Preparation method and application of phosphorus-doped polybenzimidazole derivative functionalized electrode

Abstract

The invention belongs to the technical field of battery electrode materials, and particularly relates to a preparation method and application of a phosphorus-doped polybenzimidazole derivative functionalized electrode. PBI is used as a nitrogen-oxygen-rich polymer precursor, and a high-conductivity porous carbon structure is formed on the surface of graphite felt fiber through pyrolysis; and a stable carbon layer-fiber composite body which is highly suitable for electrochemical application is constructed. Phosphorus can be integrated in the carbon layer in the heat treatment process, and a homogeneous heteroatom doped structure is formed. According to the invention, the prepared phosphorus-doped polybenzimidazole (PBI) derivative functionalized electrode is used as the negative electrode of the all-vanadium redox flow battery. By utilizing the unique electronic characteristics and synergistic effect of the phosphorus element, the reaction kinetics of the electrode to vanadium ions is remarkably enhanced, so that the power density and the energy efficiency (EE) of the battery are improved. The EE of the optimized electrode under 150 mA cm <-2 > reaches 82.27%; and after 2000 cycles at 100 mA cm <-2 >, the EE is still kept at 84% or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery electrode materials, and in particular relates to a preparation method and application of a phosphorus-doped polybenzimidazole-derived functionalized electrode. Background Art

[0002] With the large-scale application of renewable energy sources such as solar and wind power, their inherent intermittency and volatility pose severe challenges to the grid-connected stability of power systems. The development of large-scale, long-cycle energy storage technologies is crucial to improving the capacity to absorb renewable energy. Liquid flow batteries, with their inherent safety, long cycle life, and modular expansion advantages, have become a key technology to support the grid connection of renewable energy. Among them, all-vanadium liquid flow batteries (VFBs) have attracted much attention due to their ultra-high safety, power-capacity decoupling characteristics, and low cross-contamination risk. However, they still face challenges such as high cost, limited energy density, and power density restricted by electrode reaction kinetics. Therefore, the development of VFBs that are both economical and have high-rate performance is of key significance to promoting the construction of the next generation of power systems.

[0003] Electrodes, as core components of VFBs, serve as the site for vanadium ion redox reactions and play a key role in electron transfer. Commercial graphite felt (GF) electrodes are widely used due to their high mechanical strength and chemical stability. However, their inherent catalytic activity and wettability are insufficient, severely limiting the rate capability and cycling stability of VFBs. Currently, modification of commercial GF electrodes relies on two main strategies: one is to introduce high-surface-area (SSA) carbon-based catalysts into the electrode to increase the active surface area for electrode reactions. Typical materials include nanocarbon materials, graphene, two-dimensional transition metal carbides (MXenes), carbon nanofibers / nanotubes, and carbon aerogels. For example, Xing et al. successfully synthesized hollow porous carbon spheres with inner diameters of tens of nanometers using a nickel-based metal-organic framework (MOF) as a template and polyvinylpyrrolidone (PVP) as a dispersant. The PVP shell effectively inhibits nanoparticle aggregation during carbonization, fully preserving the porous structure and significantly increasing the specific surface area (SSA), thereby optimizing the utilization of the internal cavity. The second modification strategy enhances catalytic activity by depositing metal-based compounds on the surface of electrode fibers. Representative materials include bismuth, indium, copper, titanium dioxide, titanium nitride, tin dioxide, molybdenum disulfide, and ferric oxide. For example, Jiang et al. modified zirconium-based MOF nanoparticles on the surface of graphite felt via a hydrothermal synthesis method. These nanoparticles were then converted into porous ZrO2@C nanocomposites via high-temperature carbonization and pyrolysis. This catalyst exhibited excellent catalytic activity and conductivity. Despite these advances, traditional modification methods often lack strong chemical bonding, resulting in weak interfacial bonding between the modifier and the electrode fibers. Under continuous electrolyte erosion and acidic environments, the modifier is prone to shedding and dissolution, ultimately causing battery performance degradation. Therefore, developing modification strategies that can establish strong chemical bonds and exploring material systems with better chemical stability are crucial for improving the long-term service life of flow batteries.

[0004] In response to the aforementioned technical bottlenecks, heteroatom doping strategies have been widely used because they can precisely control the electronic structure of carbon materials while maintaining high chemical stability. Nitrogen (N) and oxygen (O) dual-doped carbon materials can significantly enhance electrode activity and wettability, thereby improving VFB performance. However, single / double element doping has inherent limitations and is difficult to meet the requirements of high-rate charge and discharge. Phosphorus (P) doping has attracted much attention due to its unique electronic properties (large atomic radius and low electronegativity). It can significantly change the local electronic structure of carbon materials, enhance the redox catalytic activity of vanadium ions, promote electron migration on the electrode surface, and strengthen the electrolyte-electrode interface interaction, thereby optimizing reaction kinetics.

[0005] Current research on phosphorus-modulated nitrogen-oxygen co-doped electrodes in VFBs remains insufficient, particularly in the precise control of doping sites and the analysis of structure-activity relationships. Achieving high-concentration heteroatom doping requires prioritizing the construction of a defective carbon layer. Building a functionalized carbon layer on the surface of pristine graphite felt provides a stable substrate for doping. However, under typical high flow rate conditions, the modified carbon layer is prone to exfoliation. Therefore, developing a dynamic flow-field-adaptive electrode architecture that combines structural stability with doping durability is crucial. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a preparation method of a phosphorus-doped polybenzimidazole-derived functionalized electrode and its application.

[0007] The present invention is achieved through the following technical solutions: A method for preparing a phosphorus-doped polybenzimidazole-derived functionalized electrode comprises the following steps: S1, dissolving PBI powder in N,N-dimethylacetamide (DMAC) to obtain a PBI solution; S2, immersing the original graphite felt in the solution of S1 and drying; S3, the sample obtained in S2 was immersed in 85% phosphoric acid, rinsed repeatedly with deionized water and dried twice; S4. The sample obtained in S3 is placed in a tube furnace and calcined to obtain the electrode material P-PBI@GF.

[0008] Furthermore, the concentration of the PBI solution obtained in S1 is 0.25 wt %.

[0009] Furthermore, the drying condition in S2 is oven drying at 120° C. for 20 minutes.

[0010] Furthermore, the calcination conditions of S4 were as follows: heating to 800° C. at a rate of 5° C. / min in an argon atmosphere and calcining at a constant temperature for 2 hours.

[0011] The present invention also provides a phosphorus-doped polybenzimidazole-derived functionalized electrode prepared by the above preparation method.

[0012] The present invention also provides the use of the phosphorus-doped polybenzimidazole-derived functionalized electrode in the negative electrode of an all-vanadium redox flow battery.

[0013] Beneficial technical effects of the present invention: The present invention uses PBI as a nitrogen-rich oxygen polymer precursor, and forms a highly conductive porous carbon structure on the surface of graphite felt fibers through pyrolysis, thereby constructing a stable carbon layer-fiber composite that is highly suitable for electrochemical applications. The carbon layer can integrate phosphorus elements during the heat treatment process to form a homogeneous heteroatom doped structure. The present invention uses the prepared phosphorus-doped polybenzimidazole (PBI)-derived functionalized electrode as the negative electrode of the all-vanadium liquid flow battery. Utilizing the unique electronic properties and synergistic effects of phosphorus, the reaction kinetics of the electrode to vanadium ions are significantly enhanced, thereby improving the battery power density and energy efficiency (EE). The optimized electrode is at 150 mA cm -2 EE reached 82.27% under 100 mA cm -2 After 2000 cycles, the EE still remained above 84%. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the preparation process of P-PBI@GF; Figure 2 (ac) SEM images of graphite felt (GF); (df) SEM images of PBI@GF; (gi) SEM images of P-PBI@GF; (jl) SEM images of P@GF; Figure 3 Element surface scanning distribution diagram of PBI@GF, P@GF, and P-PBI@GF; Figure 4 Nitrogen adsorption isotherms (a) and pore size distribution diagrams (b) of GF and P-PBI@GF; Figure 5 High-magnification scanning electron microscopy images of (a) PBI@GF and (b) P-PBI@GF; Figure 6 Raman spectra of GF, PBI@GF, P@GF, and P-PBI@GF; Figure 7 (a) XPS full spectrum of GF, PBI@GF, and P-PBI@GF; (b) N 1s fine spectrum; (c) O 1s fine spectrum; (d) P2p fine spectrum; Figure 8 is the P 2p fine spectrum of P@GF; Figure 9 This is the contact angle test diagram; Figure 10(a) CV curves of different samples in the potential range of -0.8 to -0.2 V (vs. saturated calomel electrode); (b) correlation between peak current density and square root of scan rate in the negative electrode reaction; (c) diffusion coefficient (D0) corresponding to each sample; (d) current density-overpotential relationship of different samples; (e) AC impedance spectroscopy measured at -0.45 V (vs. saturated calomel electrode); (f) comparison of charge transfer resistance (RCT) of negative electrode reaction; Figure 11 Cyclic voltammograms of (a) GF, (b) PBI@GF, and (c) P-PBI@GF electrodes in response to V³⁺ / V²⁺ redox reactions at different scan rates. Figure 12 The performance of vanadium redox flow batteries with different electrodes at 1-10 mA cm -2 Time-voltage curve under step-increasing current density; Figure 13 (a) Cyclic voltammograms of different electrodes in the potential range of -0.8 to -0.2 V (relative to a saturated calomel electrode); (b) Cyclic voltammograms of the P@GF electrode in response to the V³⁺ / V²⁺ redox reaction at different scan rates; (c) AC impedance spectra of different electrodes measured at -0.45 V (relative to a saturated calomel electrode); Figure 14 Charge and discharge curves of all-vanadium redox flow batteries with different electrodes at current densities of (a) 100 mA cm⁻², (b) 200 mA cm⁻², and (c) 300 mA cm⁻²; (d) comparison of Coulombic efficiency and (e) energy efficiency; (f) polarization and power density characteristic curves; (g) long-term cycle efficiency of the P-PBI@GF electrode system at 100 mA cm⁻²; Figure 15 (a) Charge-discharge curves of GF and P@GF electrodes at 100 mA cm⁻² and (b) 200 mA cm⁻²; (c) Coulombic efficiency and energy efficiency of the two electrode systems at different current densities; (d) polarization and power density characteristic curves of GF and P@GF electrodes; Figure 16 Surface charge density distribution of (a) PBI@GF and (b) P-PBI@GF electrodes; (c) comparison of the adsorption energies of the two types of electrodes for vanadium ions; (d) analysis of the number of electron transfers and electron localization functions in the presence of vanadium ions; (e) projected density of states spectra of the two types of electrodes in the presence of vanadium ions. DETAILED DESCRIPTION

[0015] Example 1 A method for preparing a phosphorus-doped polybenzimidazole-derived functionalized electrode comprises the following steps: S1. Dissolve PBI powder in 99% N,N-dimethylacetamide (DMAC) to prepare a 0.25 wt% solution at a mass ratio of 1:399 (PBI:DMAc). S2, immerse the original graphite felt in the solution of S1 and dry it in an oven at 120°C for 20 minutes; S3, the sample obtained in S2 was immersed in 85% phosphoric acid, rinsed repeatedly with deionized water and dried twice; S4. Place the sample obtained in S3 in a tube furnace, heat it to 800°C at a rate of 5°C / min in an argon atmosphere, and calcine it at this temperature for 2 hours to obtain the electrode material P-PBI@GF. Figure 1 shown.

[0016] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the concentration of the solution in S1 is 0.05 wt % solution, and the other conditions are exactly the same.

[0017] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the concentration of the solution in S1 is 0.15 wt % solution, and the other conditions are exactly the same.

[0018] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the concentration of the solution in S1 is 0.35 wt % solution, and the other conditions are exactly the same.

[0019] Comparative Example 4 The difference between Comparative Example 4 and Comparative Example 1 is that step S3 is missing, that is, calcination is performed directly after impregnation with the PBI solution. The other conditions are exactly the same, and the electrode material PBI@GF is obtained.

[0020] Comparative Example 5 The difference between Comparative Example 5 and Comparative Example 1 is that the original graphite felt is directly soaked in 85% phosphoric acid and calcined, and the other conditions are exactly the same to obtain the electrode material P@GF.

[0021] Comparative Example 6 Comparative Example 6 is untreated graphite felt GF.

[0022] Material characterization: Scanning electron microscopy (SEM) was used to characterize the micromorphology of GF, P@GF, PBI@GF and P-PBI@GF. Figure 2-3As shown, the pristine GF fibers have a smooth surface and an average diameter of approximately 10.3 μm. After PBI coating, a carbon layer forms on the fiber surface, and EDS analysis confirms the presence of nitrogen (N) and oxygen (O). Phosphoric acid treatment does not alter the morphology of the carbon layer in PBI@GF, while EDS scanning spectroscopy confirms the uniform incorporation of nitrogen (N), oxygen (O), and phosphorus (P) into the P-PBI@GF fibers. To investigate the role of phosphorus, phosphorus-doped GF (P@GF) was prepared. SEM images show little morphology change after doping, and elemental analysis confirms successful phosphorus doping.

[0023] To evaluate the change in specific surface area (SSA) caused by phosphorus-doped carbon layer, nitrogen adsorption-desorption isotherms were performed on P-PBI@GF and GF ( Figure 4 a). The SSA of P-PBI@GF is 34.50 m² / g, which is 9.25 times that of GF (3.731 m² / g). The results show that the phosphorus-doped carbon layer significantly increases the specific surface area of ​​P-PBI@GF, which is attributed to the rich structural defects on the surface of the PBI-derived carbon layer ( Figure 5 ). Corresponding pore size distribution analysis ( Figure 4 b) shows that compared with GF, the pore volume of P-PBI@GF is significantly increased in the micropore and mesopore range (<5nm). This feature is expected to provide more active sites for the V³⁺ / V²⁺ redox reaction, thereby improving the electrochemical performance.

[0024] Using Raman spectroscopy ( Figure 6 ) to study the microscopic surface structure of the sample. The D peak at 1350 cm⁻¹ and the G peak at 1590 cm⁻¹ represent the disordered carbon structure with lattice defects and the ordered graphitized carbon structure, respectively. The intensity ratio of the D peak to the G peak (I D / I G ) quantitatively evaluate the degree of graphitization. The results show that I D / I G The ratios are: P-PBI@GF (1.17)>PBI@GF (1.14)>GF (1.06), which confirms that the P-PBI@GF electrode surface has a higher density of lattice defects, thereby providing more active sites for the V³⁺ / V²⁺ redox reaction. In addition, the I D / I G The value is 1.12, indicating that phosphorus doping can introduce additional lattice defects and thus regulate the electronic structure.

[0025] The elemental composition of the samples was analyzed by X-ray photoelectron spectroscopy (XPS). Figure 7a is the full spectrum scan result, and the element contents are summarized in Table 1. The nitrogen and oxygen content shows a decreasing trend of P-PBI@GF ≈ PBI@GF > GF, and the phosphorus content is the highest in P-PBI@GF (no phosphorus was detected in GF). This indicates that P-PBI@GF has a richer content of N, O, and P elements due to the coordination structure formed by the defect-rich PBI-derived carbon layer and heteroatoms. The N 1s spectrum peak fitting of P-PBI@GF and PBI@GF shows three characteristic peaks ( Figure 7 b): pyridinic nitrogen (399.10 eV), pyrrolic nitrogen (400.17 eV), and graphitic nitrogen (402.05 eV). The O 1s spectrum of P-PBI@GF shows ( Figure 7 c): CC=O (533.70 eV), CO / PO (532.50 eV), C=O / P=O (531.25 eV), where PO / P=O is a phosphorus-containing functional group not found in other samples. In addition, the P 2p spectrum of P-PBI@GF ( Figure 7 d) presents PO (135.01 eV), PC (134.25 eV), and PN (133.48 eV), while P@GF contains only PO and PC ( Figure 8 ). Contact angle test ( Figure 9 ) showed that P-PBI@GF is hydrophilic (penetration time < 1 s). The enhanced wettability is attributed to the polar surface properties induced by heteroatom doping, which can increase the electrode-electrolyte contact area and thus improve battery performance.

[0026] Table 1. Atomic percentages of nitrogen (N), oxygen (O), and phosphorus (P) in each sample Theoretical analysis of interface electronic structure: like Figure 16 As shown in (a), the charge density difference distribution on the PBI@GF surface was studied. The electron distribution on the electrode surface containing N and O atoms was significantly disturbed: electron enrichment (yellow area) appeared around the N and O atoms, while electron depletion (blue area) appeared near the doping sites. When phosphorus atoms were introduced into the electrode surface ( Figure 16 b) Electrons are mainly localized in the pz orbital of phosphorus atoms, which can couple with the empty orbital of vanadium ions to promote electron transfer. Figure 16 (c) The adsorption energy of vanadium ions on PBI@GF and P-PBI@GF is significantly higher at the phosphorus site than at other doping sites, indicating that vanadium ions tend to bind to the phosphorus site. Analysis of the electron transfer number and electron localization function (ELF) further reveals that the binding between O atoms and vanadium ions in PBI@GF is weak and electron transfer is minimal; while significant electron localization is formed between phosphorus atoms and vanadium ions in P-PBI@GF, indicating strong binding and significant electron transfer ( Figure 16d). Projected density of states (PDOS) analysis clearly shows that the energy gap between the p-orbital center of P-PBI@GF and the d-orbital center of the vanadium ion is small and the energy level matching is high, which is conducive to the adsorption and reaction of vanadium ions ( Figure 16 e).

[0027] Electrochemical testing: The electrochemical properties of the different samples were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The potential difference between the oxidation and reduction peaks in the CV curve reflects the reversibility of the electrode reaction; a smaller peak potential difference indicates higher reversibility. The peak current intensity reflects the electrochemical activity of the electrode; a larger current value indicates greater activity. Figure 10 (a) Comparison of P-PBI@GF, PBI@GF and GF at 0.1 MV 2.5+ CV response of the original GF in V 3+ / V 2+ The redox reaction exhibited low peak currents and large peak potential differences, indicating poor electrochemical activity and reversibility. In contrast, PBI@GF and P-PBI@GF exhibited higher peak currents and smaller peak potential differences, with P-PBI@GF demonstrating the best activity and reversibility. This improvement is primarily due to the modulation of the electronic structure by phosphorus, which synergistically enhances the electrochemical activity of the electrode.

[0028] CV analysis at different scan rates ( Figure 11 ac) showed that the oxidation / reduction peak current ratio of P-PBI@GF was closest to 1, confirming that it had the best redox reversibility. Figure 10 As shown in (b), the peak current (i p ) and the square root of the scan rate (V 1 / 2 ) proves that V 3+ / V 2+ The redox reaction is diffusion controlled. The diffusion coefficient (D0) is calculated using the Randles-Sevcik equation and summarized in Figure 10 (c) shows that P-PBI@GF has the highest diffusion coefficient, indicating that the phosphorus-modulated PBI-derived carbon layer effectively promotes mass transfer at the electrode interface. The exchange current density i0 reflects the kinetic characteristics of the electrode reaction. Figure 10 d and Figure 12 As shown, the exchange current density (i0) is ranked as follows: P-PBI@GF (23.1452 mA cm -2 )>PBI@GF(6.5539 mA cm -2 )>GF(4.1979 mA cm -2 ), indicating that phosphorus doping significantly accelerates the electrode reaction kinetics.

[0029] EIS testing further supports this conclusion: Figure 10 e shows that P-PBI@GF in V 3+ / V 2+ The redox reaction shows the minimum charge transfer resistance (R CT ). Nitrogen and oxygen co-doped carbon layer makes the R CT The introduction of phosphorus reduces R CT Further reduced to 0.19Ω ( Figure 10 f), revealing the unique electronic effects and synergistic mechanisms of N, O, and P heteroatoms.

[0030] To clarify the independent contribution of phosphorus, the 2.5+ Supplementary test of P@GF in 3 mol / L H2SO4 solution system: Compared with the original GF, P@GF showed a significantly enhanced peak current ( Figure 13 a), its redox peak current ratio is closer to 1 ( Figure 13 b); More importantly, the charge transfer resistance of P@GF (0.5889 Ω) is significantly lower than that of the original GF ( Figure 13 c), which fully confirms that phosphorus doping can independently enhance the electrode reaction kinetics.

[0031] All-vanadium redox flow battery performance test The performance evaluation of all-vanadium flow battery (VFB) uses different negative electrodes (the positive electrode is all GF). Figure 14 (ac) Show the VFB of different anodes at 100, 200, and 300 mA cm -2 Among all the tested electrodes, the VFB using P-PBI@GF exhibited the lowest charge voltage and the highest discharge voltage, even at 300 mA cm -2 The VFB with P@GF exhibits a minimum overpotential at high current density. This improvement is mainly due to the phosphorus-modulated PBI-derived carbon layer effectively reducing the battery polarization. Similarly, the VFB with P@GF exhibits a high overpotential at 100 and 200 mA cm -2 The lower charge voltage and higher discharge voltage are shown in Figure 3. Figure 15 a, b), and the overpotential increases less with increasing current density, confirming that phosphorus doping can significantly suppress polarization and improve electrochemical performance.

[0032] Rate performance test at 100-350 mA cm -2 The VFB Coulombic efficiency (CE) is >97% at different current densities. Figure 14 d), indicating no electrolyte leakage during the test. The voltage efficiency (VE) is significantly affected by electrode activity: higher electrode activity reduces VFB activation polarization and increases VE. Figure 14(d) shows that the VFB using P-PBI@GF has the highest energy efficiency (EE) at all current densities. At 150 mA cm⁻², the EE reaches 82.27%, which is 12.43% higher than that of GF and 3.77% higher than that of PBI@GF. At 350 mA cm⁻², the EE still remains at 61.69%. By adjusting the concentration of PBI solution, it was found that the performance was optimal when the modification was 0.25 wt% ( Figure 14 e). In addition, the EE of the VFB using P@GF reached 77.61% at 150 mA cm⁻² ( Figure 15 c), which is 7.77% higher than that of GF, further proving the gain effect of phosphorus doping on battery performance. Polarization and power density curves ( Figure 14 f) shows that at the same current density, the VFB discharge voltage of P-PBI@GF is always higher than that of GF and PBI@GF, and its peak power density reaches 570 mW cm -2 (higher than GF’s 453 mW cm -2 ), P@GF is also better than GF ( Figure 15 d). 100 mA cm -2 The long cycle test shows that the EE of the VFB using P-PBI@GF only decays by 2.4% after 2000 cycles, showing excellent cycle stability ( Figure 14 g).

[0033] This paper proposes a phosphorus-induced strategy to regulate the electronic structure of a PBI-derived composite electrode. PBI is pyrolyzed to form a porous carbon coating rich in nitrogen and oxygen. The subsequent introduction of phosphorus significantly alters the electronic structure and accelerates the redox kinetics of vanadium ions, thereby improving electrocatalytic performance. The all-vanadium redox flow battery (VFB) using P-PBI@GF achieves a power density of 570 mW cm -2 , which is at 150 mA cm -2 The energy efficiency (EE) at 100 mA cm was 82.27%, which was 12.43% higher than that of the GF electrode. -2 After 2000 cycles, the battery's EE remained above 84% with no significant degradation. This invention provides new ideas for developing high-performance VFB electrodes and emphasizes the key role of electronic structure design in optimizing energy storage carbon-based materials.

Claims

1. A method for preparing a phosphorus-doped polybenzimidazole-derived functionalized electrode, characterized in that: The steps include: S1, dissolving PBI powder in N,N-dimethylacetamide (DMAC) to obtain a PBI solution; S2, immersing the original graphite felt in the solution of S1 and drying; S3, the sample obtained in S2 was immersed in 85% phosphoric acid, rinsed repeatedly with deionized water and dried twice; S4. The sample obtained in S3 is placed in a tube furnace and calcined to obtain the electrode material P-PBI@GF.

2. The method for preparing a phosphorus-doped polybenzimidazole-derived functionalized electrode according to claim 1, characterized in that: The concentration of the PBI solution obtained in S1 was 0.25 wt %.

3. The method for preparing a phosphorus-doped polybenzimidazole-derived functionalized electrode according to claim 1, characterized in that: The drying condition in S2 is oven drying at 120°C for 20 minutes.

4. The method for preparing a phosphorus-doped polybenzimidazole-derived functionalized electrode according to claim 1, wherein: The calcination conditions of S4 were as follows: heating to 800°C at a rate of 5°C / min in an argon atmosphere and calcining at a constant temperature for 2 hours.

5. A phosphorus-doped polybenzimidazole-derived functionalized electrode prepared by the preparation method according to any one of claims 1 to 4.

6. Use of a phosphorus-doped polybenzimidazole-derived functionalized electrode prepared by the method according to any one of claims 1 to 4 in an anode of an all-vanadium redox flow battery.

Images