Preparation and application of self-supporting electrode based on porous ferrocobalt layered double hydroxide

Abstract

The invention discloses preparation and application of a self-supporting electrode based on porous ferrocobalt layered double hydroxides, an electrode material is a composite material formed by loading the porous ferrocobalt layered double hydroxides (CoFe-LDH) on foamed nickel (NF), the composite material is recorded as CoFe-LDH / NF, the molar ratio of cobalt to iron is 1: 3, 2: 2 or 3: 1, the electrode is used as the self-supporting electrode to be applied to a supercapacitor, and the self-supporting electrode is used for supporting the supercapacitor. The electrode is prepared through a one-step hydrothermal method, in a Raman spectrum, when the potential is increased to 0.5 V from 0 V, the characteristic vibration peaks of M-OH (metal-hydroxyl) and M-O (metal-oxygen) are both weakened, and meanwhile, the vibration peak of iron / cobalt oxide appears along with the characteristic vibration peaks of M-OH (metal-hydroxyl) and M-O (metal-oxygen). And in the process of discharging from 0.5 V to 0V, the vibration peak of the iron / cobalt oxide gradually disappears, and the characteristic vibration peak intensity of the M-OH and the M-O is recovered to the intensity in the open circuit state. It is proved that Co2Fe2-LDH / NF has excellent stability and reversibility in the charging and discharging process as a supercapacitor electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode preparation, and in particular to the preparation and application of a self-supporting electrode based on porous cobalt-iron layered double hydroxide. Background Art

[0002] In recent years, due to the rapid consumption of fossil fuels and the serious environmental pollution caused by traditional energy technologies, people are in urgent need of efficient and environmentally friendly electrochemical energy storage devices. At the same time, in the fields of high-power electronic equipment, emergency power supplies and hybrid vehicles, there is also a demand for high-performance electrochemical energy storage technologies. As an emerging electrochemical energy storage device, aqueous supercapacitors have attracted widespread attention from researchers due to their advantages such as high charge and discharge rates, high power density, long service life and excellent reversibility. They are considered to be a strong candidate to fill the gap between batteries and traditional capacitors. However, the unsatisfactory energy density of aqueous supercapacitors has seriously limited their practical applications. Electrode materials are one of the core components of supercapacitor devices. Reasonable regulation and optimization of them are crucial to improving the electrochemical performance of supercapacitors. In order to achieve high specific capacitance and high energy density, it is a wise choice to construct asymmetric supercapacitors (ASCs) using metal compound electrodes. By utilizing the rapid redox reactions that occur in themselves, these asymmetric supercapacitors can operate within a wider voltage window. According to the formula E = 1 / 2CV 2 , which can significantly improve the energy density of the device. For asymmetric supercapacitors, the performance of the cathode, where the battery-type Faradaic reaction occurs, plays a decisive role in the overall performance of the asymmetric supercapacitor device. Therefore, there is an urgent need to explore new high-performance cathode materials to improve the energy density and specific capacitance of asymmetric supercapacitors.

[0003] Transition metal layered double hydroxides (LDHs), as typical electrode materials for battery-type supercapacitors, have been widely studied due to their high specific capacitance and excellent redox activity. When the abundant transition metal cations in the layered double hydroxides react with OH- in alkaline electrolytes, they have high theoretical capacities. For example, Wang et al. prepared nickel-cobalt layered double hydroxides (NiCo-LDHs) by unipolar pulse electrodeposition and achieved a specific capacitance of up to 2189.8 F g-1 in 1 M potassium hydroxide (KOH) as the electrolyte. Similarly, Pu et al. prepared vertically aligned nickel-cobalt layered double hydroxide nanosheets on a nickel foam substrate by a hydrothermal method. When used as the positive electrode material for supercapacitors, they exhibited an impressive specific capacitance of 1734 F g-1 in 3 M potassium hydroxide electrolyte. Liu et al. synthesized a nickel-cobalt layered double hydroxide (LDH) material with a high specific capacitance of 1464.7 F g⁻¹ at a current density of 1 Ag⁻¹; however, its cycling performance was poor, with only 86% of its capacity retained after 500 cycles at a current density of 20 Ag⁻¹. Although LDHs hold great potential for supercapacitor applications, issues such as slow charge transfer rates and volume expansion can lead to structural damage during cycling, shortening service life and reducing capacity, limiting their further application in supercapacitors. To enhance the performance of LDH-based supercapacitors, researchers are exploring more optimized synthesis methods, structural designs, and composite strategies to address the rate and cycling performance challenges of LDHs. One approach to optimizing electrochemical kinetics is to blend LDHs with double-layer materials, which can reduce contact resistance and charge transfer resistance, thereby improving cycling stability. However, blending powder materials significantly limits the diffusion rate of electrolyte ions, thereby reducing the kinetic performance of supercapacitor devices. Therefore, the development of free-standing electrode materials suitable for high-rate supercapacitors is crucial. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide the preparation and application of a self-supporting electrode based on a porous cobalt-iron layered double hydroxide, which solves the problems of low energy density of existing aqueous supercapacitors and performance limitations caused by slow charge transfer and volume expansion of layered double hydroxide electrodes.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] Based on a porous cobalt-iron layered double hydroxide self-supporting electrode, the electrode material is a composite material formed by porous cobalt-iron layered double hydroxide (CoFe-LDH) supported on nickel foam (NF), denoted as CoFe-LDH / NF, wherein the cobalt / iron molar ratio is 1:3, 2:2 or 3:1. The electrode is used as a self-supporting electrode in a supercapacitor, and the electrode is prepared by a one-step hydrothermal method.

[0007] Preferably, the preparation method of the porous cobalt-iron layered double hydroxide self-supporting electrode comprises the following steps:

[0008] S1: dissolving a cobalt salt, an iron salt, urea, and ammonium fluoride in deionized water to form a mixed solution, wherein the molar ratio of the cobalt salt to the iron salt is 1:3, 2:2, or 3:1;

[0009] S2: immersing the pretreated nickel foam in the mixed solution for 1 hour, wherein the pretreatment comprises washing the nickel foam with hydrochloric acid, ethanol, and deionized water in sequence, and then drying;

[0010] S3: The soaked reaction mixture was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and subjected to a hydrothermal reaction at 120°C for 6 hours;

[0011] S4: After cooling, the nickel foam is taken out, washed with deionized water several times, and vacuum dried to obtain the CoFe-LDH / NF self-supporting electrode.

[0012] Preferably, the cobalt salt is cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and the iron salt is ferric nitrate nonahydrate (Fe(NO3)3·9H2O).

[0013] Preferably, when the cobalt / iron molar ratio is 2:2, the amount of the cobalt nitrate hexahydrate is 2 mmol, the amount of the ferric nitrate nonahydrate is 2 mmol, the amount of the urea is 10 mmol, the amount of the ammonium fluoride is 40 mmol, and the amount of deionized water is 40 mL.

[0014] Preferably, the vacuum drying condition is: drying in a vacuum dryer.

[0015] Preferably, when the cobalt / iron molar ratio is 2:2, the Co2Fe2-LDH / NF electrode is 2 Specific capacitance ≥4100mF / cm 2 .

[0016] Preferably, the electrode undergoes a reversible phase transition between CoFe-LDH and FeCo2O4 during the charge and discharge process.

[0017] Preferably, the porous layer of the porous cobalt-iron layered double hydroxide has a thickness of 5-20 μm, and ammonium fluoride is used as a structure-directing agent to form the porous structure.

[0018] Preferably, based on the application of a porous cobalt-iron layered double hydroxide self-supporting electrode, the electrode is used as the negative electrode of a supercapacitor and assembled with a positive electrode material into an asymmetric supercapacitor device, wherein the positive electrode material includes activated carbon, and the asymmetric supercapacitor device operates within a voltage window of 0 to 1.6V.

[0019] Preferably, the asymmetric supercapacitor device has a current density of 5 mA / cm 2 The specific capacitance is 953.1mF / cm 2 , at an output power of 4000mW / cm 2 The energy density is 338.9mWh / cm 2 , and at 15mA / cm 2 After 10,000 cycles at a current density of 100 nm, the capacity retention rate is ≥95% and the Coulombic efficiency is close to 100%.

[0020] The present invention is based on the preparation and application of a porous cobalt-iron layered double hydroxide self-supporting electrode. The technical effects and advantages are as follows:

[0021] 1. This invention, in in-situ Raman spectroscopy, shows that when the potential rises from 0V to 0.5V, the characteristic vibration peaks of M-OH (metal-hydroxyl) and MO (metal-oxygen) both weaken, accompanied by the appearance of vibration peaks of iron / cobalt oxide. During the discharge from 0.5V to 0V, the vibration peaks of iron / cobalt oxide gradually disappear, and the intensity of the characteristic vibration peaks of M-OH and MO returns to that of the open circuit state. This confirms that Co2Fe2-LDH / NF, as a supercapacitor electrode material, has excellent stability and reversibility during the charge and discharge process.

[0022] 2. This invention designs a Co2Fe2-LDH / NF (negative electrode) / / activated carbon (AC, positive electrode) asymmetric supercapacitor device. The cyclic voltammetry (CV) curves of the asymmetric supercapacitor device are within the voltage window of 0 to 1.6V and at different scan rates (5, 10, 20, 30, 40 and 50mVs-1). The redox peak can be clearly observed at all scan rates, and the peak current density increases with the increase in scan rate, indicating that it has ideal capacitive characteristics. And the constant current charge and discharge (GCD) curves at different current densities are almost symmetrical, and the voltage drop is very small, which indicates that the device exhibits good charge and discharge characteristics.

[0023] 3. The invention subjected the device to electrochemical impedance spectroscopy (EIS) testing. The electrochemical reaction resistance (Rct) of the device was estimated to be 1.6Ω, which indicates that the negative electrode of the device has good conductivity. The assembled asymmetric supercapacitor device was tested for long-term stability at a current density of 15mAcm-2. After 10,000 electrochemical charge and discharge cycles, the capacity retention rate and coulombic efficiency were both approximately 100%. This excellent durability indicates that it has excellent reversibility, and the high current density is conducive to high-power applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the synthetic route proposed by the present invention;

[0025] Figure 2 (a) Transmission electron microscopy (TEM) image of the cobalt-iron layered double hydroxide / nickel foam (CoFe-LDH / NF) proposed in the present invention, (b, c) high-resolution transmission electron microscopy (HRTEM) images, and the inset in (c) shows the fast Fourier transform (FFT) spectrum of the rectangular area in (c). (d) X-ray diffraction (XRD) pattern, (e) Raman spectrum, (f) full-spectrum scan of X-ray photoelectron spectroscopy (XPS), (g) C 1s, (h) Fe 2p, and (i) Co 2p high-resolution X-ray photoelectron spectroscopy of Co2Fe2-LDH / NF;

[0026] Figure 3 (a) Cyclic voltammetry curves (0 to 0.5 V) at a scan rate of 5 millivolts per second (mV s-1) and (b) galvanostatic charge-discharge curves of Co1Fe3-LDH / NF, Co2Fe2-LDH / NF, and Co3Fe1-LDH / NF at a current density of 5 milliamperes per square centimeter (mA cm-2) proposed in the present invention, (c) galvanostatic charge-discharge curves of Co2Fe2-LDH / NF at different current densities, (d) Coulombic efficiency at different current densities and (e) specific capacitance, and (f) Nyquist plot;

[0027] Figure 4 The capacitive behavior of the Co2Fe2-LDH / NF in an alkaline environment proposed in this invention. (b) Potential-dependent in situ Raman spectra of Co2Fe2-LDH / NF during charge and discharge (0 to 0.5 V);

[0028] Figure 5Electrochemical performance tests of the Co2Fe2-LDH / NF / / activated carbon (AC) asymmetric supercapacitor device proposed in this invention using 1M potassium hydroxide (KOH) as the electrolyte. (a) Schematic diagram of the asymmetric supercapacitor. (b) Cyclic voltammetry curves at different scan rates and (c) galvanostatic charge-discharge curves at different current densities (voltage range 0 to 1.6 V), (d) Coulombic efficiency at different current densities within the 0 to 1.6 V voltage window and (e) specific capacitance, (f) Lagrange plot, (g) Nyquist plot, and (h) cycling stability of the asymmetric supercapacitor device after 10,000 cycles at a current density of 15 mA cm-2. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0030] It should be noted that, in this document, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus. In the absence of further restrictions, the elements defined by the sentence "include..." do not exclude the existence of other identical elements in the process, method, article or apparatus that includes the elements.

[0031] Example 1

[0032] refer to Figure 1-5 This embodiment provides the preparation and application of a self-supporting electrode based on a porous cobalt-iron layered double hydroxide, which is used for the preparation and performance testing of Co2Fe2-LDH / NF with a cobalt / iron ratio of 2:2. The specific implementation content includes:

[0033] Materials and reagents:

[0034] Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), urea (CH4N2O), ammonium fluoride (NH4F), nickel foam, hydrochloric acid, ethanol, and deionized water.

[0035] Preparation steps:

[0036] (1) Pretreatment of nickel foam: The nickel foam was ultrasonically cleaned with 3 mol / L hydrochloric acid for 20 minutes, rinsed with deionized water 5 times, then ultrasonically cleaned with ethanol for 15 minutes, rinsed with deionized water 5 times, and finally vacuum dried at 70°C for 2.5 hours;

[0037] (2) Solution preparation: Accurately weigh 2 mmol of cobalt nitrate hexahydrate, 2 mmol of ferric nitrate nonahydrate, 10 mmol of urea, and 40 mmol of ammonium fluoride, add 40 mL of deionized water, and stir magnetically for 45 minutes to form a pink solution;

[0038] (3) Soaking treatment: Immerse the pretreated nickel foam in the solution for 1 hour;

[0039] (4) Hydrothermal reaction: The solution and nickel foam were transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 120 °C for 6 h.

[0040] (5) Post-treatment: After the reactor was cooled, the nickel foam was taken out, washed with deionized water four times, and vacuum dried at 65°C for 7 hours to obtain Co2Fe2-LDH / NF.

[0041] Performance testing:

[0042] Three-electrode system specific capacitance: at 5mA / cm 2 At the current density, the specific capacitance is 4108mF / cm 2 ;30mA / cm 2 When the specific capacitance is 2646mF / cm 2 , rate performance 64.4%.

[0043] In situ Raman spectroscopy: When the potential increases from 0V to 0.5V, the characteristic vibration peaks of M-OH and MO weaken, and the vibration peaks of iron / cobalt oxide appear; when discharged to 0V, the vibration peaks of iron / cobalt oxide disappear, and the intensity of M-OH and MO peaks recovers.

[0044] Example 2

[0045] This embodiment provides the preparation and application of a self-supporting electrode based on a porous cobalt-iron layered double hydroxide, which is used for the preparation and performance testing of Co1Fe3-LDH / NF with a cobalt / iron ratio of 1:3. The specific implementation content includes:

[0046] Materials and reagents:

[0047] Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), urea (CH4N2O), ammonium fluoride (NH4F), nickel foam, hydrochloric acid, ethanol, and deionized water.

[0048] Preparation steps:

[0049] (1) Pretreatment of nickel foam: The nickel foam was ultrasonically cleaned with 3 mol / L hydrochloric acid for 20 minutes, rinsed with deionized water 5 times, then ultrasonically cleaned with ethanol for 15 minutes, rinsed with deionized water 5 times, and finally vacuum dried at 70°C for 2.5 hours;

[0050] (2) Solution preparation: Weigh 1 mmol of cobalt nitrate hexahydrate, 3 mmol of ferric nitrate nonahydrate, 10 mmol of urea, and 40 mmol of ammonium fluoride, add 40 mL of deionized water, and stir for 50 minutes to form a solution;

[0051] (3) Soaking treatment: Immerse the pretreated nickel foam in the solution for 1 hour;

[0052] (4) Hydrothermal reaction: The solution and nickel foam were transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 120 °C for 6 h.

[0053] (5) Post-treatment: After the reactor was cooled, the nickel foam was taken out, washed with deionized water four times, and vacuum dried at 65°C for 7 hours to obtain Co1Fe3-LDH / NF.

[0054] Performance testing:

[0055] Three-electrode system specific capacitance: 5mA / cm 2 At the current density, the specific capacitance is 3200mF / cm 2 ;30mA / cm 2 When the specific capacitance is 1443mF / cm 2 , rate performance 45.1%.

[0056] In situ Raman spectroscopy: presents reversible phase transition characteristics similar to those of Example 1, but the degree of phase transition is different.

[0057] Example 3

[0058] This embodiment provides the preparation and application of a self-supporting electrode based on a porous cobalt-iron layered double hydroxide, which is used for the preparation and performance testing of Co3Fe1-LDH / NF with a cobalt / iron ratio of 3:1. The specific implementation content includes:

[0059] Materials and reagents:

[0060] Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), urea (CH4N2O), ammonium fluoride (NH4F), nickel foam, hydrochloric acid, ethanol, and deionized water.

[0061] Preparation steps:

[0062] (1) Pretreatment of nickel foam: The nickel foam was ultrasonically cleaned with 3 mol / L hydrochloric acid for 20 minutes, rinsed with deionized water 5 times, then ultrasonically cleaned with ethanol for 15 minutes, rinsed with deionized water 5 times, and finally vacuum dried at 70°C for 2.5 hours;

[0063] (2) Solution preparation: Weigh 3 mmol of cobalt nitrate hexahydrate, 1 mmol of ferric nitrate nonahydrate, 10 mmol of urea, and 40 mmol of ammonium fluoride, add 40 mL of deionized water, and stir for 40 minutes to form a solution;

[0064] (3) Soaking treatment: Immerse the pretreated nickel foam in the solution for 1 hour;

[0065] (4) Hydrothermal reaction: The solution and nickel foam were transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 120 °C for 6 h.

[0066] (5) Post-treatment: After the reactor was cooled, the nickel foam was taken out, washed with deionized water four times, and dried in a vacuum at 65 °C for 7 h to obtain Co3Fe1-LDH / NF.

[0067] Performance testing:

[0068] Three-electrode system specific capacitance: 5mA / cm 2 At the current density, the specific capacitance is 1970mF / cm 2 ;30mA / cm 2 When the specific capacitance is 1120mF / cm 2 , rate performance 56.8%.

[0069] In-situ Raman spectroscopy: The reversible phase transition feature is obvious, which is different from the previous two embodiments.

[0070] Example 4

[0071] This example provides the preparation and application of a self-supporting electrode based on a porous cobalt-iron layered double hydroxide, and the preparation and performance testing of Co2Fe2-LDH / NF for changing the hydrothermal reaction time. The specific implementation includes:

[0072] Materials and reagents:

[0073] Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), urea (CH4N2O), ammonium fluoride (NH4F), nickel foam, hydrochloric acid, ethanol, and deionized water.

[0074] Preparation steps:

[0075] (1) Pretreatment of nickel foam: The nickel foam was ultrasonically cleaned with 3 mol / L hydrochloric acid for 20 minutes, rinsed with deionized water 5 times, then ultrasonically cleaned with ethanol for 15 minutes, rinsed with deionized water 5 times, and finally vacuum dried at 70°C for 2.5 hours;

[0076] (2) Solution preparation: Accurately weigh 2 mmol of cobalt nitrate hexahydrate, 2 mmol of ferric nitrate nonahydrate, 10 mmol of urea, and 40 mmol of ammonium fluoride, add 40 mL of deionized water, and stir magnetically for 45 minutes to form a pink solution;

[0077] (3) Soaking treatment: Immerse the pretreated nickel foam in the solution for 1 hour;

[0078] (4) Hydrothermal reaction: transfer the solution and nickel foam to a reactor and react at 120°C for 8 hours;

[0079] (5) Post-treatment: After the reactor was cooled, the nickel foam was taken out, washed with deionized water 4 times, and vacuum dried at 65 °C for 7 h to obtain Co2Fe2-LDH / NF.

[0080] Performance testing:

[0081] Three-electrode system specific capacitance: 5mA / cm 2 At current density, the specific capacitance is 4000mF / cm 2 ;30mA / cm 2 When the specific capacitance is 2500mF / cm 2 , rate performance 62.5%.

[0082] In situ Raman spectroscopy: The reversible phase transition characteristics are basically consistent with those in Example 1, but the peak intensity changes are slightly different.

[0083] Example 5

[0084] This example provides the preparation and application of a self-supporting electrode based on a porous cobalt-iron layered double hydroxide, and the preparation and performance testing of Co2Fe2-LDH / NF for varying urea dosage. The specific implementation includes:

[0085] Materials and reagents:

[0086] Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), urea (CH4N2O), ammonium fluoride (NH4F), nickel foam, hydrochloric acid, ethanol, and deionized water.

[0087] Preparation steps:

[0088] (1) Pretreatment of nickel foam: The nickel foam was ultrasonically cleaned with 3 mol / L hydrochloric acid for 20 minutes, rinsed with deionized water 5 times, then ultrasonically cleaned with ethanol for 15 minutes, rinsed with deionized water 5 times, and finally vacuum dried at 70°C for 2.5 hours;

[0089] (2) Solution preparation: Weigh 2 mmol of cobalt nitrate hexahydrate, 2 mmol of ferric nitrate nonahydrate, 12 mmol of urea, and 40 mmol of ammonium fluoride, add 40 mL of deionized water, and stir for 55 minutes to form a solution;

[0090] (3) Soaking treatment: Immerse the pretreated nickel foam in the solution for 1 hour;

[0091] (4) Hydrothermal reaction: transfer the solution and nickel foam to a reactor and react at 120°C for 8 hours;

[0092] (5) Post-treatment: After the reactor was cooled, the nickel foam was taken out, washed with deionized water 4 times, and vacuum dried at 65 °C for 7 h to obtain Co2Fe2-LDH / NF.

[0093] Performance testing:

[0094] Three-electrode system specific capacitance: 5mA / cm 2 At the current density, the specific capacitance is 4050mF / cm 2 ;30mA / cm 2 When the specific capacitance is 2550mF / cm 2 , rate performance 62.9%.

[0095] In-situ Raman spectroscopy: The reversible phase transition feature is obvious, with slight differences from Example 1.

[0096] Comparative Example 1

[0097] This embodiment provides a performance test of nickel foam electrode without LDH loading

[0098] Materials and processing

[0099] The nickel foam pretreated in the same manner as in Example 1 was used as an electrode.

[0100] Performance Testing

[0101] Three-electrode system specific capacitance: at 5mA / cm 2 At this current density, the specific capacitance is only 50mF / cm 2 ;30mA / cm 2 When , the specific capacitance is almost 0, and there is basically no capacitance performance.

[0102] Asymmetric supercapacitor performance: The device assembled with the nickel foam as the negative electrode and the activated carbon as the positive electrode cannot be charged and discharged normally, and there is no obvious specific capacitance and energy density data.

[0103] Comparison of Examples 1-5 and Comparative Example 1, detailed parameter comparison is shown in Table 1.

[0104] Table 1, parameter comparison between Examples 1-5 and Comparative Example 1

[0105]

[0106] The parameter comparison of the asymmetric supercapacitor performance and reversible phase change characteristics between Examples 1-5 and Comparative Example 1 is shown in Table 2.

[0107] Table 2. Comparison of asymmetric supercapacitor performance and reversible phase change characteristics between Examples 1-5 and the comparative example

[0108]

[0109] LDH loading plays a decisive role in performance

[0110] All examples significantly improved the electrochemical performance of nickel foam by loading CoFe-LDH. The comparative example (pure nickel foam without LDH loading) had almost no capacitive behavior, proving that LDH was the core active substance and nickel foam only served as a mechanical support and current collector.

[0111] The specific capacitance of Examples 1-5 (3500~4108mF / cm 2 ) is 70 to 80 times higher than that of the control group, which fully reflects the necessity of LDH loading.

[0112] Optimizing the performance of cobalt-iron ratio

[0113] The specific capacitance and energy density of Example 1 (2:2) are the best, indicating that the crystallinity, pore size distribution and electron transfer efficiency of LDH are optimal at this ratio, which is directly related to the "completely reversible phase transition" mechanism revealed by in situ Raman spectroscopy.

[0114] The performance of Examples 2 (1:3) and 3 (3:1) is slightly lower, indicating that the imbalance of the cobalt-iron ratio will affect the layered structure and phase transition reversibility of LDH, further verifying the importance of ratio control.

[0115] Marginal effects of preparation conditions

[0116] The performance of Examples 4 (extending the hydrothermal time to 8 h) and 5 (increasing the urea to 12 mmol) is close to that of Example 1, indicating that when the hydrothermal time and urea dosage fluctuate within a certain range, the core performance will not be significantly changed, and the process is robust.

[0117] However, too long a time or excessive urea may cause LDH agglomeration or a decrease in crystallinity (such as a slight decrease in specific capacitance in Example 4), indicating that the optimal conditions still need to be precisely controlled (such as 6h and 10mmol urea in Example 1).

[0118] Reversible phase transition and cycling stability

[0119] Reversible phase transition between LDH and FeCo2O4 was observed in all examples, and the capacity retention rate was ≥95% and the Coulombic efficiency was close to 100% after 10,000 cycles, while the comparative examples did not have this feature, proving that the phase transition mechanism is the core reason for the high stability.

[0120] The fully reversible phase transition of Example 1 leads to the best cycling performance, further highlighting the advantage of the 2:2 ratio.

[0121] The in-situ growth of LDH on the surface of nickel foam is achieved through a one-step hydrothermal method to form a self-supporting electrode, avoiding the defects of traditional electrodes that rely on binders and conductive additives (the comparative example does not have such a structure and its performance fails).

[0122] By precisely controlling the cobalt-iron ratio (especially 2:2) and combining it with the porous structure induced by ammonium fluoride, the synergistic optimization of "high specific capacitance-high power density-long life" is achieved, which far exceeds the effect of adjusting a single variable (for example, the performance of Examples 4 and 5 does not exceed that of Example 1).

[0123] The comparative example, through a blank experiment without LDH loading, reversely verified the core innovation of the present invention: LDH loading is the key to imparting electrochemical activity to nickel foam, and the self-supporting structure constructed by the hydrothermal method is the foundation for improved performance. Without LDH, even using the same pre-treated nickel foam, the required capacitance behavior of supercapacitors cannot be achieved, fully demonstrating the irreplaceable nature of the present invention's technical solution.

[0124] Through the above examples and comparative examples, we can clearly see the performance differences of CoFe-LDH / NF electrodes under different preparation conditions, and the significant improvement of the performance of nickel foam electrodes by loading LDH.

[0125] Those skilled in the art will appreciate that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented with electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0126] In addition, each functional module in each embodiment of the present application may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module.

[0127] The above is only a specific implementation method of the present application, but the scope of protection of the present application is not limited to this. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

[0128] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Based on a porous cobalt-iron layered double hydroxide self-supporting electrode, characterized in that: The electrode material is a composite material formed by porous cobalt-iron layered double hydroxide (CoFe-LDH) supported on nickel foam (NF), denoted as CoFe-LDH / NF, wherein the cobalt / iron molar ratio is 1:3, 2:2 or 3:

1. The electrode is used as a self-supporting electrode in a supercapacitor, and the electrode is prepared by a one-step hydrothermal method.

2. A method for preparing a self-supporting electrode based on porous cobalt-iron layered double hydroxide, characterized in that: The following steps are involved: S1: dissolving a cobalt salt, an iron salt, urea, and ammonium fluoride in deionized water to form a mixed solution, wherein the molar ratio of the cobalt salt to the iron salt is 1:3, 2:2, or 3:1; S2: immersing the pretreated nickel foam in the mixed solution for 1 hour, wherein the pretreatment comprises washing the nickel foam with hydrochloric acid, ethanol, and deionized water in sequence, and then drying; S3: The soaked reaction mixture was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and subjected to a hydrothermal reaction at 120°C for 6 hours; S4: After cooling, the nickel foam is taken out, washed with deionized water several times, and vacuum dried to obtain the CoFe-LDH / NF self-supporting electrode.

3. The self-supporting electrode based on porous cobalt-iron layered double hydroxide according to claim 2, characterized in that: The cobalt salt is cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and the iron salt is ferric nitrate nonahydrate (Fe(NO3)3·9H2O).

4. The self-supporting electrode based on porous cobalt-iron layered double hydroxide according to claim 2, characterized in that: When the cobalt / iron molar ratio is 2:2, the amount of the cobalt nitrate hexahydrate is 2 mmol, the amount of the ferric nitrate nonahydrate is 2 mmol, the amount of the urea is 10 mmol, the amount of the ammonium fluoride is 40 mmol, and the amount of deionized water is 40 mL.

5. The self-supporting electrode based on porous cobalt-iron layered double hydroxide according to claim 2, characterized in that: The vacuum drying condition is: drying in a vacuum dryer.

6. The self-supporting electrode based on porous cobalt-iron layered double hydroxide according to claim 1, characterized in that: When the cobalt / iron molar ratio is 2:2, the specific capacitance of the Co2Fe2-LDH / NF electrode is ≥4100mF / cm2 at a current density of 5mA / cm2. 2 .

7. The self-supporting electrode based on porous cobalt-iron layered double hydroxide according to claim 1, characterized in that: The electrode undergoes a reversible phase transition between CoFe-LDH and FeCo2O4 during the charge and discharge process.

8. The self-supporting electrode based on porous cobalt-iron layered double hydroxide according to claim 1, characterized in that: The porous layer of the porous cobalt-iron layered double hydroxide has a thickness of 5-20 μm, and ammonium fluoride is used as a structure-directing agent to form the porous structure.

9. Application of a self-supporting electrode based on porous cobalt-iron layered double hydroxide, characterized in that: The electrode is used as the negative electrode of a supercapacitor and assembled with a positive electrode material to form an asymmetric supercapacitor device. The positive electrode material includes activated carbon. The asymmetric supercapacitor device operates within a voltage window of 0 to 1.6V.

10. The self-supporting electrode based on porous cobalt-iron layered double hydroxide according to claim 9, characterized in that: The asymmetric supercapacitor device has a current density of 5 mA / cm 2 The specific capacitance is 953.1mF / cm 2 , at an output power of 4000mW / cm 2 The energy density is 338.9mWh / cm 2 , and at 15mA / cm 2 After 10,000 cycles at a current density of 100 nm, the capacity retention rate is ≥95% and the Coulombic efficiency is close to 100%.

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