A Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on graphite felt for use in all-vanadium redox flow batteries

Abstract

This invention belongs to the field of vanadium redox flow battery materials and discloses a Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a graphite felt for vanadium redox flow batteries: using Bi(NO3)3∙5H2O as the Bi source, CuSO4∙5H2O as the Cu source, and C4H6O6 as the complexing agent to form a Bi-containing electrode. 3+ Complex and Cu 2+ A Cu-doped Bi₂O₃ precursor electrode was prepared in situ on a graphite mat using an alkaline electrodeposition solution for the complex and a constant-voltage electrodeposition method. After the first charge in a vanadium redox flow battery, a Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on the graphite mat was obtained. This invention also discloses a method for preparing a vanadium redox flow battery by adjusting the Cu doping level in the Cu-doped oxide-derived Bi electrocatalyst to control the electronic structure of metallic Bi. When the Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a graphite mat prepared by this invention is used as the negative electrode in a vanadium redox flow battery, the battery exhibits excellent rate performance and power output, as well as excellent long-cycle stability. Simultaneously, it can effectively reduce the stack size under the same power output conditions, thereby reducing system costs. Furthermore, the preparation method of this electrode has good economic and environmental friendliness.

Description

Technical Field

[0001] This invention belongs to the field of flow battery electrode materials and electrochemical energy storage technology, specifically relating to a method for preparing a Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a graphite felt and its application in an all-vanadium redox flow battery. Background Technology

[0002] Vanadium redox flow batteries utilize vanadium ions in different valence states as the positive and negative electrode active materials, offering advantages such as high safety, independently designable power and capacity, long cycle life, and suitability for large-scale energy storage. They are among the most promising flow battery systems for industrialization. However, the large-scale application of vanadium redox flow batteries is currently constrained by high system costs, with the stack cost accounting for a significant portion. Improving the energy efficiency and power density of the battery at high current densities can help reduce the stack size while maintaining output power, thereby lowering system costs.

[0003] Graphite felt is widely used as an electrode material in vanadium redox flow batteries due to its good electrical conductivity, acid corrosion resistance, and low cost. However, the surface of commercial graphite felt is unsuitable for the negative electrode side V... 2+ / V 3+ The limited catalytic activity of redox reactions easily leads to slow reaction kinetics and increased polarization at the negative electrode, thus limiting the battery's rate performance, power density, and electrolyte utilization. Existing methods for modifying graphite felt electrodes mainly include acid treatment, heat treatment, and catalyst loading modification. However, these methods still suffer from problems such as high wastewater treatment pressure, high energy consumption, harsh process conditions, insufficient precision in controlling active sites, and limited performance improvement at high current densities, making it difficult to meet the Va requirements of the negative electrode side in vanadium redox flow batteries. 2+ / V 3+ Redox reactions necessitate the application of highly active and stable electrode materials.

[0004] Bismuth-based catalysts are used as anodes in vanadium redox flow batteries due to their high hydrogen evolution overpotential, good stability, and high catalytic activity. Current modifications of bismuth-based catalysts mainly focus on adjusting morphology and dispersibility, while controllable regulation of the electronic structure of bismuth sites remains lacking.

[0005] Therefore, it is necessary to provide a bismuth-based electrocatalytic electrode with controllable electronic structure to effectively enhance the effect of metallic Bi on V. 2+ / V 3+ The intrinsic catalytic activity of redox reactions improves the anode reaction kinetics and high power density operation performance of vanadium redox flow batteries. Summary of the Invention

[0006] The purpose of this invention is to provide an in-situ reconstructed Cu-doped oxide-derived Bi electrocatalyst electrode on graphite felt, its preparation method, and its application in an all-vanadium redox flow battery, in order to solve the problem of the limitations of existing graphite felt anodes on V... 2+ / V 3+ Problems include insufficient catalytic activity in redox reactions, large negative electrode polarization, and low battery power density at high current densities.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a graphite felt, comprising a conductive substrate and a Cu-doped oxide-derived Bi electrocatalyst supported on the surface of the conductive substrate; the Cu-doped oxide-derived Bi electrocatalyst is formed by in-situ reconstruction of a Cu-doped Bi2O3 precursor through electrochemical reduction.

[0009] Preferably, the conductive substrate is graphite felt. The electrocatalyst can be nanoparticles uniformly dispersed on the surface of graphite felt fibers.

[0010] Preferably, the Cu / Bi atomic ratio in the electrocatalyst is 1.49% to 4.45%. Within this range, the main structure of the bismuth-based active phase can be maintained, while the charge redistribution induced by Cu doping can enhance the electron-deficient characteristics of Bi sites.

[0011] A second aspect of the present invention provides a method for preparing a Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on the graphite felt, comprising the following steps:

[0012] (1) Preparation of electrodeposition solution: Bismuth nitrate pentahydrate (Bi(NO3)3∙5H2O), tartaric acid (C4H6O6), and copper sulfate pentahydrate (CuSO4∙5H2O) are dissolved in potassium hydroxide (KOH) aqueous solution to form a solution containing Bi. 3+ Complexes and Cu 2+ Alkaline electrodeposition solution for complexes;

[0013] (2) Electrodeposition preparation of Cu-doped Bi2O3 precursor electrode grown in situ on the surface of graphite felt: In the electrodeposition solution, graphite felt is used as the electrode and constant voltage method is used for electrodeposition to grow Cu-doped Bi2O3 precursor in situ on the surface of graphite felt.

[0014] (3) In-situ reconstruction: The Cu-doped Bi2O3 precursor electrode grown in situ on the obtained graphite felt surface is used as the negative electrode of the all-vanadium redox flow battery. During the first charging process of the all-vanadium redox flow battery, irreversible electrochemical reduction occurs in the acidic vanadium electrolyte to form the Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on the graphite felt.

[0015] Preferably, in step (1), Bi 3+ The concentration is 0.1 mol L. -1 Tartaric acid concentration was 0.20~0.30 mol / L.-1 Cu 2+ Concentration range: 0.003~0.020 mol L -1 .

[0016] Preferably, in step (2), the electrodeposition solution is preheated to 65°C before electrodeposition; the deposition voltage is determined to be 1.5~2.5 V using a linear sweep voltammetry method. During the electrodeposition process, Cu... 2+ By partially substituting Bi in the bismuth oxide lattice 3+ It enters the precursor structure and is accompanied by the formation of oxygen vacancies.

[0017] Preferably, in step (3), the first charge is carried out in a full vanadium redox flow battery in an acidic electrolyte. The Cu-doped Bi2O3 precursor is reduced at about -0.1 V (relative to the Ag / AgCl reference electrode) and transformed into a Cu-doped oxide-derived Bi active phase with metallic bismuth as the main component and retaining some residual oxygen structure.

[0018] A third aspect of this invention provides the application of the Cu-doped oxide-derived Bi electrocatalyst electrode in a vanadium redox flow battery, specifically, using it as the negative electrode in a vanadium redox flow battery to catalyze V. 2+ / V 3+ Redox reaction. Beneficial effects

[0019] (1) The present invention constructs a Cu-doped oxide-derived Bi active phase on the surface of graphite felt through the technical route of "precursor electrodeposition-first charge in-situ reconstruction", which avoids the problems of poor catalyst adhesion, insufficient dispersion, introduction of binder to increase electrode resistance and cover catalytic active sites in traditional loading methods.

[0020] (2) The synergistic effect of Cu doping and residual oxygen in oxide-derived metals not only enhances the electron-deficient characteristics of Bi sites, but also allows for controllable adjustment of the electronic structure of Bi by regulating the Cu doping content, thereby improving the bismuth dependence on V. 2+ and V 3+ Adsorption and interfacial charge transfer capabilities;

[0021] (3) Compared with the traditional method of loading undoped oxide-derived Bi on graphite felt and direct electrodeposition of metallic Bi, the electrode V of the present invention 2+ / V 3+ The reaction exhibits higher intrinsic catalytic activity, which can significantly reduce negative electrode polarization and improve energy efficiency, power density, and electrolyte utilization.

[0022] (4) The all-vanadium redox flow battery assembled using the electrodes of this invention operates at 200 mA cm⁻¹. -2The energy efficiency can reach 80.38%, and the peak power density can reach 1126 mW / cm². -2 At 300 mA cm -2 After 1000 cycles, the energy efficiency retention rate reached 97.8%, demonstrating excellent cycle stability. Attached Figure Description

[0023] Figure 1 The images show SEM images of the precursor electrodes in Examples 1, 2, 3, and 4, Comparative Example 1, and Comparative Example 4.

[0024] Figure 2 The images show the XRD patterns of the precursor electrodes in Examples 2, 3, and 1, and Comparative Example 4.

[0025] Figure 3 The image shows the Raman diagrams of the precursors in Example 3 and Comparative Example 1.

[0026] Figure 4 XPS images of the precursors in Example 3 and Comparative Example 1.

[0027] Figure 5 The precursor electrode in Example 3 was prepared at 0.1 mol L⁻¹ -1 V 3+ + 3 mol L -1 The first three CV plots were measured in H2SO4.

[0028] Figure 6 The diagram shows the in-situ Raman diagrams of the precursors in Example 3 and Comparative Example 1, and Comparative Example 3.

[0029] Figure 7 SEM images of Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0030] Figure 8 The images are XRD patterns of Example 3, Comparative Example 1, and Comparative Example 3.

[0031] Figure 9 The Raman diagrams are for Example 3, Comparative Example 1, and Comparative Example 3.

[0032] Figure 10 XPS graphs for Example 3, Comparative Example 1 and Comparative Example 3, and Examples 1, 2 and 4, respectively.

[0033] Figure 11 The Mott-Schottky diagrams are for Example 3, Comparative Example 1, and Comparative Example 3.

[0034] Figure 12The UPS diagrams are for Example 3, Comparative Example 1 and Comparative Example 3, and Example 1, Example 2 and Example 4, respectively.

[0035] Figure 13 The diagram shows the exchange current density of Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4.

[0036] Figure 14 The figures shown are the cyclic voltammetry test diagrams and AC impedance test diagrams for Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, respectively.

[0037] Figure 15 Using Examples 3, 1, 2, 3, and 4 as negative electrodes, the assembled batteries were tested at 300 mA cm⁻¹. -2 Charge-discharge curves at current density.

[0038] Figure 16 Examples 3, 1, 2, 3, and 4 were used as negative electrode assemblies for batteries in the range of 100-400 mA cm⁻¹. -2 A comparison of energy efficiency, voltage efficiency, and coulombic efficiency at current density.

[0039] Figure 17 Using Examples 1, 2, and 4 as negative electrodes, the assembled batteries were installed at 100-400 mA cm⁻¹. -2 A comparison of energy efficiency, voltage efficiency, and coulombic efficiency at current density.

[0040] Figure 18 The power density comparison chart shows the batteries assembled as negative electrodes in Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4.

[0041] Figure 19 Example 3 uses the negative electrode to assemble a battery at 300 mA cm⁻¹ -2 The graph shows a long-cycle test of 1000 cycles at current density. Detailed Implementation

[0042] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the raw materials and equipment used in the embodiments are all products conventionally available in the art, and the methods used are all conventional methods in the art.

[0043] Example 1: Preparation of Cu-doped oxide-derived Bi electrocatalyst electrode (Cu / Bi = 1.49%) reconstructed in situ on graphite felt

[0044] Weigh out 9.80 g Bi(NO3)3·5H2O, 8.49 g C4H6O6, and 0.151 g CuSO4·5H2O, dissolve them in KOH aqueous solution, and prepare an electrodeposition solution, wherein Bi... 3+ The concentration is 0.1 mol L. -1 Cu 2+ The concentration is 0.003 mol L. -1 A two-electrode system was used for electrodeposition, with both the anode and cathode being graphite felt. A constant voltage of 2.2 V was applied between the anode and cathode to obtain an electrode on which Cu-doped Bi₂O₃ precursor was grown in situ on the graphite felt. The Cu / Bi atomic ratio was measured to be approximately 1.69% by ICP-OES. The resulting electrode was used as the negative electrode of a vanadium redox flow battery. In an acidic vanadium electrolyte, the Cu-doped Bi₂O₃ precursor underwent in-situ and irreversible electrochemical reduction during the first charge, transforming into a Cu-doped oxide-derived Bi active phase (Cu / Bi = 1.49%).

[0045] Example 2: Preparation of Cu-doped oxide-derived Bi electrocatalyst electrode (Cu / Bi = 2.81%) reconstructed in situ on graphite felt

[0046] Following the method of Example 1, only the Cu in the electrodeposition solution was changed. 2+ The concentration of CuSO4·5H2O was changed to 0.302g, in which Bi... 3+ The concentration is 0.1 mol L. -1 Cu 2+ The concentration is 0.006 mol L. -1 An electrode with a Cu-doped Bi₂O₃ precursor grown in situ on a graphite felt was obtained, and the Cu / Bi atomic ratio was measured to be approximately 2.87% by ICP-OES. Using the obtained electrode as the negative electrode of a vanadium redox flow battery, the Cu-doped Bi₂O₃ precursor underwent in-situ and irreversible electrochemical reduction during the first charge in an acidic vanadium electrolyte, transforming into a Cu-doped oxide-derived Bi active phase (Cu / Bi = 2.81%).

[0047] Example 3: Preparation of Cu-doped oxide-derived Bi electrocatalyst electrode (Cu / Bi = 4.23%) reconstructed in situ on graphite felt

[0048] Following the method of Example 1, only the Cu in the electrodeposition solution was changed. 2+ The concentration of CuSO4·5H2O was changed to 0.504g, in which Bi... 3+ The concentration is 0.1 mol L. -1 Cu 2+ The concentration is 0.010 mol L. -1An electrode with a Cu-doped Bi₂O₃ precursor grown in situ on a graphite felt was obtained, and the Cu / Bi atomic ratio was measured to be approximately 4.40% by ICP-OES. The obtained electrode was used as the negative electrode of a vanadium redox flow battery. In an acidic vanadium electrolyte, the Cu-doped Bi₂O₃ precursor underwent irreversible reduction during the first charge, transforming into a Cu-doped oxide-derived Bi active phase (Cu / Bi = 4.23%).

[0049] Example 4: Preparation of Cu-doped oxide-derived Bi electrocatalyst electrode (Cu / Bi = 4.45%) reconstructed in situ on graphite felt

[0050] Following the method of Example 1, only the Cu in the electrodeposition solution was changed. 2+ The concentration of CuSO4·5H2O was changed to 0.656g, in which Bi... 3+ The concentration is 0.1 mol L. -1 Cu 2+ The concentration is 0.013 mol L. -1 An electrode with a Cu-doped Bi₂O₃ precursor grown in situ on a graphite felt was obtained, and the Cu / Bi atomic ratio was measured to be approximately 4.69% by ICP-OES. The obtained electrode was used as the negative electrode of a vanadium redox flow battery. In an acidic vanadium electrolyte, the Cu-doped Bi₂O₃ precursor underwent irreversible reduction during the first charge, transforming into a Cu-doped oxide-derived Bi active phase (Cu / Bi = 4.45%).

[0051] Comparative Example 1: Preparation of an oxide-derived Bi electrocatalyst electrode reconstructed in situ on a graphite felt

[0052] The procedure was followed according to Examples 1-4, except that CuSO4·5H2O was not added to the electrodeposition solution, resulting in an electrode with undoped Bi2O3 precursor grown in situ on a graphite felt. The resulting electrode was used as the negative electrode in a vanadium redox flow battery. In an acidic vanadium electrolyte, the undoped Bi2O3 precursor underwent in-situ and irreversible reduction during the first charge, transforming into an oxide-derived Bi active phase.

[0053] Comparative Example 2: Preparation of in-situ grown metal BiCu composite electrode on graphite felt

[0054] 0.235 g Bi₂O₃ and 0.013 g CuSO₄∙5H₂O were dissolved in H₂SO₄ solution to prepare an electrodeposition solution. A two-electrode system was used for the electrodeposition process, with two graphite felts serving as the anode and cathode, respectively. At room temperature, a constant voltage of 2.2 V was applied between the anode and cathode to electrodeposit BiCu nanoparticles onto the surface of the graphite felt cathode.

[0055] Comparative Example 3: Preparation of in-situ grown metal Bi electrocatalyst electrode on graphite felt

[0056] 0.235 g of Bi₂O₃ was dissolved in H₂SO₄ solution to prepare an electrodeposition solution. Electrodeposition was performed using a two-electrode system, with two graphite felts serving as the anode and cathode, respectively. At room temperature, a constant voltage of 2.2 V was applied between the anode and cathode to obtain a graphite felt electrode loaded with metallic Bi nanoparticles.

[0057] Comparative Example 4: Graphite Felt Electrode

[0058] Results Analysis

[0059] Depend on Figure 1 It can be seen that the precursors in Examples 1, 2, 3, 4 and Comparative Example 1 all grew in situ on the surface of graphite felt, and their morphologies showed no significant differences. Figure 2 It can be seen that the XRD patterns of the precursors in Examples 2, 3, and Comparative Example 1 only show a series of diffraction peaks attributed to Bi2O3. Furthermore, the magnified XRD patterns within the 2θ = 27.0-28.5° range indicate that with increasing Cu doping concentration, more Cu... 2+ Ions (0.72 Å) substituted larger Bi atoms 3+ The diffraction peaks corresponding to the (111) crystal plane of Bi₂O₃ (1.03 Å) gradually shift towards the higher 2θ direction. Figure 3 It can be seen that, compared with the precursor in Comparative Example 1, at 599 cm... -1 Compared to the Bi-O vibration peak at the same location, the precursor in Example 3, due to Cu... 2+ The lattice contraction caused by the smaller ionic radius of the dopant ions shifts the peak in its Raman spectrum to 610 cm⁻¹. -1 .Depend on Figure 4 It can be seen that in the Cu 2p spectrum of the precursor in Example 3, Cu-attributed components can be clearly observed. 2+ Cu 2p 3 / 2 and 2p 5 / 2 Characteristic peaks. Meanwhile, compared to the precursor in Comparative Example 1, the Bi 4f of the precursor in Example 3... 5 / 2 and 4f 7 / 2 The peaks generally shift towards higher binding energies, while the Bi-O peak in the O 1s XPS spectrum shifts towards lower binding energies. These results collectively indicate a strong electronic interaction between Bi, O, and Cu species. These results demonstrate that the Cu-doped Bi₂O₃ precursor has been successfully electrodeposited on the surface of graphite felt, and its structural characteristics can be described as Cu… 2+ Partially replaces Bi in the Bi2O3 lattice 3+ .

[0060] Depend on Figure 5It can be seen that the first CV curve shows a reduction peak at -0.09 V (vs. Ag / AgCl), and its potential is lower than V. 3+ The reduction correction was attributed to the reduction of the precursor in Example 3. Furthermore, this reduction peak did not reappear in subsequent CV scans, nor did it appear in V... 2+ / V 3+ A corresponding oxidation peak was detected within the potential range of the redox reaction. This indicates that during the first charge of the VRFB, the precursor in Example 3 exhibits oxidation at V0. 3+ It has already been reduced before reduction and will not be oxidized back to Bi during subsequent discharge processes. 3+ .Depend on Figure 6 It can be seen that, under open-circuit potential, the precursor in Example 3 exhibits properties at 124 and 312 cm⁻¹. -1 The characteristic Bi-O stretching vibration peak, and located at 96 cm⁻¹ -1 The Bi-Bi vibrational characteristic peaks were observed. Upon applying a bias voltage, a rapid transition of the Raman signal from oxide to metallic Bi was observed at -0.1 V (vs. Ag / AgCl), indicating that the precursor in Example 3 had been reduced to a Bi-dominated reconstructed product at this potential. Furthermore, when the potential was scanned from -0.1 V (vs. Ag / AgCl) to -0.6 V (vs. Ag / AgCl) and back to -0.1 V (vs. Ag / AgCl), the Bi-Bi vibrational peaks of Example 3 did not show significant changes. This suggests that the precursor in Example 3 undergoes electrochemical reduction during the initial charging phase of the vanadium redox flow battery, forming a Bi-dominated reconstructed product, and this in-situ reconstruction is irreversible within the battery's operating voltage window.

[0061] Depend on Figure 7 It can be seen that during the first charge of the vanadium redox flow battery, the reduction product of the precursor in Example 3 still maintained the nanoparticle morphology, and its average particle size did not change significantly and was uniformly distributed on the graphite felt surface, indicating that no obvious particle agglomeration occurred during the reduction process. Furthermore, the morphology and surface dispersibility of Example 3 were highly similar to those of Comparative Example 1, indicating that Cu doping did not change the morphological characteristics of its derivatives. Figure 8 It can be seen that the XRD pattern of Example 3 only shows diffraction peaks belonging to metallic Bi, similar to Comparative Examples 1 and 3. However, because the smaller Cu atoms (1.28 Å) partially replaced the larger Bi atoms (1.56 Å) in Example 3, its (012) diffraction peak shifted to the higher 2θ direction. Figure 9 It can be seen that Comparative Example 3 is in the range of 50-400cm. -1 The Raman spectra within the range show only two characteristic Bi-Bi lattice vibration peaks (i.e., Ei). g and A 1gIn contrast, the Raman spectra of both Example 3 and Comparative Example 1 showed two additional characteristic peaks attributable to Bi-O stretching vibrations, indicating the presence of Bi-O bond-related structural units in both samples. However, compared to Comparative Example 1, the Bi-O stretching vibration peaks in Example 3 were significantly larger at 170 and 317 cm⁻¹, respectively. -1 Blue shifted to 175 and 322 cm -1 This indicates that the introduction of Cu enhanced the polarization of the residual Bi-O species.

[0062] Depend on Figure 10 It can be seen that, compared with Comparative Example 1, Bi in Example 3 is... 0 4f 7 / 2 and 4f 5 / 2 The peak shifts approximately 0.22 eV towards higher binding energies, indicating that the introduction of Cu redistributes charge, thereby reducing the electron cloud density of Bi. Furthermore, the Bi 4f spectra from Examples 1, 2, and 3 show that with increasing Cu content, Bi... 0 4f 7 / 2 and 4f 5 / 2 The higher shift in the binding energy of the peak indicates that the electronic structure of Bi atoms in the sample can be controllably tuned by adjusting the Cu doping level. Figure 11 It can be seen that the Mott-Schottky curves of Example 3, Comparative Example 1, and Comparative Example 3 all exhibit positive slopes, indicating that they all belong to n-type semiconductors. However, compared to Comparative Example 1 and Comparative Example 3, the flat-band potential of Example 3 has shifted positively by 0.032 V and 0.128 V, respectively, indicating that its Fermi level has shifted further downward. Figure 12 As can be seen, compared with Comparative Examples 1 and 3, Example 3 exhibits a higher work function, indicating that its Fermi level is lower and it is in a more electron-deficient state. Furthermore, the changes in the work function of Examples 1, 2, and 4 demonstrate that the electronic structure of Bi atoms in the electrode can be controllably adjusted by changing the Cu doping level.

[0063] Depend on Figure 13 It can be seen that, compared with Comparative Examples 1, 2, 3 and 4, Example 3 has the highest exchange current density, indicating that it has the highest exchange current density for V. 2+ / V 3+ Redox reactions exhibit the highest intrinsic catalytic activity. Figure 14 It can be seen that Example 3 exhibits the smallest peak potential difference and the largest peak current density, indicating its effect on V 2+ / V 3+ The redox reaction exhibits optimal reversibility and the highest electrochemical activity. Furthermore, Example 3 demonstrates the effect of V... 2+ To V 3+ The oxidation process exhibits the lowest R ct This indicates that Example 3 and V2+ There is a faster charge transfer process between them.

[0064] Depend on Figure 15 It can be seen that at 300 mA cm -2 The VRFB using Example 3 as the negative electrode exhibited the highest initial discharge voltage and volumetric discharge capacity. Furthermore, the VRFB using Comparative Example 4 as the negative electrode showed a low electrolyte utilization rate of only 48.0%. After introducing a bismuth-based catalyst, the electrolyte utilization rates for Comparative Examples 3, 2, 1, and 3 increased to 63.6%, 68.5%, 69.5%, and 76.7%, respectively, indicating that the stronger electron-deficient Bi sites induced by Cu doping can effectively alleviate polarization, thereby achieving deeper capacity release and higher electrolyte utilization. Figure 16 It can be seen that at 200 mA cm -2 In the following example, the VRFB using Example 3 as the negative electrode achieved the highest energy efficiency and voltage efficiency. Figure 17 It can be seen that the rate performance of the assembled VRFB further improves with increasing Cu doping concentration. This indicates that controlling the electron-deficient characteristics of Bi sites through Cu doping is beneficial for promoting the operation of VRFB at high current densities. Figure 18 It is evident that the VRFB using Example 3 achieves the highest peak power density, highlighting the significant potential of Example 3 in improving VRFB performance and reducing system costs by minimizing the required stack area for the same output power. Figure 19 It can be seen that the VRFB assembled using Example 3 as the negative electrode operates at 300 mA cm⁻¹. -2 After 1000 cycles, the energy efficiency retention rate was as high as 97.8%, indicating that Example 3 has excellent cycle stability.

Claims

1. A Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a conductive substrate, characterized in that, It includes a conductive substrate and a Cu-doped oxide-derived Bi precursor grown in situ on the surface of the conductive substrate. The Cu-doped oxide-derived Bi electrocatalyst is formed by in-situ reconstruction of the Cu-doped Bi2O3 precursor during the first charge of an all-vanadium redox flow battery.

2. The Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a conductive substrate as described in claim 1, characterized in that, The conductive substrate is at least one of graphite felt, carbon felt, carbon paper, or carbon cloth; preferably graphite felt.

3. The Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a conductive substrate as described in claim 2, characterized in that, The Cu / Bi atomic ratio in the Cu-doped oxide-derived Bi electrocatalyst is 1.49% to 4.45%.

4. A method for preparing a Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a conductive substrate as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Preparation of electrodeposition solution: Bismuth nitrate pentahydrate (Bi(NO3)3∙5H2O), tartaric acid (C4H6O6) and copper sulfate pentahydrate (CuSO4∙5H2O) are dissolved in potassium hydroxide (KOH) aqueous solution to obtain an alkaline electrodeposition solution containing Bi source and Cu source; (2) A Cu-doped Bi2O3 precursor is grown in situ on the surface of a conductive substrate by constant voltage electrodeposition in the electrodeposition solution; (3) The Cu-doped Bi2O3 precursor electrode obtained in step (2) is grown in situ on the conductive substrate surface and assembled into a vanadium redox flow battery as a negative electrode. During the first charging process, the Cu-doped Bi2O3 precursor is subjected to in situ electrochemical reconstruction to obtain a Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on the conductive substrate.

5. The preparation method according to claim 4, characterized in that, In step (1), the alkaline aqueous solution is a KOH aqueous solution; the bismuth source is Bi(NO3)3∙5H2O, Bi 3+ The concentration is 0.10 mol L. -1 The complexing agent is C4H6O6, with a concentration of 0.20~0.30 mol / L. -1 The copper source is CuSO4∙5H2O, Cu 2+ Concentration range: 0.003~0.020 mol L -1 .

6. The preparation method according to claim 4, characterized in that, In step (2), the electrodeposition solution temperature is 50~70℃; the constant voltage is 1.5~2.5 V.

7. The preparation method according to claim 4, characterized in that, In step (3), the electrolyte used in the operation of the vanadium redox flow battery is an acidic electrolyte.

8. The application of a Cu-doped oxide-derived Bi electrocatalyst as described in any one of claims 1 to 7, characterized in that, Use it to catalyze V 2+ / V 3+ Redox reaction.

9. A vanadium redox flow battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and an ion exchange membrane; wherein the negative electrode is a Cu-doped oxide-derived Bi electrocatalyst electrode reconstructed in situ on a conductive substrate according to any one of claims 1 to 7.

10. The all-vanadium redox flow battery as described in claim 9, characterized in that, The active material of the positive electrode includes at least one of graphite felt, carbon felt, carbon paper and carbon cloth; preferably graphite felt.

Images