Composite graphite felt electrode and preparation method and application thereof

Abstract

The invention discloses a composite graphite felt electrode and a preparation method and application thereof, belongs to the technical field of all-vanadium redox flow battery electrode materials, and constructs a laminated coating formed by alternately depositing amorphous titanium nitride and transition metal nitride on a graphite felt substrate through an atomic layer deposition technology. According to the laminated coating constructed by the invention, a heterojunction is formed at the interface of the amorphous titanium nitride and the transition metal nitride by constructing a heterogeneous interface, so that an interface electronic structure is effectively regulated and controlled, charge separation and transmission efficiency in an electrode reaction process is remarkably promoted, and vanadium ion redox reaction kinetics is greatly improved. Meanwhile, due to the inherent excellent electrical conductivity and chemical stability of titanium nitride and the synergistic effect of the titanium nitride and the transition metal nitride, the electrode shows excellent corrosion resistance and structural stability in strong acid and strong oxidizing environments of the all-vanadium redox flow battery, and the battery is endowed with lower polarization, higher energy efficiency and longer cycle life together.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery electrode materials, specifically to a composite graphite felt electrode and its preparation method and application. Background Technology

[0002] With the rapid increase in the proportion of intermittent renewable energy sources such as wind power and photovoltaics in the global energy structure, the development of large-scale, long-duration, safe, and reliable energy storage technologies has become crucial for supporting new power systems. Vanadium redox flow batteries (VRBs), with their outstanding advantages such as power-capacity decoupling, extremely long cycle life, high safety, and recyclable electrolyte, are considered one of the most promising large-scale energy storage technologies. As the core component of VRBs, the performance of the electrodes directly affects the battery's energy efficiency and cycle stability. Graphite felt is widely used as an electrode material in VRBs, but its inherent hydrophobicity and insufficient surface active sites limit its catalytic activity for vanadium ion redox reactions.

[0003] To address the aforementioned issues, existing modification strategies primarily involve surface modification techniques such as heat treatment and plasma treatment to introduce oxygen-containing functional groups or heteroatoms (N, B, P, etc.) onto the graphite felt surface to improve hydrophilicity and active site density. However, such surface modifications are usually limited to the shallow surface layer; excessive etching can damage the fiber's mechanical properties, and in strong acid and oxidizing environments, oxygen-containing functional groups are easily reduced or hydrolyzed, leading to rapid degradation of electrode activity. Furthermore, some researchers have anchored noble metals, non-noble metal oxides, or carbon-based nanomaterials onto the electrode surface through impregnation-pyrolysis, in-situ polymerization, or electrodeposition to enhance electrocatalytic performance. While these methods can significantly promote charge transfer, they are often complex and costly, and suffer from issues such as catalyst agglomeration and detachment, and noble metal leaching that contaminates the electrolyte, resulting in battery capacity decay and reduced cycle life.

[0004] In recent years, transition metal nitrides have shown great potential in the modification of electrodes for all-vanadium redox flow batteries due to their unique electronic structure and noble metal-like catalytic properties. Among them, titanium nitride has attracted widespread attention for its high conductivity, excellent mechanical strength, and good corrosion resistance. However, nitride-modified graphite felt electrodes prepared by existing methods still face problems such as insufficient exposure of active sites and low electron conduction efficiency due to the difficulty in constructing uniform, dense, and precisely composed and thickness-controllable coatings on complex three-dimensional substrates and the lack of effective means to control the coating structure. This severely limits the stability and electrocatalytic efficiency of nitride-modified graphite felt electrodes at high current densities. Summary of the Invention

[0005] This invention provides a composite graphite felt electrode, its preparation method, and its application. It effectively solves the technical problem that existing methods of modifying graphite felt electrodes with nitrides still result in insufficient exposure of active sites and low electronic conduction efficiency. This invention utilizes atomic layer deposition technology to form a uniform, dense titanium nitride-based composite coating with precise composition and controllable thickness on the three-dimensional porous fiber surface of graphite felt, thereby effectively improving the hydrophilicity, electrochemical activity, and long-term stability of graphite felt.

[0006] The first objective of this invention is to provide a composite graphite felt electrode in which an amorphous titanium nitride layer and a transition metal nitride layer are alternately deposited on the surface of a graphite felt substrate, and a heterojunction is formed at the interface between the amorphous titanium nitride layer and the transition metal nitride layer to form a stacked coating of amorphous titanium nitride and transition metal nitride.

[0007] The thickness of the multilayer coating is 5 nm to 100 nm.

[0008] The transition metal nitride is selected from at least one of vanadium nitride, zirconium nitride, niobium nitride, tantalum nitride, hafnium nitride, and molybdenum nitride.

[0009] A second objective of this invention is to provide a method for preparing the composite graphite felt electrode described above, comprising the following steps: At 80℃~150℃, using graphite felt as the substrate and titanium source precursor as the raw material, the titanium source precursor is adsorbed onto the surface of graphite felt through atomic layer deposition, and then pulsed nitriding is performed with plasma of the first nitrogen-hydrogen mixed gas. The atomic layer deposition and pulsed nitriding of the first nitrogen-hydrogen mixed gas plasma are alternately cycled to form an amorphous titanium nitride layer.

[0010] Using a transition metal source precursor as raw material, the transition metal source precursor is deposited on the surface of the amorphous titanium nitride layer by atomic layer deposition, and then pulsed nitriding is performed by a second nitrogen-hydrogen mixed gas plasma. The atomic layer deposition and the second nitrogen-hydrogen mixed gas plasma pulsed nitriding are alternately cycled to form a transition metal nitride layer, thus obtaining a composite graphite felt electrode.

[0011] At temperatures ranging from 80°C to 150°C, titanium precursor molecules can directly react with active groups, such as -OH, on the surface of graphite felt to form a chemisorbed monolayer and release byproducts. This reaction is self-limiting; it automatically stops once the surface active sites are saturated. Heating provides sufficient driving force, and applying additional power would disrupt the layer-by-layer controllability of the reaction.

[0012] The nitrogen-hydrogen mixture of this invention requires the application of plasma. Nitrogen molecules have extremely strong chemical bonds and cannot react effectively with the surface at the process temperature. Plasma is needed to dissociate N2 into highly reactive nitrogen atoms or ions, which can then react with the metal intermediates adsorbed on the surface to achieve nitriding.

[0013] Before atomic layer deposition, the graphite felt undergoes pretreatment, specifically: commercial graphite felt is ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 5-30 minutes, and then dried in a vacuum oven at 80°C for 12 hours to remove surface impurities, resulting in a pretreated graphite felt substrate. The pretreated graphite felt substrate is then stabilized by first evacuating the deposition equipment to a vacuum state and then maintaining a temperature of 60°C-150°C for 30-120 minutes to achieve in-situ heat treatment of the substrate, removing impurities and volatile organic compounds adsorbed on the substrate surface, while simultaneously activating the fiber surface and enhancing its adsorption capacity for various deposition precursors.

[0014] In addition, before atomic deposition, the titanium source precursor, the transition metal source precursor, the first nitrogen source, and the second nitrogen source need to be stabilized. Specifically, the titanium source precursor, the first nitrogen source, the transition metal source precursor, and the second nitrogen source are placed in bubble flasks, and the temperature of the bubble flasks depends on the selected precursor.

[0015] When the titanium source precursor is titanium tetrachloride, the temperature of the bubbling flask is controlled at slightly above room temperature (30℃~40℃); when the titanium source precursor is tetra(dimethylamino)titanium, the temperature of the bubbling flask is controlled at 50℃~80℃; when the titanium source precursor is isopropyl titanate, the temperature of the bubbling flask is controlled at 60℃~90℃.

[0016] The nitrogen source precursor is a nitrogen-hydrogen mixed gas plasma, requiring no special temperature setting for the bubbling flask (room temperature is sufficient). When a nitrogen-hydrogen mixed gas plasma is selected as the nitrogen source precursor, the pulse duration is 0.5s to 5.0s. During the pulse, a plasma generator with a power of 100W to 300W needs to be activated simultaneously to generate stable nitrogen-hydrogen plasma. This invention, by precisely controlling the alternating deposition cycles of amorphous titanium nitride layers and transition metal nitride layers, as well as the feed ratio of each precursor within a single cycle, can precisely control the total thickness, stacked structure, and component gradient distribution of the composite coating at the nanoscale. This preparation method exhibits excellent repeatability and controllability, providing a powerful technical platform for the directional design and controllable preparation of vanadium redox flow battery electrode performance.

[0017] In the transition metal source precursors, when the vanadium source precursor is vanadium pentachloride, its bubbling flask temperature is controlled at 80℃~120℃; when the vanadium source precursor is vanadium acetylacetonate, it is controlled at 100℃~140℃; when the zirconium source precursor is tetrakis(diethylamino)zirconium, its bubbling flask temperature is controlled at 50℃~80℃; when the niobium source precursor is niobium pentachloride, its bubbling flask temperature is controlled at 120℃~150℃; when the tantalum source precursor is tert-butylimide tris(ethylmethylamino)tantalum, its bubbling flask temperature is controlled at 40℃~60℃; when the hafnium source precursor is tetrakis(dimethylamino)hafnium, its bubbling flask temperature is controlled at 120℃~150℃; and when the molybdenum source precursor is molybdenum pentachloride, its bubbling flask temperature is controlled at 120℃~150℃.

[0018] In a preferred embodiment, the vapor pulse flow rates of both the titanium source precursor and the transition metal source precursor are 50 sccm to 200 sccm, and the flow rates of both the first nitrogen-hydrogen mixture and the second nitrogen-hydrogen mixture are 20 sccm to 100 sccm.

[0019] In a preferred embodiment, the volume ratio of nitrogen to hydrogen in the first nitrogen-hydrogen mixture and the second nitrogen-hydrogen mixture is 1 to 4:1.

[0020] In a preferred embodiment, during the preparation of the amorphous titanium nitride layer, the alternating cycles of atomic layer deposition and pulsed nitridation of the first nitrogen-hydrogen mixed gas plasma are 10 to 500 times.

[0021] During the preparation of the transition metal nitride layer, the alternating cycles of atomic layer deposition and pulsed nitridation of the second nitrogen-hydrogen mixed gas plasma are 1 to 100 times.

[0022] In a preferred embodiment, the preparation process of the amorphous titanium nitride layer and the transition metal nitride layer is repeated alternately, and the number of alternating repetitions is from 1 to 500.

[0023] In a preferred embodiment, the titanium source precursor is titanium tetrachloride, tetra(dimethylamino)titanium, or isopropyl titanate; the transition metal source precursor is selected from at least one of vanadium pentachloride, vanadium acetylacetonate, tetra(diethylamino)zirconium, niobium pentachloride, tert-butylimide tris(ethylmethylamino)tantalum, tetra(dimethylamino)hafnium, and molybdenum pentachloride.

[0024] In a preferred embodiment, after adsorbing the titanium source precursor onto the graphite felt surface by atomic layer deposition, argon purging is performed for 10s to 60s; after pulsed nitriding by the first nitrogen-hydrogen mixed gas plasma, argon purging is performed for 5s to 30s; after depositing the transition metal source precursor onto the surface of the amorphous titanium nitride layer by atomic layer deposition, argon purging is performed for 10s to 60s; after pulsed nitriding by the second nitrogen-hydrogen mixed gas plasma, argon purging is performed for 5s to 30s.

[0025] In a preferred embodiment, the purging is performed using argon gas with a flow rate of 100 sccm to 300 sccm.

[0026] A third objective of this invention is to provide an application of the composite graphite felt electrode described in any of the above claims as the negative electrode of a vanadium redox flow battery.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a composite graphite felt electrode, which utilizes atomic layer deposition (ALD) technology to construct a multilayer coating of alternating deposits of amorphous titanium nitride and transition metal nitride on a graphite felt substrate. Unlike electrocatalysts used in traditional vanadium redox flow batteries, the multilayer coating constructed in this invention creates a heterojunction at the interface between the titanium nitride and transition metal nitride layers, effectively regulating the interfacial electronic structure and significantly promoting charge separation and transport efficiency during the electrode reaction process, thereby greatly enhancing the vanadium ion redox reaction kinetics. Simultaneously, the inherent excellent conductivity and chemical stability of titanium nitride, combined with the synergistic effect of the transition metal nitride, enable the electrode to exhibit superior corrosion resistance and structural stability in the strong acid and oxidizing environment of vanadium redox flow batteries, collectively contributing to lower polarization, higher energy efficiency, and longer cycle life.

[0028] This invention utilizes atomic layer deposition (ALD) technology to controllably prepare composite coatings of amorphous titanium nitride and transition metal nitrides. The composite coating exhibits long-range disorder and short-range order, revealing more unsaturated coordination sites and defects than the crystalline phase. These defects serve as highly active catalytic or adsorption sites, effectively enhancing the electrocatalytic performance of vanadium ion redox reactions. Simultaneously, the isotropic nature of the amorphous phase facilitates uniform ion transport and adsorption within the composite coating. Based on the self-limiting surface reaction and layer-by-layer growth mechanism unique to ALD technology, this invention forms a uniform, dense, and shape-preserving composite coating on the complex three-dimensional porous structure of graphite felt, perfectly replicating the microstructure of graphite felt and overcoming the technical challenge of uneven coverage in deep pores and recessed areas encountered by traditional loading methods. Furthermore, this process enables strong interfacial chemical bonding between the coating and the graphite felt fiber surface, effectively suppressing the dissolution and detachment of the active coating during long-term liquid flow erosion and intense electrochemical cycling, providing a crucial guarantee for the long-life operation of the device. Attached Figure Description

[0029] Figure 1 This is a process flow diagram for the fabrication of the composite graphite felt electrode of the present invention.

[0030] Figure 2 The images are scanning electron microscope (SEM) images of electrodes prepared in Examples 1, 3, and Comparative Examples 1 to 3 of the present invention at different magnifications; wherein, a and f are Comparative Example 1; b and g are Comparative Example 2; c and h are Comparative Example 3; d and i are Example 1; e and j are Example 3.

[0031] Figure 3 The images show scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) elemental analysis diagrams of the composite graphite felt electrode prepared in Example 1 of this invention.

[0032] Figure 4 The image shows a high-resolution transmission electron microscope image and Fourier transform result of the conductive carbon powder carried in the furnace according to Example 1 of the present invention.

[0033] Figure 5 The images show contact angle test results of electrodes prepared in Example 1 and Comparative Examples 1 to 3 of the present invention; where a is Comparative Example 1, b is Comparative Example 2, c is Comparative Example 3, and d is Example 1. Detailed Implementation

[0034] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0035] In response to the issues mentioned in the background section of this invention, when modifying graphite felt electrodes using existing nitride modification methods, it is difficult to achieve uniform, dense, and precisely controlled composition and thickness coatings on complex three-dimensional graphite felt substrates. Effective means of controlling the coating structure are lacking, and current research mostly focuses on single titanium nitride materials or simple elemental doping, still facing problems such as insufficient exposure of active sites and low electronic conduction efficiency. This severely limits its stability and electrocatalytic efficiency at high current densities. Based on the above technical problems, this invention provides a composite graphite felt electrode, its preparation method, and its applications.

[0036] The technical solution of the present invention will be analyzed and described in detail below.

[0037] This invention first provides a composite graphite felt electrode. On the surface of a graphite felt substrate, alternating layers of amorphous titanium nitride and transition metal nitride are deposited, and a heterojunction is formed at the interface between the amorphous titanium nitride and transition metal nitride layers, forming a multilayer coating of amorphous titanium nitride and transition metal nitride, thus obtaining the composite graphite felt electrode. The electronic structure is controlled by utilizing the heterojunction formed at the interface. By precisely controlling the total thickness of the multilayer coating to 5nm–100nm, problems such as incomplete coverage and insufficient catalytic activity due to excessive thinness, and increased impedance and coating peeling due to excessive thickness are effectively avoided, resulting in a high-performance composite graphite felt electrode. When the thickness is less than 5nm, the coating is difficult to continuously cover, and the number of heterojunctions is insufficient, leading to weakened substrate protection and limited improvement in catalytic performance. When the thickness is greater than 100nm, the ion / electron transport resistance is significantly increased, and the coating is prone to cracking and peeling due to internal stress, and the preparation cost is too high.

[0038] The transition metal nitride is selected from at least one of vanadium nitride, zirconium nitride, niobium nitride, tantalum nitride, hafnium nitride, and molybdenum nitride.

[0039] In the above technical solution, this invention constructs a multilayer coating of alternating depositions of amorphous titanium nitride and transition metal nitrides on a graphite felt substrate. The multilayer coating constructed by this invention forms a heterogeneous interface at the interface between titanium nitride and transition metal nitrides, effectively regulating the interface electronic structure and significantly promoting charge separation and transport efficiency during the electrode reaction process, thereby greatly improving the kinetics of vanadium ion redox reactions. Due to the inherent excellent conductivity and chemical stability of titanium nitride, its synergistic effect with transition metal nitrides enables the electrode to exhibit excellent corrosion resistance and structural stability in the strong acid and strong oxidizing environment of a vanadium redox flow battery, jointly contributing to lower polarization, higher energy efficiency, and longer cycle life.

[0040] The technical effects of the present invention will be described below with reference to specific embodiments and comparative examples.

[0041] Example 1 A method for preparing a composite graphite felt electrode, such as Figure 1 As shown, it includes the following steps: Step S1: The commercial graphite felt was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 15 min each, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, resulting in pretreated graphite felt. The pretreated graphite felt was fixed on the sample holder of the atomic layer deposition equipment, ensuring it was fully spread out. The deposition equipment was first evacuated to a vacuum state (5 × 10⁻⁶). - 4The substrate was subjected to in-situ heat treatment at 100°C for 30 minutes. The temperature of the titanium source precursor (titanium tetrachloride) was controlled at 40°C, and the temperature of the zirconium source precursor (tetra(diethylamino)zirconium) was controlled at 70°C. The nitrogen source precursor was a plasma of a nitrogen-hydrogen mixture with a volume ratio of 2:1, where the nitrogen flow rate was 40 sccm and the hydrogen flow rate was 20 sccm.

[0042] Step S2: Control the chamber temperature to 120℃ and perform 20 deposition cycles of amorphous titanium nitride layer. The single deposition process is as follows: High-purity argon gas is used to pulse titanium tetrachloride vapor at a flow rate of 100 sccm into the reaction chamber for 0.2 s, allowing the titanium source precursor to be fully adsorbed on the graphite felt surface; the titanium source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 150W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced, and the stable nitrogen-hydrogen mixture plasma is introduced into the reaction chamber for a pulse time of 2.0 s, reacting with the chemically adsorbed titanium source precursor to generate titanium nitride and release byproducts; the plasma generator power is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, obtaining an amorphous titanium nitride layer.

[0043] Step S3: Switch to the zirconium source precursor and continue with 5 more zirconium nitride deposition cycles. The single deposition process is as follows: use high-purity argon gas to pulse tetra(diethylamino)zirconium vapor at a flow rate of 80 sccm into the reaction chamber for 0.05 s to allow the zirconium source precursor to be fully adsorbed; turn off the zirconium source precursor and purge with high-purity argon gas at a flow rate of 150 sccm for 30 s to remove excess precursor and byproducts from the chamber; turn on the 150W plasma generator and purge with a nitrogen-hydrogen mixture of the above volume ratio of 2:1, and send the stable nitrogen-hydrogen mixture plasma into the reaction chamber for 1.0 s to react with the chemically adsorbed zirconium source precursor to generate zirconium nitride and release byproducts; turn off the plasma generator and purge with high-purity argon gas at a flow rate of 150 sccm for 30 s to remove excess reactants and byproducts, thus obtaining the zirconium nitride layer.

[0044] Step S4: Alternately repeat steps S2 and S3, repeating them 20 times each, for a total of 500 deposition cycles, to prepare an in-situ laminated coating of 15 nm thick amorphous titanium nitride and zirconium nitride layers.

[0045] Step S5: After deposition, high-purity nitrogen gas is continuously introduced and purged for 30 minutes at the deposition temperature to ensure that the reactants in the chamber are completely removed; the sample is taken out after it is naturally cooled to room temperature in the chamber to obtain the composite graphite felt electrode.

[0046] Example 2 A method for preparing a composite graphite felt electrode includes the following steps: Step S1: The commercial graphite felt was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 15 min each, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, resulting in pretreated graphite felt. The pretreated graphite felt was fixed on the sample holder of the atomic layer deposition equipment, ensuring it was fully spread out. The deposition equipment was first evacuated to a vacuum state (5 × 10⁻⁶). - 4 The substrate was subjected to in-situ heat treatment at 100℃ for 30 minutes. The bubbling flask containing the titanium source precursor (titanium tetrachloride) was maintained at 40℃, and the bubbling flask containing the niobium source precursor (niobium pentachloride) was maintained at 140℃. The nitrogen source precursor was a plasma containing a nitrogen-hydrogen mixture with a volume ratio of 2:1, where the nitrogen flow rate was 60 sccm and the hydrogen flow rate was 30 sccm.

[0047] Step S2: Control the chamber temperature at 150℃ and perform 30 deposition cycles of titanium nitride layer. The single deposition process is as follows: High-purity argon gas is used to pulse titanium tetrachloride vapor at a flow rate of 100 sccm into the reaction chamber for 0.2 s, allowing the titanium source precursor to be fully adsorbed on the graphite felt surface; the titanium source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 200W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced, and the stable nitrogen-hydrogen mixture plasma is sent into the reaction chamber for a pulse time of 2.0 s, reacting with the chemically adsorbed titanium source precursor to generate titanium nitride and release byproducts; the plasma generator power is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, obtaining an amorphous titanium nitride layer.

[0048] Step S3: Switch to the niobium source precursor and continue with 10 niobium nitride deposition cycles. The single deposition process is as follows: High-purity argon gas is used to pulse niobium pentachloride vapor at a flow rate of 120 sccm into the reaction chamber for 0.1 s to allow the niobium source precursor to be fully adsorbed; the niobium source precursor is turned off, and high-purity nitrogen gas at a flow rate of 150 sccm is continuously purged for 45 s to remove excess precursor and byproducts from the chamber; a 150 W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced to deliver the stable nitrogen-hydrogen mixture plasma into the reaction chamber for 1.0 s to react with the chemically adsorbed niobium source precursor, generating niobium nitride and releasing byproducts; the plasma generator is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, resulting in the niobium nitride layer.

[0049] Step S4: Alternately repeat steps S2 and S3, repeating them 20 times each, for a total of 800 deposition cycles, to prepare an in-situ 20nm thick amorphous titanium nitride and zirconium nitride laminated coating.

[0050] Step S5: After deposition, high-purity nitrogen gas is continuously introduced and purged for 30 min at the deposition temperature to ensure that the reactants in the chamber are completely removed; the sample is taken out after it is naturally cooled to room temperature in the chamber to obtain the composite graphite felt electrode.

[0051] Example 3 A method for preparing a composite graphite felt electrode includes the following steps: Step S1: The commercial graphite felt was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 15 min each, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, resulting in pretreated graphite felt. The pretreated graphite felt was fixed on the sample holder of the atomic layer deposition equipment, ensuring it was fully spread out. The deposition equipment was first evacuated to a vacuum state (5 × 10⁻⁶). - 4 The substrate was subjected to in-situ heat treatment at 100℃ for 30 minutes. The bubbling flask containing the titanium source precursor (titanium tetrachloride) was maintained at 40℃, and the bubbling flask containing the molybdenum source precursor (molybdenum pentachloride) was maintained at 140℃. The nitrogen source precursor was a plasma containing a nitrogen-hydrogen mixture with a volume ratio of 2:1, where the nitrogen flow rate was 60 sccm and the hydrogen flow rate was 30 sccm.

[0052] Step S2: Control the chamber temperature at 150℃ and perform 20 deposition cycles of titanium nitride layer. The single deposition process is as follows: High-purity argon gas is used to pulse titanium tetrachloride vapor at a flow rate of 100 sccm into the reaction chamber for 0.2 s to allow the titanium source precursor to be fully adsorbed on the graphite felt surface; the titanium source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 150W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced to deliver the stable nitrogen-hydrogen mixture plasma into the reaction chamber for a pulse time of 5.0 s to react with the chemically adsorbed titanium source precursor, generating titanium nitride and releasing byproducts; the plasma generator power is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, resulting in an amorphous titanium nitride layer.

[0053] Step S3: Switch to the molybdenum source precursor and continue with 5 more molybdenum nitride deposition cycles. The single deposition process is as follows: Molybdenum pentachloride vapor at a flow rate of 120 sccm is pulsed into the reaction chamber using high-purity argon gas for 0.15 s to allow the molybdenum source precursor to be fully adsorbed; the molybdenum source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 250W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced to deliver the stable nitrogen-hydrogen mixture plasma into the reaction chamber for 3.0 s to react with the chemically adsorbed molybdenum source precursor, generating molybdenum nitride and releasing byproducts; the plasma generator is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, resulting in the molybdenum nitride layer.

[0054] Step S4: Alternately repeat steps S2 and S3, repeating each step 30 times, for a total of 750 deposition cycles, to prepare an in-situ laminated coating of amorphous titanium nitride and zirconium nitride with a thickness of 35 nm.

[0055] Step S5: After deposition, high-purity nitrogen gas is continuously introduced and purged for 30 min at the deposition temperature to ensure that the reactants in the chamber are completely removed; the sample is taken out after it is naturally cooled to room temperature in the chamber to obtain the composite graphite felt electrode.

[0056] To further illustrate the technical effects of the present invention, comparative examples are also provided, as follows: Comparative Example 1 The difference from Example 1 is that the blank control group used pretreated graphite felt as the electrode.

[0057] Commercial graphite felt was ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 15 min in sequence, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, thus obtaining a pretreated graphite felt electrode.

[0058] Comparative Example 2 Compared with Example 1, the difference is that only an amorphous titanium nitride layer is deposited, that is, in step S2, the number of titanium nitride deposition cycles is 500; steps S3 to S4 are omitted. Thus, a graphite felt electrode modified with an amorphous single titanium nitride coating with a thickness of 20 nm can be obtained in situ.

[0059] A method for preparing a composite graphite felt electrode includes the following steps: Step S1: The commercial graphite felt was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 15 min each, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, resulting in pretreated graphite felt. The pretreated graphite felt was fixed on the sample holder of the atomic layer deposition equipment, ensuring it was fully spread out. The deposition equipment was first evacuated to a vacuum state (5 × 10⁻⁶). - 4 The substrate was subjected to in-situ heat treatment at 100°C for 30 minutes. The temperature of the titanium source precursor (titanium tetrachloride) was controlled at 40°C, and the temperature of the zirconium source precursor (tetra(diethylamino)zirconium) was controlled at 70°C. The nitrogen source precursor was a plasma of a nitrogen-hydrogen mixture with a volume ratio of 2:1, where the nitrogen flow rate was 40 sccm and the hydrogen flow rate was 20 sccm.

[0060] Step S2: Control the chamber temperature at 120℃ and perform 500 deposition cycles of amorphous titanium nitride layer. The single deposition process is as follows: High-purity argon gas is used to pulse titanium tetrachloride vapor at a flow rate of 100 sccm into the reaction chamber for 0.2 s, allowing the titanium source precursor to be fully adsorbed on the graphite felt surface; the titanium source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 150W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced, and the stable nitrogen-hydrogen mixture plasma is introduced into the reaction chamber for a pulse time of 2.0 s, reacting with the chemically adsorbed titanium source precursor to generate titanium nitride and release byproducts; the plasma generator power is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, obtaining an amorphous titanium nitride layer.

[0061] Step S5: After deposition, high-purity nitrogen gas is continuously introduced and purged for 30 minutes at the deposition temperature to ensure that the reactants in the chamber are completely removed; the sample is taken out after it is naturally cooled to room temperature in the chamber to obtain the composite graphite felt electrode.

[0062] Comparative Example 3 The difference compared to Example 1 is that a multilayer coating of crystalline titanium nitride and zirconium nitride is prepared.

[0063] A method for preparing a composite graphite felt electrode includes the following steps: Step S1: The commercial graphite felt was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 15 min each, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, resulting in pretreated graphite felt. The pretreated graphite felt was fixed on the sample holder of the atomic layer deposition equipment, ensuring it was fully spread out. The deposition equipment was first evacuated to a vacuum state (5 × 10⁻⁶). - 4 The substrate was subjected to in-situ heat treatment at 100°C for 30 minutes. The temperature of the titanium source precursor (titanium tetrachloride) was controlled at 40°C, and the temperature of the zirconium source precursor (tetra(diethylamino)zirconium) was controlled at 70°C. The nitrogen source precursor was a plasma of a nitrogen-hydrogen mixture with a volume ratio of 2:1, where the nitrogen flow rate was 40 sccm and the hydrogen flow rate was 20 sccm.

[0064] Step S2: Control the chamber temperature to 120℃ and perform 20 deposition cycles of amorphous titanium nitride layer. The single deposition process is as follows: High-purity argon gas is used to pulse titanium tetrachloride vapor at a flow rate of 100 sccm into the reaction chamber for 0.2 s, allowing the titanium source precursor to be fully adsorbed on the graphite felt surface; the titanium source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 150W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced, and the stable nitrogen-hydrogen mixture plasma is introduced into the reaction chamber for a pulse time of 2.0 s, reacting with the chemically adsorbed titanium source precursor to generate titanium nitride and release byproducts; the plasma generator power is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, obtaining an amorphous titanium nitride layer.

[0065] Step S3: Switch to the zirconium source precursor and continue with 5 more zirconium nitride deposition cycles. The single deposition process is as follows: use high-purity argon gas to pulse tetra(diethylamino)zirconium vapor at a flow rate of 80 sccm into the reaction chamber for 0.05 s to allow the zirconium source precursor to be fully adsorbed; turn off the zirconium source precursor and purge with high-purity argon gas at a flow rate of 150 sccm for 30 s to remove excess precursor and byproducts from the chamber; turn on the 150W plasma generator and purge with a nitrogen-hydrogen mixture of the above volume ratio of 2:1, and send the stable nitrogen-hydrogen mixture plasma into the reaction chamber for 1.0 s to react with the chemically adsorbed zirconium source precursor to generate zirconium nitride and release byproducts; turn off the plasma generator and purge with high-purity argon gas at a flow rate of 150 sccm for 30 s to remove excess reactants and byproducts, thus obtaining the zirconium nitride layer.

[0066] Step S4: Alternately repeat steps S2 and S3, repeating them 20 times each, for a total of 500 deposition cycles, to prepare an in-situ laminated coating of 15 nm thick amorphous titanium nitride and zirconium nitride layers.

[0067] Step S5: After deposition, high-purity nitrogen gas is continuously introduced and purged for 30 minutes at the deposition temperature to ensure that the reactants in the chamber are completely removed; the sample is taken out after it is naturally cooled to room temperature in the chamber to obtain the primary composite graphite felt electrode.

[0068] Step S6: In a nitrogen atmosphere, the primary composite graphite felt electrode is heated to 500℃ at 5℃ / min and held for 1h to prepare a crystalline titanium nitride and zirconium nitride stacked coating modified composite graphite felt electrode with a thickness of 15nm.

[0069] Comparative Example 4 The difference compared to Example 2 is that a multilayer coating of crystalline titanium nitride and niobium nitride is prepared.

[0070] A method for preparing a composite graphite felt electrode includes the following steps: Step S1: The commercial graphite felt was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 15 min each, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, resulting in pretreated graphite felt. The pretreated graphite felt was fixed on the sample holder of the atomic layer deposition equipment, ensuring it was fully spread out. The deposition equipment was first evacuated to a vacuum state (5 × 10⁻⁶). - 4The substrate was subjected to in-situ heat treatment at 100℃ for 30 minutes. The bubbling flask containing the titanium source precursor (titanium tetrachloride) was maintained at 40℃, and the bubbling flask containing the niobium source precursor (niobium pentachloride) was maintained at 140℃. The nitrogen source precursor was a plasma containing a nitrogen-hydrogen mixture with a volume ratio of 2:1, where the nitrogen flow rate was 60 sccm and the hydrogen flow rate was 30 sccm.

[0071] Step S2: Control the chamber temperature at 150℃ and perform 30 deposition cycles of titanium nitride layer. The single deposition process is as follows: High-purity argon gas is used to pulse titanium tetrachloride vapor at a flow rate of 100 sccm into the reaction chamber for 0.2 s, allowing the titanium source precursor to be fully adsorbed on the graphite felt surface; the titanium source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 200W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced, and the stable nitrogen-hydrogen mixture plasma is sent into the reaction chamber for a pulse time of 2.0 s, reacting with the chemically adsorbed titanium source precursor to generate titanium nitride and release byproducts; the plasma generator power is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, obtaining an amorphous titanium nitride layer.

[0072] Step S3: Switch to the niobium source precursor and continue with 10 niobium nitride deposition cycles. The single deposition process is as follows: High-purity argon gas is used to pulse niobium pentachloride vapor at a flow rate of 120 sccm into the reaction chamber for 0.1 s to allow the niobium source precursor to be fully adsorbed; the niobium source precursor is turned off, and high-purity nitrogen gas at a flow rate of 150 sccm is continuously purged for 45 s to remove excess precursor and byproducts from the chamber; a 150 W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced to deliver the stable nitrogen-hydrogen mixture plasma into the reaction chamber for 1.0 s to react with the chemically adsorbed niobium source precursor, generating niobium nitride and releasing byproducts; the plasma generator is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, resulting in the niobium nitride layer.

[0073] Step S4: Alternately repeat steps S2 and S3, repeating them 20 times each, for a total of 800 deposition cycles, to prepare an in-situ 20nm thick amorphous titanium nitride and zirconium nitride laminated coating.

[0074] Step S5: After deposition, high-purity nitrogen gas is continuously introduced and purged for 30 min at the deposition temperature to ensure that the reactants in the chamber are completely removed; the sample is taken out after it is naturally cooled to room temperature in the chamber to obtain the primary composite graphite felt electrode.

[0075] Step S6: In a nitrogen atmosphere, the primary composite graphite felt electrode is heated to 500℃ at 5℃ / min and held for 1h to prepare a crystalline titanium nitride and niobium nitride stacked coating modified composite graphite felt electrode with a thickness of 20nm.

[0076] Comparative Example 5 The difference compared to Example 3 is that a multilayer coating of crystalline titanium nitride and molybdenum nitride was prepared.

[0077] A method for preparing a composite graphite felt electrode includes the following steps: Step S1: The commercial graphite felt was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 15 min each, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, resulting in pretreated graphite felt. The pretreated graphite felt was fixed on the sample holder of the atomic layer deposition equipment, ensuring it was fully spread out. The deposition equipment was first evacuated to a vacuum state (5 × 10⁻⁶). - 4 The substrate was subjected to in-situ heat treatment at 100℃ for 30 minutes. The bubbling flask containing the titanium source precursor (titanium tetrachloride) was maintained at 40℃, and the bubbling flask containing the molybdenum source precursor (molybdenum pentachloride) was maintained at 140℃. The nitrogen source precursor was a plasma containing a nitrogen-hydrogen mixture with a volume ratio of 2:1, where the nitrogen flow rate was 60 sccm and the hydrogen flow rate was 30 sccm.

[0078] Step S2: Control the chamber temperature at 150℃ and perform 20 deposition cycles of titanium nitride layer. The single deposition process is as follows: High-purity argon gas is used to pulse titanium tetrachloride vapor at a flow rate of 100 sccm into the reaction chamber for 0.2 s to allow the titanium source precursor to be fully adsorbed on the graphite felt surface; the titanium source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 150W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced to deliver the stable nitrogen-hydrogen mixture plasma into the reaction chamber for a pulse time of 5.0 s to react with the chemically adsorbed titanium source precursor, generating titanium nitride and releasing byproducts; the plasma generator power is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, resulting in an amorphous titanium nitride layer.

[0079] Step S3: Switch to the molybdenum source precursor and continue with 5 more molybdenum nitride deposition cycles. The single deposition process is as follows: Molybdenum pentachloride vapor at a flow rate of 120 sccm is pulsed into the reaction chamber using high-purity argon gas for 0.15 s to allow the molybdenum source precursor to be fully adsorbed; the molybdenum source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 250W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced to deliver the stable nitrogen-hydrogen mixture plasma into the reaction chamber for 3.0 s to react with the chemically adsorbed molybdenum source precursor, generating molybdenum nitride and releasing byproducts; the plasma generator is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, resulting in the molybdenum nitride layer.

[0080] Step S4: Alternately repeat steps S2 and S3, repeating each step 30 times, for a total of 750 deposition cycles, to prepare an in-situ laminated coating of amorphous titanium nitride and zirconium nitride with a thickness of 35 nm.

[0081] Step S5: After deposition, high-purity nitrogen gas is continuously introduced and purged for 30 min at the deposition temperature to ensure that the reactants in the chamber are completely removed; the sample is taken out after it is naturally cooled to room temperature in the chamber to obtain the primary composite graphite felt electrode.

[0082] Step S6: In a nitrogen atmosphere, the primary composite graphite felt electrode is heated to 500℃ at 5℃ / min and held for 1h to prepare a crystalline composite graphite felt electrode modified with a titanium nitride and molybdenum nitride stacked coating with a thickness of 35nm.

[0083] Comparative Example 6 Compared with Example 1, the difference is that in step S3, only the pulse and purge of the zirconium source precursor are performed, while the pulse purge of the nitrogen source is omitted. The other preparation processes are completely consistent with Example 1. Finally, a zirconium-doped titanium nitride composite coating modified graphite felt electrode with a thickness of 14 nm was prepared.

[0084] A method for preparing a zirconium-doped titanium nitride composite graphite felt electrode includes the following steps: Step S1: The commercial graphite felt was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 15 min each, and then dried in a vacuum oven at 80°C for 12 h to remove surface impurities, resulting in pretreated graphite felt. The pretreated graphite felt was fixed on the sample holder of the atomic layer deposition equipment, ensuring it was fully spread out. The deposition equipment was first evacuated to a vacuum state (5 × 10⁻⁶). - 4The substrate was subjected to in-situ heat treatment at 100°C for 30 minutes. The temperature of the titanium source precursor (titanium tetrachloride) was controlled at 40°C, and the temperature of the zirconium source precursor (tetra(diethylamino)zirconium) was controlled at 70°C. The nitrogen source precursor was a plasma of a nitrogen-hydrogen mixture with a volume ratio of 2:1, where the nitrogen flow rate was 40 sccm and the hydrogen flow rate was 20 sccm.

[0085] Step S2: Control the chamber temperature to 120℃ and perform 20 deposition cycles of amorphous titanium nitride layer. The single deposition process is as follows: High-purity argon gas is used to pulse titanium tetrachloride vapor at a flow rate of 100 sccm into the reaction chamber for 0.2 s, allowing the titanium source precursor to be fully adsorbed on the graphite felt surface; the titanium source precursor is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess precursor and byproducts from the chamber; a 150W plasma generator is turned on, and a nitrogen-hydrogen mixture with a volume ratio of 2:1 is introduced, and the stable nitrogen-hydrogen mixture plasma is introduced into the reaction chamber for a pulse time of 2.0 s, reacting with the chemically adsorbed titanium source precursor to generate titanium nitride and release byproducts; the plasma generator power is turned off, and high-purity argon gas at a flow rate of 150 sccm is continuously purged for 30 s to remove excess reactants and byproducts, obtaining an amorphous titanium nitride layer.

[0086] Step S3: Switch to the zirconium source precursor and perform 5 pulse-purge cycles containing only the zirconium source precursor. The single operation process of the cycle is as follows: use high-purity argon to pulse tetra(diethylamino)zirconium vapor at a flow rate of 100 sccm into the reaction chamber for a pulse duration of 0.05 s to allow the zirconium source precursor to be fully adsorbed; turn off the zirconium source precursor and purge with high-purity argon at a flow rate of 150 sccm for 30 s to remove excess precursor and byproducts from the chamber.

[0087] Step S4: Alternately repeat steps S2 and S3, repeating each step 20 times, for a total of 500 deposition cycles, to prepare a zirconium-doped titanium nitride composite coating with a thickness of 14 nm in situ.

[0088] Step S5: After deposition, high-purity nitrogen gas is continuously introduced and purged for 30 minutes at the deposition temperature to ensure that the reactants in the chamber are completely removed; the sample is taken out after it is naturally cooled to room temperature in the chamber to obtain zirconium-doped titanium nitride composite graphite felt electrode.

[0089] The morphology and properties of the composite graphite felt electrodes prepared in Examples 1 to 3 and the electrodes prepared in Comparative Examples 1 to 6 of the present invention were characterized, and the results are as follows.

[0090] 1. Scanning electron microscopy tests at different resolutions were performed on the electrode materials described in Examples 1, 3, 1, 2, and 3.

[0091] like Figure 2 As shown in the low-magnification observations, all samples modified by atomic layer deposition (ALD) (Examples 1, 3, Comparative Examples 2 and 3) completely retained the three-dimensional porous structure of the graphite felt, and the fiber surface exhibited a uniform variation in light and dark contrast, indicating that ALD technology can achieve uniform coating coverage on complex three-dimensional structures. In the high-magnification observations, the surface of the unmodified graphite felt fiber in Comparative Example 1 was smooth, while the surface roughness of the carbon fibers in all samples modified by ALD (Examples 1, 3, Comparative Examples 2 and 3) increased significantly. Furthermore, in Comparative Example 3, the carbon fiber surface modified with the annealed crystalline titanium nitride / zirconium nitride laminated composite coating showed a relatively continuous and dense sheet-like coating layer, directly demonstrating that ALD technology can form a uniform film with good shape preservation on complex substrates.

[0092] 2. Elemental analysis of the electrode material described in Example 1 was performed using an energy dispersive spectrometer.

[0093] like Figure 3 As shown in Example 1, titanium, zirconium, and nitrogen elements exhibit a uniformly dispersed signal distribution on the surface of graphite felt carbon fibers, confirming the successful construction of a uniformly covered titanium nitride / zirconium nitride composite coating on the three-dimensional fiber surface using atomic layer deposition (ALD). Simultaneously, only trace amounts of oxygen were detected, and their distribution characteristics were highly consistent with the composite coating, indicating that oxygen interference was effectively eliminated during the deposition process. This uniformly distributed trace oxygen is attributed to the high specific surface area of ​​the deposited amorphous nano-coating, which readily adsorbs oxygen and moisture when exposed to the atmosphere, forming an extremely thin surface oxide layer. These results fully demonstrate that, based on the unique self-limiting surface reaction and layer-by-layer growth mechanism of ALD, this invention can form a uniform, dense, and shape-preserving composite coating on the surface of the complex three-dimensional porous structure of graphite felt, perfectly replicating the microstructure of graphite felt and overcoming the technical challenge of uneven coverage in deep pores and recessed areas using traditional loading methods.

[0094] 3. The electrode material described in Example 1 was characterized by transmission electron microscopy and selected-area Fourier transform.

[0095] like Figure 4As shown, the amorphous titanium nitride / zirconium nitride composite coating obtained in Example 1 has a uniform thickness, averaging approximately 15 nm, consistent with the expected coating thickness set by the atomic layer deposition cycle number, indicating that this method possesses excellent thickness controllability. No obvious lattice fringes were observed in the high-resolution transmission image of this coating, and the Fourier transform results of the selected area showed a diffuse halo-like diffraction pattern, jointly confirming the successful in-situ preparation of the amorphous composite coating. These results fully demonstrate that by precisely controlling the alternating deposition cycle number of the titanium nitride layer and the transition metal nitride layer, as well as the feed ratio of each precursor within a single cycle, the present invention can precisely control the total thickness, stacked structure, and component distribution of the composite coating at the nanoscale, exhibiting good process repeatability. This provides a reliable technical platform for the directional design and controllable preparation of vanadium redox flow battery electrode performance.

[0096] 4. Water contact angle tests were performed on the electrode materials described in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0097] like Figure 5 As shown, the contact angle of the unmodified graphite felt is 143.06°, exhibiting hydrophobicity. Although titanium nitride is inherently hydrophobic, the hydrophilicity of the titanium nitride-based composite coatings prepared by atomic layer deposition (ALD) is significantly improved. This is due to the self-limiting surface reaction and layer-by-layer growth mechanism unique to ALD technology. This mechanism allows the coating to form a uniform, dense, and well-form-preserving film on the surface of the complex three-dimensional porous structure of the graphite felt, laying the structural foundation for optimizing hydrophilicity. Among them, Example 1, by constructing rich heterogeneous interfaces, has better hydrophilicity than Comparative Example 2 with a single structure, ultimately reaching a superhydrophilic state. Its amorphous coating surface also spontaneously forms hydrophilic titanium oxide or titanium oxynitride thin layers, which, combined with the "hydrophilic amplification effect" of nanoscale roughness, provides a smooth liquid-solid interface for vanadium ion transport. In contrast, the crystalline sample of Comparative Example 3, after annealing, has reduced surface active sites due to the high-temperature annealing treatment. Although its hydrophilicity is better than that of the unmodified graphite felt, it is lower than that of the deposited sample. The above results fully demonstrate that amorphous structures can enhance hydrophilicity through surface hydrophilic layers and nanoscale roughness, while the introduction of heterogeneous interfaces can further optimize hydrophilicity by regulating the electronic structure of the interface. The two work together to improve the mass transfer performance of vanadium ions.

[0098] 5. Using the electrode materials prepared in the comparative examples and embodiments above as negative electrodes, and uniformly using the unmodified graphite felt electrode material described in Comparative Example 1 as the positive electrode, assemble an all-vanadium redox flow battery and test it under the same conditions (100 mA / cm²). 2 Constant current charge-discharge tests were performed on the battery, and the coulombic efficiency, voltage efficiency, and energy efficiency of the battery were recorded. The energy efficiency of the battery after 500 cycles was also recorded, as shown in Table 1.

[0099] Table 1. Electrode performance of embodiments and comparative examples of the present invention. As shown in Table 1, compared with the unmodified graphite felt electrode of Comparative Example 1, all graphite felt electrodes modified by atomic layer deposition (Examples 1-3, Comparative Examples 2-6) showed significant improvements in key indicators such as coulombic efficiency, voltage efficiency, and energy efficiency when assembled into vanadium redox flow batteries. This is due to the self-limiting surface reaction and layer-by-layer growth mechanism of atomic layer deposition, which allows the coating to form a uniform and dense conformal layer on the complex three-dimensional porous structure of the graphite felt, and to form a strong interfacial chemical bond with the fiber surface. This effectively inhibits the dissolution and detachment of the active coating during long-term scouring and intense electrochemical cycling. The energy efficiency after 500 cycles is still significantly better than that of the unmodified graphite felt. Among them, Examples 1-3 precisely controlled the interfacial electronic structure by constructing a titanium nitride / transition metal nitride heterostructure interface. The amorphous structure of Examples 1-3 accelerates charge separation and transport, significantly improving the kinetics of vanadium ion redox reactions, achieving energy efficiencies of 90.1%, 90.5%, and 89.9%, respectively. These efficiencies are significantly superior to the single titanium nitride layer in Comparative Example 3 and the element-doped structure in Comparative Example 4. Furthermore, after 500 cycles, these efficiencies maintain energy efficiencies of 86%, 86.5%, and 85.3%, respectively, demonstrating optimal performance stability. Meanwhile, the amorphous coatings of Examples 1-3, due to their long-range disorder and short-range order, expose more unsaturated coordination sites and defects than crystalline phases. Their isotropic nature facilitates uniform ion transport and adsorption within the coating, resulting in significantly better performance than the corresponding crystalline electrodes of Comparative Examples 3-5. This advantage further expands after 500 cycles, showcasing the superior cycling stability of amorphous structures. These results indicate that the synergy between amorphous structure design and heterogeneous interface engineering is a key technological approach to achieving high-performance all-vanadium redox flow battery electrodes. The amorphous composite coating constructed by the present invention through atomic layer deposition technology has the core advantages of improved electrocatalytic kinetics, enhanced structural stability, and precise and controllable preparation, providing comprehensive protection for the efficient and long-term operation of batteries.

[0100] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A composite graphite felt electrode, characterized in that, The composite graphite felt electrode is formed by alternately depositing amorphous titanium nitride layers and transition metal nitride layers on the surface of a graphite felt substrate, and forming a heterojunction at the interface between the amorphous titanium nitride layer and the transition metal nitride layer, thus forming a multilayer coating of amorphous titanium nitride and transition metal nitride. The thickness of the multilayer coating is 5 nm to 100 nm; The transition metal nitride is selected from at least one of vanadium nitride, zirconium nitride, niobium nitride, tantalum nitride, hafnium nitride, and molybdenum nitride.

2. A method for preparing the composite graphite felt electrode according to claim 1, characterized in that, Includes the following steps: At 80℃~150℃, using graphite felt as the substrate and titanium source precursor as the raw material, the titanium source precursor is adsorbed onto the surface of graphite felt by atomic layer deposition, and then pulsed nitriding is performed by plasma of the first nitrogen-hydrogen mixed gas. The atomic layer deposition and pulsed nitriding of the first nitrogen-hydrogen mixed gas plasma are alternately cycled to form an amorphous titanium nitride layer. Using a transition metal source precursor as raw material, the transition metal source precursor is deposited on the surface of the amorphous titanium nitride layer by atomic layer deposition, and then pulsed nitriding is performed by a second nitrogen-hydrogen mixed gas plasma. The atomic layer deposition and the second nitrogen-hydrogen mixed gas plasma pulsed nitriding are alternately cycled to form a transition metal nitride layer, thus obtaining a composite graphite felt electrode.

3. The method for preparing the composite graphite felt electrode according to claim 2, characterized in that, The vapor pulse flow rates of the titanium source precursor and the transition metal source precursor are both 50 sccm to 200 sccm, and the flow rates of the first nitrogen-hydrogen mixture and the second nitrogen-hydrogen mixture are both 20 sccm to 100 sccm.

4. The method for preparing the composite graphite felt electrode according to claim 3, characterized in that, In the first nitrogen-hydrogen mixture and the second nitrogen-hydrogen mixture, the volume ratio of nitrogen to hydrogen is 1 to 4:

1.

5. The method for preparing the composite graphite felt electrode according to claim 2, characterized in that, During the preparation of the amorphous titanium nitride layer, the alternating cycles of atomic layer deposition and pulsed nitridation of the first nitrogen-hydrogen mixed gas plasma are 10 to 500 times. During the preparation of the transition metal nitride layer, the alternating cycles of atomic layer deposition and pulsed nitridation of the second nitrogen-hydrogen mixed gas plasma are 1 to 100 times.

6. The method for preparing the composite graphite felt electrode according to claim 2, characterized in that, The preparation process of the amorphous titanium nitride layer and the transition metal nitride layer is repeated alternately, and the number of alternating repetitions is from 1 to 500.

7. The method for preparing the composite graphite felt electrode according to claim 2, characterized in that, The titanium source precursor is titanium tetrachloride, tetra(dimethylamino)titanium, or isopropyl titanate; the transition metal source precursor is selected from at least one of vanadium pentachloride, vanadium acetylacetonate, tetra(diethylamino)zirconium, niobium pentachloride, tert-butylimide tri(ethylmethylamino)tantalum, tetra(dimethylamino)hafnium, and molybdenum pentachloride.

8. The method for preparing the composite graphite felt electrode according to claim 2, characterized in that, After adsorbing the titanium source precursor onto the graphite felt surface by atomic layer deposition, purging with argon gas for 10s to 60s; after pulsed nitriding with the first nitrogen-hydrogen mixed gas plasma, purging with argon gas for 5s to 30s; after depositing the transition metal source precursor onto the surface of the amorphous titanium nitride layer by atomic layer deposition, purging with argon gas for 10s to 60s; after pulsed nitriding with the second nitrogen-hydrogen mixed gas plasma, purging with argon gas for 5s to 30s.

9. The method for preparing the composite graphite felt electrode according to claim 8, characterized in that, All purging was performed using argon gas with a flow rate of 100 sccm to 300 sccm.

10. The application of the composite graphite felt electrode of claim 1 as the negative electrode of a vanadium redox flow battery.

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