Preparation method of NOBi co-doped carbon nanofiber electrode material and application of NOBi co-doped carbon nanofiber electrode material in iron-chromium flow battery

Abstract

The invention belongs to the technical field of battery materials and energy storage, and particularly relates to application of a preparation method of an NOBi co-doped carbon nanofiber electrode material in an iron-chromium flow battery. The preparation method comprises the following steps: by taking ammonium bismuth citrate as a functional component, adding the ammonium bismuth citrate into a solution of polyacrylonitrile and N, N-dimethylformamide to prepare an electrospinning precursor solution; the preparation method comprises the following steps: preparing polyacrylonitrile-based three-dimensional nanofiber containing ammonium bismuth citrate by utilizing an electrostatic spinning technology, then pre-oxidizing and carbonizing the obtained fiber, and simultaneously introducing active functional components of nitrogen, oxygen and bismuth into the carbon fiber by utilizing pyrolysis of ammonium bismuth citrate in the process, so that the carbon fiber is prepared. Therefore, the carbon nanofiber electrode material is endowed with relatively high hydrogen evolution overpotential and good electrocatalytic activity. When the composite material is used as the negative electrode material of the iron-chromium flow battery, the synergistic effect of all the components can be fully exerted, and the energy conversion efficiency and the rate capability of the battery are effectively improved. The method is simple, efficient and suitable for large-scale production, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of battery materials and energy storage technology, specifically relating to the application of a method for preparing N\O\Bi co-doped carbon nanofiber electrode material in iron-chromium redox flow batteries. Background Technology

[0002] Renewable energy can effectively address the shortage of traditional fossil fuel resources; however, the intermittency and volatility of renewable energy make it difficult to meet electricity demand. Large-scale energy storage technology is key to achieving grid connection of new energy sources. Flow batteries, as an important large-scale energy storage technology, can effectively solve the problems of discontinuous and unstable renewable energy, providing important support for the large-scale development of renewable energy and the adjustment and transformation of my country's energy structure.

[0003] The energy of a redox flow battery is determined by the concentration and volume of the electrolyte, while the power is determined by the size of the stack, thus achieving decoupling of energy and power. In addition, it boasts advantages such as large capacity, flexible design, long cycle life, high safety, and flexible site selection. These unique advantages make it one of the most suitable technologies for large-scale energy storage. Currently, the most mature and commercially viable flow battery is the all-vanadium redox flow battery. However, the finite nature of vanadium resources severely limits its large-scale development. Developing other low-cost aqueous flow batteries is of great significance for promoting the development of clean energy and large-scale energy storage technologies.

[0004] Iron-chromium redox flow batteries use iron and chromium as the active materials for both the positive and negative electrodes. These raw materials are naturally abundant and offer a significant cost advantage. However, the chromium content in the negative electrode... 3+ / Cr 2+ Electrochemical redox kinetics are very slow and are greatly affected by hydrogen evolution side reactions. Appropriate electrode materials are needed to promote the main reaction and inhibit the hydrogen evolution side reactions in order to effectively improve the overall performance of the battery.

[0005] Currently, the most widely used electrode material for flow batteries is polyacrylonitrile-based carbon fiber electrode material, which has advantages such as low cost, high conductivity, and good stability. However, its small electrochemical reactive surface area severely limits battery performance. Furthermore, the vertical fibers of carbon felt can damage the separator, requiring appropriate measures to protect the separator and extend battery life. In recent years, the highly controllable and simple electrospinning technology has been widely used to regulate the microstructure of carbon fiber electrode materials to prepare high-performance flow battery electrode materials. Electrospun carbon nanofibers (ECNFs) electrodes have a higher specific surface area and electrochemical activity compared to carbon felt electrodes. In addition, by introducing suitable catalysts into the precursor solution, the electrocatalytic performance of the material can be easily and effectively improved, and specific functionalities, such as hydrogen evolution inhibition, can be specifically assigned to the electrode. However, the close-packed structure of electrospun carbon nanofibers is not suitable for electrolyte transport, but combining them with carbon felt electrodes can simultaneously achieve rapid electrolyte transport and effective improvement of electrochemical activity. In addition, the carbon nanofibers in the electrospun carbon nanofiber electrode catalyst layer are arranged in a planar manner and there are no vertical fibers. Placing them between the separator and the carbon felt will protect the separator and further improve the cycle stability of the battery. Summary of the Invention

[0006] To address the bottleneck issues of poor anode reaction kinetics and severe hydrogen evolution reaction in current iron-chromium redox flow batteries, this invention provides an anode electrode material for iron-chromium redox flow batteries that combines high hydrogen evolution overpotential and high electrocatalytic activity.

[0007] The specific technical solution is: a method for preparing N\O\Bi co-doped carbon nanofiber electrode material, comprising the following steps: 1) Bismuth ammonium citrate C6H 13 BiN2O7·H2O was dispersed in N,N-dimethylformamide DMF solution, and after being ultrasonically dispersed evenly, polyacrylonitrile (PAN) was added. After heating and stirring to mix evenly, a polyacrylonitrile-based electrospinning precursor solution containing bismuth ammonium citrate was obtained. 2) The polyacrylonitrile-based electrospinning precursor solution containing bismuth ammonium citrate obtained in step 1) is electrospinned to collect polyacrylonitrile-based three-dimensional nanofiber precursor containing bismuth ammonium citrate. 3) Place the polyacrylonitrile-based three-dimensional nanofiber precursor containing bismuth ammonium citrate obtained in step 2) between corundum plates and place it in a box furnace for pre-oxidation treatment to obtain polyacrylonitrile-based pre-oxidized fiber. 4) The polyacrylonitrile-based pre-oxidized fiber obtained in step 3) is subjected to carbonization treatment to obtain a highly active carbon nanofiber electrode material co-doped with N, O and Bi.

[0008] In the above-mentioned method for preparing N\O\Bi co-doped carbon nanofiber electrode material, in step 1), the number average molecular weight of polyacrylonitrile (PAN) is 90,000 to 150,000.

[0009] The above-mentioned method for preparing an N\O\Bi co-doped carbon nanofiber electrode material involves using bismuth ammonium citrate (C6H2O) 13 In a mixture of BiN2O7·H2O, polyacrylonitrile (PAN), and N,N-dimethylformamide (DMF), the PAN concentration was 12–18 wt%, and bismuth ammonium citrate (C6H) was added. 13 The amount of BiN2O7·H2O added to PAN is 1:100 to 1:10 by mass.

[0010] In the above-mentioned method for preparing an N\O\Bi co-doped carbon nanofiber electrode material, in step 1), bismuth ammonium citrate (C6H) 13 The mixing and dissolution conditions of BiN2O7·H2O, polyacrylonitrile (PAN), and N,N-dimethylformamide (DMF) were controlled as follows: temperature 60–90 °C, magnetic stirring for 6–12 h.

[0011] In the above-mentioned method for preparing N\O\Bi co-doped carbon nanofiber electrode material, step 2) involves the following electrospinning conditions: receiver roller speed of 100–300 r / min; voltage of 16–25 kV; receiving distance of 8–15 cm; spinning temperature of 20–50 ℃; spinning humidity of 30–60 RH; and pushing speed of 10–60 μL / min. In the above-mentioned method for preparing an N\O\Bi co-doped carbon nanofiber electrode material, step 3) involves pre-oxidation treatment under the following conditions: heat treatment at 250-350 °C for 0.5-3 h in an air atmosphere.

[0012] In the above-mentioned method for preparing N\O\Bi co-doped carbon nanofiber electrode material, step 4) involves the following carbonization treatment conditions: heat treatment at 900-1200 °C for 1-5 h in a vacuum, nitrogen, or inert atmosphere to obtain the N\O\Bi co-doped carbon nanofiber electrode material.

[0013] Application of N\O\Bi co-doped carbon nanofiber electrode materials prepared by the above method in iron-chromium redox flow batteries.

[0014] In the above application, the N\O\Bi co-doped carbon nanofiber electrode material prepared according to the above preparation method is used as the negative electrode catalyst layer and placed between the negative electrode carbon felt electrode and the separator to assemble an iron-chromium flow battery.

[0015] In the above applications, the thickness ratio of the negative electrode catalyst layer to the negative electrode carbon felt electrode is 1:200 to 1:50.

[0016] The beneficial effects of this invention are: 1. This invention utilizes the strong designability of electrospinning technology. By introducing a single functional component, bismuth ammonium citrate, into the electrospinning precursor solution, the hydrogen evolution inhibitor bismuth, electrocatalytic heteroatoms nitrogen and oxygen can be introduced simultaneously. The method is simple, efficient, universal, and suitable for large-scale production.

[0017] 2. The electrode material prepared by this invention contains bismuth, nitrogen and oxygen functional components, and has high catalytic activity for the electrochemical reaction of chromium ions at the negative electrode, a large active area and a high overpotential for the hydrogen evolution side reaction. It can promote the negative electrode reaction process while inhibiting the hydrogen evolution side reaction. As a negative electrode material for iron-chromium redox flow batteries, it can effectively reduce the kinetic difference between the positive and negative electrode reactions of iron-chromium redox flow batteries, thereby improving the electrolyte utilization rate and improving battery performance.

[0018] 3. The N\O\Bi co-doped carbon nanofiber material prepared in this invention is used as a catalyst layer and combined with the carbon felt electrode. When assembling the battery, the catalyst layer is placed between the separator and the carbon felt. This not only enhances the electrochemical reaction activity but also protects the separator, effectively improving the cycle life of the battery. Attached Figure Description

[0019] Figure 1 Scanning electron microscope images of blank carbon nanofiber electrode materials (ECNFs) (a) and N\O\Bi co-doped carbon nanofiber electrode materials (NOBi@ECNFs) (b) prepared in Example 1.

[0020] Figure 2 Cyclic voltammetry curves (scan rate: 5 mV·s) of blank carbon nanofiber electrode materials (ECNFs) and N\O\Bi co-doped carbon nanofiber electrode materials (NOBi@ECNFs) prepared in Example 1 in 1 M CrCl3 + 1 M FeCl2 + 3 M HCl. -1 ). Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] Example 1

[0023] (I) Preparation of N\O\Bi co-doped carbon nanofiber electrode materials

[0024] 1) Preparation of polyacrylonitrile-based three-dimensional nanofiber precursors containing bismuth ammonium citrate

[0025] 1 g of bismuth ammonium citrate (C6H) 13BiN2O7·H2O), 7 g of polyacrylonitrile (PAN) powder with a molecular weight of 150,000 were dried and mixed with 43 g of N,N-dimethylformamide (DMF) solution. The three were magnetically stirred at 80 °C for 12 h until completely dissolved to obtain a polyacrylonitrile-based electrospinning precursor solution containing bismuth ammonium citrate.

[0026] A polyacrylonitrile-based electrospinning precursor solution containing bismuth ammonium citrate was loaded into a syringe and placed on a syringe pump. The tubing was connected, and an aluminum foil-attached stainless steel roller was used as a receiver to collect the polyacrylonitrile-based three-dimensional nanofiber precursors containing bismuth ammonium citrate. Electrospinning conditions: receiver roller speed 150 r / min; voltage 20 kV; receiving distance 13 cm; spinning temperature 27℃; spinning humidity 30% RH; push speed 30 μL / min; spinning time 2 h.

[0027] 2) Preparation of N\O\Bi co-doped carbon nanofiber electrode material (NOBi@ECNFs)

[0028] The polyacrylonitrile-based three-dimensional nanofiber precursor containing bismuth ammonium citrate prepared above was placed between corundum plates and placed in a box furnace for pre-oxidation treatment. In an air atmosphere, the heating rate was 2 ℃ / min, and the furnace was heat-treated at 280 ℃ for 60 min to obtain polyacrylonitrile-based pre-oxidized fiber.

[0029] The obtained polyacrylonitrile-based pre-oxidized filaments were subjected to carbonization treatment, namely, heat treatment at 1000 ℃ for 120 min in a nitrogen atmosphere with a heating rate of 5 ℃ / min. The resulting N\O\Bi co-doped carbon nanofiber electrode material was labeled NOBi@ECNFs.

[0030] (II) Comparative Example - Preparation of Blank Polyacrylonitrile Carbon Nanofiber Electrode Materials (ECNFs)

[0031] Electrospinning was performed using the electrospinning precursor solution prepared under the same conditions as in step (I), except without the addition of bismuth ammonium citrate. A stainless steel roller with aluminum foil attached was used as a receiver to collect the fiber precursors, thus obtaining blank polyacrylonitrile carbon nanofiber precursors. These blank polyacrylonitrile carbon nanofiber precursors were then heat-treated under the same pre-oxidation and carbonization conditions as those used in the preparation of NOBi@ECNFs to obtain blank polyacrylonitrile carbon nanofiber electrode materials, labeled (ECNFs).

[0032] Figure 1 Scanning electron microscope images of blank carbon nanofiber electrode materials (ECNFs) (a) and N\O\Bi co-doped carbon nanofiber electrode materials (NOBi@ECNFs) (b) prepared in Example 1. Figure 1As shown in (a): the blank polyacrylonitrile carbon nanofiber electrode material (ECNFs) has a fiber diameter of approximately 200 nm and a relatively smooth surface. Figure 1 As shown in (b), the N\O\Bi co-doped carbon nanofiber electrode material (NOBi@ECNFs) has a more uniform diameter distribution and a slightly smaller diameter, approximately 150 nm. This may be due to the addition of bismuth ammonium citrate, which increases the conductivity of the precursor spinning solution, strengthens the electric field, and results in a smaller fiber diameter and more uniform and continuous spun nanofibers.

[0033] Example 2 Electrochemical Performance Testing

[0034] Methods: The electrochemical performance of the materials was tested using a three-electrode system. The N\O\Bi co-doped carbon nanofiber electrode material (NOBi@ECNFs) prepared in Example 1 and the blank polyacrylonitrile carbon nanofiber electrode material (ECNFs) were used as working electrodes, a 232-type saturated calomel electrode was used as the reference electrode, a platinum sheet was used as the auxiliary electrode, and 1 M CrCl3 + 1 M FeCl2 + 3 MHCl was used as the electrolyte. Cyclic voltammetry (CV) curves and electrochemical impedance spectroscopy (EIS) were performed.

[0035] Figure 2 (a) shows the cyclic voltammetry curves measured on the two sets of electrode materials. The redox current of chromium ions at the negative electrode of the N\O\Bi co-doped carbon nanofiber electrode material (NOBi@ECNFs) is significantly greater than that of ECNFs, and the redox peak position difference is reduced, indicating that it has better electrochemical activity and electrochemical reversibility. In addition, the interference of hydrogen evolution reaction is significantly reduced, indicating that the electrode material has a higher hydrogen evolution overpotential and can effectively suppress hydrogen evolution side reactions.

[0036] Figure 2 (b) Nyquist plots of electrochemical impedance spectroscopy (EIS) measured on the two sets of electrode materials. The Nyquist plot measured on the N\O\Bi co-doped carbon nanofiber electrode material (NOBi@ECNFs) consists of a semicircular arc and a straight line, indicating that the electrochemical reaction process of chromium ions on its surface is jointly controlled by charge transfer and diffusion. Furthermore, the Nyquist plot measured on the NOBi@ECNFs electrode has a smaller arc radius and a larger linear slope, indicating a faster mass and charge transfer rate on its surface. This further demonstrates the excellent electrocatalytic activity of this electrode material for the redox reaction of chromium ions at the negative electrode. The above electrochemical test results show that the N\O\Bi co-doped carbon nanofiber electrode material (NOBi@ECNFs) prepared in this invention has good application feasibility in iron-chromium flow batteries, can effectively improve the hysteretic electrode reaction process of chromium ions at the negative electrode, and helps to improve battery performance.

[0037] Example 3 Battery Testing

[0038] Method: The N\O\Bi co-doped carbon nanofiber electrode material (NOBi@ECNFs) prepared in Example 1 was used as the negative electrode catalyst layer and placed between the negative electrode carbon felt electrode and the separator. The electrode area was 3×3 cm. 2 The catalyst layer was 20 µm thick, the carbon felt was 2.5 mm thick, Nafion 212 was used as the ion exchange membrane, and 1.0 M CrCl3 + 1.0 M FeCl2 + 3.0 M HCl was used as the electrolyte. The electrolyte volume for both the positive and negative electrodes was 10 ml. The charge / discharge cutoff voltages were 1.65 V and 1.0 V, respectively. The battery was tested at 200, 300, and 400 mA·cm⁻¹. -2 The rate performance of the battery was tested at different current densities, with 6 cycles at each current density.

[0039] Table 1 shows the coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of batteries assembled with NOBi@ECNFs as electrodes at different current densities, with comparisons made to ECNFs. The batteries assembled with NOBi@ECNFs can still operate stably at high current densities, and at 200 mA·cm⁻¹... -2 The battery's voltage efficiency and energy efficiency reached 83.6% and 80.7%, respectively.

[0040] Table 1

Claims

1. A preparation method of N\O\Bi co-doped carbon nanofiber electrode material, characterized in that, The method comprises the following steps: 1) Bismuth ammonium citrate C6H 13 BiN2O7.H2O was dispersed in N,N-dimethylformamide DMF solution, and after ultrasonic dispersion was uniform, polyacrylonitrile PAN was added, and after heating and stirring were mixed uniformly, a polyacrylonitrile-based electrospinning precursor solution containing bismuth ammonium citrate was obtained; 2) electrospinning the polyacrylonitrile-based precursor solution containing ammonium bismuth citrate obtained in step 1) to collect polyacrylonitrile-based three-dimensional nanofiber filaments containing ammonium bismuth citrate; 3) placing the polyacrylonitrile-based three-dimensional nanofiber filaments containing ammonium bismuth citrate obtained in step 2) between corundum plates and placing them in a box furnace for pre-oxidation treatment to obtain polyacrylonitrile-based pre-oxidized filaments; 4) carbonizing the polyacrylonitrile-based pre-oxidized filaments obtained in step 3) to obtain N\O\Bi co-doped high-activity carbon nanofiber electrode materials.

2. The method for preparing an N\O\Bi co-doped carbon nanofiber electrode material according to claim 1, characterized in that, In step 1), the number average molecular weight of the polyacrylonitrile (PAN) is 90-150 thousand.

3. The method for preparing an N\O\Bi co-doped carbon nanofiber electrode material according to claim 1, characterized in that, BiN2O7»H2O, polyacrylonitrile (PAN) and N,N-dimethylformamide (DMF) mixture, the concentration of PAN is 12-18 wt %, the concentration of BiN2O7»H2O is 0.1-0.5 wt %, the concentration of DMF is 80-88 wt %. 13 BiN2O7»H2O, polyacrylonitrile (PAN) and N,N-dimethylformamide (DMF) mixture, the concentration of PAN is 12-18 wt %, the concentration of BiN2O7»H2O is 0.1-0.5 wt %, the concentration of DMF is 80-88 wt %. 13 The addition amount of BiN2O7»H2O and PAN is 1:100-1:10 by mass ratio.

4. The method for preparing an N\O\Bi co-doped carbon nanofiber electrode material according to claim 1, characterized in that, In step 1), the bismuth ammonium citrate C6H 13 The mixed dissolution conditions of BiN2O7·H2O, polyacrylonitrile PAN and N, N-dimethylformamide DMF are controlled as follows: temperature is 60-90 ℃, and magnetic stirring is 6-12 h.

5. The method according to claim 1, wherein the method is characterized by, In step 2), the electrospinning conditions are as follows: the rotating speed of the receiver roller is 100-300 r / min; the voltage is 16-25 kV; the receiving distance is 8-15 cm; the spinning temperature is 20-50 ℃; the spinning humidity is 30-60 %RH; and the pushing speed is 10-60 μL / min.

6. The method for preparing an N\O\Bi co-doped carbon nanofiber electrode material according to claim 1, characterized in that, In step 3), the pre-oxidation treatment conditions are as follows: heat treatment at 250-350 ℃ for 0.5-3 h in an air atmosphere.

7. The method for preparing an N\O\Bi co-doped carbon nanofiber electrode material according to claim 1, characterized in that, In step 4), the carbonization treatment conditions are as follows: heat treatment at 900-1200 ℃ for 1-5 h in a vacuum, nitrogen or inert atmosphere, to obtain N\O\Bi co-doped carbon nanofiber electrode materials.

8. The use of the N\O\Bi co-doped carbon nanofiber electrode materials prepared by the preparation method of any one of claims 1-7 in iron-chromium liquid flow batteries.

9. Use according to claim 8, characterized in that, The N\O\Bi co-doped carbon nanofiber electrode materials prepared by the preparation method of any one of claims 1-5 are used as a negative electrode catalytic layer and are placed between a negative electrode carbon felt electrode and a separator to assemble an iron-chromium liquid flow battery.

10. Use according to claim 9, characterized in that, The thickness ratio of the negative electrode catalytic layer to the negative electrode carbon felt electrode is 1:200-1:50.

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