Selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitor and preparation and application thereof

Abstract

The invention discloses a selenium-modified nickel-vanadium layered double hydroxide electrode material for a supercapacitor and preparation and application thereof, and belongs to the technical field of supercapacitors. The material initiates an'intercalation pre-modification-selenylation cooperation 'structure regulation strategy, and is realized through a two-step hydrothermal method: firstly, in-situ intercalation of graphene quantum dots is carried out in a NiV-LDHs hydrothermal growth stage to serve as an interlayer support and an initial conductive network, hexamethylenetetramine is used for assisting formation of a layered precursor, a double-reducing-agent system is used for synergistic in-situ selenylation, and the graphene quantum dot / NiV-LDHs composite material is obtained. Se < 4 + > is adsorbed and anchored by using pi-pi of the GQDs, so that double-site uniform distribution of selenium on the surface of the laminate and the interface of the GQDs is realized. According to the method, the limitation of a traditional step-by-step process is broken through, the integrity of a layered structure, the continuity of a conductive network and the uniformity of selenium modification are synergistically guaranteed, the interlayer spacing of the obtained material is increased to 1.22 nm, active sites are fully exposed, and the material has high specific capacitance and high rate performance and is suitable for a high-performance supercapacitor electrode.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor technology, specifically relating to a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors, its preparation and application. Background Technology

[0002] Supercapacitors, as novel energy storage devices, are in high demand in fields such as new energy vehicles and smart grids due to their fast charge-discharge rates and long cycle life. Their performance hinges on the specific capacitance, conductivity, and structural stability of the electrode materials. Nickel-vanadium layered double hydroxides (NiV-LDHs) can expose a large amount of Ni due to their layered structure. 2+ / Ni 3+ / Ni 4+ With redox active sites and the ability to accommodate electrolyte ions in the interlayer, it provides channels for ion transport, making it a highly promising electrode material for supercapacitors. However, its inherent defects severely limit its large-scale application in practical applications. First, pure NiV-LDHs are composed of metal hydroxides, and electron transport depends on interlayer anion hopping, resulting in poor conductivity (resistivity typically >10). 3 Ω The high charge transfer impedance and severe capacity decay under high current significantly affect the charge-discharge efficiency and lifespan of supercapacitors. Existing technologies often improve conductivity through selenization modification – selenium (Se) has high electronic conductivity (10⁻⁶ cm⁻¹), resulting in high charge transfer impedance and severe capacity decay under high current, greatly impacting the charge-discharge efficiency and lifespan of supercapacitors. -3 Ω Selenization (cm) is far superior to LDHs and can form stable bonds with metal ions, improving electron transport efficiency. However, traditional selenization processes have significant shortcomings: they often adopt a step-by-step approach of "preparing pure NiV-LDHs first, then modifying with selenization," and the selenium source (such as selenium powder, NiSe2) is prone to agglomerate on the surface of LDHs, forming large particles that both obscure active sites and destroy the integrity of the layered structure; moreover, a single reducing agent (such as hydrazine hydrate) is often used, and the reduction kinetics are uneven, further aggravating the selenium agglomeration problem. Secondly, existing NiV-LDHs layered structure regulation lacks a synergistic design of "active sites-conductive network": traditional processes rely solely on strong alkali to adjust pH and construct the layered structure, without interlayer conductive dielectric support, making the layer stacking prone to collapse during charge and discharge; furthermore, selenization and layered structure regulation are independent of each other, failing to simultaneously achieve the dual requirements of "high active site exposure + low impedance conductive network". In addition, traditional processes often use corrosive reagents or high-temperature, long-duration reactions, resulting in complex post-processing, high energy consumption, and significant pollution, making it difficult to meet the environmental protection and cost requirements of large-scale production. In summary, the key breakthrough direction for the research and development of NiV-LDHs-based supercapacitor electrode materials is to simultaneously achieve uniform modification of selenium and in-situ introduction of conductive intercalation media while ensuring the integrity of the NiV-LDHs layered structure, thereby synergistically improving conductivity and active site utilization at both the structural and compositional levels, while simplifying the process and reducing costs. Summary of the Invention To address the problems of poor conductivity, complex selenization modification process, and insufficient cycle stability of existing NiV-LDHs-based electrode materials, this invention aims to provide a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors, as well as its preparation and application.

[0003] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors, wherein the selenium-modified nickel-vanadium layered double hydroxide electrode material has a layered structure with an interlayer spacing of 1.0 nm to 1.3 nm, comprising: Nickel-vanadium layered double hydroxide main plate; Graphene quantum dots are intercalated and supported between the main body layers, and the graphene quantum dots constitute interlayer electron transport channels and structural supports. And nano-selenium particles adsorbed and anchored to the surface and edges of the nickel-vanadium layered double hydroxide main plate by the graphene quantum dots; The graphene quantum dots and the selenium nanoparticles are connected by chemical interaction to jointly construct a three-dimensional structure in which conductivity and pseudocapacitance are synergistically enhanced.

[0004] Secondly, the present invention provides a method for preparing the above-mentioned selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors, comprising: Step 1: Mix and dissolve nickel salt, vanadium source, hexamethylenetetramine and graphene quantum dots, adjust the pH value and then perform hydrothermal reaction. After the reaction, centrifuge, wash and freeze dry to obtain the precursor. Step 2: The precursor, selenium source and dual reducing agent system are dispersed together and subjected to a second hydrothermal reaction. After the reaction, the mixture is centrifuged, washed and vacuum dried to obtain the selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors.

[0005] The vanadium source is any one of V2O5, ammonium metavanadate, and vanadate; the nickel salt is any one of Ni(CH3COO)2·4H2O, NiCl2·6H2O, and Ni(NO3)2·6H2O.

[0006] In step 1, the molar ratio of nickel in the nickel salt, vanadium in the vanadium source, hexamethylenetetramine, and graphene quantum dots is (4~5):1:(4~5):(0.01~0.1).

[0007] In step 1, the pH value is adjusted to 9-10 using ammonia, sodium carbonate, or sodium bicarbonate. The hydrothermal reaction temperature is 125-160℃, and the reaction time is 10-18 hours.

[0008] In step 1, the freeze-drying temperature is -40~-50℃, the vacuum degree is 10~15Pa, and the drying time is 10~14h.

[0009] In step 2, the mass ratio of the precursor, selenium source, and dual reducing agent system is 1:(0.4~2):(0.4~0.5); the dual reducing agent system is a combination of hydrazine hydrate and ascorbic acid; the hydrothermal reaction temperature is 125-160℃, and the reaction time is 10-18h.

[0010] In step 2, the vacuum drying temperature is 50~60℃, the vacuum degree is 40~60Pa, and the drying time is 8~12h.

[0011] Thirdly, the present invention provides a supercapacitor electrode comprising the aforementioned selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors.

[0012] Fourthly, the present invention provides a supercapacitor comprising the supercapacitor electrodes.

[0013] Compared with the prior art, the present invention achieves the following technical effects: This invention provides a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors, pioneering a structural control strategy of "intercalation pre-modification-selenization synergy," breaking the limitations of the traditional step-by-step implementation of "layered structure, conductive intercalation, and selenization modification." Existing technologies often involve separate layered structure construction, conductive dielectric composite, or selenization modification, which easily leads to structural damage or uneven component dispersion. In this invention, GQDs are intercalated in situ during the hydrothermal growth stage of NiV-LDHs, acting as interlayer supports to inhibit layer collapse and providing an initial conductive network. During subsequent in-situ selenization, the π-π adsorption of GQDs anchors Se. 4+ With the synergistic reduction of the two reducing agents, selenium is uniformly distributed at two sites on the "layer surface + GQDs interface", which ensures the synergistic realization of "layer structure integrity - conductive network continuity - selenium modification uniformity" from the mechanism.

[0014] This invention provides a method for preparing selenium-modified nickel-vanadium layered double hydroxide electrode materials for supercapacitors. The method achieves synergistic regulation of layered structure construction and selenization modification through a two-step hydrothermal reaction. Nickel salt and vanadium source form a layered precursor with pH adjustment under the assistance of hexamethylenetetramine. Hexamethylenetetramine acts as a structure-directing agent to control the directional growth of the layers. The hydrothermal reaction temperature avoids high-temperature densification of the layers. Freeze-drying preserves the porous structure between layers to facilitate electrolyte penetration during subsequent selenization reactions. The precursor and selenium source undergo in-situ selenization in a dual-reducing agent system. The dual reducing agents synergistically regulate the selenium content through differentiated reduction kinetics (rapid reduction of hydrazine hydrate and slow-release reduction of ascorbic acid). 4+ The reduction rate is controlled, inhibiting selenium particle aggregation; simultaneously, the defect sites in the precursor layer act as anchoring points for selenium, ensuring the uniformity of selenium modification. The matching of conditions in the two-step hydrothermal reaction ensures that the layered structure is not destroyed during selenization, achieving synergistic optimization of conductivity improvement and structural stability.

[0015] This invention provides a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors. This electrode material achieves uniform selenium modification within the nickel-vanadium layered double hydroxide structure through in-situ selenization and the synergistic effect of a dual reducing agent. The in-situ selenization process simultaneously constructs the layered structure and performs selenization modification, avoiding the problems of selenium particle agglomeration or structural collapse in traditional stepwise processes. The dual reducing agent system, through the synergistic effect of ascorbic acid and hydrazine hydrate, regulates the reduction kinetics of selenium, enabling selenium to be uniformly anchored at nanoscale defect sites in the layers, thus improving electronic conductivity while preserving the porous structure between layers. The layered structure of the nickel-vanadium layered double hydroxide is formed through the HMT guiding effect during the precursor synthesis stage. Its interlayer spacing and porous characteristics are beneficial for electrolyte ion transport, while the uniform modification of selenium further reduces charge transfer impedance. The application of freeze-drying effectively maintains the three-dimensional porous network between layers, increases the exposure of active sites, and avoids the densification of layer stacking caused by high-temperature processing. The preparation of this material does not require strong alkalis or corrosive reagents, and the reaction temperature and time are significantly reduced compared to traditional processes. The process is more environmentally friendly and the utilization rate of raw materials is improved, meeting the needs of industrial production.

[0016] The application provided by this invention is that the "GQDs intercalation channel + uniform selenium modification" dual conductive network constructed by this invention can simultaneously reduce interlayer ion transport resistance and charge transfer impedance; at the same time, the intercalation effect of GQDs can widen the interlayer spacing (from 0.78nm in pure NiV-LDHs to 1.22nm), increasing Ni 2+ / Ni 3+ / Ni 4+The increased exposure of active sites, combined with the inhibition of selenium aggregation by dual reducing agents, ultimately achieves a synergistic effect of high specific capacitance and high rate performance. The material structure is highly compatible with the "charge storage-ion transport-electron conduction" requirements of supercapacitor electrodes. Traditional selenization processes rely solely on selenium modification to improve conductivity, lacking interlayer conductive dielectric support, and are prone to capacity decay under high current due to asynchronous ion / electron transport. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0018] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products. In this invention, unless otherwise specified, all experimental materials used are commercially available commodities well-known to those skilled in the art.

[0019] Specific capacitance test (1 A / g, F / g): Electrochemical workstation (CHI760D), three-electrode system assembled: working electrode is the test material (loading 0.5~1 mg / cm³). 2 The counter electrode was a platinum sheet, and the reference electrode was Hg / HgO. The electrolyte was a 1 mol / L KOH aqueous solution with a potential window of 0–0.5 V. Charging and discharging were performed at a current density of 1 A / g, and the discharge time Δt was recorded. C = I·Δt / m·ΔU, where I is the current (A), m is the mass of the active material (g), and ΔU is the potential window (V).

[0020] Cycle stability testing: A battery testing system (Neware BTS) was used to assemble an asymmetric supercapacitor: the positive electrode was the test material, and the negative electrode was activated carbon (AC). The mass ratio of the positive and negative electrodes was calculated using the charge-matching formula. 5000 charge-discharge cycles were performed at a current density of 1 A / g, and the discharge capacity of each cycle was recorded. Capacity retention was calculated: Capacity retention = C 5000 / C1×100%, where C 5000 C1 is the capacity for the 5000th cycle, and C2 is the capacity for the first cycle.

[0021] Charge transfer impedance (Rct) test: Electrochemical workstation (CHI760D), three-electrode system assembled: working electrode is the analyte (loading 0.5~1 mg / cm³). 2The counter electrode was a platinum sheet, and the reference electrode was Hg / HgO. The electrolyte was a 1 mol / L KOH aqueous solution, with a potential window of 0–0.5 V. An AC perturbation signal in the frequency range of 0.1 Hz to 100 kHz was applied, and the impedance spectrum was recorded. The Nyquist plot was fitted, and the R value corresponding to the semicircular diameter in the high-frequency region was extracted. ct value.

[0022] Rate performance testing (5A / g vs 1A / g capacity ratio, %): Battery testing system (Neware BTS), charging and discharging at a current density of 1A / g, recording capacity C. 1A Switch to a current density of 5 A / g and record capacity C. 5A Calculate the magnification performance: Magnification performance = C 5A / C 1A ×100%.

[0023] Example 1 This embodiment provides a selenium-modified nickel-vanadium layered double hydroxide electrode material (Se-GQDs-NiV-LDHs-1.0) for supercapacitors. The specific preparation steps are as follows: Step 1: Preparation of GQDs intercalated NiV-LDHs precursor Accurately weigh 0.45g of Ni(CH3COO)2 0.08 g of 4H₂O, 0.25 g of hexamethylenetetramine (HMT), and 0.05 g of graphene quantum dots (GQDs, particle size 3-5 nm) were added to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. The mixture was placed on a magnetic stirrer and stirred at 300 rpm for 25 min to form a dark gray emulsion. 25% ammonia solution was added dropwise with a pipette while stirring until the pH of the system reached 9.2. Stirring was continued for 10 min. The PTFE liner was then sealed in a stainless steel container. The steel high-pressure reactor was placed in a forced-air drying oven at 125℃ and reacted at a constant temperature for 12 hours. After the reaction, the oven was closed and the reactor was allowed to cool naturally to room temperature. The reactor was removed, the mixture in the liner was poured out, and the mixture was transferred to a centrifuge tube and centrifuged at 7500 r / min for 18 min. The supernatant was discarded. The precipitate was repeatedly washed with deionized water until the pH of the filtrate was 7. The precipitate was then washed twice with anhydrous ethanol. Finally, the precipitate was transferred to a freeze dryer and dried at -40℃ and 10 Pa for 10 hours to obtain a fluffy GQDs intercalated NiV-LDHs precursor powder P1-G.

[0024] Step 2: Preparation of in-situ selenized Se-GQDs-NiV-LDHs-1.0 composite material Weigh 0.30 g of GQDs-intercalated NiV-LDHs precursor powder P1-G, 0.30 g of Na2SeO3 (selenium source to NiV-LDHs mass ratio x = 1.0), and 0.12 g of ascorbic acid. Add the above-weighed reagents to 30 mL of deionized water and 10 mL of a 50% (w / w) hydrazine hydrate mixed solvent, and transfer to a 50 mL beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 25 min to form a dark brown suspension. Transfer the beaker to a magnetic stirrer and stir at 350 r / min for 30 min to ensure system homogeneity. Transfer the suspension to a 50 mL PTFE liner, seal it in a stainless steel reactor, place it in an oven, set the temperature to 160℃, and react at a constant temperature for 18 h. After cooling, remove the liner, transfer the reaction solution to a centrifuge tube, centrifuge at 8500 r / min for 20 min, and discard the supernatant. Wash the precipitate four times with deionized water until the filtrate is free of Se. 2- The precipitate was detected (no black precipitate was found when tested with 0.1 mol / L CuSO4 solution); the precipitate was transferred to a vacuum drying oven and dried at 60℃ and 50 Pa for 8 h to obtain Se-GQDs-NiV-LDHs-1.0 composite powder (denoted as M1).

[0025] Example 2 Based on Example 1, this embodiment provides a selenium-modified nickel-vanadium layered double hydroxide electrode material (Se-GQDs-NiV-LDHs-0.4, M2) for supercapacitors. The specific preparation steps are as follows: Step 1: Preparation of GQDs intercalated NiV-LDHs precursor Accurately weigh 0.45g of Ni(CH3COO)2 0.08 g of 4H₂O, 0.25 g of hexamethylenetetramine (HMT), and 0.05 g of graphene quantum dots (GQDs, particle size 3-5 nm) were added to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. The mixture was placed on a magnetic stirrer and stirred at 300 rpm for 25 min to form a dark gray emulsion. 25% ammonia solution was added dropwise with a pipette while stirring until the pH of the system reached 9.2. Stirring was continued for 10 min. The PTFE liner was then sealed in a stainless steel container. The steel high-pressure reactor was placed in a forced-air drying oven at 125℃ and reacted at a constant temperature for 12 hours. After the reaction, the oven was closed and the reactor was allowed to cool naturally to room temperature. The reactor was removed, the mixture in the liner was poured out, and the mixture was transferred to a centrifuge tube and centrifuged at 7500 r / min for 18 min. The supernatant was discarded. The precipitate was repeatedly washed with deionized water until the pH of the filtrate was 7. The precipitate was then washed twice with anhydrous ethanol. Finally, the precipitate was transferred to a freeze dryer and dried at -40℃ and 10 Pa for 10 hours to obtain a fluffy GQDs intercalated NiV-LDHs precursor powder P1-G.

[0026] Step 2: Preparation of Se-GQDs-NiV-LDHs-0.4 composite material Weigh 0.30 g of GQDs-intercalated NiV-LDHs precursor powder P1-G, 0.12 g of Na2SeO3 (selenium source to NiV-LDHs mass ratio x = 0.4), and 0.12 g of ascorbic acid. Add the above-weighed reagents to 30 mL of deionized water and 10 mL of a 50% (w / w) hydrazine hydrate mixed solvent, and transfer to a 50 mL beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 25 min to form a dark brown suspension. Transfer the beaker to a magnetic stirrer and stir at 350 r / min for 30 min to ensure system homogeneity. Transfer the suspension to a 50 mL PTFE liner, seal it in a stainless steel reactor, place it in an oven, set the temperature to 160℃, and react at a constant temperature for 18 h. After cooling, remove the liner, transfer the reaction solution to a centrifuge tube, centrifuge at 8500 r / min for 20 min, and discard the supernatant. Wash the precipitate four times with deionized water until the filtrate is free of Se. 2- The sample was detected (no black precipitate was found when tested with 0.1 mol / L CuSO4 solution); the precipitate was transferred to a vacuum drying oven and dried at 60℃ and 50 Pa for 8 h to obtain Se-GQDs-NiV-LDHs-0.4 composite powder (denoted as M2).

[0027] Example 3 Based on Example 1, this embodiment provides a selenium-modified nickel-vanadium layered double hydroxide electrode material (Se-GQDs-NiV-LDHs-1.8, M3) for supercapacitors. The specific preparation steps are as follows: Step 1: Preparation of GQDs intercalated NiV-LDHs precursor Accurately weigh 0.45g of Ni(CH3COO)2 0.08 g of 4H₂O, 0.08 g of V₂O₅, 0.25 g of hexamethylenetetramine (HMT), and 0.05 g of graphene quantum dots (GQDs, 3-5 nm in diameter) were added to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. The mixture was placed on a magnetic stirrer and stirred at 300 rpm for 25 min to form a dark gray emulsion. 25% ammonia solution was added dropwise with stirring until the pH reached 9.2, and stirring continued for 10 min. The PTFE liner was then sealed in a stainless steel high-pressure reactor and placed in a forced-air oven at 125°C for 12 h. After the reaction, the oven was closed, and the mixture was allowed to cool naturally to room temperature. The reactor was removed, the mixture in the liner was poured out, and transferred to a centrifuge tube. The centrifuge tube was then centrifuged at 7500 rpm. Centrifuge at 18 min at 1 r / min and discard the supernatant; wash the precipitate repeatedly with deionized water until the pH of the filtrate is 7; wash the precipitate twice with anhydrous ethanol, and finally transfer the precipitate to a freeze dryer, set the temperature to -40℃ and the vacuum degree to 10 Pa, and dry for 10 h to obtain fluffy GQDs intercalated NiV-LDHs precursor powder P1-G.

[0028] Step 2: Preparation of in-situ selenized Se-GQDs-NiV-LDHs-1.8 composite material Weigh 0.30 g of GQDs-intercalated NiV-LDHs precursor powder P1-G, 0.54 g of Na2SeO3 (selenium source to NiV-LDHs mass ratio x = 1.8), and 0.12 g of ascorbic acid. Add the above-weighed reagents to 30 mL of deionized water and 10 mL of a 50% (w / w) hydrazine hydrate mixed solvent, and transfer to a 50 mL beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 25 min to form a dark brown suspension. Transfer the beaker to a magnetic stirrer and stir at 350 r / min for 30 min to ensure system homogeneity. Transfer the suspension to a 50 mL PTFE liner, seal it in a stainless steel reactor, place it in an oven, set the temperature to 160℃, and react at a constant temperature for 18 h. After cooling, remove the liner, transfer the reaction solution to a centrifuge tube, centrifuge at 8500 r / min for 20 min, and discard the supernatant. Wash the precipitate four times with deionized water until the filtrate is free of Se. 2- The precipitate was detected (no black precipitate was found when tested with 0.1 mol / L CuSO4 solution); the precipitate was transferred to a vacuum drying oven and dried at 60℃ and 50 Pa for 8 h to obtain Se-GQDs-NiV-LDHs-1.8 composite powder (denoted as M3).

[0029] Example 4 Based on Example 1, this embodiment provides a selenium-modified nickel-vanadium layered double hydroxide electrode material (Se-GQDs(0.08g)-NiV-LDHs-1.0, M4) for supercapacitors. The specific preparation steps are as follows: Step 1: Preparation of GQDs intercalated NiV-LDHs precursor Accurately weigh 0.45g of Ni(CH3COO)2 0.08 g of 4H₂O, 0.08 g of V₂O₅, 0.25 g of hexamethylenetetramine (HMT), and 0.08 g of graphene quantum dots (GQDs, particle size 3-5 nm) were added to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. The container was then placed on a magnetic stirrer and stirred at 300 rpm for 25 minutes. A dark gray emulsion was formed after 10 min. 25% ammonia solution was added dropwise with a pipette while stirring until the pH of the system reached 9.2. Stirring was continued for 10 min. The PTFE liner was sealed in a stainless steel high-pressure reactor and placed in a forced-air drying oven at 125℃ for 12 h. After the reaction, the oven was closed and the mixture was allowed to cool naturally to room temperature. The reactor was removed, the mixture in the liner was poured out, and the mixture was transferred to a centrifuge tube and centrifuged at 7500 r / min for 18 min. The supernatant was discarded. The precipitate was repeatedly washed with deionized water until the pH of the filtrate reached 7. The precipitate was then washed twice with anhydrous ethanol. Finally, the precipitate was transferred to a freeze dryer and dried at -40℃ and 10 Pa for 10 h to obtain a fluffy GQDs intercalated NiV-LDHs precursor powder P1-G.

[0030] Step 2: Preparation of in-situ selenized Se-GQDs (0.08g)-NiV-LDHs-1.0 composite material Weigh 0.30 g of GQDs-intercalated NiV-LDHs precursor powder P1-G, 0.30 g of Na2SeO3 (selenium source to NiV-LDHs mass ratio x = 1.0), and 0.12 g of ascorbic acid. Add the above-weighed reagents to 30 mL of deionized water and 10 mL of a 50% (w / w) hydrazine hydrate mixed solvent, and transfer to a 50 mL beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 25 min to form a dark brown suspension. Transfer the beaker to a magnetic stirrer and stir at 350 r / min for 30 min to ensure system homogeneity. Transfer the suspension to a 50 mL PTFE liner, seal it in a stainless steel reactor, place it in an oven, set the temperature to 160℃, and react at a constant temperature for 18 h. After cooling, remove the liner, transfer the reaction solution to a centrifuge tube, centrifuge at 8500 r / min for 20 min, and discard the supernatant. Wash the precipitate four times with deionized water until the filtrate is free of Se. 2- The sample was detected (no black precipitate was found when tested with 0.1 mol / L CuSO4 solution); the precipitate was transferred to a vacuum drying oven and dried at 60℃ and 50 Pa for 8 h to obtain Se-GQDs(0.08 g)-NiV-LDHs-1.0 composite powder (denoted as M4).

[0031] Example 5 Based on Example 1, this embodiment provides a selenium-modified nickel-vanadium layered double hydroxide electrode material (Se-GQDs-NiV-LDHs-1.0-0.15gAA, M5) for supercapacitors. The specific preparation steps are as follows: Step 1: Preparation of GQDs intercalated NiV-LDHs precursor Accurately weigh 0.45g of Ni(CH3COO)2 0.08 g of 4H₂O, 0.25 g of hexamethylenetetramine (HMT), and 0.05 g of graphene quantum dots (GQDs, particle size 3-5 nm) were added to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. The mixture was placed on a magnetic stirrer and stirred at 300 rpm for 25 min to form a dark gray emulsion. 25% ammonia solution was added dropwise with a pipette while stirring until the pH of the system reached 9.2. Stirring was continued for 10 min. The PTFE liner was then sealed in a stainless steel container. The steel high-pressure reactor was placed in a forced-air drying oven at 125℃ and reacted at a constant temperature for 12 hours. After the reaction, the oven was closed and the reactor was allowed to cool naturally to room temperature. The reactor was removed, the mixture in the liner was poured out, and the mixture was transferred to a centrifuge tube and centrifuged at 7500 r / min for 18 min. The supernatant was discarded. The precipitate was repeatedly washed with deionized water until the pH of the filtrate was 7. The precipitate was then washed twice with anhydrous ethanol. Finally, the precipitate was transferred to a freeze dryer and dried at -40℃ and 10 Pa for 10 hours to obtain a fluffy GQDs intercalated NiV-LDHs precursor powder P1-G.

[0032] Step 2: Preparation of in-situ selenized Se-GQDs-NiV-LDHs-1.0-0.15gAA composite material Weigh 0.30 g of GQDs-intercalated NiV-LDHs precursor powder P1-G, 0.30 g of Na2SeO3 (selenium source to NiV-LDHs mass ratio x = 1.0), and 0.15 g of ascorbic acid. Add the above-weighed reagents to 30 mL of deionized water and 10 mL of a 50% (w / w) hydrazine hydrate mixed solvent, and transfer to a 50 mL beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 25 min to form a dark brown suspension. Transfer the beaker to a magnetic stirrer and stir at 350 r / min for 30 min to ensure system homogeneity. Transfer the suspension to a 50 mL PTFE liner, seal it in a stainless steel reactor, place it in an oven, set the temperature to 160℃, and react at a constant temperature for 18 h. After cooling, remove the liner, transfer the reaction solution to a centrifuge tube, centrifuge at 8500 r / min for 20 min, and discard the supernatant. Wash the precipitate four times with deionized water until the filtrate is free of Se. 2-The sample was detected (no black precipitate was found when tested with 0.1 mol / L CuSO4 solution); the precipitate was transferred to a vacuum drying oven and dried at 60℃ and 50 Pa for 8 h to obtain Se-GQDs-NiV-LDHs-1.0-0.15gAA composite powder (denoted as M5).

[0033] Example 6 Based on Example 1, this embodiment provides a selenium-modified nickel-vanadium layered double hydroxide electrode material (Se-GQDs-NiV-LDHs-1.0-pH8.5, M6) for supercapacitors. The specific preparation steps are as follows: Step 1: Preparation of GQDs intercalated NiV-LDHs precursor Accurately weigh 0.45g of Ni(CH3COO)2 0.08 g of 4H₂O, 0.25 g of hexamethylenetetramine (HMT), and 0.05 g of graphene quantum dots (GQDs, particle size 3-5 nm) were added to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. The mixture was placed on a magnetic stirrer and stirred at 300 rpm for 25 min to form a dark gray emulsion. 25% ammonia solution was added dropwise with a pipette while stirring until the pH of the system reached 8.5. Stirring was continued for 10 min. The PTFE liner was then sealed in a stainless steel container. The steel high-pressure reactor was placed in a forced-air drying oven at 125℃ and reacted at a constant temperature for 12 hours. After the reaction, the oven was closed and the reactor was allowed to cool naturally to room temperature. The reactor was removed, the mixture in the liner was poured out, and the mixture was transferred to a centrifuge tube and centrifuged at 7500 r / min for 18 min. The supernatant was discarded. The precipitate was repeatedly washed with deionized water until the pH of the filtrate was 7. The precipitate was then washed twice with anhydrous ethanol. Finally, the precipitate was transferred to a freeze dryer and dried at -40℃ and 10 Pa for 10 hours to obtain a fluffy GQDs intercalated NiV-LDHs precursor powder P1-G.

[0034] Step 2: Preparation of in-situ selenized Se-GQDs-NiV-LDHs-1.0-pH8.5 composite material Weigh 0.30 g of GQDs-intercalated NiV-LDHs precursor powder P1-G, 0.30 g of Na2SeO3 (selenium source to NiV-LDHs mass ratio x = 1.0), and 0.12 g of ascorbic acid. Add the above-weighed reagents to 30 mL of deionized water and 10 mL of a 50% (w / w) hydrazine hydrate mixed solvent, and transfer to a 50 mL beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 25 min to form a dark brown suspension. Transfer the beaker to a magnetic stirrer and stir at 350 r / min for 30 min to ensure system homogeneity. Transfer the suspension to a 50 mL PTFE liner, seal it in a stainless steel reactor, place it in an oven, set the temperature to 160℃, and react at a constant temperature for 18 h. After cooling, remove the liner, transfer the reaction solution to a centrifuge tube, centrifuge at 8500 r / min for 20 min, and discard the supernatant. Wash the precipitate four times with deionized water until the filtrate is free of Se. 2- The sample was detected (no black precipitate was found when tested with 0.1 mol / L CuSO4 solution); the precipitate was transferred to a vacuum drying oven and dried at 60℃ and 50 Pa for 8 h to obtain Se-GQDs-NiV-LDHs-1.0-pH8.5 composite powder (denoted as M6).

[0035] Comparative Example 1: Preparation of pure NiV-LDHs The process is consistent with that of Example 1, except that only step one of Example 1 is performed (but GQDs are removed), and the in-situ selenization in step two is not performed. Pure NiV-LDHs precursor is used directly as electrode material (denoted as D1). The specific preparation steps are as follows: Step 1: Preparation of NiV-LDHs precursors Accurately weigh 0.45g of Ni(CH3COO)2 Add 0.08 g of 4H₂O, 0.08 g of V₂O₅, and 0.25 g of hexamethylenetetramine (HMT) to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. Place the liner on a magnetic stirrer and stir at 300 rpm for 25 min to form a dark gray emulsion. Add 25% ammonia solution dropwise with a pipette while stirring until the pH reaches 9.2, then continue stirring for 10 min. Seal the PTFE liner in a stainless steel high-pressure reactor and place it in a forced-air drying oven. The temperature was set at 125℃ and the reaction was carried out at a constant temperature for 12 hours. After the reaction was completed, the oven was turned off and the mixture was allowed to cool naturally to room temperature. The reaction vessel was removed, the mixture in the liner was poured out, and the mixture was transferred to a centrifuge tube and centrifuged at 7500 r / min for 18 min. The supernatant was discarded. The precipitate was washed repeatedly with deionized water until the pH of the filtrate was 7. The precipitate was then washed twice with anhydrous ethanol. Finally, the precipitate was transferred to a freeze dryer, and the temperature was set at -40℃ and the vacuum degree at 10 Pa. The precipitate was dried for 10 hours to obtain NiV-LDHs precursor powder as electrode material (denoted as D1).

[0036] Comparative Example 2: Preparation of Se-NiV-LDHs-1.0-Single Reducing Agent Composite Material Comparative Example 2 is based on Example 1, except that GQDs are removed in step one. All other steps are the same as in Example 1. The final product is denoted as Se-NiV-LDHs-1.0-GQD-free (D2). The specific preparation steps are as follows: Step 1: Preparation of NiV-LDHs precursors Accurately weigh 0.45g of Ni(CH3COO)2 Add 4H₂O, 0.08 g of V₂O₅, and 0.25 g of hexamethylenetetramine (HMT) to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. Place the liner on a magnetic stirrer and stir at 300 rpm for 25 min to form a dark gray emulsion. Add 25% ammonia solution dropwise with a pipette while stirring until the pH reaches 9.2, and continue stirring for 10 min. Seal the PTFE liner in a stainless steel high-pressure reactor and place... The mixture was placed in a forced-air drying oven at 125℃ and reacted at a constant temperature for 12 hours. After the reaction, the oven was closed and the mixture was allowed to cool naturally to room temperature. The reaction vessel was removed, the mixture in the liner was poured out, and the mixture was transferred to a centrifuge tube and centrifuged at 7500 r / min for 18 min. The supernatant was discarded. The precipitate was washed repeatedly with deionized water until the pH of the filtrate was 7. The precipitate was then washed twice with anhydrous ethanol. Finally, the precipitate was transferred to a freeze dryer and dried at -40℃ and 10 Pa for 10 hours to obtain NiV-LDHs precursor powder P1.

[0037] Step 2: Preparation of in-situ selenized Se-NiV-LDHs-1.0-GQD-free composite material Weigh 0.30 g of NiV-LDHs precursor powder P1, 0.30 g of Na2SeO3 (selenium source to NiV-LDHs mass ratio x = 1.0), and 0.12 g of ascorbic acid. Add the above-weighed reagents to 30 mL of deionized water and 10 mL of a 50% (w / w) hydrazine hydrate mixed solvent, and transfer to a 50 mL beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 25 min to form a dark brown suspension. Transfer the beaker to a magnetic stirrer and stir at 350 r / min for 30 min to ensure system homogeneity. Transfer the suspension to a 50 mL PTFE liner, seal it in a stainless steel reactor, place it in an oven, set the temperature to 160℃, and react at a constant temperature for 18 h. After cooling, remove the liner, transfer the reaction solution to a centrifuge tube, centrifuge at 8500 r / min for 20 min, and discard the supernatant. Wash the precipitate four times with deionized water until the filtrate is free of Se. 2-The sample was detected (no black precipitate was found when tested with 0.1 mol / L CuSO4 solution); the precipitate was transferred to a vacuum drying oven and dried at 60℃ and 50 Pa for 8 h to obtain Se-NiV-LDHs-1.0-GQDs-free composite powder (denoted as D2).

[0038] Comparative Example 3: Preparation of Se-GQDs-NiV-LDHs-1.0-Single Reducing Agent Composite Material Compared with the process in Example 1, ascorbic acid is removed in step two, and only 10 mL of 50% hydrazine hydrate is used as a reducing agent. The rest is the same as in Example 1. The final product is named Se-GQDs-NiV-LDHs-1.0-single reducing agent (D3). The specific preparation steps are as follows: Step 1: Preparation of GQDs intercalated NiV-LDHs precursor Accurately weigh 0.45g of Ni(CH3COO)2 0.08 g of 4H₂O, 0.25 g of hexamethylenetetramine (HMT), and 0.05 g of graphene quantum dots (GQDs, particle size 3-5 nm) were added to a 50 mL polytetrafluoroethylene (PTFE) liner containing 40 mL of deionized water. The mixture was placed on a magnetic stirrer and stirred at 300 rpm for 25 min to form a dark gray emulsion. 25% ammonia solution was added dropwise with a pipette while stirring until the pH of the system reached 9.2. Stirring was continued for 10 min. The PTFE liner was then sealed in a stainless steel container. The steel high-pressure reactor was placed in a forced-air drying oven at 125℃ and reacted at a constant temperature for 12 hours. After the reaction, the oven was closed and the reactor was allowed to cool naturally to room temperature. The reactor was removed, the mixture in the liner was poured out, and the mixture was transferred to a centrifuge tube and centrifuged at 7500 r / min for 18 min. The supernatant was discarded. The precipitate was repeatedly washed with deionized water until the pH of the filtrate was 7. The precipitate was then washed twice with anhydrous ethanol. Finally, the precipitate was transferred to a freeze dryer and dried at -40℃ and 10 Pa for 10 hours to obtain a fluffy GQDs intercalated NiV-LDHs precursor powder P1-G.

[0039] Step 2: Preparation of in-situ selenized Se-GQDs-NiV-LDHs-1.0-single reducing agent composite material Weigh 0.30 g of GQDs-intercalated NiV-LDHs precursor powder P1-G and 0.30 g of Na2SeO3 (selenium source to NiV-LDHs mass ratio x = 1.0). Add the above-weighed reagents to 30 mL of deionized water and 10 mL of a 50% (w / w) hydrazine hydrate mixed solvent, and transfer to a 50 mL beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 25 min to form a dark brown suspension. Transfer the beaker to a magnetic stirrer and stir at 350 r / min for 30 min to ensure system homogeneity. Transfer the suspension to a 50 mL PTFE liner, seal it in a stainless steel reactor, place it in an oven, set the temperature to 160℃, and react at a constant temperature for 18 h. After cooling, remove the liner, transfer the reaction solution to a centrifuge tube, centrifuge at 8500 r / min for 20 min, and discard the supernatant. Wash the precipitate four times with deionized water until the filtrate is free of Se. 2- The sample was detected (no black precipitate was observed when tested with 0.1 mol / L CuSO4 solution); the precipitate was transferred to a vacuum drying oven and dried at 60℃ and 50 Pa for 8 hours to obtain Se-GQDs-NiV-LDHs-1.0-single reducing agent composite powder (denoted as D3). Based on Examples 1-6 and Comparative Examples 1-3, relevant performance tests were conducted on the above electrode materials, and the specific results are shown in Table 1.

[0040] Table 1: Comparison of Performance of Different Electrode Materials

[0041] As can be clearly seen from the data in Table 1, the core process parameters of this invention (selenium source ratio, GQDs dosage, ascorbic acid dosage, and pH value) have a significant regulatory effect on the structure and electrochemical performance of the Se-GQDs-NiV-LDHs composite material. Furthermore, the synergistic effect of "GQDs intercalation-double reducing agent selenization" is the key to improving performance, as detailed below: Regulation and Mechanism of Selenium Source Ratio (x): A comparison of Examples 1 (x=1.0), 2 (x=0.4), and 3 (x=1.8) shows that there is an optimal range for the selenium source ratio. When x=0.4, the selenium loading is insufficient, and only discontinuous conductive sites can be formed on the surface of the layer, resulting in a specific capacitance of only 1780 F / g and a charge transfer impedance of 11.3 Ω. When x=1.0, selenium uniformly covers the interface between the layer and GQDs under the synergistic effect of GQDs adsorption and dual reducing agents, forming a continuous conductive network, with a specific capacitance of 2015 F / g and an impedance reduced to 8.7 Ω. When x=1.8, excess selenium is prone to agglomeration (selenium particles with a diameter of about 50 nm can be observed by SEM characterization), blocking part of Ni. 2+ / Ni 3+ / Ni 4+The presence of active sites resulted in a decrease in specific capacitance to 1920 F / g, and a slight reduction in rate performance from 88.3% to 86.7%. This indicates that an appropriate selenium loading (around x=1.0) is key to balancing the continuity of the conductive network with the exposure of active sites.

[0042] The impact of GQD dosage on layer structure and transport performance: A comparison between Example 1 (0.05g GQDs) and Example 4 (0.08g GQDs) shows that increasing the amount of GQDs can further optimize the structure and performance. In Example 4, the interlayer spacing increased from 1.22nm to 1.25nm because more GQDs were inserted into the interlayer to form support, effectively suppressing layer stacking; simultaneously, the density of interlayer conductive channels increased, the charge transfer impedance decreased to 8.2Ω, and the rate performance improved to 89.1% (maintaining high capacity at 10A / g). More GQDs is not necessarily better (when the amount of GQDs exceeds 0.1g, GQD aggregation can cause blockage of interlayer channels, and the specific capacitance actually decreases to 1850F / g). 0.05-0.08g is the optimal dosage range that balances structural stability and conductivity.

[0043] The optimization logic of ascorbic acid dosage in the dual reducing agent system: The performance difference between Example 1 (0.12 g ascorbic acid) and Example 5 (0.15 g ascorbic acid) confirms the key role of ascorbic acid in inhibiting selenium aggregation. Ascorbic acid can not only react with Se... 4+ The formation of temporary complexes slows down the reduction rate and can also form hydrogen bonds with the hydroxyl groups on the surface of GQDs through hydroxyl groups, further anchoring Se species. When the amount of ascorbic acid increased from 0.12g to 0.15g, the particle size of selenium particles decreased from 20-30nm to 10-15nm, and the dispersion uniformity was significantly improved. This resulted in an increase in specific capacitance from 2015F / g to 2080F / g, an increase in cycle stability from 95.2% to 96.1% (after 10,000 cycles), and a decrease in charge transfer impedance to 7.9Ω, making it the group with the best performance among all examples.

[0044] The decisive role of pH value in the formation of layered structures: A comparison between Example 1 (pH=9.2) and Example 6 (pH=8.5) shows that the strength of the alkaline environment directly affects the layered growth of NiV-LDHs. At pH=9.2, the OH- provided by ammonia water... - With appropriate concentration, it can react with Ni 2+ V 5+ It forms stable hydroxide lamellae and can synergistically regulate the lamellae growth rate with HMT, ultimately forming a regular layered structure; while at pH=8.5, OH - Insufficient concentration, some V 5+The inability to fully convert vanadate into vanadate to participate in the construction of the laminations leads to an increase in defects in the layered structure, a reduction in interlayer spacing to 1.18 nm, a decrease in the exposure of active sites, a drop in specific capacitance to 1850 F / g, and an increase in impedance to 10.8 Ω.

[0045] The performance data of the comparative examples further highlight the innovation of the process of this invention: Comparative Example 1 (selenium-free, GQDs-free) suffers from poor conductivity (resistivity > 10) due to the inherent poor conductivity of pure NiV-LDHs. 3 Ω The interlayer spacing was only 0.78 nm, the specific capacitance was only 1050 F / g, and the cycle stability was only 72.3%, all of which were significantly lower than those of Example 1, confirming the necessity of selenium modification and GQDs intercalation. Comparative Example 2 (without GQDs), although selenized with two reducing agents, suffered from layer collapse during charge and discharge due to the lack of interlayer support. The interlayer spacing was only 0.81 nm, and the specific capacitance of 1560 F / g and cycle stability of 84.7% were significantly lower than those of Example 1, demonstrating the core role of GQDs intercalation in structural stability. Comparative Example 3 (single reducing agent), due to reduction with only hydrazine hydrate, showed that the Se... 4+ The reduction rate was too fast, resulting in the formation of large selenium agglomerates (particle size > 100 nm). The conductive network was discontinuous, with a specific capacitance of 1680 F / g and an impedance of 13.6 Ω. The performance was far inferior to that of Example 1, demonstrating the key value of synergistic reduction by dual reducing agents.

[0046] In summary, this invention synergistically constructs a regular layered structure through "GQDs intercalation + HMT guidance + ammonia pH control", and achieves uniform modification of selenium by combining "dual reducing agents + GQDs adsorption and anchoring". The resulting Se-GQDs-NiV-LDHs composite material exhibits excellent electrochemical performance, and the regulation rules of each parameter provide clear guidance for process optimization in industrial production.

[0047] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors, characterized in that, The electrode material has a layered structure with an interlayer spacing of 1.0 nm to 1.3 nm, comprising: Nickel-vanadium layered double hydroxide main plate; Graphene quantum dots are intercalated and supported between the main body layers, and the graphene quantum dots constitute interlayer electron transport channels and structural supports. And nano-selenium particles adsorbed and anchored to the surface and edges of the nickel-vanadium layered double hydroxide main plate by the graphene quantum dots; The graphene quantum dots and the selenium nanoparticles are connected by chemical interaction to jointly construct a three-dimensional structure in which conductivity and pseudocapacitance are synergistically enhanced.

2. The method for preparing a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors according to claim 1, characterized in that, include: Step 1: Mix and dissolve nickel salt, vanadium source, hexamethylenetetramine and graphene quantum dots, adjust the pH value and then perform hydrothermal reaction. After the reaction, centrifuge, wash and freeze dry to obtain the precursor. Step 2: The precursor, selenium source and dual reducing agent system are dispersed together and subjected to a second hydrothermal reaction. After the reaction, the mixture is centrifuged, washed and vacuum dried to obtain the selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors.

3. The method for preparing a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors according to claim 2, characterized in that, The vanadium source is any one of V2O5, ammonium metavanadate, and vanadate; the nickel salt is any one of Ni(CH3COO)2·4H2O, NiCl2·6H2O, and Ni(NO3)2·6H2O.

4. The method for preparing a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors according to claim 2, characterized in that, In step 1, the molar ratio of nickel in the nickel salt, vanadium in the vanadium source, hexamethylenetetramine, and graphene quantum dots is (4~5):1:(4~5):(0.01~0.1).

5. The method for preparing a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors according to claim 2, characterized in that, In step 1, the pH value is adjusted to 9-10 using ammonia, sodium carbonate, or sodium bicarbonate. The hydrothermal reaction temperature is 125-160℃, and the reaction time is 10-18 hours.

6. The method for preparing a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors according to claim 2, characterized in that, In step 1, the freeze-drying temperature is -40~-50℃, the vacuum degree is 10~15Pa, and the drying time is 10~14h.

7. The method for preparing a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors according to claim 2, characterized in that, In step 2, the mass ratio of the precursor, selenium source, and dual reducing agent system is 1:(0.4~2):(0.4~0.5); the dual reducing agent system is a combination of hydrazine hydrate and ascorbic acid; the hydrothermal reaction temperature is 125-160℃, and the reaction time is 10-18h.

8. The method for preparing a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors according to claim 2, characterized in that, In step 2, the vacuum drying temperature is 50~60℃, the vacuum degree is 40~60Pa, and the drying time is 8~12h.

9. A supercapacitor electrode, characterized in that, The supercapacitor electrode comprises a selenium-modified nickel-vanadium layered double hydroxide electrode material for supercapacitors as described in claim 1.

10. A supercapacitor, characterized in that, It includes the supercapacitor electrode as described in claim 9.

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