Nitrogen-doped porous carbon electrode material and preparation method and application thereof

Abstract

The invention relates to a nitrogen-doped porous carbon electrode material and a preparation method and application thereof. According to the preparation method, stress-assisted pre-oxidation is introduced, and the nitrogen-doped porous carbon electrode material with high specific surface area, nitrogen doping characteristic and high conductivity is obtained. The problems that an existing electrode material is low in activity and poor in stability in electrochemical bromine extraction are solved. The electrode shows excellent performance of high efficiency, low energy consumption and stability in electrochemical bromine extraction and synergistic hydrogen production, and has remarkable practical value and industrial prospect.

Description

Technical Field

[0001] The present application relates to the fields of electrochemical energy storage and materials science, and particularly to a nitrogen-doped porous carbon electrode material with high specific surface area and high conductivity, a preparation method of the nitrogen-doped porous carbon electrode material, and an application of the carbon electrode material in electrochemical bromine extraction. More specifically, the present application relates to an efficient nitrogen-doped porous carbon electrode material prepared by needleless electrospinning, and its applications in electrochemical bromine extraction and energy storage systems. Background Art

[0002] With the development of the energy and chemical industries, the demand for bromine resources continues to grow, but the efficient extraction of low-grade brine remains a technical challenge. Electrochemical bromine extraction has become an effective approach due to its green, clean, and easy-to-control characteristics. Carbon-based electrode materials are widely used because of their high specific surface area and excellent conductivity. However, traditional carbon electrodes have low electrooxidation activity, high overpotential, and poor cycle stability, making it difficult to meet the requirements. Research has shown that nitrogen doping can significantly improve the conductivity of carbon electrodes and the bromide ion adsorption capacity. However, existing nitrogen-doped carbon materials are prone to corrosion, loss of activity, and high cost at high current densities, which limits their industrial applications. Therefore, the development of efficient, stable, and low-cost self-supporting electrode materials is the key to improving electrochemical bromine extraction technology.

[0003] Traditional carbon fiber felts are usually composed of micron-sized fibers with a relatively large fiber diameter (usually in the range of 4.5 - 7.5 μm), resulting in a limited specific surface area and insufficient electrochemically active area. The process of electrochemical bromine extraction requires a high specific surface area to provide sufficient active sites, and micron-sized fibers are difficult to meet this requirement. In addition, micron-sized fibers have poor flexibility and are difficult to adapt to mechanical stresses in complex electrochemical environments.

[0004] During the preparation process of carbon fibers, the heat treatment temperature has a significant impact on the specific surface area, electrochemical activity, and conductivity of the material. Although a higher heat treatment temperature can significantly improve the conductivity of the material, high temperatures consume more energy. A lower heat treatment temperature may lead to insufficient graphitization degree, thereby limiting the improvement of conductivity. Therefore, how to effectively balance the specific surface area, electrochemical activity, and conductivity during the heat treatment process has become a key challenge in the preparation of high-performance carbon fiber felts.

[0005] The diameter of the polyacrylonitrile-based carbon fibers described in Patent Document 1 is 4.5 μm - 7.5 μm; or the average diameter is 5.1 μm - 5.2 μm, and its fiber diameter is relatively large (usually in the range of 4.5 - 7.5 μm), resulting in a limited specific surface area.

[0006] The technology described in Patent Document 2 requires adding up to 20 wt% of 2,4,6-triaminopyrimidine and barbituric acid to polyacrylonitrile as nitrogen sources. Its fiber diameter is in the micron range, and the raw material cost increases significantly. Moreover, excessive doping easily leads to deterioration of the homogeneity of the spinning solution, requiring additional process control. At the same time, under high doping, nitrogen atoms are prone to agglomeration during the carbonization process to form inactive graphitized nitrogen, resulting in an insufficient proportion of effective active sites and causing waste of resources.

[0007] The carbon fiber preparation method disclosed in Patent Document 3, by regulating the crystallinity and graphitization degree, although reduces the porosity, its technical solution has significant limitations: the electrical conductivity is not clearly optimized: the fiber conductivity indicators (such as electrical conductivity, carrier mobility) are not mentioned throughout the text. The high crystallinity and dense structure may inhibit the construction of charge transport channels, limiting its application potential in flexible electronics or electrochemical devices; the fiber diameter is relatively large (~400 nm). The relatively wide fiber size results in a limited specific surface area, making it difficult to meet the requirements of high-sensitivity sensing or efficient catalytic reaction interfaces, and the flexibility may be inferior to that of ultra-fine fibers (<200 nm).

[0008] The MOF-based nanofiber membrane technology disclosed in Patent Document 4, although realizes the regulation of the fiber diameter in the range of 50 - 800 nm (or 100 - 600 nm), its solution does not involve strategies for improving the fiber conductivity or test data. The interfacial compatibility between MOF and the fiber matrix may limit the charge transport efficiency, making it difficult for the material to adapt to scenarios with high electrical conductivity requirements such as electromagnetic shielding and flexible electrodes; the fiber diameter distribution is broad (the upper limit reaches 800 nm): the overly wide size range (especially the high proportion of micron-scale fibers) leads to a significant reduction in the specific surface area, insufficient exposure of active sites, and poor flexibility of thick fibers, making it difficult to meet the performance requirements of wearable devices or high-precision catalytic carriers.

[0009] The carbon fiber technology disclosed in Patent Document 5, although can achieve a cross-sectional diameter of 100 - 250 nm and a surface microporous (<2 nm) structure, its solution does not provide key data such as electrical conductivity, and it is impossible to verify its charge transport efficiency. The relatively large number of micropores and hierarchical pores may instead limit the electrical conductivity due to the grain boundary scattering effect; the fiber diameter range is relatively wide (100 - 250 nm): compared with ultra-fine fibers (such as <100 nm), there is still room for improvement in the specific surface area and flexibility, making it difficult to adapt to the requirements of miniaturized devices; and it relies on metal doping and complex processes: introducing metal components to regulate the structure increases the raw material cost and process complexity, and metal residues may trigger interfacial side reactions.

[0010] Therefore, there is a continuous need in this field to develop carbon electrode materials with high activity and good stability in electrochemically extracting bromine, as well as their preparation methods and applications.

[0011] Patent Document 1: Publication No. CN119308032A, "PAN as-spun fiber, PAN-based carbon fiber and preparation method thereof".

[0012] Patent Document 2: Publication No. CN119308042A, "Preparation method of ultra high draw ratio carbon fiber, carbon fiber and application thereof".

[0013] Patent Document 3: Publication No. CN 119287559 A, "High-performance PAN-based carbon fiber and preparation method thereof".

[0014] Patent Document 4: Publication No. CN 119208640A, "Carbon felt electrode with loaded catalytic layer for flow battery electrode, preparation method and application thereof".

[0015] Patent Document 5: Publication No. CN114883528 A, "Carbon fiber negative electrode material, preparation method thereof and lithium ion battery". Summary of the Invention

[0016] The purpose of the present application is to provide a nitrogen-doped porous carbon electrode with high specific surface area and high conductivity based on needleless electrospinning technology, and a preparation method thereof, so as to solve the problems of low activity and poor stability of existing electrode materials in electrochemical bromine extraction. By optimizing the spinning solution, heat treatment process and nitrogen source doping, the high conductivity, high specific surface area, hierarchical pore structure and good nitrogen functionalization characteristics of the electrode material are realized, and its performance in electrochemical bromine extraction is significantly improved.

[0017] Compared with the prior art, the present invention is based on needleless electrospinning technology. Through a metal-free doping green process, the melamine loading and carbonization process are regulated. While the fiber diameter can be controllably abbreviated to an extremely fine range of 70 nm, it can not only be used as a self-supporting electrode, but also improve the conductivity to 4505 S / cm, with both high specific surface area and fast charge transport characteristics, better breaking through the bottleneck that it is difficult to synergistically optimize the "conductivity-structure" of traditional composite fibers. It expands the multi-scenario applicability of carbon fibers, and successfully prepares a porous carbon electrode material with both high electrocatalytic activity and stability. The process simplicity significantly reduces the large-scale production cost, providing a feasible solution to meet the industrial bromine extraction demand.

[0018] In order to solve the above technical problems, the present application provides the following technical solutions.

[0019] In the first aspect, the present application provides a preparation method of a porous carbon electrode material, which includes the following steps: S1: Mix carbon sources to obtain a spinning solution; S2: Through a needleless electrospinning process, stretch the spinning solution into a nanofiber composite membrane under a high-voltage electric field and collect it on a substrate film; S3: Perform ordinary pre-oxidation or stress-assisted pre-oxidation treatment on the nano-composite fiber membrane to obtain a pre-oxidized nano-composite fiber membrane; S4: Under an inert atmosphere, perform carbonization or graphitization on the pre-oxidized nano-composite fiber membrane to obtain the porous carbon electrode material.

[0020] In one embodiment, the stress-assisted pre-oxidation treatment includes the following steps: Fix the nano-composite fiber membrane between two smooth splints, and then heat them together for a predetermined period of time.

[0021] In one embodiment of the first aspect, the carbon source is a mixture of polyacrylonitrile and N,N-dimethylformamide. Preferably, the mass ratio of polyacrylonitrile to N,N-dimethylformamide in the spinning solution is 0.05 - 0.10. Preferably, the mass ratio of polyacrylonitrile to N,N-dimethylformamide in the spinning solution is 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 or the range or sub-range between any two of these values.

[0022] In one embodiment of the first aspect, under the conditions of a high-voltage electric field of 35 - 80 kV and a temperature of 30 - 60 °C during the electrospinning process, stretch the spinning solution into ultrafine nano-composite fibers. Preferably, the high-voltage electric field is 35 kV, 40 kV, 45 kV, 50 kV, 55 kV, 60 kV, 65 kV, 70 kV, 75 kV, 80 kV or the range or sub-range between any two of these values. Preferably, the electrospinning time is 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C or the range or sub-range between any two of these values.

[0023] During the pre-oxidation treatment process, the temperature is 180 - 300 °C and the time is 2 - 3 hours. Preferably, the temperature during the pre-oxidation process is 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, 300 °C or the range or sub-range between any two of these values. Preferably, the time during the pre-oxidation process is 2 hours, 2.5 hours, 3 hours or the range or sub-range between any two of these values.

[0024] In one embodiment of the first aspect, the atmosphere for the carbonization treatment includes nitrogen (N2), hydrogen (H2), argon (Ar) or a hydrogen-argon mixed gas (H2 / Ar).

[0025] In an embodiment of the first aspect, the temperature of the carbonization treatment is 700 °C to 1000 °C, and the time is 2 to 8 hours. Preferably, the temperature of the carbonization treatment is 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C, 760 °C, 770 °C, 780 °C, 790 °C, 800 °C, 810 °C, 820 °C, 830 °C, 840 °C, 850 °C, 860 °C, 870 °C, 880 °C, 890 °C, 900 °C, 910 °C, 920 °C, 930 °C, 940 °C, 950 °C, 960 °C, 970 °C, 980 °C, 990 °C, 1000 °C, or the range or sub-range between any two of these values. Preferably, the time of the carbonization treatment is 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, or the range or sub-range between any two of these values.

[0026] In the second aspect, the present application provides a method for preparing a nitrogen-doped porous carbon electrode material, which includes the following steps: S10: Mix a carbon source and a nitrogen source to obtain a spinning solution; S20: By a needleless electrospinning process, stretch the spinning solution into a nano-composite fiber membrane under a high-voltage electric field and collect it on a substrate film; S30: Perform ordinary pre-oxidation or stress-assisted pre-oxidation treatment on the nano-composite fiber membrane to obtain a pre-oxidized nano-composite fiber membrane; S40: Under an inert atmosphere, perform carbonization or graphitization on the pre-oxidized nano-composite fiber membrane to obtain the nitrogen-doped porous carbon electrode material, and this nitrogen-doped porous carbon electrode material includes a hierarchical pore structure.

[0027] In an embodiment of the second aspect, the stress-assisted pre-oxidation treatment includes the following steps: Fix the nano-composite fiber membrane between two smooth splints, and then heat them together for a predetermined period of time.

[0028] In an embodiment of the second aspect, the carbon source is polyacrylonitrile, and the nitrogen sources are melamine and polyacrylonitrile. Preferably, the mass ratio of melamine to polyacrylonitrile in the spinning solution is 1% - 3%.

[0029] In an embodiment of the second aspect, during the needleless electrospinning process, the applied high-voltage electric field is 35 - 80 kV, the temperature is 30 - 60 °C, and the spinning solution is stretched into ultrafine nano-composite fibers. Preferably, the high-voltage electric field is 35 kV, 40 kV, 45 kV, 50 kV, 55 kV, 60 kV, 65 kV, 70 kV, 75 kV, 80 kV, or a range or sub-range between any two of these values. Preferably, the time for electrospinning is 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, or a range or sub-range between any two of these values.

[0030] During the stress-assisted pre-oxidation treatment, the temperature is 180 - 300 °C and the time is 2 - 3 hours. Preferably, the temperature during the pre-oxidation treatment is 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, 300 °C, or a range or sub-range between any two of these values. Preferably, the time during the pre-oxidation treatment is 2 hours, 2.5 hours, 3 hours, or a range or sub-range between any two of these values.

[0031] In an embodiment of the second aspect, in step S40, the inert atmosphere is argon or a hydrogen-argon mixture; the carbonization temperature is 1000 - 1500 °C and the time is 2 - 8 hours. Preferably, the carbonization temperature is 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C, 1500 °C, or a range or sub-range between any two of these values. Preferably, the time for carbonization is 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, or a range or sub-range between any two of these values.

[0032] In the third aspect, the present application provides a carbon electrode material, which includes a porous carbon electrode material prepared by the preparation method as described in the first aspect or a nitrogen-doped porous carbon electrode material prepared by the preparation method as described in the second aspect.

[0033] In the fourth aspect, the present application provides the application of the carbon electrode material as described in the third aspect in electrochemically extracting bromine.

[0034] In the fifth aspect, the present application provides an electrochemically bromine extraction device, which includes a sealed flow cell. An anode and a cathode are arranged in the sealed flow cell. The anode uses the nitrogen-doped porous carbon electrode as described in the third aspect, and the anode and the cathode are separated by a cation exchange membrane.

[0035] Compared with the prior art, the positive effects of the present invention are as follows: The present invention provides a nitrogen-doped porous carbon electrode material based on needleless electrospinning technology, its preparation method and application, which solves the problems of low activity and poor stability of existing electrode materials in electrochemical bromine extraction. This electrode material exhibits excellent performance of high efficiency, low energy consumption and stability in electrochemical bromine extraction and co-production of hydrogen, and has significant practical value and industrial prospects. Description of the Drawings

[0036] Figure 1 shows the influence of the stress-assisted method on the pre-oxidation of fibers in Example 1, where (a) is the pre-oxidation by the stress-assisted method; (b) is the pre-oxidation by the ordinary method.

[0037] Figure 2 is the SEM image of Example 2 (a) before pre-oxidation; (b) 180 - 2h; (c) 200 - 2h; (d) 250 - 2h; (e) 250 - 3h; (f) 300 - 2h. Figure 2 The numbers of the six figures in it are (a), (b) and (c) from left to right in the top row, and (d), (e) and (f) from left to right in the bottom row.

[0038] Figure 3 is the (a) SEM image and (b) TEM image of Example 4.

[0039] Figure 4 is the TEM image of Example 7 and Example 8.

[0040] Figure 5 is the XRD pattern of Example 9 - Example 11 and Comparative Example 1.

[0041] Figure 6 is the infrared spectrum of Example 9 - Example 11 and Comparative Example 1.

[0042] Figure 7 is the Raman spectrum of Example 9 - Example 11 and Comparative Example 1.

[0043] Figure 8 is the contact angle test image of Example 10.

[0044] Figure 9 is the nitrogen adsorption - desorption isotherm and pore size distribution diagram of Example 10.

[0045] Figure 10 is the TEM image of the nitrogen-doped porous carbon electrode prepared in Example 10.

[0046] Figure 11 is the EIS diagram of Example 9 - Example 11 and Comparative Example 1.

[0047] Figure 12It is the HR-TEM image of the nitrogen-doped porous carbon electrode prepared in Example 10.

[0048] Figure 13 They are the N1S XPS spectra of the carbon electrode materials of Examples 16 - 18 and Comparative Example 3.

[0049] Figure 14 They are the constant-current bromine extraction diagrams measured for Examples 16 - 18 and Comparative Example 3.

[0050] Figure 15 It is the constant-current plus constant-voltage bromine extraction performance of Example 18. Detailed implementation manners

[0051] Unless otherwise specified, implied from the context, or in accordance with the convention of the prior art, all parts and percentages in this application are based on weight, and the testing and characterization methods used are synchronous with the filing date of this application. Where applicable, any patents, patent applications, or published content referred to in this application are incorporated herein by reference in their entirety, and their equivalent family patents are also incorporated by reference.

[0052] The numerical ranges in this application are approximate values, so unless otherwise specified, they may include values outside the range. The numerical range includes all values from the lower limit value to the upper limit value increased by 1 unit, provided that there is an interval of at least 2 units between any lower value and any higher value.

[0053] When referring to chemical compounds, unless explicitly stated, the singular includes all isomeric forms, and vice versa (e.g., "hexane" includes all isomers of hexane individually or collectively). Additionally, unless explicitly stated, nouns described by "a", "an", or "the" also include their plural forms.

[0054] The terms "comprising", "including", "having", and their derivatives do not exclude the existence of any other components, steps, or processes, and are independent of whether these other components, steps, or processes are disclosed in this application. To eliminate any doubt, unless explicitly stated, all compositions using the terms "comprising", "including", or "having" in this application may contain any additional additives, excipients, or compounds. In contrast, the term "consisting essentially of" excludes any other components, steps, or processes from the scope described below any such term, except for those necessary for the operating performance. The term "consisting of" does not include any components, steps, or processes not specifically described or listed. Unless explicitly stated, the term "or" refers to the individual members listed or any combination thereof.

[0055] In a specific implementation manner, the present invention provides a preparation method of a nitrogen-doped porous carbon electrode material, specifically including the following steps: Spinning solution preparation: Mix polyacrylonitrile (PAN) and N,N-dimethylformamide (DMF) at a mass ratio of 0.05 - 0.10. The number-average molecular weight of PAN is 50,000 - 150,000. Add melamine as a nitrogen source, and the mass ratio of melamine to PAN is 0.01 - 0.03, then stir evenly. Electrospinning: Adopt needleless electrospinning technology to stretch the spinning solution into ultrafine nanofibers under a high-voltage electric field (35 - 80 kV) and a temperature of 30 - 60 °C, and collect them on a polypropylene (PP) film to form a nanofiber composite membrane.

[0056] Pre-oxidation treatment: Pre-oxidation treatment: Use the common method and stress-assisted method to carry out pre-oxidation treatment in an air atmosphere at 180 - 300 °C for 2 - 3 hours. Among them, the stress-assisted pre-oxidation method can significantly improve the fiber orientation and structural stability. The specific operation of stress-assisted pre-oxidation is as follows: Fix the nanofiber composite membrane prepared by needleless electrospinning between two smooth glass splints, and put the fixed nanofiber composite membrane into a muffle furnace for pre-oxidation treatment at a certain temperature in an air atmosphere.

[0057] Carbonization treatment: Under the protection of an inert gas (such as nitrogen or a hydrogen-argon mixture (hydrogen volume fraction is 5% (V / V))), carbonize at 700 - 1000 °C for 2 - 8 hours to form a porous carbon electrode material (NPC-X) with a hierarchical pore structure and nitrogen doping.

[0058] Electrode structure and characteristics The nitrogen-doped porous carbon electrode material of this application includes a hierarchical pore structure. Micropores are used to provide abundant active sites and improve ion transport. Mesopores are used to shorten the diffusion path between brine and the electrode and optimize the mass transfer performance.

[0059] The nitrogen doping of this application is achieved by introducing nitrogen atoms through melamine, enhancing the electrocatalytic performance and selective oxidation ability of the electrode.

[0060] The nitrogen-doped porous carbon electrode material of this application has high conductivity. After nitrogen atoms are embedded in the carbon lattice, the electronic structure is optimized, the free carrier density is increased, and at the same time, the three-dimensional staggered porous network forms an efficient electron transport channel, synergistically improving the conductivity.

[0061] This application uses characterization methods such as SEM, TEM, and nitrogen adsorption-desorption to confirm that the electrode has a high specific surface area and abundant active sites.

[0062] Electrochemical bromine extraction application The devices and configurations used in the electrochemical bromine extraction application in this application are described as follows. A hydrogen bromide flow electrolytic cell (HBFC) device is used, and the anode and cathode are separated by a cation exchange membrane (such as Nafion 117). Bromine extraction mother liquor containing 17 g / L Cl - and 1 g / L Br - is added to the anode chamber, and 0.5 M H2SO4 is added to the cathode chamber as the cathode electrolyte.

[0063] The operating conditions for constant current bromine extraction are described as follows. At room temperature (25 ± 3 °C), the constant current method (current value of 15 mA) or constant voltage (voltage value of 1.3 V) is used for electrochemical bromine extraction. The bromine generated in the aqueous phase is extracted with carbon tetrachloride, and the bromine extraction amount is analyzed by ion chromatography.

[0064] The process of co-producing hydrogen is described as follows. During the electrochemical bromine extraction process, the H2SO4 electrolyte in the cathode chamber promotes the hydrogen evolution reaction (HER), realizing the synergistic effect of bromine extraction and hydrogen production.

[0065] The advantages of the nitrogen-doped porous carbon electrode material of the present invention include efficient bromine extraction, excellent stability, optimized mass transfer, low-cost preparation, and high conductivity.

[0066] The electrode material has a high specific surface area and abundant active sites, significantly improving the electrochemical oxidation efficiency of bromide ions. Therefore, the nitrogen-doped porous carbon electrode material of this application can extract bromine efficiently.

[0067] This application optimizes the pre-oxidation and carbonization processes to ensure that the electrode material has stable electrochemical properties. Therefore, the nitrogen-doped porous carbon electrode material of this application has excellent stability.

[0068] The hierarchical pore structure of this application significantly improves the mass transfer performance and reaction kinetics of the electrode, so the mass transfer process can be optimized.

[0069] This application uses needleless electrospinning technology to avoid nozzle blockage and realize the large-scale preparation of electrode materials. The cost is significantly lower than that of noble metal electrodes, so it has the advantage of low preparation cost.

[0070] In this application, nitrogen atoms are successfully embedded in the carbon lattice, optimizing the electronic structure of the carbon material. Moreover, the hierarchical pore network of the material can form an efficient electron transport channel. These two factors cooperate with each other to significantly improve the conductivity of the material, making the prepared nitrogen-doped porous carbon electrode material have high conductivity.

[0071] Embodiment The technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Unless otherwise specified, the reagents and raw materials used can be purchased through commercial channels. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product instructions.

[0072] In the following examples, the instrument equipment and specific sample preparation processes used for different characterizations are as described below.

[0073] SEM The equipment model is Nova Nano SEM 230 (USA). The sample is directly cut into small pieces and fixed on a conductive tape for sample preparation. The surface morphology (such as fiber structure, pore morphology) is observed through SEM.

[0074] TEM A transmission electron microscope (TEM, model Talos F200X, acceleration voltage 200 kV) is used to characterize the surface morphology and structure of the sample. During sample preparation, the sample is dispersed in DMF and then dropped onto a microgrid and dried. The surface characteristics and elemental composition of the NPC electrode are analyzed by energy-dispersive X-ray spectroscopy (EDS) elemental mapping analysis technology.

[0075] XRD A Shimadzu XRD-6100 diffractometer (Cu-Kα radiation, 40 kV / 30 mA) is used for testing. The scanning range is 10 - 40° (2θ), the step size is 0.02°, and the crystal phase and grain size are analyzed by comparing with the ICDD standard card and the Scherrer formula.

[0076] XPS The equipment model is Thermo Fisher Scientific (USA). After the sample is dried, it is directly placed on the XPS sample stage for sample preparation. Peak fitting of C 1s (sp² carbon, C-OH, C=O, etc.) and N 1s (pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen, etc.) is carried out.

[0077] Nitrogen adsorption and desorption method A BSD-660M (China) instrument is used to carry out N2 adsorption - desorption method testing under liquid nitrogen environment (77 K). BET specific surface area, average pore volume and pore diameter analysis are also carried out.

[0078] Raman spectroscopy: Using Thermo Fisher Scientific, the sample is directly flattened without special sample preparation, and the ID / IG ratio is analyzed.

[0079] FT-IR: Tested with a Thermo Fisher Nicolet iS50 Fourier transform infrared spectrometer. The sample was mixed with KBr and pressed into a tablet for sample preparation.

[0080] Contact angle measurement: Tested with a Thermo Fisher DXR laser confocal Raman spectrometer (532 nm laser). The sample needs to be pressed flat, and the sessile drop method was used to measure the contact angle synchronously.

[0081] Ion chromatograph test The bromide ion concentration of the electrolyte before and after extracting bromine water was tested with a Thermo Fisher ICS5000+ ion chromatograph. The electrolyte before and after extracting bromine water was extracted with carbon tetrachloride multiple times, diluted, and directly injected after filtration through a membrane filter.

[0082] For the electrochemical impedance spectroscopy (EIS) test, a saturated calomel electrode (SCE, Shanghai CH Instrument Co., Ltd.) was used as the reference electrode, and a platinum electrode (1 cm × 1 cm, Tianjin Gauss United Optoelectronic Technology Co., Ltd.) was used as the counter electrode. The test was carried out at the open circuit potential, with a frequency range of 1 MHz to 0.1 Hz, using a Zahner Zennium electrochemical workstation (Zahner Company, Germany). The potential data was converted to the standard hydrogen electrode (SHE) scale through the following formula: E(vs. SHE)=E(vs. SCE)+0.244 V Flow electrolytic cell electrochemical test The flow channel of the flow electrolytic cell adopts a diagonal staggered channel structure (integrated graphite flow field plate), and the electrodes in the electrolytic cell are in an embedded configuration. As Figure 1 shown, the hydrogen-bromine flow electrolytic cell (HBFC) device operates in a sealed environment at room temperature (25 ± 3 °C) to achieve the selective oxidation of bromide ions. The cathode chamber is separated from the sealed anode chamber by a cation exchange membrane (Nafion 117, Sigma-Aldrich).

[0083] 1. Electrolyte preparation: The anolyte was prepared from sodium chloride and sodium bromide, with a bromide ion concentration of 1 g / L and a chloride ion concentration of 17 g / L, as the basic electrolyte. During the experiment, 40 mL of the basic electrolyte was placed in the first reactor, and another 20 mL of the basic electrolyte was mixed with 20 mL of carbon tetrachloride and placed in the second reactor.

[0084] The catholyte was 15 mL of 0.5 M sulfuric acid solution, which was used for bromine extraction and simultaneously promoted the hydrogen evolution reaction.

[0085] 2. Electrochemical performance characterization: The electrocatalytic performance of the electrode was investigated by linear sweep voltammetry in a mixed solution containing 1 g / L Br - and 17 g / L Cl - . The test potential range was set to 0.4 - 1.4 V (vs. RHE).

[0086] In the experiment, NPC-X (X = 0, 1, 2, 3) was used as the anode electrode in the embedded configuration, and the Pt-AHGF electrode was used as the cathode electrode. The bromine extraction experiment was carried out in a constant current or constant voltage mode. Unless otherwise specified, the anode current was set to 15 mA (controlled by the DH7000C electrochemical workstation of Jiangsu Donghua Analytical Instrument Co., Ltd.), or the constant voltage was 1.3 V. The bromine generated during the oxidation process was directly introduced into a container containing carbon tetrachloride, and subsequent quantitative analysis was carried out by ion chromatography. Meanwhile, in the cathode chamber, protons obtained electrons on the surface of the Pt-AHGF electrode to generate hydrogen gas.

[0087] Example 1 This example relates to a preparation method of a porous carbon electrode material, which includes the following steps: 1 Spinning solution preparation: PAN with a number average molecular weight of 85000 and DMF were mixed according to the slurry mass ratio of PAN / DMF = 0.076, and after stirring evenly, it was used as the spinning solution; 2 Electrospinning: Using needleless electrospinning technology, the spinning solution was stretched into ultrafine nanofibers under a high-voltage electric field (60 kV) and collected on a PP film to form a nanofiber composite membrane; 3 Pre-oxidation treatment: The nanofiber composite membrane was pre-oxidized in air by two methods (250 °C, 2 hours), such as Figure 1 the SEM image of the material prepared by the stress-assisted method as shown in Figure 1 (a), and the SEM image of the material prepared by the ordinary pre-oxidation method as shown in (b); Figure 1 4 The specific operation of stress-assisted pre-oxidation is as follows: The nanofiber composite membrane prepared by needleless electrospinning was fixed between two smooth glass splints, and the fixed nanofiber composite membrane was placed in a muffle furnace and pre-oxidized at a temperature of 250 °C for 2 hours in an air atmosphere. As shown in Figure 1 (a), the stress-assisted method significantly improved the fiber orientation and structural stability, and avoided the problems of fiber breakage and uneven structure in the ordinary pre-oxidation method ( (b)).

[0088] This example relates to a preparation method of a porous carbon electrode material, which includes the following steps: 1 Spinning solution preparation: PAN with a number-average molecular weight of 85000 and DMF were mixed at a slurry mass ratio of PAN / DMF = 0.076, and after stirring evenly, it was used as the spinning solution; 2 Electrospinning: Using needleless electrospinning technology, the spinning solution was stretched into ultrafine nanofibers under a high-voltage electric field (60 kV) and collected on a PP film to form a nanofiber composite membrane; 3 Pre-oxidation treatment: As Figure 2 Figure (a) is the SEM image of the nanofiber composite membrane before pre-oxidation in air. As Figure 2 As shown in (b)-(f), the pre-oxidation conditions were respectively (b)-(f) 180 °C - 2 h; 200 °C - 2 h; 250 °C - 2 h; 250 °C - 3 h; 300 °C - 2 h, providing structural stability for subsequent carbonization.

[0089] Example 3 This example relates to a preparation method of a porous carbon electrode material, which includes the following steps: 1 Spinning solution preparation: PAN with a number-average molecular weight of 85000 and DMF were mixed at a slurry mass ratio of PAN / DMF = 0.076 and stirred evenly; 2 Electrospinning: A nanofiber composite membrane was prepared under a high-voltage electric field (60 kV); 3 Pre-oxidation treatment: Pre-oxidation was carried out in air by the stress-assisted method (250 °C, 2 hours); 4 Carbonization treatment: Carbonization was carried out in a tubular furnace under a hydrogen-argon mixed gas atmosphere (700 °C, 2 hours).

[0090] 5 The measured specific surface area is shown in Table 1.

[0091] Example 4 This example relates to a preparation method of a porous carbon electrode material, which includes the following steps: 1 Spinning solution preparation: PAN with a number-average molecular weight of 85000 and DMF were mixed at a slurry mass ratio of PAN / DMF = 0.076 and stirred evenly; 2 Electrospinning: A nanofiber composite membrane was prepared under a high-voltage electric field (60 kV); 3 Pre-oxidation treatment: Pre-oxidation was carried out in air (250 °C, 2 hours); 4 Carbonization treatment: Carbonization was carried out in a hydrogen-argon mixed gas atmosphere (1000 °C, 2 hours), and its morphology is as Figure 3 shown in (a) SEM image and (b) TEM.

[0092] 5 The measured specific surface area is shown in Table 1.

[0093] Example 5 This embodiment relates to a preparation method of a porous carbon electrode material, which comprises the following steps: 1 Spinning solution preparation: Mix PAN with a number average molecular weight of 150,000 and DMF according to the slurry mass ratio of PAN / DMF = 0.05, and stir evenly; 2 Electrospinning: Prepare a nanofiber composite membrane under a high-voltage electric field (80 kV); 3 Pre-oxidation treatment: Pre-oxidize in air (250 °C, 2 hours); 4 Carbonization treatment: Carbonize in a hydrogen-argon mixed gas atmosphere (700 °C, 8 hours).

[0094] 5 The measured specific surface area is shown in Table 1.

[0095] Example 6 This embodiment relates to a preparation method of a porous carbon electrode material, which comprises the following steps: 1 Spinning solution preparation: Mix PAN with a number average molecular weight of 50,000 and DMF according to the slurry mass ratio of PAN / DMF = 0.1, and stir evenly; 2 Electrospinning: Prepare a nanofiber composite membrane under a high-voltage electric field (35 kV); 3 Pre-oxidation treatment: Pre-oxidize in air by the stress-assisted method (250 °C, 2 hours); 4 Carbonization treatment: Carbonize in a nitrogen atmosphere in a tube furnace (700 °C, 2 hours).

[0096] 5 The measured specific surface area is shown in Table 1.

[0097] Example 7 This embodiment relates to a preparation method of a porous carbon electrode material, which comprises the following steps: 1 Spinning solution preparation: Mix PAN with a number average molecular weight of 85,000 and DMF according to the slurry mass ratio of PAN / DMF = 0.076, and stir evenly to obtain a spinning solution; 2 Electrospinning: Adopt needleless electrospinning technology to stretch the spinning solution into ultrafine nanofiber composites under a high-voltage electric field (50 kV), and collect them on a PP film to form a nanofiber composite membrane; 3 Stress-assisted pre-oxidation and carbonization treatment: Perform graphitization under the protection of a hydrogen-argon mixed gas (800 °C, 2 hours) to obtain a porous carbon electrode, and its conductivity is shown in Table 1.

[0098] 4 Perform SEM morphological characterization on it, as Figure 4 shown.

[0099] Example 8 This embodiment relates to a preparation method of a porous carbon electrode material, which comprises the following steps: 1 Preparation of spinning solution: PAN with a number-average molecular weight of 85000 and DMF were mixed at a mass ratio of PAN / DMF = 0.076 in the slurry, and after being stirred evenly, it was used as the spinning solution; 2 Electrospinning: Using needleless electrospinning technology, the spinning solution was stretched into ultrafine nano-composite fibers under a high-voltage electric field (60 kV) and collected on a PP film to form a nano-composite fiber membrane; 3 Stress-assisted pre-oxidation and subsequent carbonization treatment: Graphitization (900 °C, 2 hours) was carried out under the protection of a hydrogen-argon gas mixture to obtain a porous carbon electrode, and its conductivity is shown in Table 1.

[0100] 4 SEM morphological characterization was carried out on Example 8, as Figure 4 。

[0101] Table 1 Specific surface area of the porous carbon electrode materials in Examples 3-8

[0102] Example 9: This example relates to a preparation method of a nitrogen-doped porous carbon electrode material, which includes the following steps: PAN / DMF = 0.076 in the slurry was mixed with melamine (the mass ratio of melamine to PAN was 0.01), and after being stirred evenly, it was used as the spinning solution. Using needleless electrospinning technology, under the conditions of a high-voltage electric field (60 kV) and a temperature of 50 °C, the spinning solution was stretched into ultrafine nano-composite fibers, and a cyclic and multiple electrospinning process was adopted to gradually increase the film thickness layer by layer to obtain a uniformly distributed electrospun film, marked as NPC-1. Subsequently, the nano-composite fiber membrane was pre-oxidized in air (250 °C, 2 hours), and then graphitized under the protection of a hydrogen-argon gas mixture (1000 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0103] Furthermore, its conductivity was measured as shown in Table 2.

[0104] Furthermore, its specific surface area and pore size distribution are shown in Table 3, and the microporous and mesoporous structures are synergistically distributed, which is beneficial to improving the electrochemical performance.

[0105] Furthermore, Figure 5 the XRD spectrum of the example was given.

[0106] Furthermore, Figure 6 the FT-IR spectrum of the example was given.

[0107] Furthermore, Figure 7 the Raman spectrum of the example was given.

[0108] Furthermore, in 0.2 g / L Br -in the solution of Figure 10 The EIS test of the examples was carried out using a three-electrode system.

[0109] Furthermore, the XPS of N1s is as Figure 13 shown.

[0110] Example 10: This example relates to a preparation method of a nitrogen-doped porous carbon electrode material, which includes the following steps: PAN / DMF = 0.076 and melamine (the mass ratio of melamine to PAN is 0.02) were mixed according to the mass ratio of the slurry, and after stirring evenly, it was used as the spinning solution. Using the needleless electrospinning technique, under the conditions of a high-voltage electric field (60 kV) and a temperature of 50 °C, the spinning solution was stretched into ultrafine nanocomposite fibers. The cyclic and multiple spinning processes were adopted to gradually increase the film thickness layer by layer to obtain a uniformly distributed spinning film, marked as NPC-2. Subsequently, the nanocomposite fiber film was pre-oxidized in air (250 °C, 2 hours), and then graphitized under the protection of a hydrogen-argon mixed gas (1000 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0111] Furthermore, its conductivity is measured as shown in Table 2.

[0112] Furthermore, its specific surface area and pore size distribution are shown in Table 3. The microporous and mesoporous structures are synergistically distributed, which is beneficial to improving the electrochemical performance.

[0113] Furthermore, Figure 5 The XRD spectrum of the example is given.

[0114] Furthermore, Figure 6 The FT-IR spectrum of the example is given.

[0115] Furthermore, Figure 7 The Raman spectrum of the example is given, indicating the basic structure of NPC-1.

[0116] Furthermore, Figure 8 The contact angle diagram of the example is given. Doping can also improve the hydrophilicity of NPC-X. The static contact angle (SCA) is used as an index to characterize the change in the hydrophilicity of the electrode material. It can be seen that NPC-2 is hydrophilic. This phenomenon is mainly attributed to the rich pore structure and nitrogen doping in NPC-2. The excellent hydrophilic performance helps the diffusion of aqueous solution and ions on the electrode surface.

[0117] Furthermore, Figure 9 The N2 adsorption-desorption curve and pore size distribution curve of the example are given. According to the N2 adsorption-desorption curve and pore size distribution curve ( Figure 9(Illustration), for NPC-2 of the example, the hierarchical pores mainly have micropores, and the average pore width of BJH is about 1.94 nm (Table 3).

[0118] Furthermore, its TEM is as Figure 10 shown. The surface morphology of the carbonized NPC-2 sample was observed, and it can be seen that the fiber diameter of the example is as small as about 70 nm, and more micropores and defects are introduced, enhancing the denseness of the fiber.

[0119] Furthermore, in a solution of 0.2 g / L Br - , Figure 11 the EIS test was carried out on the example using a three-electrode system.

[0120] Its HR-TEM is as Figure 12 shown. HRTEM observation shows clear lattice fringes with a spacing of about 0.37 nm, which is larger than that of graphite (002) (0.335 nm), proving that element N is successfully doped into the C material.

[0121] Furthermore, the XPS of N1s of the example is as Figure 13 shown.

[0122] Example 11: This example relates to a preparation method of a nitrogen-doped porous carbon electrode material, which includes the following steps: Mix PAN / DMF = 0.076 and melamine (the mass ratio of melamine to PAN is 0.03) according to the mass ratio of the slurry, and stir evenly to obtain a spinning solution. Using the needleless electrospinning technique, under the conditions of a high-voltage electric field (60 kV) and a temperature of 50 °C, the spinning solution is stretched into ultrafine nano-composite fibers. Adopting a cyclic and multiple spinning process, the film thickness is increased layer by layer to obtain a uniformly distributed spinning film, marked as NPC-3. Subsequently, the nano-composite fiber film is pre-oxidized in air (250 °C, 2 hours), and then graphitized under the protection of a hydrogen-argon mixed gas (1000 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0123] Furthermore, its conductivity is measured as shown in Table 2.

[0124] Furthermore, its specific surface area and pore size distribution are shown in Table 3. The micropore and mesopore structures are distributed synergistically, which is beneficial to improving the electrochemical performance.

[0125] Furthermore, Figure 5 the XRD spectrum of the example is given, indicating the basic structure of NPC-3. The basic structure of NPC-X before and after N doping is not significantly affected.

[0126] Furthermore, Figure 6The FT-IR spectra of the examples are given to illustrate the basic structure of NPC-3.

[0127] Furthermore, Figure 7 The Raman spectra of the examples are given to illustrate the basic structure of NPC-3.

[0128] Furthermore, in a solution of 0.2 g / L Br - , Figure 11 The EIS test of the examples was carried out using a three-electrode system.

[0129] Furthermore, the XPS of N1s of the examples is as Figure 13 shown.

[0130] Comparative Example 1: According to the mass ratio of the slurry PAN / DMF = 0.076 without doping melamine, after stirring evenly, it was used as a spinning solution. Using the needleless electrospinning technique, under the conditions of a high-voltage electric field (60 kV) and a temperature of 50 °C, the spinning solution was stretched into ultrafine nanocomposite fibers and collected on a PP film to form a nanocomposite fiber membrane, marked as NPC-0. Subsequently, the nanocomposite fiber membrane was pre-oxidized in air (250 °C, 2 hours), and then graphitized under the protection of a hydrogen-argon mixed gas (1000 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0131] Both Comparative Example 1 and Example 4 have a mass ratio of PAN to DMF of 0.076, but do not contain doped melamine material, and are carbonized under a hydrogen-argon mixed gas at 1000 °C for 2 hours.

[0132] Furthermore, its conductivity is measured as shown in Table 2.

[0133] Furthermore, its specific surface area and pore size distribution are shown in Table 3. The synergistic distribution of micropores and mesopores is beneficial to improving the electrochemical performance.

[0134] Furthermore, Figure 5 The XRD spectra of the examples are given to illustrate that the basic structure of NPC-X before and after N doping is not significantly affected, indicating that co-spinning with doped melamine does not affect the basic structure of NPC.

[0135] Furthermore, Figure 6 The FT-IR spectra of the examples are given.

[0136] Furthermore, Figure 7 The Raman spectra of the examples are given. The carbon defects of NPC and NPC-X samples were further evaluated using Raman spectroscopy. All samples were at 1350 cm -1 (disorder and defect characteristics) and 1580 cm -1(Graphitization characteristics) shows D peak and G peak. In particular, the area ratio of D peak to G peak (I D / I G ) reflects the degree of disorder of carbon and the abundance of defects. NPC-2 has the smallest ID / IG, indicating the highest degree of graphitization. Obviously, this result is highly consistent with the XPS analysis. The degree of graphitization first increases and then decreases with the increase of melamine doping, and NPC-2 has the highest degree of graphitization and certain defect sites.

[0137] Furthermore, in a solution of 0.2 g / L Br - , Figure 11 the three-electrode system was used to perform EIS tests on the electrode.

[0138] Furthermore, the XPS of Example N1s is as Figure 13 shown.

[0139] Furthermore, Figure 6 the FT-IR spectra of the examples are given. It can be seen that NPC-0 and NPC-X simultaneously show two new absorption peaks at 1635 and 1039 cm -1 , which can be attributed to the absorption peaks of C=N and C-N bonds respectively. And all samples show a characteristic peak at around 3450 cm -1 , which is the stretching vibration peak of graphene sheets adsorbing H-O-H in water. This proves that the carbon materials prepared by needleless electrospinning of PAN have achieved the purpose of modified nitrogen doping, and the FT-IR spectra of NPC-X with different melamine doping amounts change little.

[0140] Comparative Example 2 This example relates to a preparation method of a nitrogen-doped porous carbon electrode material, which includes the following steps: Mix PAN / DMF = 0.076 and melamine (the mass ratio of melamine to PAN is 0.06) according to the slurry mass ratio, stir evenly and use it as the spinning solution. Using the needleless electrospinning technology, under the conditions of a high-voltage electric field (60 kV) and a temperature of 50 °C, the spinning solution is stretched into ultrafine nano-composite fibers. Adopt the cyclic and multiple spinning processes to gradually increase the film thickness layer by layer to obtain a uniformly distributed spinning film, marked as NPC-6. Subsequently, the nano-composite film is pre-oxidized in air (250 °C, 2 hours), and then graphitized under the protection of a hydrogen-argon mixed gas (1000 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0141] Example 12: This example relates to a preparation method of a nitrogen-doped porous carbon electrode material, which includes the following steps: Mix PAN / DMF = 0.076 and melamine (the mass ratio of melamine to PAN is 0.02) according to the mass ratio of the slurry, and stir evenly to obtain a spinning solution. Using needleless electrospinning technology, under the conditions of a high-voltage electric field (60 kV) and a temperature of 50 °C, stretch the spinning solution into ultrafine nanofibers and collect them on a PP film to form a nanofiber composite film. Subsequently, pre-oxidize the nanofiber composite film in air (250 °C, 2 hours), and then graphitize it under the protection of a hydrogen-argon mixed gas (1200 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0142] Furthermore, its conductivity is measured as shown in Table 2.

[0143] Example 13: This example relates to a preparation method of a nitrogen-doped porous carbon electrode material, which includes the following steps: Mix PAN / DMF = 0.076 and melamine (the mass ratio of melamine to PAN is 0.02) according to the mass ratio of the slurry, and stir evenly to obtain a spinning solution. Using needleless electrospinning technology, under the conditions of a high-voltage electric field (60 kV) and a temperature of 50 °C, stretch the spinning solution into ultrafine nanofibers and collect them on a PP film to form a nanofiber composite film. Subsequently, pre-oxidize the nanofiber composite film in air (250 °C, 2 hours), and then graphitize it under the protection of a hydrogen-argon mixed gas (1300 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0144] Furthermore, its conductivity is measured as shown in Table 2.

[0145] Example 14: This example relates to a preparation method of a nitrogen-doped porous carbon electrode material, which includes the following steps: Mix PAN / DMF = 0.076 and melamine (the mass ratio of melamine to PAN is 0.02) according to the mass ratio of the slurry, and stir evenly to obtain a spinning solution. Using needleless electrospinning technology, under the conditions of a high-voltage electric field (60 kV) and a temperature of 30 °C, stretch the spinning solution into ultrafine nanofibers and collect them on a PP film to form a nanofiber composite film. Subsequently, pre-oxidize the nanofiber composite film in air (250 °C, 2 hours), and then graphitize it under the protection of a hydrogen-argon mixed gas (1400 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0146] Furthermore, its conductivity is measured as shown in Table 2.

[0147] Example 15: This example relates to a preparation method of a nitrogen-doped porous carbon electrode material, which includes the following steps: Mix PAN / DMF = 0.076 and melamine (the mass ratio of melamine to PAN is 0.02) according to the mass ratio of the slurry, stir evenly and use it as the spinning solution. Adopt needleless electrospinning technology, under the conditions of high-voltage electric field (60 kV) and temperature 50 °C, stretch the spinning solution into ultrafine nano-composite fibers, and collect them on the PP film to form a nano-composite fiber membrane. Subsequently, pre-oxidize the nano-composite fiber membrane in air (250 °C, 2 hours), and then graphitize it under the protection of a hydrogen-argon mixed gas (1500 °C, 2 hours) to finally obtain a nitrogen-doped porous carbon electrode.

[0148] Furthermore, its conductivity is measured as shown in Table 2.

[0149] Table 2 Conductivity of the carbon electrode materials of Examples 9 - 15 and Comparative Examples 1 - 2

[0150] Example 16: In an aqueous halogen solution of 1 g / L Br - and 17 g / L Cl - , use the porous carbon nitride material prepared in Example 9 as the anode for the electrochemistry bromine extraction experiment, and measure its bromine extraction efficiency and energy consumption. The experiment is carried out in a hydrogen bromine fuel cell (HBFC) device, which operates in a sealed flow cell at room temperature (25 ± 3 °C) to achieve the selective oxidation of bromide ions. The cathode and the sealed anode chamber are separated by a cation exchange membrane (Nafion 117, Sigma - Aldrich). On the anode liquid side, two containers are respectively filled with 40 mL of anode liquid, and another container is filled with 20 mL of anode liquid and 20 mL of CCl4; in the cathode chamber, a sufficient amount of 0.5 M H2SO4 is added as the cathode electrolyte to ensure the electron transfer matching the Br - oxidation reaction and promote the hydrogen evolution reaction (HER). The electrolyte is fully mixed and circulated by a flow pump for bromine extraction.

[0151] Furthermore, the measured constant - current bromine extraction diagram is shown in Figure 14 .

[0152] Furthermore, its measured bromine extraction efficiency, Faraday efficiency, and energy consumption (kJ / g) are shown in Table 3.

[0153] Furthermore, under the conditions of constant current followed by constant voltage, the bromine extraction efficiency is further increased to 99.7%. The measured constant - current - then - constant - voltage bromine extraction diagram is shown in Figure 15 .

[0154] Example 17: In 1 g / L Br - and 17 g / L Cl -In a bromide aqueous solution, the porous carbon nitride material prepared in Example 10 was used as the anode for the electrochemically bromine extraction experiment to measure its bromine extraction efficiency and energy consumption. The experiment was carried out in a hydrogen bromide fuel cell (HBFC) device, which was operated in a sealed flow cell at room temperature (25 ± 3 °C) to achieve the selective oxidation of bromide ions. The cathode and the sealed anode chamber were separated by a cation exchange membrane (Nafion 117, Sigma - Aldrich). On the anode side, two containers were respectively filled with 40 mL of anode solution, and another container was filled with 20 mL of anode solution and 20 mL of CCl4; in the cathode chamber, sufficient 0.5 M H2SO4 was added as the cathode electrolyte to ensure the electron transfer matching the Br - oxidation reaction and to promote the hydrogen evolution reaction (HER). The electrolyte was fully mixed and circulated by a flow pump for bromine extraction.

[0155] Furthermore, the measured constant - current bromine extraction diagram is shown in Figure 14 .

[0156] Furthermore, the measured bromine extraction efficiency, Faraday efficiency, and energy consumption (kJ / g) are shown in Table 3.

[0157] Example 18: In a bromide aqueous solution of 1 g / L Br - and 17 g / L Cl - , the porous carbon nitride material prepared in Example 11 was used as the anode for the electrochemically bromine extraction experiment to measure its bromine extraction efficiency and energy consumption. The experiment was carried out in a hydrogen bromide fuel cell (HBFC) device, which was operated in a sealed flow cell at room temperature (25 ± 3 °C) to achieve the selective oxidation of bromide ions. The cathode and the sealed anode chamber were separated by a cation exchange membrane (Nafion 117, Sigma - Aldrich). On the anode side, two containers were respectively filled with 40 mL of anode solution, and another container was filled with 20 mL of anode solution and 20 mL of CCl4; in the cathode chamber, sufficient 0.5 M H2SO4 was added as the cathode electrolyte to ensure the electron transfer matching the Br - oxidation reaction and to promote the hydrogen evolution reaction (HER). The electrolyte was fully mixed and circulated by a flow pump for bromine extraction.

[0158] Furthermore, the measured constant - current bromine extraction diagram is shown in Figure 14 .

[0159] Furthermore, the measured bromine extraction efficiency, Faraday efficiency, and energy consumption (kJ / g) are shown in Table 3.

[0160] Table 3 Bromine extraction efficiency of the carbon electrode materials in Examples 16 - 18 and Comparative Examples 3 - 4

[0161] Comparative Example 3: In a bromine-containing aqueous solution of 1 g / L Br - and 17 g / L Cl - using the porous carbon nitride material prepared in Comparative Example 1 as the anode for the electrochemically bromine extraction experiment, and measuring its bromine extraction efficiency and energy consumption. The experiment was carried out in a hydrogen bromine fuel cell (HBFC) device, which was operated in a sealed flow cell at room temperature (25 ± 3 °C) to achieve the selective oxidation of bromide ions. The cathode and the sealed anode chamber were separated by a cation exchange membrane (Nafion 117, Sigma-Aldrich). On the anode side, two containers were respectively filled with 40 mL of the anolyte, and another container was filled with 20 mL of the anolyte and 20 mL of CCl4; in the cathode chamber, a sufficient amount of 0.5 M H2SO4 was added as the cathode electrolyte to ensure the electron transfer matching the Br - oxidation reaction and to promote the hydrogen evolution reaction (HER). The electrolyte was fully mixed and circulated by a flow pump for bromine extraction.

[0162] Furthermore, the measured constant current bromine extraction diagram is shown in Figure 14 .

[0163] Furthermore, the measured bromine extraction efficiency, Faraday efficiency, and energy consumption (kJ / g) are shown in Table 3.

[0164] Comparative Example 4 In a bromine-containing aqueous solution of 1 g / L Br - and 17 g / L Cl - using the porous carbon nitride material prepared in Comparative Example 2 as the anode for the electrochemically bromine extraction experiment, and measuring its bromine extraction efficiency and energy consumption. The experiment was carried out in a hydrogen bromine fuel cell (HBFC) device, which was operated in a sealed flow cell at room temperature (25 ± 3 °C) to achieve the selective oxidation of bromide ions. The cathode and the sealed anode chamber were separated by a cation exchange membrane (Nafion 117, Sigma-Aldrich). On the anode side, two containers were respectively filled with 40 mL of the anolyte, and another container was filled with 20 mL of the anolyte and 20 mL of CCl4; in the cathode chamber, a sufficient amount of 0.5 M H2SO4 was added as the cathode electrolyte to ensure the electron transfer matching the Br - oxidation reaction and to promote the hydrogen evolution reaction (HER). The electrolyte was fully mixed and circulated by a flow pump for bromine extraction. The measured bromine extraction efficiency, Faraday efficiency, and energy consumption (kJ / g) are shown in Table 3.

[0165] XPS Characterization To further study the mechanism of obtaining high bromine extraction efficiency for the nitrogen-doped porous carbon electrode materials described in this paper, the XPS of the carbon electrode materials of Examples 16-18 and Comparative Examples 3-4 was also characterized, and the results are respectively as Figure 11 shown in and Table 4.

[0166] Table 4: XPS Characterization Results of Carbon Electrode Materials of Examples 16-18 and Comparative Examples 3-4

[0167] Nitrogen is one of the most common heteroatoms in carbon material doping. Introducing nitrogen atoms into the graphite structure of carbon materials will significantly change their atomic and electronic structures, forming a sp 2 delocalized conjugate system. Since the sizes of nitrogen atoms and carbon atoms are similar, the process of nitrogen atoms replacing carbon atoms causes very little damage to the carbon material skeleton structure, so the stability of the carbon material can be maintained. Generally speaking, as the nitrogen content increases, the conductivity of the carbon material will first increase and then decrease. When a small amount of nitrogen atoms are doped into the carbon material, it can provide more free electrons for the conduction band, thus improving the conductivity. However, too high a nitrogen content will cause the carbon material skeleton structure to collapse, introducing too many defect sites and reducing the conductivity instead. According to the position of nitrogen atoms, nitrogen-doped carbon materials are mainly divided into three structures: graphitic nitrogen (400.8 eV), pyridinic nitrogen (398.4 eV), and nitrogen oxides (402.1 eV), and these structures can be detected by X-ray photoelectron spectroscopy. Research shows that these nitrogen-doped structures exhibit different properties due to their different electronic structures, among which graphitic nitrogen and pyridinic nitrogen play a significant role in improving the conductivity of carbon materials. As the doping amount of melamine increases, the proportion of graphitic nitrogen in nitrogen species first increases and then decreases, so the conductivity of NPC-2 is relatively high. And it has relatively more pyridinic nitrogen and more defect sites. The NPC-2 sample includes 72.6% graphitic nitrogen, 22.5% pyridinic nitrogen, and 5.0% nitrogen oxides, which can provide good conductivity and high defect sites at the same time, so its electrochemical performance is better than that of NPC-0, NPC-1, NPC-3, and NPC-6.

[0168] In response to the demand for bromine extraction from brine, this study designed and prepared a nitrogen-doped porous carbon electrode with low mass transfer resistance based on needleless electrospinning technology. Using melamine and polyacrylonitrile as nitrogen sources and polyacrylonitrile as the carbon source, a multi-scale PAN nanofiber composite membrane (NPC-2) composed of approximately 70 nm ultrafine nanofibers was prepared by co-electrospinning. The smaller fiber diameter provides a larger specific surface area, enhancing the contact between the fiber and the bromide solution, thereby improving the adsorption effect; at the same time, the nanoscale structure shortens the ion diffusion path and accelerates the migration of bromide ions to the fiber surface. After carbonization, the fiber structure is uniform and the pore distribution is reasonable, further enhancing the capture and mass transfer efficiency of bromide ions. In addition, the excellent thermal stability and mechanical strength of the material ensure its structural integrity during the bromine extraction process. Nitrogen doping not only changes the microstructure of the carbon material, promotes the internal cross-linking reaction of the fiber and the volume shrinkage during carbonization, reducing the fiber diameter to approximately 70 nm, but also introduces more micropores and defects, enhancing the densification of the fiber. In addition, after nitrogen atoms are embedded in the carbon lattice, the electronic structure is optimized, the free carrier density is increased, and at the same time, the three-dimensional staggered porous network forms an efficient electron transport channel, synergistically improving the conductivity. These characteristics work together to significantly improve the bromine extraction performance of the electrode.

[0169] The above description of the embodiments is intended to enable those of ordinary skill in the art to understand and apply this application. It is obvious that those who are familiar with the technology in this field can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, this application is not limited to the embodiments here, and the improvements and modifications made by those skilled in the art based on the content disclosed in this application without departing from the scope and spirit of this application are within the scope of this application.

Claims

1. A preparation method of a nitrogen-doped porous carbon electrode material, characterized in that, The method includes the following steps: S10: Mix a carbon source and a nitrogen source to obtain a spinning solution; wherein the carbon source is polyacrylonitrile, the nitrogen source is melamine and polyacrylonitrile, and the mass ratio of melamine to polyacrylonitrile in the spinning solution is 0.01 - 0.03; S20: By a needleless electrospinning process, stretch the spinning solution into a nanocomposite fiber membrane at 35 - 80 kV and 30 - 60 °C, and collect it on a substrate film; S30: Perform stress-assisted pre-oxidation treatment on the nanocomposite fiber membrane to obtain a pre-oxidized nanocomposite fiber membrane; S40: Under an inert atmosphere, perform carbonization or graphitization on the pre-oxidized nanocomposite fiber membrane to obtain the nitrogen-doped porous carbon electrode material, and this nitrogen-doped porous carbon electrode material includes a hierarchical pore structure; Among them, the stress-assisted pre-oxidation treatment includes the following steps: Fix the nanocomposite fiber membrane between two smooth splints, and then heat them together for a predetermined period of time.

2. The preparation method according to claim 1, characterized in that, During the stress-assisted pre-oxidation treatment, the temperature is 180 - 300 °C and the time is 2 - 3 hours.

3. The preparation method according to claim 1, characterized in that, In step S40, the inert atmosphere is argon or a hydrogen-argon mixed gas; the carbonization temperature is 700 - 1500 °C and the time is 2 - 8 hours.

4. A nitrogen-doped porous carbon electrode material prepared by the preparation method according to any one of claims 1 - 3.

5. Use of the nitrogen-doped porous carbon electrode material according to claim 4 in electrochemically extracting bromine.

6. An electrochemistry bromine extraction device, characterized in that, The electrochemically extracting bromine device includes a sealed flow cell, an anode and a cathode are arranged in the sealed flow cell, the anode uses the nitrogen-doped porous carbon electrode material according to claim 4, and the anode and the cathode are separated by a cation exchange membrane.

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