at current density -1 The high specific capacitance and excellent rate performance indicate that the material has an efficient charge transport mechanism and good reversibility of reaction.

[0061] Figure 10 This refers to the specific capacitance retention rate of the Co-MOF-TA@DR nanocomposite material after 3000 cycles. The Co-MOF-TA@DR composite material exhibits excellent electrochemical cycling stability through systematic constant current charge-discharge testing at 10 A·g⁻¹. -1 Under high current density conditions, it can still maintain 80% of the initial specific capacitance after 3000 consecutive charge-discharge cycles. This cycle retention rate is significantly better than that of previously reported transition metal oxide-based electrode materials.

Claims

1. A method for preparing supercapacitor electrode materials based on waste biomass durian peel through tannic acid interface modification and growth of Co-MOF, characterized in that... Includes the following steps: (1) Pre-treatment of durian peel: Wash fresh durian peel, slice it, and dry it; (2) Preparation of porous biochar: The dried durian peel was subjected to a first-stage pyrolysis under an inert atmosphere to obtain pre-carbonized biochar; After mixing with an activator, a second stage of activation was carried out, followed by washing and drying to obtain durian peel-based porous biochar. (3) Preparation of Co-MOF-TA@DR precursor: Cobalt salt, organic ligand, tannic acid and biochar obtained in step (2) are dispersed in a mixed solvent, and after hydrothermal reaction, washed and dried to obtain Co-MOF-TA@DR precursor; (4) High-temperature heat treatment: The precursor obtained in step (3) is subjected to high-temperature heat treatment in an inert atmosphere, and after cooling, the Co-MOF-TA@DR composite material is obtained. Step 1: Durian peel pretreatment: Fresh durian peel is repeatedly rinsed with running water, the washed durian peel is cut into uniform thin slices, and dried in an oven.

2. The method according to claim 1, characterized in that: In step (1), the drying temperature is 50-70℃ and the drying time is 10-14 hours; preferably, it is dried at 60℃ for 12 hours.

3. The method according to claim 1, characterized in that: In step (2), the first stage of pyrolysis is carried out at 2-10℃•min. -1 Heating rate increased to 350-450℃, held for 1-3 hours; preferably 5℃•min -1 Heat to 400℃ and keep warm for 2 hours.

4. The method according to claim 1, characterized in that: In step (2), the activator is one or more of KOH, NaOH, and ZnCl2; the mass ratio of the activator to the pre-carbonized biochar is 1:1 to 3:1; preferably KOH, with a mass ratio of 2:

1.

5. The method according to claim 1, characterized in that: In step (2), the activation temperature of the second stage is 800-1000℃ and the activation time is 1-3 hours; preferably, the activation temperature is 900℃ for 2 hours.

6. The method according to claim 1, characterized in that: In step (3), the cobalt salt is one or more of cobalt nitrate hexahydrate, cobalt chloride, and cobalt acetate; the organic ligand is one or more of 2,5-dihydroxyterephthalic acid, terephthalic acid, and trimesic acid.

7. The method according to claim 1, characterized in that: In step (3), the amount of tannic acid added is 5%-50% of the mass of cobalt salt; the mass ratio of biochar to cobalt salt is 1:10-10:

1.

8. The method according to claim 1, characterized in that: In step (3), the hydrothermal reaction temperature is 100-150℃ and the reaction time is 12-36 hours; preferably, the reaction is carried out at 120℃ for 24 hours.

9. The method according to claim 1, characterized in that: In step (4), the heating rate of the high-temperature heat treatment is 2-10℃•min. -1 The heat treatment temperature is 700-1000℃, and the holding time is 1-3 hours; preferably 5℃·min -1 Heat to 900℃ and keep warm for 2 hours.

10. The supercapacitor electrode material according to claim 10, characterized in that: The electrode material is prepared by mixing active material, conductive agent and binder in a mass ratio of (7-9):(0.5-1.5):(0.5-1.5) to form a slurry, which is then coated onto the current collector; preferably, the mass ratio is 8:1:

1. The supercapacitor is either a symmetrical supercapacitor or an asymmetrical supercapacitor. The electrolyte is an alkaline electrolyte, an acidic electrolyte, or a neutral electrolyte; preferably a 6 M KOH aqueous solution.

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