Foamed nickel-loaded 3D chromium-doped carbon nanosheet supercapacitor electrode and preparation process and application thereof

Abstract

The invention belongs to the technical field of energy storage, and particularly discloses a foamed nickel loaded 3D chromium-doped carbon nanosheet supercapacitor electrode and a preparation process and application thereof. Foamed nickel is adopted as a substrate, a ZIF-67 nanosheet grows on the substrate through a liquid phase self-assembly method, then a chromium-doped carbon film is deposited through a magnetron sputtering technology, and the three-dimensional nanosheet array electrode is formed. The method is simple in process, low in cost and environment-friendly, and does not involve the use of toxic and harmful solvents. The prepared electrode has high specific surface area, excellent charge transfer capability and electrochemical stability, the specific capacitance, the energy density and the power density of the electrode are remarkably improved, and the electrochemical performance of the electrode is optimized. The method is not only suitable for preparation of supercapacitor electrode materials, but also can be expanded to development of other energy storage materials and devices, and has important practical application value and industrial application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of energy storage, in particular to a foam nickel loaded 3D chromium-doped carbon nanosheet supercapacitor electrode with high energy density and power density and a preparation process and application thereof. BACKGROUND

[0002] Existing supercapacitor electrode preparation technologies and material research have made significant progress, and various innovative methods have been widely explored and applied. In terms of preparation methods, laser pyrolysis realizes efficient integrated integration of graphene electrode materials and micro supercapacitors; hydrothermal method can prepare electrode materials with specific morphology and structure by adjusting reaction conditions, such as Co3V2O8 / CNTs composite material and NiCo-LDH@MnCo-LDH core-shell heterostructure; hard template method precisely controls the electrode structure by using template materials, such as in-situ growth of NiCo-MOF and formation of oxygen vacancies by hard template method; self-supporting electrode preparation technology takes carbon nanotubes as the substrate, combines in-situ growth and electrodeposition process, and solves the problem of poor conductivity of MOF; superfast molten salt synthesis method greatly improves the preparation efficiency, and the synthesized porous carbon exhibits high specific surface area and energy density; the “urchin-like” NiCo-LDH / carbon microsphere composite material prepared by microwave hydrothermal and activation technology has high specific capacitance and good cycle stability.

[0003] However, in terms of preparation methods, the problems of high cost, complex process, environmental impact, slow speed and low precision of 3D printing technology limit its large-scale application. In terms of electrode materials, the problems of low capacity, low power density and low energy density caused by poor material consistency, interface defects and self-discharge phenomenon restrict the performance improvement. SUMMARY

[0004] In view of the key problems of developing supercapacitors with excellent performance such as high capacity, high power density and high energy density, and at the same time meeting the requirements of low cost and green and environmentally friendly process, the application proposes a solution based on magnetron sputtering technology.

[0005] The process realizes the low cost and green and environmentally friendly goal in the following ways:

[0006] 1. Low cost: Commercial high-purity chromium target and graphite target (purity > 99.999%) are used, the initial procurement cost is controllable (about 4000 yuan RMB), and the service life of the target material is up to two years, which significantly reduces the core material cost per device.

[0007] 2. Green and environmentally friendly: Only high-purity argon gas is used as the working gas in the sputtering process, and there is no harmful by-product or pollutant emission, which meets the requirements of environmentally friendly process.

[0008] To achieve the goals of high capacity, high power density and high energy density, the core strategy of the present application is to design and construct a composite electrode structure of metal-organic framework (MOFs) material (ZIF-67 nanosheet) and carbon-based material:

[0009] 1. High specific surface area and active sites: ZIF-67 nanosheet provides significantly increased electrode specific surface area, exposing abundant electrochemically active sites, effectively improving charge storage capacity.

[0010] 2. Enhanced charge transport kinetics: The introduction of chromium doping strategy optimizes the intrinsic electrochemical activity of active sites and constructs additional ion transport channels, significantly improving the charge transfer rate within the electrode.

[0011] The combination of the above material design and process synergistically improves the specific capacitance of the electrode and the overall device performance: the obtained single electrode exhibits excellent area-specific capacitance (up to 1508 mF cm -2 ), and the assembled supercapacitor device realizes the balance of high energy density (up to 32.6 mWh cm -2 ) and high power density (up to 2002.7 mW cm -2 ).

[0012] The specific technical solutions adopted by the present application are as follows:

[0013] In a first aspect, the present application provides a preparation process for a foam nickel loaded 3D chromium doped carbon nanosheet supercapacitor electrode, comprising the following steps:

[0014] S1. Cut and clean the foam nickel and dry it for standby;

[0015] S2. Place the foam nickel in a mixed solution of cobalt nitrate hexahydrate and dimethyl imidazole, and let it stand for reaction, to obtain a foam nickel with a purple ZIF-67 nanosheet array by liquid phase self-assembly method, denoted as ZIF-67@NF;

[0016] S3. Deposit chromium-doped carbon film on ZIF-67@NF using magnetron sputtering technology to form a three-dimensional nanosheet array electrode.

[0017] Preferably, in step S1, the foam nickel is sequentially cleaned with dilute hydrochloric acid, anhydrous ethanol and deionized water under ultrasonic cleaning.

[0018] Preferably, in step S2, the molar concentration ratio of cobalt nitrate hexahydrate to dimethyl imidazole is 1:8 to ensure uniform growth of nanosheets. The inventors tried molar concentration ratios of 1:1, 1:4 and 1:10, but the results were all nanosheet synthesis failure, with inconsistent and uneven growth size.

[0019] Preferably, in step S2, the reaction is allowed to stand for 4h, and the product is washed with deionized water after the reaction is completed, and dried at 60℃ for 12h to obtain the ZIF-67@NF.

[0020] Preferably, in step S3, the magnetron sputtering chamber is vacuumed to 3.0*10-5 Torr before film plating, and the total pressure is maintained at 1.0*10-3 Torr during deposition; argon gas is used as the sputtering gas, and the gas flow rate is 20sccm; during deposition, the bias voltage is maintained at -60V.

[0021] Preferably, in step S3, the magnetron sputtering is first performed using a chromium target to form a transition layer between the ZIF-67@NF substrate and the thin film, and then chromium and carbon targets are used for synchronous sputtering to form a chromium-doped carbon thin film. Without the transition layer, the interfacial bonding force is insufficient, which will lead to easy peeling or falling off of the thin film during electrochemical cycling, thereby significantly reducing the structural stability of the electrode and damaging its long cycle life.

[0022] Further, in step S3, the chromium target is first sputtered at 5A for 5min to form a transition layer; then the sputtering current of the chromium target is adjusted to 0.3-3A (more preferably 0.3A), the sputtering current of the carbon target is set to 6A, and the chromium-doped carbon thin film is deposited for 1h. The sputtering current directly controls the chromium doping concentration (20-40% is optimal), and by balancing the double-layer capacitance (carbon matrix) and the pseudo-capacitance (chromium compound), the specific capacitance is synergistically improved (>1500mF / cm 2 ); excessive doping (>40%) will reduce the conductivity and accelerate the cycle decay.

[0023] In a second aspect, the application provides a foam nickel loaded 3D chromium-doped carbon nanosheet supercapacitor electrode prepared by the above preparation process.

[0024] In a third aspect, the application provides a supercapacitor using the foam nickel loaded 3D chromium-doped carbon nanosheet supercapacitor electrode as an electrode material.

[0025] In a fourth aspect, the application provides applications of the foam nickel loaded 3D chromium-doped carbon nanosheet supercapacitor electrode or the supercapacitor in the field of electronic devices, intelligent sensors, micro robots, etc. that require fast charging and discharging and high power output.

[0026] The technical scheme of the application has the following innovative points:

[0027] 1) Unique material combination and structural design:

[0028] A novel composite electrode structure was constructed by creatively combining ZIF-67 nanosheets with chromium-doped carbon films. This unique heterostructure not only utilizes the high surface area and porous nature of the ZIF-67 nanosheets to increase ion transport channels, but also significantly enhances the electrode's charge transfer capacity and electrochemical stability through chromium doping. This synergistic effect is uncommon in existing research, as most studies focus on optimizing single materials or simple composite structures. However, this invention achieves significant performance improvements through the design of a heterostructure.

[0029] 2) Unique role of chromium doping:

[0030] Chromium doping plays a key role in this invention, promoting efficient electron conduction and increasing available active sites for ion storage by forming a chromium-carbon composite structure. This mechanism of action differs significantly from the non-elemental doping commonly used in the prior art, such as nitrogen and phosphorus. Because chromium, as a transition metal, is doped, it not only changes the electronic structure of the electrode material but also, through synergistic effects with carbon, significantly improves the electrode's specific capacitance and energy density, optimizing its electrochemical performance. This unique doping strategy is rarely reported in existing literature and is highly innovative.

[0031] 3) Synergistic mechanism of nickel foam substrate and ZIF-67 nanosheets:

[0032] Using nickel foam as a substrate for growing ZIF-67 nanosheets, the researchers demonstrate a synergistic effect between the substrate and the nanosheets, a mechanism not readily apparent in existing techniques. The three-dimensional porous structure of nickel foam provides excellent support for the growth of ZIF-67 nanosheets while enhancing the overall conductivity of the electrode. This synergistic effect not only improves the mechanical stability of the electrode but also optimizes its electrochemical performance, offering significant advantages over conventional flat substrates or single-material electrodes.

[0033] 4) The inevitable connection between optimized sputtering conditions and high performance:

[0034] By optimizing the sputtering conditions, uniform deposition and high performance of chromium-doped carbon films were achieved. This optimized sputtering condition not only ensures the uniformity and adhesion of the film, but also maximizes the electrode performance by precisely controlling the chromium doping concentration. This fine control of the preparation process parameters is not common in existing technologies, because most studies focus on optimizing the material itself while ignoring the direct impact of the preparation process parameters on performance. Under the optimized conditions, the electrode material exhibits excellent electrochemical properties, such as a single electrode area specific capacitance of 1508mF cm -2 , the device energy density reaches 32.6mWh cm -2 , the power density reaches 2002.7mW cm -2 .

[0035] 5) Combination of environmentally friendly design and high performance:

[0036] While pursuing high performance, attention is also paid to environmentally friendly design. The entire preparation process does not involve the use of toxic and harmful solvents, meeting the requirements of sustainable development. This green and pollution-free preparation process has high innovation in the prior art, because the preparation of many high-performance electrode materials often requires the use of organic solvents or other harmful substances, and the present application realizes the dual goals of high performance and environmental friendliness through innovative process design.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] 1) Low process cost: The present application uses foamed nickel as a substrate, grows ZIF-67 nanosheets thereon, and then deposits chromium-doped carbon film, so the preparation process is simple and low in cost. Compared with some existing complex preparation processes, it does not require the use of expensive equipment and complex operation steps, and has significant economic advantages.

[0039] 2) Simple process route: The entire preparation process includes the growth of ZIF-67 nanosheets and the deposition of chromium-doped carbon film, and the operation flow is simple and easy to implement, control and optimize. This simple process route is conducive to large-scale production and industrial application.

[0040] 3) Environmentally friendly: In the preparation process, no toxic and harmful solvents are used, avoiding the environmental pollution problems commonly seen in traditional preparation methods. For example, compared with the polyhedral structure ZIF-67 in the prior art, which needs to be synthesized in methanol and the product has static electricity which is not conducive to the next processing, the present application is more green and environmentally friendly.

[0041] 4) Green and pollution-free: The preparation process of the present application meets the requirements of sustainable development, is friendly to the environment and has no pollution. In the deposition process of the chromium-doped carbon film, no organic solvents harmful to the environment are used, meeting the growing demand for sustainable energy storage solutions. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a 3D Cr-CNA electrode preparation process route diagram of the present application.

[0043] Figure 2 is a 3D Cr-CNA morphology diagram of the present application. In the figure, a-f are macroscopic morphology diagrams of 0Cr-CAN, 0.3Cr-CAN, 1Cr-CAN, 2Cr-CAN, 3Cr-CAN, and ZIF-67@NF samples, respectively; a'-f' are local enlarged views of a-f.

[0044] Figure 3XRD pattern of 3D Cr-CNA of the application. In the figure, a is the XRD pattern of 3D Cr-CNA and ZIF-67, and b is the enlarged view of the XRD pattern of 3D Cr-CNA and ZIF-67.

[0045] Figure 4 Wetting contact angle test diagram of ZIF-67 nanosheet array and 3D Cr-CNA of the application. In the figure, a-f are respectively the test results of ZIF-67@NF, 0Cr-CAN, 0.3Cr-CAN, 1Cr-CAN, 2Cr-CAN and 3Cr-CAN samples.

[0046] Figure 5 Electrochemical test diagram of 3D Cr-CNA single electrode of the application, wherein (a) is the cyclic voltammetry (CV) diagram with a scanning rate of 100 mV / s; (b) is the galvanostatic charge-discharge (GCD) test diagram with a current density of 2 mA / cm 2 ; (c) is the EIS Nyquist diagram; and (d) is the EIS Bode diagram.

[0047] Figure 6 1000-cycle charge-discharge test diagram of the application at a current density of 60 mA / cm 2 .

[0048] Figure 7 Symmetric button type supercapacitor test diagram of the application, wherein (a) is the CV test diagram; (b) is the GCD charge-discharge test diagram; (c) is the environmental impact assessment system test diagram; (d) is the schematic diagram of assembling a symmetric button type supercapacitor; (e) is the voltage measurement diagram after charging; and (f) is the LED light-emitting experiment diagram. DETAILED DESCRIPTION

[0049] A preparation process of a foam nickel loaded 3D chromium doped carbon nanosheet supercapacitor electrode is disclosed.

[0050] 1. Synergistic optimization of microstructure and performance: By growing ZIF-67 nanosheets on the foam nickel, a good substrate structure is provided for the subsequent deposition of chromium doped carbon film. The porous structure of ZIF-67 nanosheets increases the specific surface area of the electrode and provides more channels for ion transmission, thereby improving the electrochemical performance of the electrode.

[0051] 2. Innovative application of chromium doping: Depositing a chromium doped carbon film on the ZIF-67 nanosheet, through the formation of chromium-carbon composite structure, the charge transfer capacity and electrochemical stability of the electrode are significantly enhanced. The doping of chromium not only improves the electrical conductivity of the electrode, but also increases the available active sites for ion storage, thereby improving the specific capacitance and energy density of the electrode.

[0052] 3. Process simplification and cost control: The preparation process adopted by this technology is simple, without the need for complex equipment and expensive materials, reducing production costs. At the same time, by optimizing the sputtering conditions, large-area, uniform and excellent adhesion thin film deposition is achieved, improving the scalability and repeatability of production.

[0053] 4. Performance improvement: The binder-free electrode prepared by magnetron sputtering always shows superior performance compared to the electrode prepared by traditional methods. This performance improvement is attributed to the elimination of non-conductive binder, the improvement of active material utilization rate, and the enhancement of electrical conductivity between active material and current collector.

[0054] 5. Environmental benefits: The binder-free characteristics of magnetron sputtered electrodes eliminate the use of environmentally harmful organic solvents commonly used in traditional electrode preparation processes, meeting the growing demand for sustainable energy storage solutions.

[0055] The specific way technology roadmap is shown in Figure 1 The present application is further illustrated below in conjunction with the accompanying drawings and specific examples.

[0056] The preparation materials are as follows: Foam nickel (pore size 110 ppi, thickness 1.5 mm) was purchased from Kunshan Shangte New Materials Co., Ltd. Graphite target (purity 99.999%) and metal chromium target (99.99%) were purchased from Suzhou Liuji New Materials Technology Co., Ltd. Cobalt nitrate hexahydrate (analytical pure), dimethylimidazole (analytical pure), and anhydrous ethanol (analytical pure) were purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd. Deionized water was purchased from Zhejiang Nanda Industry Co., Ltd. Krypton standard titration solution (0.5 mol L -1 ) was purchased from Guangzhou He Wei Pharmaceutical Technology Co., Ltd. Button cell components and water-based cellulose hydrophilic separator (95 um) were purchased from Tianjin Avisin Chemical Technology Co., Ltd.

[0057] Example 1: Preparation of 3D Cr-CNA electrode

[0058] I. Synthesis of ZIF-67@NF

[0059] ZIF-67@NF nanosheet arrays were synthesized by a liquid self-assembly method. A mixed solution of cobalt nitrate hexahydrate and dimethylimidazole with a molar concentration ratio of 1:8 was prepared, and the ZIF-67 nanosheet array with the most uniform and largest area was grown. The specific configuration and operation are as follows:

[0060] The foam nickel was cut into an area of 4×4 cm 2 , and 0.5 mol L -1Krypton standard titration solution of dilute hydrochloric acid, anhydrous ethanol, deionized water, ultrasonic cleaning of foamed nickel for 10 minutes to remove the oil stains and other impurities on the surface of foamed nickel, and dried in an oven at 150°C for 5 hours for standby. At room temperature, 0.05M of cobalt nitrate hexahydrate was dissolved in 40ml of deionized water to obtain a purple solution, and the solution was ultrasonically dispersed for 5 minutes; at the same time, 0.4M of dimethyl imidazole was dissolved in 40ml of deionized water to obtain a transparent solution, and the solution was also ultrasonically dispersed for 5 minutes. After the ultrasonic ended, the purple solution was slowly poured into the transparent solution and ultrasonically dispersed for 3 minutes. Then the dried foamed nickel (4×4cm 2 ) was vertically placed in the mixed solution and stood for 4 hours. After the reaction was completed, the foamed nickel covered with purple ZIF-67 nanosheet array was washed with deionized water for three times respectively. Subsequently, the obtained sample was dried in an oven at 60°C for 12 hours to obtain the foamed nickel on which the purple ZIF-67 nanosheet array was grown, which was recorded as ZIF-67@NF.

[0061] II. Preparation of 3D Cr-C nanosheet array by magnetron sputtering

[0062] A chromium-doped carbon thin film was deposited on ZIF-67@NF by using the British Teer Coatings UDP650 / 4 multi-target vacuum coating equipment by using the magnetron sputtering technology. Before coating, the magnetron sputtering chamber was vacuumed to 3.0×10 -5 Torr, and the total pressure was kept at 1.0×10 -3 Torr during the deposition process. Argon gas was used as the sputtering gas, and the gas flow rate was 20sccm. A rotating support with self-rotation was used to rotate at a speed of 5rpm / min to realize uniform deposition on both sides. During the deposition process, the bias voltage was kept at -60V. The chromium target sputtering current was set to 5A, and the carbon target sputtering current was set to 0A. The chromium target was sputtered at 5A for 5min to form a transition layer between the substrate and the thin film. Then, the sputtering current of the chromium target was adjusted to 0A, 0.3A, 1A, 2A and 3A, while the sputtering current of the carbon target was increased to 6A and kept constant. The deposition lasted for 1 hour to obtain a three-dimensional chromium-doped carbon nanorod array, in which the chromium-doped carbon thin film was directly deposited on ZIF-67@NF to obtain a Cr-C@ZIF-67 nanosheet composite material. According to the chromium sputtering current, the Cr-C@ZIF-67 samples were divided into 0Cr-CNA, 0.3Cr-CNA, 1Cr-CNA, 2Cr-CNA and 3Cr-CNA.

[0063] Example 2: Characterization and performance test of 3D Cr-CNA electrode

[0064] 1. The 0Cr-CNA, 0.3Cr-CNA, 1Cr-CNA, 2Cr-CNA and 3Cr-CNA samples were observed under a scanning electron microscope.

[0065] The results are as follows Figure 2 Field emission scanning electron microscopy macro- and microscopic images of 3D Cr-CNA are shown in Figures a-e and a'-e'. Cr-C@ZIF-67 nanosheet arrays are uniformly coated on the NF and vertically protrude from the NF surface. Figure 2 f and f' are the macroscopic and microscopic images of ZIF-67@NF obtained by field emission scanning electron microscopy. The average thickness of Cr-C@ZIF-67 nanosheets increases with the increase of chromium doping amount, which are 353nm, 364nm, 373nm, 400nm, and 568nm, respectively, which is at least 1.6 times the average thickness of ZIF-67 nanosheets of 215nm. Figure 2 The three-dimensional morphology and coverage of the nanosheet arrays are clearly revealed, and the highly rough surface provides more electrochemically active sites. The abundant spaces between adjacent Cr-C@ZIF-67 nanosheets facilitate electrolyte penetration.

[0066] 2. XRD tests were performed on 0Cr-CNA, 0.3Cr-CNA, 1Cr-CNA, 2Cr-CNA and 3Cr-CNA samples.

[0067] The results are as follows Figure 3 As shown in (a, b are the original image and the local enlarged image, respectively), it can be seen that the ZIF-67 nanosheet has a good crystal structure. The strong peaks of the ZIF-67 nanosheet correspond to the (200), (211), (310), (222), (411), (422), (521), (440) and (530) crystal planes. In the Cr-C@ZIF-67 nanosheet composite material, the intensity of the diffraction peak of the Cr-C film is too weak compared with the ZIF-67 nanosheet, and the characteristic peak of the Cr-C film cannot be seen as a whole. Therefore, the diffraction peak between 42°-48° is magnified ( Figure 4 b). It can be found that all diffraction patterns of Cr-C@ZIF-67 nanosheet composites show broad features at 44°-46°. This indicates that the Cr-C film is mainly amorphous. The broad peak centered at 44.7° originates from the amorphous chromium carbide phase, as this peak is centered around the strongest diffraction peaks of two stable carbides, Cr7C3 (PDF#00-011-0550) and CrC (PDF#00-047-1424). Figure 4b) Based on the Scherrer formula, the length of the correlation domain was estimated to be about 2.33 nm based on the only measurable feature at 44.7°, which confirmed the amorphous nature of the carbide phase. The broad peak at 44.7° for the Cr-C thin film could be attributed to the chromium transition layer or interfacial diffusion effects between the chromium transition layer and the top Cr-C coating. At the same time, all Cr-C@ZIF-67 nanosheet composites showed similar features, including four strong characteristic diffraction peaks corresponding to the (200), (211), (310), and (411) crystal planes of ZIF-67, which indicated that the deposition of the Cr-C thin film during the in-situ synthesis process was not destroyed or destroyed the structure of ZIF-67 in the composite. The incorporation of chromium elements and the transition layer not only enhanced the binding force between the Cr-C thin film and the ZIF-67 nanosheet, but also the presence of Cr-C with excellent chemical stability would enhance the corrosion behavior of the electrode material, both of which would make the electrode material have excellent cycle service life.

[0068] 3. The wettability contact angle test was performed on the XRD samples of 0Cr-CNA, 0.3Cr-CNA, 1Cr-CNA, 2Cr-CNA and 3Cr-CNA samples.

[0069] The results are shown in Figure 4 It can be found that the original ZIF-67 nanosheet has a contact angle of 123°, which is almost hydrophobic. The 0_Cr-C@ZIF-67 sample prepared by depositing undoped carbon thin film shows hydrophilicity, with a contact angle of 59.65°, which greatly improves the hydrophilicity of ZIF-67 nanosheet. However, with the increase of chromium doping amount, the wettability contact angle gradually increases from 59.65° to 113.6°, because with the increase of chromium doping amount, more and more sp 2 hybridization, sp 2 cluster phase is conducive to reducing the surface energy, and the relative content of sp 2 hybridization bond increases with the increase of Cr element, so the hydrophobic characteristics are more obvious. But finally the overall deposition of chromium-doped carbon thin film ZIF-67 nanosheet is more hydrophilic than ZIF-67 nanosheet. This helps the electrolyte molecules to penetrate into the gap between the surface structure, thereby promoting more efficient electrochemical processes.

[0070] 4. CV, GCD and EIS tests were performed on 0Cr-CNA, 0.3Cr-CNA, 1Cr-CNA, 2Cr-CNA and 3Cr-CAN, and the test methods and results are as follows:

[0071] All electrochemical tests were performed on a Swiss-made Autolab electrochemical workstation. The measurements were performed using a three-electrode system with a single electrode: the reference electrode was a mercury / mercury oxide electrode, and the counter electrode was a platinum foil. The working electrode was the deposited thin film sample, with an effective test area of 1.0 x 1.0 cm 2 . The electrolyte was a 6 mol L -1 KOH solution. All electrochemical experiments were performed under atmospheric conditions. Before testing, the sample was immersed in the KOH solution for 30 minutes at the open circuit potential to ensure stability.

[0072] (1) CV test: performed at a scan rate of 10-100 mV / s in a voltage window of 0-0.5 V, the results are shown in Figure 5 a. It can be seen that as the chromium doping amount increases from 0A to 0.3A, the CV curve integral area of the material increases significantly, indicating that the specific capacitance is improved. This is mainly due to the fact that the appropriate chromium doping introduces more active sites on the surface of the carbon thin film nanosheet, optimizes the electronic structure, and produces more ion channels, thereby enhancing the utilization rate of the electrochemically active material.

[0073] (2) GCD test: performed at a current of 2-10 mA cm -2 in a voltage of 0-0.5 V for the single electrode, the results are shown in Figure 5 b. It can be seen that the results are consistent with the CV test results (from 587.6 mF / cm 2 of 0Cr-CNA to 1508 mF / cm 2 of 0.3Cr-CNA). However, when the chromium doping amount is further increased (1A, 2A, 3A), the specific capacitance shows a downward trend (882 mF / cm 2 , 828.4 mF / cm 2 , 686.4 mF / cm 2 ). Further analysis found that excessive chromium doping may cause the surface active sites of the carbon thin film to be excessively passivated, making it difficult for electrolyte ions to fully contact and embed the active material; at the same time, excessive doping of chromium atoms may change the chemical state of the material surface, leading to a decrease in the charge transfer efficiency of the electrode / electrolyte interface.

[0074] (3) EIS test: obtained using a sinusoidal potential modulation of 5 mV in a frequency range of 0.01 Hz to 100 kHz, the results are shown in Figure 5As shown in cd, the equivalent series resistance (Rs) of each sample determined by the intercept on the real axis of the Nyquist curve is 0.411Ω, 0.219Ω, 0.276Ω, 0.308Ω, and 0.369Ω, respectively, indicating that the smaller internal resistance is mainly attributed to the good conductivity of the Cr-C transition metal chromium-doped carbon film and its excellent adhesion to the current collector. The 0.3Cr-CNA sample has the lowest Rs value, indicating that the appropriate amount of chromium doping effectively reduces the interfacial contact resistance between the material and the electrolyte and improves the electron transfer efficiency; while the Rs of the high chromium doping sample shows an upward trend, which is because excessive chromium doping may change the surface chemical state of the film, such as decreased wettability and increased resistance. Combined with Figure 5 The Bode plot analysis of d shows that the 0.3Cr-CNA sample exhibits a higher phase angle and a smaller impedance modulus in the medium and low frequency regions, indicating that it has better charge transfer characteristics and ion diffusion ability, which is consistent with the Figure 5 The parameter changes in the fitted equivalent circuit diagram (c) are consistent: CPE1 (reflecting the interfacial charge storage capacity) and CPE2 (associated with the diffusion process) reach optimal matching at a chromium doping level of 0.3A, while Rct (charge transfer resistance) is minimized, indicating that the charge transfer efficiency at the electrode / electrolyte interface is highest at this point. The change in the slope of the Warburg impedance W also indicates that the ion diffusion process is optimized. Appropriate doping can effectively adjust the electronic structure and surface chemical state of the material, thereby improving its overall electrochemical performance.

[0075] 5. Test the 0.3Cr-CNA sample at 60mA / cm 2 1000 cycles of charge and discharge test at the same current density.

[0076] The results are as follows Figure 6 As shown in Figure 2, it can be seen that the capacitance retention and Coulombic efficiency are both 76%. In addition, the device highlights the extremely reversible nature of the working charge storage mechanism on the 0.3Cr-CNA surface, as shown in Figure 2. Figure 6 As shown in the inset of b, there is no obvious change in the shape of the GCD curve between the first 10 cycles and the last 10 cycles of charge and discharge, and the FSEM inset shows that the electrode structure of the 0.3Cr-CNA nanosheet array remains basically good before and after the long cycle test, further highlighting its structural stability and potential for long service life.

[0077] 6. A symmetrical button-type supercapacitor was assembled using 0.3Cr-CNA sample (as electrode material), aqueous cellulose hydrophilic membrane and button battery components, and CV test, GCD test and EIS test were performed.

[0078] The test results are as follows Figure 7As shown, the cyclic voltammetry test under 0-1 V voltage window shows good electrochemical stability and reversibility of the symmetrical button supercapacitor, with symmetrical and repeatable curves, indicating that the electrode material has excellent charge-discharge reversibility in this voltage range, as shown in Figure 7 a. Figure 7 The constant current charge-discharge test of b shows that the capacitor achieves a specific capacitance of 234.4 mF / cm 2 at a current density of 0.2 mA / cm 2 , and the energy density is calculated to be 32.6 mWh / cm 2 , and the power density is as high as 2002.7 mW / cm 2 . This outstanding performance is attributed to the high efficiency of the capacitor in storing and releasing electrical energy, and the high energy density means that a large amount of electrical energy can be stored in a unit volume, and the high power density reflects the ability of fast charging and discharging. The Ragone plot Figure 7 c) is used to compare the energy density and power density of the supercapacitor electrode material of the application with other thin films, and it can be found that it is better than most thin films published so far. Figure 7 The Nyquist plot of c illustrates the frequency response characteristics of the capacitor: the slope in the low frequency region reflects the ion diffusion behavior, and the diameter of the semicircle in the high frequency region corresponds to the charge transfer resistance. A smaller semicircle diameter reveals high charge transfer efficiency and low internal resistance, which is crucial for improving the overall performance of the capacitor. The element parameters such as resistance, constant phase element and Warburg impedance in the fitting circuit accurately reflect the complex processes of charge transfer and ion diffusion inside the capacitor. Figure 7 d to Figure 7 f verify the performance of the capacitor from the perspective of physical assembly and application. Figure 7 d shows a symmetrical button supercapacitor with 0.3Cr-CNA as the electrode material, which has a reasonable and compact structure design. Figure 7 e shows that after being fully charged, the voltage of a single capacitor measured by a multimeter is 1.56 V, which exceeds the theoretical value, proving that the capacitor has good electrical energy storage efficiency. ​ f further demonstrates the application potential of the capacitor by lighting two 1.5V LED lamp beads: a single lamp bead can be stably powered for more than 8 minutes, and two lamp beads in parallel can be powered for 3 minutes, which not only reflects the high energy output capacity of the capacitor, but also highlights its excellent electrochemical stability.

[0079] From this embodiment, it can be concluded that the sample prepared under a sputtering current doping amount of 0.3 A (0.3Cr-CNA) has the best performance, with a single electrode area specific capacitance of 1508 mF cm -2 , a device energy density of 32.6 mWh cm -2 , and a power density of 2002.7 mW cm-2 .

[0080] In summary, the preparation process of the application is simple, low cost and environmentally friendly, and can stably prepare high-performance supercapacitor electrode materials. Experimental data show that the process has strong repeatability, and multiple experiments can stably prepare electrode materials with similar experimental test results, excellent and stable performance indicators. Most importantly, the process route is simple, suitable for large-scale industrial production, and does not involve the use of toxic and harmful solvents, meeting the requirements of sustainable development. The significance of its technical progress lies in significantly improving the electrode performance through chromium doping, while having multifunctionality and wide applicability, not only suitable for the preparation of supercapacitor electrode materials, but also can be extended to the development of other energy storage materials and devices, having important practical application value and industrial application prospect.

[0081] The specific embodiment is only an explanation of the application, not a limitation of the application, and any change made by a person skilled in the art after reading the specification of the application will be protected by the patent law as long as it is within the scope of the claims of the application.

Claims

1. A preparation process for nickel foam loaded 3D chromium-doped carbon nanosheet supercapacitor electrode, characterized in that: The following steps are involved: S1. Cut and clean the nickel foam and dry it for later use; S2. Nickel foam was placed in a mixed solution of cobalt nitrate hexahydrate and dimethylimidazole and allowed to react. A purple ZIF-67 nanosheet array, designated ZIF-67@NF, was grown on the nickel foam via liquid-phase self-assembly. S3. Cr-doped carbon films were deposited on ZIF-67@NF using magnetron sputtering technology to form three-dimensional nanosheet array electrodes.

2. The preparation process according to claim 1, characterized in that In step S1, the nickel foam is ultrasonically cleaned using dilute hydrochloric acid, anhydrous ethanol, and deionized water in sequence.

3. The preparation process according to claim 1, characterized in that In step S2, the molar concentration ratio of the cobalt nitrate hexahydrate to dimethylimidazole is 1:

8.

4. The preparation process according to claim 1, characterized in that In step S2, the reaction was allowed to stand for 4 hours. After the reaction was completed, the product was washed with deionized water and dried at 60° C. for 12 hours to obtain the ZIF-67@NF.

5. The preparation process according to claim 1, characterized in that: In step S3, the magnetron sputtering chamber is vacuumed to 3.0×10 -5 Torr, the total pressure was maintained at 1.0×10 -3 Torr; argon was used as the sputtering gas with a gas flow rate of 20 sccm; during the deposition process, the bias voltage was maintained at -60 V.

6. The preparation process according to claim 1, characterized in that In step S3, magnetron sputtering is first performed using a chromium target to sputter a transition layer between the ZIF-67@NF substrate and the thin film, and then a chromium target and a carbon target are synchronously sputtered to form a chromium-doped carbon thin film.

7. The preparation process according to claim 6, characterized in that: In step S3, the chromium target is first sputtered at 5A for 5 minutes to form a transition layer; then the sputtering current of the chromium target is adjusted to 0.3-3A, and the sputtering current of the carbon target is set to 6A, and deposition is performed for 1 hour to form a chromium-doped carbon film.

8. A nickel foam-loaded 3D chromium-doped carbon nanosheet supercapacitor electrode prepared by the preparation process according to any one of claims 1 to 7.

9. A supercapacitor, characterized in that: The nickel foam loaded 3D chromium-doped carbon nanosheet supercapacitor electrode according to claim 8 is used as the electrode material.

10. Use of the supercapacitor electrode according to claim 8 or the supercapacitor according to claim 9 in the fields of electronic devices, smart sensors, and micro robots.

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