Composite electrode, method for preparing the same, and flow battery

Abstract

The application discloses a composite electrode, a preparation method thereof and a flow battery. The composite electrode comprises a carbon fiber substrate and a nitrogen-doped bismuth-based catalytic material loaded on the surface of the carbon fiber substrate, and the valence of bismuth in the nitrogen-doped bismuth-based catalytic material ranges from 1 to 3. The nitrogen-doped bismuth-based catalyst can maintain a high oxidation state of bismuth sites in long-term cycles, greatly improves the negative electrode kinetic reaction rate and the cycle stability, and effectively solves the problem of catalytic activity attenuation of existing bismuth-based catalysts caused by the reduction of the oxidation state in the reaction process.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a composite electrode, its preparation method, and a flow battery. Background Technology

[0002] Vanadium redox batteries are redox batteries that use vanadium as the active material in a circulating liquid state. They offer significant advantages for large-scale, long-term energy storage, featuring high safety, capacity-power decoupling, long lifespan, and flexible configuration, making them a promising industrial technology. Among these components, the electrodes, acting as vanadium ion reaction carriers, are the core components determining the battery's power density, energy efficiency, and system cost.

[0003] Currently, carbon-based materials have become the mainstream choice for electrodes in vanadium redox flow batteries due to their excellent conductivity, chemical stability, and low cost. However, the surface chemistry of traditional carbon electrodes is inert, and their reaction kinetics with the negative electrode are extremely slow, resulting in high overpotential and low energy efficiency under high current operation.

[0004] Therefore, in related technologies, the overpotential during the conversion of active materials is reduced by loading catalysts on carbon electrodes to improve their electrochemical performance; however, the carbon materials loaded with catalysts in related technologies have low catalyst activity and cannot maintain stability for long-term operation, resulting in limited improvement in the energy efficiency and power density of vanadium redox flow batteries. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a composite electrode, a method for preparing the same, and a flow battery.

[0006] Specifically, the first aspect of this application provides a composite electrode.

[0007] A second aspect of this application also provides a method for preparing the composite electrode described above.

[0008] A third aspect of this application also provides a flow battery including the aforementioned composite electrode.

[0009] The composite electrode according to an embodiment of the first aspect of the present invention comprises: A carbon fiber matrix, and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix; The valence state of bismuth in the nitrogen-doped bismuth-based catalytic material ranges from 1 to 3.

[0010] The composite electrode according to embodiments of the present invention has at least the following beneficial effects: This invention introduces nitrogen-doped bismuth-based materials loaded onto a carbon fiber matrix, thereby regulating the electronic structure (Bi-N local structure) of the bismuth-based catalyst. This effectively improves the stability and utilization of catalytic active sites and optimizes the charge transport performance at the electrode interface. Furthermore, the nitrogen-doped bismuth-based catalyst can maintain a high oxidation state of bismuth sites during long-term cycling, significantly improving the negative electrode kinetic reaction rate and cycle stability. This effectively solves the problem of catalytic activity decay caused by the reduction of oxidation state in existing bismuth-based catalysts during the reaction process.

[0011] According to some embodiments of the present invention, the carbon fiber matrix is ​​a porous carbon fiber electrode; According to some embodiments of the present invention, the porous carbon fiber electrode is any one of graphite felt, carbon felt, carbon cloth, carbon paper and carbon foam.

[0012] Using porous carbon fiber as the matrix, it has advantages such as a high specific surface area to increase active sites, excellent electrochemical activity to promote reaction rate, high effective porosity to ensure electrolyte penetration, good conductivity to reduce internal resistance, and tolerance to strong acid, strong alkali and strong redox environments. It is also inexpensive, has good electrochemical performance and good chemical stability.

[0013] According to some embodiments of the present invention, the percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 0.5% to 1.5%.

[0014] According to some embodiments of the present invention, the percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 0.8% to 1.5%.

[0015] According to some embodiments of the present invention, the percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 0.8% to 1.2%.

[0016] According to some embodiments of the present invention, the percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 1.0% to 1.2%.

[0017] According to some embodiments of the present invention, the percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 1.0%.

[0018] According to some embodiments of the present invention, the percentage content of Bi atoms in the nitrogen-doped bismuth-based catalytic material is 7% to 8%.

[0019] According to some embodiments of the present invention, the percentage content of Bi atoms in the nitrogen-doped bismuth-based catalytic material is 7.5% to 8%.

[0020] According to some embodiments of the present invention, the percentage content of Bi atoms in the nitrogen-doped bismuth-based catalytic material is 7.6% to 8%.

[0021] According to some embodiments of the present invention, the percentage content of Bi atoms in the nitrogen-doped bismuth-based catalytic material is 7.6%.

[0022] According to some embodiments of the present invention, the valence state of bismuth in the nitrogen-doped bismuth-based catalytic material is in the range of 2 to 3.

[0023] According to some embodiments of the present invention, the valence state of bismuth in the nitrogen-doped bismuth-based catalytic material is in the range of 2.5 to 3.

[0024] According to some embodiments of the present invention, the valence state of bismuth in the nitrogen-doped bismuth-based catalytic material is in the range of 2.9 to 3.

[0025] According to some embodiments of the present invention, the valence state range of bismuth in the nitrogen-doped bismuth-based catalytic material is 2.9.

[0026] Due to Bi 0 Due to its susceptibility to oxidation, oxidized Bi sites inevitably form during catalytic reactions. Excessively low oxidation state of Bi sites after the reaction leads to decreased catalytic activity. Oxidized metal sites can optimize the adsorption strength of reaction intermediates and increase electron transfer rates, thereby lowering the energy barrier of redox reactions.

[0027] A method for preparing a composite electrode according to an embodiment of the second aspect of the present invention includes: Heat-treated carbon fibers are obtained by heat treatment. An impregnation solution is prepared by mixing a nitrogen source, a bismuth source, and a solvent. The heat-treated carbon fiber and the impregnation solution are mixed and then thermally decomposed.

[0028] According to some embodiments of the present invention, the atmosphere for the heat treatment includes either air or an oxygen-containing atmosphere.

[0029] According to some embodiments of the present invention, the heating rate of the heat treatment is 1℃ / min to 20℃ / min.

[0030] According to some embodiments of the present invention, the heating rate of the heat treatment is 3°C / min to 10°C / min.

[0031] According to some embodiments of the present invention, the heating rate of the heat treatment is 5°C / min to 8°C / min.

[0032] According to some embodiments of the present invention, the temperature of the heat treatment is 300°C to 800°C.

[0033] According to some embodiments of the present invention, the temperature of the heat treatment is 400°C to 600°C.

[0034] According to some embodiments of the present invention, the temperature of the heat treatment is 450°C to 550°C.

[0035] According to some embodiments of the present invention, the heat treatment holding time is 0.5h to 10h.

[0036] According to some embodiments of the present invention, the heat treatment holding time is 2h to 8h.

[0037] According to some embodiments of the present invention, the heat treatment holding time is 4h to 6h.

[0038] According to some embodiments of the present invention, the molar concentration of nitrogen in the impregnation solution is 0.5 mol / L to 10 mol / L.

[0039] According to some embodiments of the present invention, the molar concentration of nitrogen in the impregnation solution is 2 mol / L to 5 mol / L.

[0040] According to some embodiments of the present invention, the molar concentration of nitrogen in the impregnation solution is 2 mol / L to 3.5 mol / L.

[0041] According to some embodiments of the present invention, the molar concentration of nitrogen in the impregnation solution is 2 mol / L.

[0042] According to some embodiments of the present invention, the molar concentration of bismuth in the impregnation solution is 10 mmol / L to 37 mmol / L.

[0043] According to some embodiments of the present invention, the molar concentration of bismuth in the impregnation solution is 15 mmol / L to 25 mmol / L.

[0044] According to some embodiments of the present invention, the molar concentration of bismuth in the impregnation solution is 19 mmol / L.

[0045] According to some embodiments of the present invention, the mass-volume concentration of the heat-treated carbon fiber and the impregnation solution is 0.005 g / mL to 0.015 g / mL.

[0046] According to some embodiments of the present invention, the mass-volume concentration of the heat-treated carbon fiber and the impregnation solution is 0.01 g / mL to 0.014 g / mL.

[0047] According to some embodiments of the present invention, the mass-volume concentration of the heat-treated carbon fiber and the impregnation solution is 0.012 g / mL to 0.013 g / mL.

[0048] According to some embodiments of the present invention, the mass-volume concentration of the heat-treated carbon fiber and the impregnation solution is 0.0128 g / mL.

[0049] According to some embodiments of the present invention, the nitrogen source includes at least one selected from urea, thiourea, melamine, ammonium chloride, ammonium nitrate, and ammonia monohydrate.

[0050] According to some embodiments of the present invention, the solvent includes at least one of ethylene glycol, ethanol, acetone, N,N-dimethylformamide, dichloroethane, chloroform, and water.

[0051] According to some embodiments of the present invention, the bismuth source includes at least one of bismuth halides and bismuth oxyanions.

[0052] According to some embodiments of the present invention, the bismuth halide is at least one of bismuth fluoride, bismuth chloride, bismuth bromide or bismuth iodide.

[0053] According to some embodiments of the present invention, the bismuth halide is bismuth chloride.

[0054] According to some embodiments of the present invention, the bismuth oxyacid salt is at least one selected from bismuth sulfate, bismuth nitrate, bismuth phosphate, bismuth formate, and bismuth acetate.

[0055] According to some embodiments of the present invention, the bismuth oxyacid salt is bismuth nitrate.

[0056] According to some embodiments of the present invention, the atmosphere for thermal decomposition is either an inert gas or an oxygen-containing atmosphere.

[0057] According to some embodiments of the present invention, the heating rate of the thermal decomposition is 1℃ / min to 20℃ / min.

[0058] According to some embodiments of the present invention, the heating rate of the thermal decomposition is 3°C / min to 10°C / min.

[0059] According to some embodiments of the present invention, the heating rate of the thermal decomposition is 5°C / min to 8°C / min.

[0060] According to some embodiments of the present invention, the temperature of the thermal decomposition is 300°C to 500°C.

[0061] According to some embodiments of the present invention, the temperature of the thermal decomposition is 400°C to 500°C.

[0062] According to some embodiments of the present invention, the holding time for thermal decomposition is 0.5h to 5h.

[0063] According to some embodiments of the present invention, the heat preservation time for thermal decomposition is 1h to 2h.

[0064] According to a third aspect of the invention, a flow battery is also provided.

[0065] According to some embodiments of the present invention, the flow battery includes an all-vanadium redox flow battery.

[0066] According to some embodiments of the present invention, the composite electrode is used as the negative electrode of the flow battery.

[0067] According to some embodiments of the present invention, the all-vanadium redox flow battery further includes a separator.

[0068] According to some embodiments of the present invention, the all-vanadium redox flow battery further includes an electrolyte.

[0069] According to some embodiments of the present invention, the all-vanadium redox flow battery further includes a positive electrode.

[0070] According to some embodiments of the present invention, the separator of the all-vanadium redox flow battery is Nafion-212.

[0071] According to some embodiments of the present invention, the electrolyte of the vanadium redox flow battery is a VOSO4 H2SO4 solution.

[0072] According to some embodiments of the present invention, the positive electrode of the all-vanadium redox flow battery is a heat-treated porous graphite felt. Attached Figure Description

[0073] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0074] Figure 1 The bismuth particle graphite felt (Bi), nitrogen-doped bismuth particle graphite felt (NBi), and heat-treated porous graphite felt (TGF) prepared in Comparative Example 1 and Example 1 of this invention were subjected to a temperature of 5 mV s. -1 Cyclic voltammetry test graph at scan rate.

[0075] Figure 2 These are XPS images of the Bi element in the bismuth particle graphite felt and the nitrogen-doped bismuth particle graphite felt prepared in Comparative Example 1 and Example 1 of this invention.

[0076] Figure 3 This is a SEM image (scale bar is 2 nm) of the nitrogen-doped bismuth particle graphite felt prepared in Example 1.

[0077] Figure 4 This is a SEM image (scale bar is 2 μm) of the nitrogen-doped bismuth particle graphite felt prepared in Example 1.

[0078] Figure 5This is a SEM image (scale bar is 10 μm) of the nitrogen-doped bismuth particle graphite felt prepared in Example 1.

[0079] Figure 6 These are normalized Bi L3-edge XANES spectra of different absorption edge energies of the bismuth particle graphite felt and nitrogen-doped bismuth particle graphite felt prepared in Comparative Example 1 and Example 1 of this invention.

[0080] Figure 7 This is a graph showing the relationship between the Bi oxidation state and the absorption edge energy of the bismuth particle graphite felt and nitrogen-doped bismuth particle graphite felt prepared in Comparative Example 1 and Example 1 of this invention.

[0081] Figure 8 The diagram shows the energy efficiency of the bismuth particle graphite felt prepared in Comparative Example 1 and Example 1 of this invention, with nitrogen-doped bismuth particle graphite felt and heat-treated porous graphite felt serving as negative electrodes to form a full cell, and the cell was tested under charge-discharge cycles at different current densities.

[0082] Figure 9 The bismuth particle graphite felt prepared in Comparative Example 1 and Example 1 of this invention, nitrogen-doped bismuth particle graphite felt and heat-treated porous graphite felt are used as negative electrodes to assemble an all-vanadium redox flow battery, with a speed of 200 mA / cm². 2 Energy efficiency graph after 600 charge-discharge cycles at current density. Detailed Implementation

[0083] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0084] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0085] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0086] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0087] Example 1 This embodiment is a composite electrode, which consists of a carbon fiber matrix and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix.

[0088] The specific parameters for using porous graphite felt as the carbon fiber matrix are as follows: Carbon content (%): >99; Ash content / %: <0.3; Bulk density (g / cm³): 0.08-0.11; Specific surface area / (m² / g): 2.3-4; Felt shedding rate (g / gram of felt): 2-3; Oxidation rate (weight loss / hour @ 600℃ air): ≤3%; Porosity / %: 90-95; Surface resistivity (Ω / cm²): <0.15; Graphite felt for flow battery electrodes; The battery test dimensions are: width (cm): 4x4; thickness (mm): 1.6; The electrochemical test dimensions are: width (cm): 1 x 1.5; thickness (mm): 1.6. In the nitrogen-doped bismuth-based catalytic material, the percentage content of Bi atoms is 7.6%, and the percentage content of N atoms is 1.0%.

[0089] The preparation steps of this composite electrode are as follows: S1. The porous graphite felt is heat-treated at a temperature of 500℃, an initial temperature of 25℃, a heat treatment time of 5h, and a heating rate of 5℃ / min to obtain the heat-treated porous graphite felt. Bismuth nitrate, urea, and ethylene glycol are mixed to prepare an impregnation solution; The concentration of bismuth nitrate solution was 19.0 mmol / L, and the concentration of urea solution was 2.0 mol / L. S2. The heat-treated porous graphite felt is immersed in the impregnation solution and stirred for 1 to 2 hours to obtain the impregnated porous graphite felt. The mass-volume concentration of the heat-treated carbon fiber and the impregnation solution was 0.0128 g / mL. S3. The impregnated porous graphite felt is kept at 500 ℃ for 1 h in air atmosphere. The initial temperature is 25 ℃ and the heating rate is 5 ℃ / min to obtain the composite electrode.

[0090] After natural cooling to room temperature, a nitrogen-doped bismuth-based composite electrode (NBi) is obtained.

[0091] The composite electrode prepared in this embodiment is used as the negative electrode of an all-vanadium battery. The battery preparation process is as follows: The composite electrode prepared in this embodiment is used as the negative electrode, the separator is Nafion-212 separator, and the positive electrode is heat-treated porous graphite felt. Then the positive electrode, negative electrode and separator are assembled. The electrolyte is 45 mL of 1.7 M VOSO4 / 4.7 M H2SO4 electrolyte, and the electrolyte is injected into the battery using a peristaltic pump.

[0092] Example 2 This embodiment is a composite electrode, which consists of a carbon fiber matrix and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix.

[0093] The composite electrode in this embodiment is basically the same as that in Example 1, except that the mass of bismuth pentahydrate nitrate in the nitrogen-doped bismuth-based catalytic material is 0.23 g and the mass of urea is 0.75 g.

[0094] The preparation process of this composite electrode is basically the same as that in Example 1, except that the molar concentration of the urea solution is 0.50 mol / L.

[0095] The composite electrode prepared in this embodiment is used as the negative electrode of an all-vanadium battery, and the battery preparation process is the same as in Example 1.

[0096] Example 3 This embodiment is a composite electrode, which consists of a carbon fiber matrix and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix.

[0097] The composite electrode in this embodiment is basically the same as that in Example 1, except that the mass of bismuth pentahydrate nitrate in the nitrogen-doped bismuth-based catalytic material is 0.23 g and the mass of urea is 5.25 g.

[0098] The preparation process of this composite electrode is basically the same as that in Example 1, except that the molar concentration of the urea solution is 3.50 mol / L.

[0099] The composite electrode prepared in this embodiment is used as the negative electrode of an all-vanadium battery, and the battery preparation process is the same as in Example 1.

[0100] Example 4 This embodiment is a composite electrode, which consists of a carbon fiber matrix and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix.

[0101] The composite electrode in this embodiment is basically the same as that in Example 1, except that the mass of bismuth pentahydrate nitrate in the nitrogen-doped bismuth-based catalytic material is 0.23 g and the mass of urea is 7.5 g.

[0102] The preparation process of this composite electrode is basically the same as that in Example 1, except that the molar concentration of the urea solution is 5.0 mol / L.

[0103] The composite electrode prepared in this embodiment is used as the negative electrode of an all-vanadium battery, and the battery preparation process is the same as in Example 1.

[0104] Example 5 This embodiment is a composite electrode, which consists of a carbon fiber matrix and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix.

[0105] The composite electrode in this embodiment is basically the same as that in Example 1, except that the mass of bismuth pentahydrate nitrate in the nitrogen-doped bismuth-based catalytic material is 0.23 g and the mass of urea is 9.75 g.

[0106] The preparation process of this composite electrode is basically the same as that in Example 1, except that the molar concentration of the urea solution is 6.5 mol / L.

[0107] The composite electrode prepared in this embodiment is used as the negative electrode of an all-vanadium battery, and the battery preparation process is the same as in Example 1.

[0108] Example 6 This embodiment is a composite electrode, which consists of a carbon fiber matrix and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix.

[0109] The composite electrode in this embodiment is basically the same as that in Example 1, except that the mass of bismuth pentahydrate nitrate in the nitrogen-doped bismuth-based catalytic material is 0.23 g and the mass of urea is 12 g.

[0110] The preparation process of this composite electrode is basically the same as that in Example 1, except that the molar concentration of the urea solution is 8.0 mol / L.

[0111] The composite electrode prepared in this embodiment is used as the negative electrode of an all-vanadium battery, and the battery preparation process is the same as in Example 1.

[0112] Example 7 This embodiment is a composite electrode, which consists of a carbon fiber matrix and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix.

[0113] The composite electrode in this embodiment is basically the same as that in Example 1, except that the mass of bismuth pentahydrate nitrate in the nitrogen-doped bismuth-based catalytic material is 0.23 g and the mass of urea is 14.25 g.

[0114] The preparation process of this composite electrode is basically the same as that in Example 1, except that the molar concentration of the urea solution is 9.5 mol / L.

[0115] The composite electrode prepared in this embodiment is used as the negative electrode of an all-vanadium battery, and the battery preparation process is the same as in Example 1.

[0116] Comparative Example 1: This comparative example provides a composite electrode (Bi) composed of a carbon fiber matrix and bismuth oxide material loaded on the carbon fiber matrix, wherein the carbon fiber matrix is ​​a porous graphite felt and the Bi atomic percentage content is 14.6%.

[0117] The preparation process of this composite electrode is basically the same as that in Example 1, except that... In step S2, the precursor solution consisted only of bismuth nitrate solution with a concentration of 19.0 mmol / L. The other conditions and parameters were the same as in Example 1, resulting in the composite electrode (Bi) containing the aforementioned material.

[0118] The composite electrode prepared in this comparative example is used as the negative electrode of an all-vanadium battery, and the battery preparation process is the same as in Example 1.

[0119] Comparative Example 2: This comparative example provides a composite electrode (Bi) composed of a carbon fiber matrix and a nitrogen source material loaded on the carbon fiber matrix, wherein the carbon fiber matrix is ​​a porous graphite felt with a nitrogen atom percentage of 4.55%.

[0120] The preparation process of this composite electrode is basically the same as that in Example 1, except that... In step S2, the precursor solution consists only of urea solution with a concentration of 2.0 mol / L. The other conditions and parameters are the same as in Example 1, resulting in the composite electrode (Bi) containing the aforementioned material.

[0121] The composite electrode prepared in this comparative example is used as the negative electrode of an all-vanadium battery, and the battery preparation process is the same as in Example 1.

[0122] Comparative Example 3 This comparative example provides an electrode (TGF) composed of heat-treated porous graphite felt. The specific parameters of the porous graphite felt used as the carbon fiber matrix are the same as in Example 1.

[0123] The preparation process of this electrode is as follows: The porous graphite felt was subjected to heat treatment with an initial temperature of 25℃, a heat treatment temperature of 500℃, a heat treatment time of 5h, and a heating rate of 5℃ / min.

[0124] Test example: At 400mA / cm respectively 2 350 mA / cm 2 300 mA / cm 2 250 mA / cm 2 200 mA / cm 2 150 mA / cm 2 200 mA / cm 2 The battery was then subjected to charge-discharge cycle tests.

[0125] The concentrations of bismuth nitrate and urea in each group of the examples and the comparative examples are shown in Table 1 below.

[0126] Table 1

[0127] The specific test results are shown in Table 2.

[0128] Table 2

[0129] All relevant data in this embodiment are in the appendix. Figure 1-7 As given in, by Figure 1 The CV results show that the nitrogen-doped Bi-based catalyst exhibits the best electrochemical performance. Figure 2 XPS analysis showed that, compared to Comparative Example 1, the nitrogen-doped Bi-based catalyst obtained in this example exhibited a significant Bi-N coordination peak, proving that nitrogen successfully bonded with bismuth and achieving nitrogen doping modification. Figure 2The XPS spectra shown indicate that the Bi-O characteristic peaks (168 eV~172 eV) in the nitrogen-doped Bi-based catalyst exhibit a significant positive shift in binding energy compared to the Bi-O characteristic peaks (164 eV~166 eV) in the pure bismuth sample catalyst (Bi). This is due to the formation of Bi-N4, which alters the oxidation state and electronic delocalization of Bi atoms. The strong electronegativity difference between N and Bi atoms leads to electron transfer from Bi sites to N sites. This electronic regulation effect not only stabilizes the high valence state of bismuth but also provides the basis for active sites in subsequent electrocatalytic reactions. Furthermore, a distinct Bi-N coordination characteristic peak was observed at 165 eV~167 eV, indicating the formation of a stable Bi-N4 coordination structure on the catalyst surface. This coordination effectively inhibits excessive aggregation and shedding of the bismuth-based active components, allowing the active sites to be stably anchored on the electrode surface, thus exhibiting a uniform loading characteristic in the microstructure. Figure 3-5 SEM images of nitrogen-doped bismuth particle graphite felt prepared in Example 1 at different magnifications. Figure 3 Some nanoparticles showed agglomeration, but the overall coverage remained continuous and uniform. Figure 5 This indicates that the pore size of the nitrogen-doped bismuth particle graphite felt prepared in this application is mainly due to the macropores formed by the arrangement between fibers.

[0130] X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses were performed on the prepared samples, such as... Figure 6 As shown, its electronic structure and local coordination environment can be studied in depth. The Bi L3 edge absorption threshold of the sample is between that of the metallic Bi foil and the Bi2O3 reference sample, proving that the oxidation state of Bi is between 0 and +3 (denoted as Biδ). + ,0<δ<3). Figure 7 Further quantitative fitting results showed that the oxidation state of Bi was approximately +2.9, indicating that the electrode maintained a high oxidation state after redox treatment and did not undergo complete reduction to a low valence or metallic state.

[0131] ICP test results showed that the Bi element loading in the nitrogen-doped bismuth-based composite electrode (NBi) was 5551.39 mg / kg, corresponding to a Bi atomic percentage of 7.6% and a N atomic percentage of 1%; while the undoped Bi control sample had a Bi atomic percentage as high as 14.6%. Although the bismuth loading of the NBi sample was significantly lower than that of the control sample, it still exhibited superior rate performance and long-cycle stability in the all-vanadium redox flow battery. This indicates that nitrogen doping can effectively regulate the dispersion and electronic structure of bismuth, forming highly active Bi-N coordination sites, significantly improving the atomic utilization efficiency and intrinsic catalytic activity of bismuth, thereby achieving efficient and stable electrocatalytic performance at a lower loading.

[0132] As shown in Table 2, there are significant differences in the electrochemical performance of samples with different Bi contents, among which the catalytic performance of Example 1 (NBi electrode) is the best.

[0133] Figure 1 The oxidation and reduction peaks in V correspond to V respectively. 2+ / V 3+ The oxidation and reduction processes of the vanadium redox couple. In this application, a saturated KCl-type Ag / AgCl electrode is used as the reference electrode. To unify the potential reference and facilitate mechanism analysis, the abscissa of the potential of all cyclic voltammetry tests is corrected to the standard hydrogen electrode (SHE). At room temperature (25°C), the reference potential of the Ag / AgCl reference electrode compared to the standard hydrogen electrode is 0.197 V. The peak potential difference (ΔEp) between the two peaks is a key indicator for evaluating the catalytic activity and reversibility of the electrode. The smaller the ΔEp, the higher the catalytic activity of the electrode for the vanadium redox couple reaction. At a scan rate of 5 mVs... -1 Under the specified conditions, the NBi electrode exhibited the smallest peak potential difference, approximately 0.40 V, significantly lower than that of other examples and comparative examples. The reduction in ΔEp indicates that the nitrogen-doped in-situ modified Bi-based catalyst has a significant effect on V... 2+ / V 3+ Electron-coupled reactions exhibit superior catalytic activity.

[0134] Meanwhile, the peak current density directly reflects the reaction kinetic rate: the reduction peak current density of the NBi electrode is -0.1676 mA cm⁻¹. -2 The oxidation peak current density is 0.1509 mA cm⁻¹. -2 All were significantly higher than those of the pure Bi electrode (reduction peak -0.1346 mA cm⁻¹). -2 Oxidation peak at 0.1271 mA cm⁻¹ -2 ) and TGF substrate (reduction peak -0.083 mA cm⁻¹) -2 Oxidation peak at 0.0354 mA cm⁻¹ -2 This indicates that the NBi electrode has a stronger catalytic ability for both the oxidation and reduction of vanadium ions.

[0135] In addition, the current ratio (Io) of the oxidation peak and the reduction peak in the cyclic voltammetry curve pa / I pc The ratio reflects the reversibility of the reaction; the closer this ratio is to 1, the better the reversibility of the reaction. Test data shows that the peak current ratio of the NBi electrode is approximately 0.94, significantly better than other electrodes, further confirming that the Bi-based catalyst in a high oxidation state after N-doping modification can effectively promote V2. 2+ / V 3+The charge transfer process of the redox couple significantly enhances the reaction kinetic rate. The NBi electrode exhibits clear and symmetrical redox peak pairs, along with the smallest peak potential difference, the highest peak current density, and the peak current ratio closest to 1, indicating its excellent electrochemical activity and ability to effectively improve Vo. 2+ / V 3+ Reversibility and kinetics of redox couple reactions.

[0136] The all-vanadium redox flow battery of this invention exhibits significantly higher energy efficiency. Figure 8 Energy efficiency values ​​at different current densities and Figure 9 Long-cycle testing leads to the conclusion that the nitrogen-doped Bi-based particle composite graphite felt electrode prepared in this embodiment exhibits better electrochemical performance compared to the original and activated graphite felt. The high oxidation state of bismuth significantly improves the durability of the composite electrode within the battery.

[0137] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A composite electrode, characterized in that, It includes a carbon fiber matrix and a nitrogen-doped bismuth-based catalytic material supported on the surface of the carbon fiber matrix; The valence state of bismuth in the nitrogen-doped bismuth-based catalytic material ranges from 1 to 3.

2. The composite electrode as described in claim 1, characterized in that, It satisfies at least one of the following characteristics (1) to (2): (1) The carbon fiber matrix is ​​a porous carbon fiber electrode; (2) The porous carbon fiber electrode is any one of graphite felt, carbon felt, carbon cloth, carbon paper and foam carbon.

3. The composite electrode as described in claim 1, characterized in that, It satisfies at least one of the following characteristics (1) to (7): (1) The percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 0.5%~1.5%; (2) The percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 0.8%~1.5%; (3) The percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 0.8%~1.2%; (4) The percentage content of N atoms in the nitrogen-doped bismuth-based catalytic material is 1.0%~1.2%; (5) The percentage content of Bi atoms in the nitrogen-doped bismuth-based catalytic material is 7%~8%; (6) The percentage content of Bi atoms in the nitrogen-doped bismuth-based catalytic material is 7.5%~8%; (7) The percentage content of Bi atoms in the nitrogen-doped bismuth-based catalytic material is 7.6%~8%.

4. The composite electrode as described in claim 1, characterized in that, It satisfies at least one of the following characteristics (1) to (3): (1) The valence state of bismuth in the nitrogen-doped bismuth-based catalytic material is in the range of 2 to 3; (2) The valence state of bismuth in the nitrogen-doped bismuth-based catalytic material is in the range of 2.5 to 3; (3) The valence state of bismuth in the nitrogen-doped bismuth-based catalytic material is in the range of 2.9 to 3.

5. A method for preparing a composite electrode as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Heat-treated carbon fibers are obtained by heat treatment. The heat-treated carbon fiber, nitrogen source, bismuth source, and solvent are mixed and then thermally decomposed.

6. The method for preparing the composite electrode as described in claim 5, characterized in that, It satisfies at least one of the following characteristics (1) to (9): (1) The atmosphere for the heat treatment includes either air or an oxygen-containing atmosphere; (2) The heating rate of the heat treatment is 1℃ / min to 20℃ / min; (3) The heating rate of the heat treatment is 3℃ / min~10℃ / min; (4) The heating rate of the heat treatment is 5℃ / min to 8℃ / min; (5) The temperature of the heat treatment is 300℃~800℃; (6) The temperature of the heat treatment is 400℃~600℃; (7) The temperature of the heat treatment is 450℃~550℃; (8) The heat treatment holding time is 2h~8h; (9) The heat treatment holding time is 4h~6h.

7. The method for preparing the composite electrode as described in claim 5, characterized in that, It satisfies at least one of the following characteristics (1) to (9): (1) The nitrogen source, bismuth source and solvent are mixed to prepare the impregnation solution; The heat-treated carbon fiber and impregnation solution are then mixed and thermally decomposed. (2) The molar concentration of nitrogen in the impregnation solution is 0.5 mol / L to 10 mol / L; (3) The molar concentration of nitrogen in the impregnation solution is 2 mol / L to 5 mol / L; (4) The molar concentration of nitrogen in the impregnation solution is 2 mol / L to 3.5 mol / L; (5) The molar concentration of bismuth in the impregnation solution is 10 mmol / L to 37 mmol / L; (6) The molar concentration of bismuth in the impregnation solution is 15 mmol / L to 25 mmol / L; (7) The mass-volume concentration of the heat-treated carbon fiber and the impregnation solution is 0.005 g / mL to 0.015 g / mL; (8) The mass-volume concentration of the heat-treated carbon fiber and the impregnation solution is 0.01 g / mL to 0.014 g / mL; (9) The mass volume concentration of the heat-treated carbon fiber and the impregnation liquid is 0.012 g / mL to 0.013 g / mL.

8. The method for preparing the composite electrode as described in claim 5, characterized in that, It satisfies at least one of the following characteristics (1) to (7): (1) The solvent includes at least one of ethylene glycol, ethanol, acetone, N,N-dimethylformamide, dichloroethane, chloroform and water; (2) The nitrogen source includes at least one of urea, thiourea, melamine, ammonium chloride, ammonium nitrate, and ammonia monohydrate; (3) The bismuth source includes at least one of bismuth halide and bismuth oxyanion salt; (4) The bismuth halide is at least one of bismuth fluoride, bismuth chloride, bismuth bromide and bismuth iodide; (5) The bismuth halide is bismuth chloride; (6) The bismuth oxyacid salt is at least one of bismuth sulfate, bismuth nitrate, bismuth nitrate pentahydrate, bismuth phosphate, bismuth formate, and bismuth acetate; (7) The bismuth oxyacid salt is bismuth nitrate.

9. The method for preparing the composite electrode as described in claim 5, characterized in that, It satisfies at least one of the following characteristics (1) to (7): (1) The atmosphere of the thermal decomposition process is either an inert gas or an oxygen-containing atmosphere. (2) The heating rate of the thermal decomposition is 3℃ / min~10℃ / min; (3) The heating rate of the thermal decomposition is 5℃ / min~8℃ / min; (4) The temperature of the thermal decomposition is 300℃~500℃; (5) The temperature of the thermal decomposition is 400℃~500℃; (6) The heat preservation time for the thermal decomposition is 0.5h to 5h; (7) The heat preservation time for thermal decomposition is 1h~2h.

10. A flow battery, characterized in that, This includes the composite electrode as described in any one of claims 1 to 4 or the composite electrode prepared by the preparation method as described in any one of claims 5 to 9.

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