A single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, a preparation method, application and an electrochemical device

Abstract

This invention belongs to the field of vanadium redox flow batteries, and relates to a monolayer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, its preparation method, application, and electrochemical device. The monolayer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode includes a carbon cloth substrate, an intermediate layer, and an active layer. The intermediate layer is a monolayer reduced graphene oxide coated on the surface of the carbon cloth substrate, and the active layer is S, N co-doped niobium oxide composite nanoparticles containing Nb-S bonds. Some of the composite nanoparticles are loaded on the surface of the carbon cloth substrate, while the rest are encapsulated by the monolayer reduced graphene oxide. The niobium oxide composite nanoparticles contain both NbO2 and Nb2O5 phases. The monolayer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode of this invention achieves a balance between high conductivity, high catalytic activity, and long-term cycle stability through the synergistic structural design of the carbon cloth substrate, the monolayer reduced graphene oxide intermediate layer, and the S, N co-doped niobium oxide active layer.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery technology, specifically to a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, its preparation method, application, and electrochemical device. Background Technology

[0002] Vanadium redox flow batteries, as a large-scale energy storage technology, have shown broad application prospects in renewable energy grid integration, grid peak shaving, and frequency regulation due to their advantages such as independent power capacity design, long cycle life, and high safety and reliability. As the core component of vanadium redox flow batteries, the intrinsic activity and structural stability of electrode materials directly determine the electrochemical kinetic rate of vanadium ion redox reactions and the long-term operating efficiency of the battery system.

[0003] Carbon cloth materials, with their flexible three-dimensional woven structure, good electrolyte permeability, and high porosity, have been widely used as electrode substrate materials for vanadium redox flow batteries. However, unmodified commercial carbon cloth electrodes have significant performance shortcomings, including limited intrinsic conductivity and a lack of surface catalytic active sites, especially under high current density conditions. 2+ / VO2 + With V 2+ / V 3+ The charge transfer rate of the redox couple is severely limited, leading to a significant increase in battery polarization and a substantial decrease in voltage and energy efficiency. Furthermore, the surface chemical state and microstructure of the carbon cloth electrode are prone to degradation in strongly acidic electrolyte environments and during long-term electrochemical cycling, with interfacial resistance continuously increasing over time, further restricting the service life and reliability of the vanadium redox flow battery.

[0004] To address the aforementioned issues, existing technologies have explored various approaches, including conductive network construction, introduction of catalytically active components, and composite coating modification. For example, existing technologies employ carbon nanotubes combined with reduced graphene oxide to enhance the conductivity of carbon cloth electrodes, or introduce niobium oxide into carbon cloth electrodes to improve vanadium ion reaction kinetics, or utilize metal oxides such as TiO2 and SnO2 to synergistically coat graphene to form a core-shell structure to improve the corrosion resistance of carbon cloth electrodes. However, none of these approaches have been able to simultaneously meet the comprehensive requirements of high conductivity, high catalytic activity, and long-term cycling stability in practical applications. Specifically, conductive network construction approaches offer limited improvement in electrode catalytic activity; introducing catalytically active components generally suffers from common problems such as poor dispersion of niobium oxide particles, easy aggregation, and weak interfacial bonding with the carbon substrate, resulting in low utilization of active sites and easy detachment failure; while composite coating approaches suffer from decreased conductivity and increased interfacial resistance.

[0005] Therefore, there is a need to provide a carbon cloth electrode for all-vanadium redox flow batteries that combines high conductivity, high catalytic activity, and long-term cycle stability. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the problem that existing modified carbon cloth electrodes cannot simultaneously achieve high conductivity, high catalytic activity, and long-term cycling stability, this invention provides a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, its preparation method, application, and electrochemical device.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0010] In a first aspect, the present invention provides a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, comprising a carbon cloth substrate, an intermediate layer and an active layer;

[0011] The intermediate layer is a single layer of reduced graphene oxide coated on the surface of a carbon cloth substrate;

[0012] The active layer consists of S and N co-doped niobium oxide composite nanoparticles, wherein some of the S and N co-doped niobium oxide composite nanoparticles are loaded on the surface of a carbon cloth substrate, and the other part of the S and N co-doped niobium oxide composite nanoparticles are encapsulated by a single layer of reduced graphene oxide and loaded on an intermediate layer; the S and N co-doped niobium oxide composite nanoparticles contain Nb-S bonds.

[0013] The niobium oxide composite nanoparticles contain both NbO2 and Nb2O5 phases.

[0014] In the monolayer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode described above, preferably, the monolayer reduced graphene oxide accounts for 1-5 wt% of the total mass of the composite modified carbon cloth electrode, the S and N co-doped niobium oxide composite nanoparticles account for 5-20 wt% of the total mass of the composite modified carbon cloth electrode, and the carbon cloth substrate accounts for 75-90 wt% of the total mass of the composite modified carbon cloth electrode;

[0015] In S and N co-doped niobium oxide composite nanoparticles, the percentage of S atoms is 1-3 at% and the percentage of N atoms is 0.5-2 at%.

[0016] In niobium oxide composite nanoparticles, the molar ratio of NbO2 phase to Nb2O5 phase is (1-1.5):1.

[0017] Secondly, the present invention provides a method for preparing the above-mentioned monolayer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, comprising the following steps:

[0018] S1: Disperse monolayer reduced graphene oxide in a solution, then add the first dispersant and the second dispersant to obtain a monolayer reduced graphene oxide dispersion;

[0019] S2: Niobium source, sulfur powder and reducing compound are added to a single-layer reduced graphene oxide dispersion to obtain a multi-component impregnation solution;

[0020] S3: Immerse the carbon cloth substrate in a multi-component impregnation solution, remove and dry to obtain a carbon cloth substrate loaded with precursor;

[0021] S4: The carbon cloth substrate with the supported precursor is subjected to a two-stage calcination process under an inert atmosphere, and after cooling, a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode is obtained.

[0022] In the preparation method described above, preferably, in step S1, monolayer reduced graphene oxide is dispersed in a mixed solution of ethanol and hydrochloric acid, and then a first dispersant and a second dispersant are added, and a monolayer reduced graphene oxide dispersion is obtained by ultrasonic dispersion treatment.

[0023] The first dispersant is dodecyl dimethylamine hydantoin, hexadecyl trimethylammonium bromide, or polyvinyl alcohol; the second dispersant is polyvinylpyrrolidone, polyethylene glycol, or sodium dodecyl sulfate.

[0024] In the preparation method described above, preferably, the mass ratio of the first dispersant to the second dispersant is (0.5-1):1, and the mass ratio of the monolayer reduced graphene oxide to the sum of the first dispersant and the second dispersant is (40-60):(30-40).

[0025] In the preparation method described above, preferably, in step S2, the reducing compound is ascorbic acid, citric acid, or sodium citrate; the mass ratio of niobium source, sulfur powder, and reducing compound is (3-5):(3-5):(0.8-1.2), and the mass ratio of monolayer reduced graphene oxide to niobium source in the monolayer reduced graphene oxide dispersion is 1:(3-5).

[0026] The niobium source is NbCl5 or niobium oxalate.

[0027] In the preparation method described above, preferably, in step S3, before immersing the carbon cloth substrate into the multi-component impregnation solution, the carbon cloth substrate is pretreated with a solvent, and then the pretreated carbon cloth substrate is immersed in the multi-component impregnation solution and ultrasonically treated at a power of 150-200W for 100-150 min. After removal, it is dried at 60-80℃ for 4-5 h to obtain the carbon cloth substrate loaded with the precursor.

[0028] In the preparation method described above, preferably, in step S4, under an inert atmosphere, the temperature is first raised to 280-320℃ at a heating rate of 3-5℃ / min and held for 1-2 hours, and then the temperature is further raised to 650-700℃ at a heating rate of 3-5℃ / min and held for 3-4 hours to obtain a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode.

[0029] Thirdly, the present invention provides an application of the above-mentioned composite modified carbon cloth electrode or the composite modified carbon cloth electrode prepared by the above-mentioned preparation method in vanadium redox flow batteries, zinc-bromine flow batteries, iron-chromium flow batteries, supercapacitors, water electrolysis for hydrogen production, or metal-air batteries.

[0030] Fourthly, the present invention also provides an electrochemical device, comprising the above-described composite modified carbon cloth electrode or the composite modified carbon cloth electrode prepared by the above-described preparation method;

[0031] The electrochemical device is a vanadium redox flow battery, a zinc-bromine redox flow battery, an iron-chromium redox flow battery, a supercapacitor, a water electrolysis hydrogen production device, or a metal-air battery.

[0032] (III) Beneficial Effects

[0033] In the monolayer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode of this invention, the carbon cloth substrate serves as the skeletal support of the electrode. Its inherent three-dimensional woven structure endows the electrode with excellent flexibility and macroscopic conductive pathways, while ensuring sufficient penetration and uniform distribution of the electrolyte within the electrode. Based on this, a monolayer reduced graphene oxide interlayer tightly coats the surface of the carbon cloth fibers, constructing a two-dimensional conductive network layer with a high specific surface area. The addition of the monolayer reduced graphene oxide interlayer significantly increases the effective contact area between the electrode and the electrolyte, and provides an additional fast electron transport channel beyond the original conductive skeleton of the carbon fiber, effectively reducing the ohmic resistance and interfacial charge transfer impedance within the electrode, thereby maintaining excellent electronic conduction efficiency even under high current density conditions.

[0034] The active layer, through multi-phase synergy and dual-element co-doping, significantly enhances the catalytic activity of the electrode for the redox reaction of vanadium ions. Specifically, the active layer consists of S and N co-doped niobium oxide composite nanoparticles, some of which are loaded onto the surface of a carbon cloth substrate, while the rest are encapsulated by a monolayer of reduced graphene oxide. The niobium oxide composite nanoparticles contain both NbO2 and Nb2O5 phases. The NbO2 phase exhibits high conductivity, providing a rapid electron transport pathway for the electrochemical reaction, while the Nb2O5 phase possesses high catalytic activity, providing abundant surface active sites to promote the adsorption and conversion of vanadium ions. Regarding the doping elements, the introduction of sulfur (S) forms an Nb-S bond with Nb atoms, significantly increasing the adsorption of vanadium ions on the electrode surface and enhancing the intrinsic activity of the catalytic sites. N doping optimizes the hydrophilicity of the electrode surface, improving the wetting and ion diffusion behavior of the electrolyte near the active sites, further accelerating the electrode reaction process.

[0035] Furthermore, in this invention, part of the active layer particles are anchored to the exposed area of ​​the carbon cloth fiber, while another part is covered by a monolayer of reduced graphene oxide shell, forming a multi-site firmly bonded loading morphology. The sheet structure of the monolayer reduced graphene oxide can physically interlock and bridge the interface of the niobium oxide particles, effectively inhibiting the aggregation, shedding, and loss of nanoparticles during electrochemical cycling, ensuring the long-term effectiveness and structural integrity of the catalytic active sites. The carbon cloth substrate, the reduced graphene oxide interlayer, and the active niobium oxide particles synergistically construct a point-line-plane three-dimensional composite structure, which not only improves the initial electrochemical performance of the electrode but also significantly enhances the long-term cycling stability of the electrode under strong acidic electrolyte scouring and long-cycle charge-discharge conditions. Attached Figure Description

[0036] Figure 1 Scanning electron microscope image of the NbO2 / Nb2O5@rGO / CC electrode prepared in Example 1;

[0037] Figure 2 Comparison of the four-probe resistivity test results of the carbon cloth electrodes prepared in Example 1 and Comparative Examples 1-4;

[0038] Figure 3 Comparison of the coulombic efficiency, voltage efficiency, and energy efficiency of the carbon cloth electrodes prepared in Example 1 and Comparative Examples 1-4;

[0039] Figure 4 The graph shows a comparison of the voltage efficiency of the carbon cloth electrodes prepared in Example 1 and Comparative Examples 1-4 during 1000 charge-discharge cycles. Detailed Implementation

[0040] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] This invention provides a monolayer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, comprising a carbon cloth substrate, an intermediate layer, and an active layer. The intermediate layer is a monolayer reduced graphene oxide (rGO) coated on the surface of the carbon cloth substrate. The active layer consists of S and N co-doped niobium oxide composite nanoparticles. Some of the S and N co-doped niobium oxide composite nanoparticles are loaded on the surface of the carbon cloth substrate, while another portion is encapsulated by the monolayer reduced graphene oxide and loaded on the intermediate layer. The S and N co-doped niobium oxide composite nanoparticles contain Nb-S bonds. The niobium oxide composite nanoparticles comprise both NbO2 and Nb2O5 phases.

[0042] In the single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode of the present invention, the carbon cloth substrate serves as the skeleton support of the electrode. Its inherent three-dimensional braided structure can give the electrode good flexibility and macroscopic conductive pathways, while ensuring the full penetration and uniform distribution of electrolyte inside the electrode.

[0043] Monolayer reduced graphene oxide can adhere tightly to the surface of carbon fiber through physical adsorption and π-π interactions, forming a two-dimensional conductive network layer. The introduction of the monolayer reduced graphene oxide interlayer has a dual effect: on the one hand, the graphene sheets have an extremely high specific surface area, which, when covering the surface of the carbon fiber, can significantly increase the effective contact area between the electrode and the electrolyte, providing more anchoring points for the subsequent loading of active components. On the other hand, the excellent oriented conductivity of graphene can provide additional fast electron transport channels outside the original conductive skeleton of the carbon fiber, effectively reducing the ohmic resistance and interfacial charge transfer impedance inside the electrode, thereby maintaining excellent electronic conduction efficiency under high current density conditions. In addition, the monolayer reduced graphene oxide sheets in this invention do not cover the carbon fiber in a completely dense and flat form, but rather exhibit a partially covered microstructure with wrinkled and undulating surfaces. This partially covered structural design retains some exposed areas of the carbon fiber for direct loading of niobium oxide particles, while avoiding the problems of electrolyte penetration obstruction and ion transport path extension caused by full coverage. The wrinkled structure of the graphene sheets can provide physical intercalation sites for the subsequently loaded niobium oxide nanoparticles, enhancing the anchoring stability of the particles.

[0044] The active layer, through multi-phase synergy and dual-element co-doping, significantly enhances the catalytic activity of the electrode for the redox reaction of vanadium ions. The niobium oxide composite nanoparticles simultaneously contain both NbO2 and Nb2O5 phases. The NbO2 phase exhibits high conductivity, providing a rapid electron transport pathway for the electrochemical reaction, while the Nb2O5 phase possesses high catalytic activity, offering abundant surface active sites to promote the adsorption and conversion of vanadium ions. The coexistence and synergy of these two phases at the nanoscale achieve functional complementarity between conductivity and catalytic activity. Regarding doping elements, the introduction of sulfur (S) forms an Nb-S bond with Nb atoms, significantly increasing the adsorption of vanadium ions on the electrode surface and enhancing the intrinsic activity of the catalytic sites. N doping optimizes the hydrophilicity of the electrode surface, improving electrolyte wetting and ion diffusion near the active sites, further accelerating the electrode reaction process.

[0045] Furthermore, the loading morphology of the active layer particles exhibits multi-site anchoring characteristics. Specifically, some nanoparticles are encapsulated by monolayer reduced graphene oxide sheets through the physical interlocking effect of the graphene's wrinkled structure, achieving loading in the intermediate layer. Another portion is directly loaded onto the exposed carbon fiber areas not covered by graphene. The monolayer reduced graphene oxide sheets and their wrinkled morphology can physically interlock and bridge the interface of the niobium oxide particles, effectively inhibiting the aggregation, shedding, and loss of nanoparticles during electrochemical cycling, ensuring the long-term effectiveness and structural integrity of the catalytic active sites. The carbon cloth substrate, the reduced graphene oxide intermediate layer, and the active niobium oxide particles synergistically construct a point-line-surface three-dimensional composite structure. This significantly enhances the electrode's long-term cycling stability under strong acidic electrolyte scouring and long-cycle charge-discharge conditions, improving its initial electrochemical performance by more than double the lifespan of existing commercial carbon cloth electrodes.

[0046] Preferably, monolayer reduced graphene oxide accounts for 1-5 wt% of the total mass of the composite modified carbon cloth electrode. If the content of monolayer reduced graphene oxide is less than 1 wt%, it is difficult to form a continuous and effective two-dimensional conductive network on the carbon fiber surface, and the electron transport enhancement effect is not significant; if it is higher than 5 wt%, the graphene sheets may stack and agglomerate, which will increase the interfacial resistance and hinder the electrolyte penetration. S and N co-doped niobium oxide composite nanoparticles account for 5-20 wt% of the total mass of the composite modified carbon cloth electrode. If the content of niobium oxide composite nanoparticles is less than 5 wt%, the number of catalytic active sites is insufficient, and the improvement of vanadium ion reaction kinetics is limited; if it is higher than 20 wt%, the particles are prone to agglomeration, resulting in a decrease in the utilization rate of active sites, and an excessively thick active layer will increase the ion diffusion resistance. The carbon cloth substrate accounts for 75-90 wt% of the total mass of the composite modified carbon cloth electrode. As the main skeleton of the electrode, the content range of the carbon cloth substrate ensures that the electrode has both good mechanical strength and a suitable loading of active components. In S and N co-doped niobium oxide composite nanoparticles, the percentage of S atoms is 1-3 at%, and the percentage of N atoms is 0.5-2 at%. The molar ratio of NbO2 to Nb2O5 phases in the niobium oxide composite nanoparticles is (1-1.5):1, more preferably 1.2:1. When the molar ratio of the two phases is within this range, the highly conductive NbO2 phase and the highly active Nb2O5 phase can achieve optimal functional synergy, ensuring both the overall electron transport efficiency of the electrode and maximizing catalytic activity.

[0047] This invention also provides a method for preparing a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, comprising the following steps:

[0048] S1: Add monolayer reduced graphene oxide to a mixed solution of ethanol and hydrochloric acid, then add a first dispersant and a second dispersant, and obtain a monolayer reduced graphene oxide dispersion by ultrasonic dispersion treatment.

[0049] S2: Add niobium source, sulfur powder and reducing compound to the single-layer reduced graphene oxide dispersion, stir evenly and then add an appropriate amount of deionized water to adjust the viscosity to obtain a multi-component impregnation solution.

[0050] S3: Immerse the pretreated carbon cloth substrate in the multi-component impregnation solution obtained in step S2, ultrasonically impregnate, and then remove and dry to obtain the carbon cloth substrate loaded with the precursor.

[0051] S4: The carbon cloth substrate with the supported precursor is subjected to a two-stage calcination process under an inert atmosphere. After calcination, it is naturally cooled to room temperature under the protection of an inert atmosphere to obtain a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode.

[0052] In step S1, ethanol is used as the main solvent, exhibiting good volatility and wettability to graphene. The addition of hydrochloric acid adjusts the pH of the solution to a weakly acidic state, enhancing its hydrophilicity and dispersibility. The first dispersant is preferably dodecyl dimethylamine acetate (BS-12), hexadecyl trimethylammonium bromide (CTAB), or polyvinyl alcohol (PVA). The second dispersant is preferably polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), or sodium dodecyl sulfate (SDS). BS-12 is an amphoteric surfactant containing both amino and carboxyl groups in its molecular structure. These amphoteric groups can form hydrogen bonds with the oxygen-containing functional groups on the surface of reduced graphene oxide, thus firmly adsorbing onto the graphene sheet surface. The quaternary ammonium cation of CTAB can bind to the negatively charged groups on the graphene surface through electrostatic adsorption, while the hydroxyl groups of PVA can interact with the oxygen-containing functional groups on the graphene surface through hydrogen bonds. PVP and PEG are nonionic polymeric surfactants; their long-chain structures provide significant steric hindrance, effectively preventing the re-aggregation of graphene sheets in the solution. The hydrophobic alkyl chains of SDS can adsorb onto the graphene surface, and the negatively charged sulfate head groups provide an electrostatic repulsion effect, effectively preventing the graphene sheets from re-aggregating in solution. The combined use of the first and second dispersants produces a synergistic dispersion effect: the combined action of the first and second dispersants enables monolayer reduced graphene oxide to achieve excellent dispersion stability in solution. Furthermore, when BS-12 is selected as the first dispersant, the nitrogen element contained in its molecule can serve as a nitrogen source precursor for subsequent S and N co-doping while also playing a dispersing role, achieving in-situ N doping during high-temperature calcination. Experiments show that the dispersion prepared using the above-mentioned composite dispersant showed no obvious stratification after standing for 72 hours, while the dispersion using only the second dispersant showed significant sedimentation within 24 hours.

[0053] Preferably, in step S1, the mass ratio of the first dispersant to the second dispersant is (0.5-1):1, and the mass ratio of the monolayer reduced graphene oxide to the sum of the first and second dispersants is (40-60):(30-40). The volume ratio of ethanol to hydrochloric acid can be 20:0.1, etc. The preferred ultrasonic dispersion power is 250-350W, the frequency is 30-50kHz, and the time is 30-50min.

[0054] In step S2 above, the niobium source can be niobium pentachloride or niobium oxalate. The niobium source can complex or electrostatically adsorb with oxygen-containing functional groups on the surface of monolayer reduced graphene oxide, pre-anchoring niobium species to the graphene sheet surface. This complexation process is crucial for the subsequent in-situ growth of niobium oxide particles on the graphene surface. Sulfur powder, as the sulfur source, provides sulfur (S) during the subsequent calcination process to form Nb-S bonds and achieve S doping. The reducing compound is preferably ascorbic acid, citric acid, sodium citrate, etc. These substances play a dual role in this step: firstly, as a reducing agent, they partially remove Nb... 5+ Restored to Nb 4+ This allows for the regulation of the coexistence of NbO2 and Nb2O5 phases during subsequent calcination. Secondly, as a dispersant, its multiple hydroxyl groups can coordinate with niobium species, preventing premature aggregation of nanoparticles in solution and ensuring the uniformity and stability of the impregnation solution. Furthermore, ascorbic acid, citric acid, and sodium citrate, as reducing agents, are crucial for achieving a molar ratio of NbO2 to Nb2O5 of (1-1.5):1, balancing electron transport and reactivity.

[0055] Preferably, in step S2, the mass ratio of niobium source, sulfur powder and reducing compound is (3-5):(3-5):(0.8-1.2), and the mass ratio of monolayer reduced graphene oxide to niobium source in the monolayer reduced graphene oxide dispersion is 1:(3-5).

[0056] In step S3, the pretreatment of the carbon cloth substrate typically involves ultrasonic cleaning sequentially with acetone, ethanol, and deionized water, with each cleaning session preferably lasting 20-40 minutes. Acetone effectively removes organic sizing agents and oil stains from the carbon cloth surface, ethanol removes residual acetone and further cleans the surface, and deionized water thoroughly cleans and restores the hydrophilicity of the carbon cloth surface. A clean pretreated carbon cloth surface facilitates the uniform spreading of the impregnation solution and the adhesion of subsequent components.

[0057] The impregnation process preferably employs ultrasonic-assisted impregnation, with an ultrasonic power of 150-200W and an impregnation time of 100-150 minutes. Ultrasonic treatment allows the impregnating solution to fully penetrate the internal pores of the carbon cloth fiber bundles, while simultaneously promoting the uniform adhesion of the monolayer reduced graphene oxide sheets and their loaded niobium precursor to the carbon fiber surface. After impregnation, the carbon cloth is removed and dried at 60-80℃ for 4-6 hours, preferably in a vacuum drying oven. This drying temperature effectively removes the solvent without causing premature decomposition of the precursor components or thermal damage to the carbon cloth. After drying, the carbon fiber surface is uniformly loaded with a precursor layer containing niobium, sulfur, nitrogen, and graphene.

[0058] In step S4, the inert atmosphere can be nitrogen or argon, and the gas flow rate is preferably 30-80 mL / min. More preferably, the two-stage calcination is as follows: under an inert atmosphere, the temperature is first raised to 280-320℃ at a heating rate of 3-5℃ / min and held for 1-2 hours, and then the temperature is further raised to 650-700℃ at a heating rate of 3-5℃ / min and held for 3-4 hours to obtain a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode.

[0059] Within the temperature range of 280-320℃, the organic components in the precursor undergo thermal decomposition and gradual volatilization, while the monolayer reduced graphene oxide sheet structure is stabilized, preventing graphene sheet collapse or agglomeration caused by direct high-temperature impact. Furthermore, the niobium precursor is initially converted into amorphous niobium oxide at this stage, and sulfur powder and niobium species undergo preliminary reactions. Controlling the heating rate of the low-temperature pre-calcination at 3-5℃ / min ensures the stable decomposition of organic matter, preventing coating cracking or peeling caused by gas impact due to excessively rapid decomposition.

[0060] Within the temperature range of 650-700℃, the niobium precursor further transforms into a crystalline NbO2 and Nb2O5 composite phase. Sulfur reacts with niobium atoms to form Nb-S bonds, achieving S doping. Nitrogen is simultaneously doped into the niobium oxide lattice or carbon framework, completing S and N co-doping. During high-temperature calcination, lattice defects in monolayer reduced graphene oxide are partially repaired, further improving conductivity. Simultaneously, its wrinkled structure provides strong physical anchoring points for niobium oxide particles. Research shows that two-stage calcination has significant advantages over direct one-step high-temperature calcination: firstly, it allows for precise control of the NbO2 to Nb2O5 phase ratio, avoiding phase segregation that may occur with single high-temperature calcination. Secondly, it can enhance the stability of S and N doping and the bonding strength of Nb-S bonds. Experimental data shows that compared with directly heating to 650-700℃, the Nb-S bond binding energy after two-stage calcination increases from about 161.5 eV to about 162.3 eV, and the bonding strength increases by about 4.8%. Thirdly, low-temperature pre-calcination can pre-decompose organic matter and reduce energy consumption in the high-temperature stage, which can reduce energy consumption by about 15% compared with single high-temperature calcination.

[0061] The composite modified carbon cloth electrode prepared by this invention exhibits excellent comprehensive electrochemical performance in an all-vanadium redox flow battery:

[0062] Regarding conductivity, the four-probe resistivity test results show that the conductivity of the composite modified carbon cloth electrode prepared in this invention can reach around 185 S / cm, which is much higher than that of the unmodified carbon cloth electrode and the control electrode modified with only a single component. This is because rGO coats the surface of the carbon cloth to form a two-dimensional conductive layer, and niobium oxide particles are anchored on the rGO surface to construct a three-dimensional network of points, lines, and surfaces, reducing electron transport resistance by about 49.5%.

[0063] Regarding catalytic activity, the composite modified carbon cloth electrode prepared in this invention was assembled into a vanadium redox flow battery for charge-discharge testing, achieving a charge-discharge ratio of 250 mA / cm². 2 Under high current density conditions, the coulombic efficiency is >95%, the voltage efficiency is >85%, and the energy efficiency is >80%. The high coulombic efficiency indicates that the electrode has good selectivity and reversibility for the redox reaction of vanadium ions. The high voltage efficiency reflects that the electrode has a low polarization overpotential, indicating that S and N co-doping and Nb-S bonded active sites significantly accelerate the reaction kinetics of vanadium ions.

[0064] In terms of long-term cycling stability, the composite modified carbon cloth electrode prepared by this invention exhibits a voltage efficiency decay rate of less than 5% after 1000 charge-discharge cycles, which is significantly better than electrodes prepared using a single dispersant, without S / N co-doping, without a graphene interlayer, or with a single temperature calcination.

[0065] The single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode provided by this invention has excellent conductivity, catalytic activity and structural stability, and can be used as an electrode material in a variety of electrochemical energy storage and energy conversion devices, with broad application prospects.

[0066] In vanadium redox flow battery energy storage systems, the composite modified carbon cloth electrode of this invention can be directly assembled into the battery stack as either a positive or negative electrode, replacing traditional graphite felt or carbon paper electrodes. The monolayer graphene provides a fast electron transport channel, and niobium oxide catalyzes V... 3+ / V 2+ VO 2+ / VO2 + The electrochemical reactions of redox pairs and the porous structure of carbon cloth ensure uniform electrolyte penetration. These three factors work together to improve the battery's energy efficiency, voltage efficiency, and cycle life.

[0067] The composite modified carbon cloth electrode of this invention also shows good application potential in other flow battery energy storage systems. In zinc-bromine flow batteries, this electrode can serve as a positive electrode to catalyze Br₂. - / Br3 - The redox reaction simultaneously inhibits the diffusion and leakage of elemental bromine, improving battery safety and cycle stability. In iron-chromium redox flow batteries, it can serve as the negative electrode, improving the performance of Cr... 3+ / Cr 2+ Addressing the issue of sluggish reaction kinetics and reducing battery polarization losses.

[0068] In the field of supercapacitors, the composite modified carbon cloth electrode of this invention can be directly used to fabricate flexible supercapacitor devices, suitable for energy storage units in wearable electronic devices such as smart bracelets and flexible displays, possessing both high energy density and high power density. Furthermore, this electrode can also serve as the negative electrode of hybrid supercapacitors, matching with positive electrodes of metal oxides such as manganese dioxide and cobalt tetroxide to broaden the operating voltage window and improve the cycle life of the device.

[0069] In the field of hydrogen production by water electrolysis, the composite modified carbon cloth electrode of the present invention can be used as a cathode or anode electrode to replace precious metal catalysts such as platinum and ruthenium oxide, effectively reducing the cost of hydrogen production by water electrolysis and making it suitable for large-scale hydrogen production plants using renewable energy green electricity.

[0070] In the field of metal-air batteries, the composite modified carbon cloth electrode of the present invention can be used as the air electrode of zinc-air batteries, catalyzing the reduction and evolution reactions of oxygen, improving the charge-discharge efficiency and cycle performance of the battery, and is suitable for scenarios such as portable power supplies and backup power supplies for electric vehicles.

[0071] In summary, the single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode provided by this invention, with its unique structural design and excellent comprehensive performance, has important application value and broad industrialization prospects in all-vanadium redox flow batteries and other electrochemical energy storage and conversion systems.

[0072] To further clarify the present invention and its technological advancements, the following description is provided in conjunction with specific embodiments and technical effects.

[0073] Example 1:

[0074] This embodiment provides a method for preparing a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, including the following steps:

[0075] S1: Monolayer reduced graphene oxide was added to a mixed solution of ethanol and hydrochloric acid, followed by the addition of BS-12 and PVP. The mixture was ultrasonically dispersed at 300 W and 40 kHz for 40 min to obtain a dispersion of monolayer reduced graphene oxide. In step S1, the mass ratio of BS-12 to PVP was 0.75:1, and the mass ratio of monolayer reduced graphene oxide to the sum of BS-12 and PVP was 50:35. The volume ratio of ethanol to hydrochloric acid was 20:0.1, and the mass-to-volume ratio of monolayer reduced graphene oxide to the mixed solution was 2.5 mg:1 mL.

[0076] S2: Niobium pentachloride was added to the monolayer reduced graphene oxide dispersion, and the mixture was stirred at 300 rpm for 30 min. Sulfur powder and ascorbic acid were then added, and the mixture was stirred for 20 min. Deionized water was then added, and the mixture was stirred for 10 min to obtain a multi-component impregnation solution. In this step, the mass ratio of niobium pentachloride, sulfur powder, and ascorbic acid was 4:4:1, and the mass ratio of monolayer reduced graphene oxide to niobium source in the monolayer reduced graphene oxide dispersion was 1:4.

[0077] S3: The carbon cloth substrate was ultrasonically cleaned for 30 minutes with acetone, ethanol and deionized water respectively. Then the carbon cloth substrate was immersed in the multi-component impregnation solution obtained in step S2 and impregnated for 120 minutes with an ultrasonic power of 200W. After being removed, it was dried in a vacuum drying oven at 80°C for 5 hours to obtain the carbon cloth substrate loaded with the precursor.

[0078] S4: The carbon cloth substrate with the precursor was placed in a tube furnace. Under a nitrogen atmosphere and a nitrogen flow rate of 50 mL / min, the temperature was first increased to 300℃ at a heating rate of 5℃ / min and held for 1.5 h. Then, the temperature was increased to 680℃ at a heating rate of 5℃ / min and held for 3.5 h to obtain a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, named NbO2 / Nb2O5@rGO / CC.

[0079] Testing revealed that in the NbO2 / Nb2O5@rGO / CC prepared in this embodiment, single rGO accounted for 4 wt%, S and N co-doped niobium oxide composite nanoparticles accounted for 13 wt%, and CC accounted for 83 wt%. In the S and N co-doped niobium oxide composite nanoparticles, the percentage of S doped atoms was 2.1 at%, and the percentage of N doped atoms was 1.4 at%. Furthermore, in the niobium oxide composite nanoparticles, the molar ratio of NbO2 phase to Nb2O5 phase was approximately 1.2:1.

[0080] Example 2:

[0081] This embodiment provides a method for preparing a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, including the following steps:

[0082] S1: Monolayer reduced graphene oxide was added to a mixed solution of ethanol and hydrochloric acid, followed by the addition of CTAB and PEG. The mixture was ultrasonically dispersed at 250 W and 30 kHz for 30 min to obtain a dispersion of monolayer reduced graphene oxide. In this step, the mass ratio of CTAB to PEG was 0.5:1, and the mass ratio of monolayer reduced graphene oxide to the sum of CTAB and PEG was 40:30. The volume ratio of ethanol to hydrochloric acid was 20:0.1, and the mass-to-volume ratio of monolayer reduced graphene oxide to the mixed solution was 2 mg:1 mL.

[0083] S2: Niobium oxalate was added to the monolayer reduced graphene oxide dispersion, and the mixture was stirred at 250 rpm for 35 min. Sulfur powder and citric acid were then added, and the mixture was stirred for 25 min. Deionized water was then added, and the mixture was stirred for 8 min to obtain a multi-component impregnation solution. In this step, the mass ratio of niobium oxalate, sulfur powder, and citric acid was 3:3:0.8, and the mass ratio of monolayer reduced graphene oxide to niobium source in the monolayer reduced graphene oxide dispersion was 1:3.

[0084] S3: The carbon cloth substrate was ultrasonically cleaned for 25 minutes each with acetone, ethanol and deionized water. Then the carbon cloth substrate was immersed in the multi-component impregnation solution obtained in step S2 and impregnated for 100 minutes with an ultrasonic power of 150W. After being removed, it was dried in a vacuum drying oven at 60°C for 4 hours to obtain the carbon cloth substrate loaded with the precursor.

[0085] S4: The carbon cloth substrate supporting the precursor was placed in a tube furnace. Under a nitrogen atmosphere and a nitrogen flow rate of 30 mL / min, the temperature was first increased to 280℃ at a heating rate of 3℃ / min and held for 1 h. Then, the temperature was increased to 650℃ at a heating rate of 3℃ / min and held for 3 h to obtain NbO2 / Nb2O5@rGO / CC.

[0086] Upon testing, the NbO2 / Nb2O5@rGO / CC prepared in this embodiment contained 5 wt% rGO, 20 wt% S and N co-doped niobium oxide composite nanoparticles, and 75 wt% CC. In the S and N co-doped niobium oxide composite nanoparticles, the percentage of S atoms was 1 at% and the percentage of N atoms was 0.5 at%. Furthermore, the molar ratio of NbO2 phase to Nb2O5 phase in the niobium oxide composite nanoparticles was approximately 1:1.

[0087] Example 3:

[0088] This embodiment provides a method for preparing a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, including the following steps:

[0089] S1: Monolayer reduced graphene oxide was added to a mixed solution of ethanol and hydrochloric acid, followed by the addition of PVA and SDS. The mixture was ultrasonically dispersed at 350 W and 50 kHz for 50 min to obtain a dispersion of monolayer reduced graphene oxide. In this step, the mass ratio of PVA to SDS was 1:1, and the mass ratio of monolayer reduced graphene oxide to the sum of PVA and SDS was 60:40. The volume ratio of ethanol to hydrochloric acid was 20:0.2, and the mass-to-volume ratio of monolayer reduced graphene oxide to the mixed solution was 2.5 mg:1 mL.

[0090] S2: Niobium pentachloride was added to the monolayer reduced graphene oxide dispersion, and the mixture was stirred at 250 rpm for 30 min. Sulfur powder and sodium citrate were then added, and the mixture was stirred for 20 min. Deionized water was then added, and the mixture was stirred for 12 min to obtain a multi-component impregnation solution. In this step, the mass ratio of niobium pentachloride, sulfur powder, and sodium citrate was 5:5:1.2, and the mass ratio of monolayer reduced graphene oxide to niobium source in the monolayer reduced graphene oxide dispersion was 1:5.

[0091] S3: The carbon cloth substrate was ultrasonically cleaned for 30 minutes with acetone, ethanol and deionized water respectively. Then the carbon cloth substrate was immersed in the multi-component impregnation solution obtained in step S2 and impregnated for 150 minutes with an ultrasonic power of 180W. After being removed, it was dried in a vacuum drying oven at 70°C for 6 hours to obtain the carbon cloth substrate loaded with the precursor.

[0092] S4: The carbon cloth substrate supporting the precursor was placed in a tube furnace. Under a nitrogen atmosphere and a nitrogen flow rate of 80 mL / min, the temperature was first increased to 320℃ at a heating rate of 4℃ / min and held for 2 h. Then, the temperature was increased to 700℃ at a heating rate of 4℃ / min and held for 4 h to obtain NbO2 / Nb2O5@rGO / CC.

[0093] Testing revealed that in the NbO2 / Nb2O5@rGO / CC prepared in this embodiment, single rGO accounted for 1 wt%, S and N co-doped niobium oxide composite nanoparticles accounted for 9 wt%, and CC accounted for 90 wt%. In the S and N co-doped niobium oxide composite nanoparticles, the percentage of S doping atoms was 3 at% and the percentage of N doping atoms was 2 at%. Furthermore, the molar ratio of NbO2 phase to Nb2O5 phase in the niobium oxide composite nanoparticles was 1.5:1.

[0094] Example 4:

[0095] This embodiment provides a method for preparing a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, including the following steps:

[0096] S1: Monolayer reduced graphene oxide was added to a mixed solution of ethanol and hydrochloric acid, followed by the addition of BS-12 and PVP. The mixture was ultrasonically dispersed at 300 W and 35 kHz for 35 min to obtain a dispersion of monolayer reduced graphene oxide. In this step, the mass ratio of BS-12 to PVP was 0.8:1, and the mass ratio of monolayer reduced graphene oxide to the sum of BS-12 and PVP was 55:37. The volume ratio of ethanol to hydrochloric acid was 20:0.1, and the mass-to-volume ratio of monolayer reduced graphene oxide to the mixed solution was 2.5 mg:1 mL.

[0097] S2: Niobium pentachloride was added to the monolayer reduced graphene oxide dispersion, and the mixture was stirred at 350 rpm for 25 min. Sulfur powder and ascorbic acid were then added, and the mixture was stirred for 15 min. Deionized water was then added, and the mixture was stirred for 9 min to obtain a multi-component impregnation solution. In this step, the mass ratio of niobium pentachloride, sulfur powder, and ascorbic acid was 3.5:4.5:1.1, and the mass ratio of monolayer reduced graphene oxide to niobium source in the monolayer reduced graphene oxide dispersion was 1:3.7.

[0098] S3: The carbon cloth substrate was ultrasonically cleaned for 30 minutes with acetone, ethanol and deionized water respectively. Then the carbon cloth substrate was immersed in the multi-component impregnation solution obtained in step S2 and impregnated for 130 minutes with an ultrasonic power of 190W. After being removed, it was dried in a vacuum drying oven at 75°C for 4.5 hours to obtain the carbon cloth substrate loaded with the precursor.

[0099] S4: The carbon cloth substrate with the supported precursor was placed in a tube furnace. Under a nitrogen atmosphere and a nitrogen flow rate of 55 mL / min, the temperature was first increased to 295℃ at a heating rate of 3℃ / min and held for 1 h. Then, the temperature was increased to 678℃ at a heating rate of 4℃ / min and held for 3.3 h to obtain NbO2 / Nb2O5@rGO / CC.

[0100] Testing revealed that in the NbO2 / Nb2O5@rGO / CC prepared in this embodiment, single rGO accounted for 5 wt%, S and N co-doped niobium oxide composite nanoparticles accounted for 5 wt%, and CC accounted for 90 wt%. In the S and N co-doped niobium oxide composite nanoparticles, the percentage of S doping atoms was 1.9 at% and the percentage of N doping atoms was 0.98 at%. Furthermore, in the niobium oxide composite nanoparticles, the molar ratio of NbO2 phase to Nb2O5 phase was 1.3:1.

[0101] Example 5:

[0102] This embodiment provides a method for preparing a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, including the following steps:

[0103] S1: Monolayer reduced graphene oxide was added to a mixed solution of ethanol and hydrochloric acid, followed by the addition of BS-12 and PVP. The mixture was ultrasonically dispersed at 320 W and 46 kHz for 33 min to obtain a monolayer reduced graphene oxide dispersion. In this step, the mass ratio of BS-12 to PVP was 0.9:1, and the mass ratio of monolayer reduced graphene oxide to the sum of BS-12 and PVP was 56:38. The volume ratio of ethanol to hydrochloric acid was 20:0.1, and the mass-to-volume ratio of monolayer reduced graphene oxide to the mixed solution was 2.5 mg:1 mL.

[0104] S2: Niobium oxalate was added to the monolayer reduced graphene oxide dispersion, and the mixture was stirred at 300 rpm for 30 min. Sulfur powder and ascorbic acid were then added, and the mixture was stirred for 20 min. Deionized water was then added, and the mixture was stirred for 10 min to obtain a multi-component impregnation solution. In this step, the mass ratio of niobium oxalate, sulfur powder, and ascorbic acid was 3.2:4.6:1.2, and the mass ratio of monolayer reduced graphene oxide to niobium source in the monolayer reduced graphene oxide dispersion was 1:3.

[0105] S3: The carbon cloth substrate was ultrasonically cleaned for 30 minutes with acetone, ethanol and deionized water respectively. Then the carbon cloth substrate was immersed in the multi-component impregnation solution obtained in step S2 and impregnated for 140 minutes with an ultrasonic power of 200W. After being removed, it was dried in a vacuum drying oven at 60°C for 6 hours to obtain the carbon cloth substrate loaded with the precursor.

[0106] S4: The carbon cloth substrate supporting the precursor was placed in a tube furnace. Under a nitrogen atmosphere and a nitrogen flow rate of 30 mL / min, the temperature was first increased to 280℃ at a heating rate of 5℃ / min and held for 1.4 h. Then, the temperature was increased to 685℃ at a heating rate of 5℃ / min and held for 3.5 h to obtain NbO2 / Nb2O5@rGO / CC.

[0107] Testing revealed that in the NbO2 / Nb2O5@rGO / CC prepared in this embodiment, single rGO accounted for 3 wt%, S and N co-doped niobium oxide composite nanoparticles accounted for 11 wt%, and CC accounted for 86 wt%. In the S and N co-doped niobium oxide composite nanoparticles, the percentage of S doping atoms was 2.3 at%, and the percentage of N doping atoms was 1.6 at%. Furthermore, in the niobium oxide composite nanoparticles, the molar ratio of NbO2 phase to Nb2O5 phase was 1.1:1.

[0108] Comparative Example 1:

[0109] This comparative example provides a method for preparing a carbon cloth electrode. The difference from Example 1 is that in step S1, only PVP is used as a dispersant, and the amount of BS-12 added is 0. The amount of PVP added in this comparative example is the sum of PVP and BS-12 in Example 1, and the other steps are completely consistent with Example 1.

[0110] Comparative Example 2:

[0111] This comparative example provides a method for preparing a carbon cloth electrode. The difference from Example 1 is that the amount of sulfur powder and ascorbic acid added in step S2 is 0, while the other steps are completely the same as in Example 1.

[0112] Comparative Example 3:

[0113] This comparative example provides a method for preparing a carbon cloth electrode. The difference from Example 1 is that in step S1, no monolayer rGO is added. Instead, BS-12 and PVP are directly added to the ethanol-hydrochloric acid solution before proceeding to the subsequent steps.

[0114] Comparative Example 4:

[0115] This comparative example provides a method for preparing a carbon cloth electrode. The difference from Example 1 is that in step S4, pre-calcination at 300°C is not performed. Instead, the temperature is directly increased to 680°C at 5°C / min and held for 5 hours. The other steps are completely consistent with Example 1.

[0116] Performance testing and analysis:

[0117] The NbO2 / Nb2O5@rGO / CC prepared in Example 1 was observed by scanning electron microscopy, and the results are as follows: Figure 1 As shown. From Figure 1 It is evident that the three-dimensional network structure of carbon cloth fibers supports two forms of S, N co-doped NbO2 / Nb2O5 composite nanoparticles: some nanoparticles are directly loaded onto the surface of the carbon cloth substrate, while others are tightly wrapped by a single-layer reduced graphene oxide (i.e., single-walled reduced graphene oxide) shell, forming obvious wrinkles, and are loaded on the single-layer reduced graphene oxide interlayer. The particle size is between 50nm and 100nm, and the particles are uniformly dispersed without obvious agglomeration. This indicates that the preparation method of this invention can obtain catalytic materials with uniform particle size, effectively avoiding the problem of nanoparticle agglomeration.

[0118] Similarly, the NbO2 / Nb2O5@rGO / CC prepared in Examples 2-5 were observed by scanning electron microscopy, and their microstructures were basically the same as those in Example 1. In all examples, the electrodes formed SN co-doped NbO2 / Nb2O5 nanospheres on the carbon cloth fiber surface, partially encapsulated by a single layer of reduced graphene oxide and partially directly loaded onto the carbon cloth substrate surface. The particle size was distributed in the range of 50nm-100nm, and the particles were uniformly dispersed without obvious agglomeration.

[0119] X-ray diffraction analysis was performed on the NbO2 / Nb2O5@rGO / CC electrodes prepared in Examples 1-5. The results showed that the electrodes prepared in each example exhibited obvious characteristic diffraction peaks of the NbO2 phase, Nb2O5 phase, carbon, and reduced graphene oxide. The above XRD results fully confirm that the method of the present invention successfully achieved the coexistence of the NbO2 phase and the Nb2O5 phase, and that both phases crystallize well, forming a stable composite structure with the carbon substrate and reduced graphene oxide.

[0120] The conductivity of the carbon cloth electrodes prepared in each embodiment and comparative example was tested using a four-probe resistivity meter. Figure 2 As shown, the NbO2 / Nb2O5@rGO / CC electrode prepared in Example 1 exhibits a high electrode conductivity of 185 S / cm. Furthermore, the electrode conductivity measured in Example 2 was 182 S / cm, in Example 3 it was 184 S / cm, in Example 4 it was 183 S / cm, and in Example 5 it was 181 S / cm. The conductivity of all examples remained at a high level above 180 S / cm, significantly higher than that of Examples 1-4, indicating that the multi-phase composite material obtained by the method of this invention possesses good electronic conductivity under different process parameters. The synergistic conductive network of the monolayer reduced graphene oxide interlayer and the NbO2 phase can effectively improve the electron transport efficiency during the vanadium redox flow battery reaction process.

[0121] The carbon cloth electrodes prepared in each embodiment and comparative example were assembled into vanadium redox flow batteries, respectively, at 250 mA / cm². 2 Constant current charge-discharge tests were performed at a current density, and the coulombic efficiency, voltage efficiency, and energy efficiency were recorded.

[0122] like Figure 3 As shown, the NbO2 / Nb2O5@rGO / CC electrode prepared in Example 1 has a current of 250 mA / cm. 2 At the specified current density, the coulombic efficiency reached 96.2%, the voltage efficiency reached 86.5%, and the energy efficiency reached 83.2%. These results indicate that the electrode of Example 1 possesses excellent electronic conductivity and catalytic activity, effectively accelerating the kinetics of vanadium ion redox reaction and reducing battery polarization losses.

[0123] Furthermore, under the same test conditions, the electrode of Example 2 exhibited a coulombic efficiency of 95.8%, a voltage efficiency of 85.9%, and an energy efficiency of 82.3%. The electrode of Example 3 showed a coulombic efficiency of 95.5%, a voltage efficiency of 85.2%, and an energy efficiency of 81.4%. The electrode of Example 4 achieved a coulombic efficiency of 96.0%, a voltage efficiency of 86.1%, and an energy efficiency of 82.7%. The electrode of Example 5 also exhibited a coulombic efficiency of 95.7%, a voltage efficiency of 85.7%, and an energy efficiency of 82.0%. The coulombic efficiency of each example was greater than 95%, the voltage efficiency was greater than 85%, and the energy efficiency was greater than 80%, indicating that the composite modified carbon cloth electrode provided by this invention maintains excellent and stable electrochemical performance under different process conditions.

[0124] The efficiencies of the electrode in Comparative Example 1 were significantly lower than those in the Example, due to poor dispersion and severe agglomeration of niobium oxide particles, resulting in low utilization of catalytic active sites. The efficiencies of the electrode in Comparative Example 2 were also significantly lower than those in the Example, indicating that the lack of S-N co-doping and Nb-S bonded active sites significantly reduced the electrode's catalytic ability for the vanadium ion redox reaction. The electrode in Comparative Example 3 exhibited the lowest efficiencies across all three parameters, indicating that the absence of the monolayer reduced graphene oxide interlayer led to an incomplete conductive network, hindering electron transport. Simultaneously, the weakened interfacial bonding between niobium oxide particles and the carbon cloth substrate affected the overall performance. Although the efficiencies of the electrode in Comparative Example 4 were better than the other comparative examples, they were still lower than those in the Example.

[0125] The composite modified carbon cloth electrodes prepared in each embodiment and comparative example were assembled in an all-vanadium redox flow battery, and the results were obtained at 250 mA / cm². 2 The voltage efficiency was recorded as it decreased with the number of cycles after 1000 charge-discharge cycles at the current density.

[0126] like Figure 4 As shown, the NbO2 / Nb2O5@rGO / CC electrode prepared in Example 1 exhibited excellent long-term cycling stability with a voltage efficiency decay rate of 3.2% after 1000 cycles. Furthermore, under the same test conditions, the NbO2 / Nb2O5@rGO / CC electrode prepared in Example 2 showed a voltage efficiency decay rate of 3.5% after 1000 cycles, while Example 3 showed 3.8%, Example 4 3.4%, and Example 5 3.6%. The voltage efficiency decay rate of each example was controlled within 5%, indicating that the synergistic effect of the monolayer reduced graphene oxide encapsulation and SN co-doping in this invention effectively prevents the shedding and failure of niobium oxide particles during cycling, ensuring the long-term integrity of the electrode structure.

[0127] Under the same test conditions, the voltage efficiency decay rate of Comparative Example 1 was 6.2%, Comparative Example 2 was 7.5%, Comparative Example 3 was 9.1%, and Comparative Example 4 was 5.7%. Comparative Example 3 had the highest decay rate, further confirming the defects of weak adhesion and easy detachment of niobium oxide particles to the carbon cloth substrate without the rGO interlayer. Although the decay rate of Comparative Example 4 was lower than the other comparative examples, it was still significantly higher than that of Example 1, indicating the key role of two-stage calcination in enhancing the adhesion between the coating and the substrate and improving cycle stability.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode, characterized in that, It includes a carbon cloth substrate, an intermediate layer, and an active layer; The intermediate layer is a single layer of reduced graphene oxide coated on the surface of a carbon cloth substrate; The active layer consists of S and N co-doped niobium oxide composite nanoparticles, wherein some of the S and N co-doped niobium oxide composite nanoparticles are loaded on the surface of a carbon cloth substrate, and the other part of the S and N co-doped niobium oxide composite nanoparticles are encapsulated by a single layer of reduced graphene oxide and loaded on an intermediate layer; the S and N co-doped niobium oxide composite nanoparticles contain Nb-S bonds. The niobium oxide composite nanoparticles contain both NbO2 and Nb2O5 phases. 2.The single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode according to claim 1, characterized in that, The monolayer reduced graphene oxide accounts for 1-5 wt% of the total mass of the composite modified carbon cloth electrode, the S and N co-doped niobium oxide composite nanoparticles account for 5-20 wt% of the total mass of the composite modified carbon cloth electrode, and the carbon cloth substrate accounts for 75-90 wt% of the total mass of the composite modified carbon cloth electrode. In S and N co-doped niobium oxide composite nanoparticles, the percentage of S atoms is 1-3 at% and the percentage of N atoms is 0.5-2 at%. In niobium oxide composite nanoparticles, the molar ratio of NbO2 phase to Nb2O5 phase is (1-1.5):

1.

3. A method for preparing the single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode according to any one of claims 1-2, characterized in that, Includes the following steps: S1: Disperse monolayer reduced graphene oxide in a solution, and then add the first dispersant and the second dispersant to obtain a monolayer reduced graphene oxide dispersion; S2: Niobium source, sulfur powder and reducing compound are added to a single-layer reduced graphene oxide dispersion to obtain a multi-component impregnation solution; S3: Immerse the carbon cloth substrate in a multi-component impregnation solution, remove and dry to obtain a carbon cloth substrate loaded with precursor; S4: The carbon cloth substrate with the supported precursor is subjected to a two-stage calcination process under an inert atmosphere, and after cooling, a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode is obtained.

4. The production method according to claim 3, characterized by, In step S1, monolayer reduced graphene oxide is dispersed in a mixed solution of ethanol and hydrochloric acid, and then a first dispersant and a second dispersant are added. The monolayer reduced graphene oxide dispersion is obtained by ultrasonic dispersion treatment. The first dispersant is dodecyl dimethylamine hydantoin, hexadecyl trimethylammonium bromide, or polyvinyl alcohol; the second dispersant is polyvinylpyrrolidone, polyethylene glycol, or sodium dodecyl sulfate.

5. The preparation method according to claim 3, characterized in that, In step S1, the mass ratio of the first dispersant to the second dispersant is (0.5-1):1, and the mass ratio of the monolayer reduced graphene oxide to the sum of the first and second dispersants is (40-60):(30-40).

6. The preparation method according to claim 3, characterized in that, In step S2, the reducing compound is ascorbic acid, citric acid, or sodium citrate; the mass ratio of niobium source, sulfur powder, and reducing compound is (3-5):(3-5):(0.8-1.2), and the mass ratio of monolayer reduced graphene oxide to niobium source in the monolayer reduced graphene oxide dispersion is 1:(3-5). The niobium source is NbCl5 or niobium oxalate.

7. The preparation method according to claim 3, characterized in that, In step S3, before immersing the carbon cloth substrate into the multi-component impregnation solution, the carbon cloth substrate is pretreated with a solvent. Then, the pretreated carbon cloth substrate is immersed in the multi-component impregnation solution and ultrasonically treated at a power of 150-200W for 100-150 minutes. After removal, it is dried at 60-80℃ for 4-5 hours to obtain the carbon cloth substrate loaded with the precursor.

8. The preparation method according to claim 3, characterized in that, In step S4, under an inert atmosphere, the temperature is first increased to 280-320℃ at a heating rate of 3-5℃ / min and held for 1-2 hours. Then, the temperature is increased to 650-700℃ at a heating rate of 3-5℃ / min and held for 3-4 hours to obtain a single-layer reduced graphene oxide / niobium oxide composite modified carbon cloth electrode.

9. The application of a composite modified carbon cloth electrode according to any one of claims 1-2 or a composite modified carbon cloth electrode prepared by the preparation method according to any one of claims 3-8 in a vanadium redox flow battery, a zinc-bromine flow battery, an iron-chromium flow battery, a supercapacitor, a water electrolysis hydrogen production battery, or a metal-air battery.

10. An electrochemical device, characterized by, The composite modified carbon cloth electrode according to any one of claims 1-2 or the composite modified carbon cloth electrode prepared by the preparation method according to any one of claims 3-8; The electrochemical device is a vanadium redox flow battery, a zinc-bromine redox flow battery, an iron-chromium redox flow battery, a supercapacitor, a water electrolysis hydrogen production device, or a metal-air battery.

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