A method for modifying a graphite felt electrode with manganese dioxide nanoparticles and applications thereof

Abstract

The application discloses a method for modifying graphite felt electrodes with manganese dioxide nanoparticles and application. The method comprises the following steps: using an electrochemical method and selecting an ammonium sulfate electrolyte to pretreat graphite felt to improve the surface wettability; continuing to use the electrochemical method and selecting a DMF dispersion solution of graphene to etch the pretreated graphite felt to obtain a three-dimensional porous graphite felt; finally, using a hydrothermal reaction to make manganese dioxide nanoparticles directly generate on the surface and inside of the three-dimensional porous graphite felt to obtain a porous carbon fiber confined manganese dioxide nanoparticle modified graphite felt electrode. The method confines manganese dioxide nanoparticles with high catalytic activity in the porous carbon fibers of the graphite felt electrode material, the heterostructure has rich hierarchical pores and high specific surface area, the number of active sites on the surface of the graphite felt electrode material is increased, the electrochemical activity of the graphite felt electrode is significantly improved, and an organic aqueous solution flow battery assembled therefrom has good electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of organic battery technology in electrochemical energy storage, specifically to a method and application of manganese dioxide nanoparticle-modified graphite felt electrode. Background Technology

[0002] With the impact of global warming and climate change, countries worldwide are striving to reduce greenhouse gas emissions, and renewable energy has gained widespread attention due to its low pollution levels. There is an urgent need to improve renewable energy collection and storage technologies. Currently, electrochemical energy storage offers advantages over other energy storage methods, including lower construction costs, greater adaptability to different operating environments, and ease of operation. Compared to other energy storage batteries, flow batteries are considered the most promising energy storage system due to their low cost, high safety, and good rate performance. Organic flow batteries, which utilize organic active materials instead of traditional metals and halogens, are being further researched and developed, distinguishing them from traditional flow batteries.

[0003] Graphite felt is currently the most widely used electrode material in flow batteries. Graphite felt is a felt-like fibrous material with high porosity, resulting in large gaps that facilitate the flow of electrolyte and the conduction of active materials. However, when used directly as an electrode material without any treatment, graphite felt suffers from poor surface wettability and high resistivity. Furthermore, as the site of redox reactions in flow batteries, untreated graphite felt exhibits low electrochemical activity, affecting the mass transfer rate of active molecules. Therefore, graphite felt must be modified to improve its electrochemical activity before use as an electrode material.

[0004] Many existing methods exist for modifying the electrochemical activity of graphite felt, including heat treatment, chemical treatment, electrochemical methods, metal ion doping modification, non-metal element doping modification, and carbon-carbon composite modification. While these methods all have some limitations, the electrochemical method, which uses an inert electrode such as platinum or graphite felt as one electrode and a suitable electrolyte to form an electrochemical reaction cell, allows for electrochemical oxidation and etching of the graphite felt surface under an electric field. This process alters the oxygen-containing functional groups and specific surface area on the graphite felt surface, thereby improving its electrochemical performance and stability. Furthermore, graphite felt modified by this method can be further enhanced with nanoparticle modification to increase the specific surface area and electrochemical reaction active sites, thus further improving the performance of the graphite felt electrode. Summary of the Invention

[0005] Based on the above-mentioned technical problems, the purpose of this invention is to provide a method and application for modifying graphite felt electrodes with manganese dioxide nanoparticles.

[0006] This invention protects a method for modifying a graphite felt electrode with manganese dioxide nanoparticles, specifically comprising the following steps:

[0007] Step 1: Prepare an ammonium sulfate electrolyte of a certain concentration. Place two graphite felts as the positive and negative electrodes in the ammonium sulfate electrolyte, respectively. Apply a certain voltage to the two ends of the electrodes and perform electrolytic pretreatment on the graphite felts for 2 minutes. After the electrolytic pretreatment is completed, rinse with deionized water and then place in an oven to dry for later use.

[0008] Step 2: Prepare a DMF dispersion of graphene with a certain concentration. Place the pre-treated positive and negative graphene felt electrodes in the DMF dispersion of graphene. Apply a certain voltage to both ends of the electrodes and perform electrochemical etching on the graphene felt for a certain time of 3 to 100 minutes. After the electrochemical etching is completed, rinse with deionized water and then dry in an oven to obtain a three-dimensional porous graphene felt for later use.

[0009] Step 3: Dissolve an appropriate amount of KMnO4 in 65 mL of deionized water, stir until completely dissolved, and then continuously add anhydrous ethanol while stirring until homogeneous. Place the electrochemically etched graphite felt in a polytetrafluoroethylene (PTFE) liner, and simultaneously place the entire KMnO4 and anhydrous ethanol mixture in a 100 mL PTFE liner. Place the PTFE liner in a reaction vessel and then in an oven for a certain period of time to obtain a porous carbon fiber confined manganese dioxide nanoparticle modified graphite felt electrode.

[0010] Furthermore, in step 1, the concentration of the ammonium sulfate electrolyte is 0.1–0.4 mol / L; the voltage applied across the electrodes is 5–10 V; the drying temperature in the oven is 80 °C, and the drying time is 24 h.

[0011] Furthermore, in step 2, the concentration of the DMF dispersion of graphene is 0.05–0.2 mg / mL; the voltage applied across the electrodes is 5–10 V; the processing time is 3–100 min; the drying temperature in the oven is 80 °C; and the drying time is 24 h.

[0012] Furthermore, in step 3, the amount of KMnO4 used is 0.1-0.4g, and the amount of anhydrous ethanol added dropwise is 2-5mL; the oven temperature is 150-180℃, and the holding time is 10-20h.

[0013] The present invention also protects the application of the above-mentioned manganese dioxide nanoparticle modified graphite felt electrode, which is used in organic aqueous phase flow batteries.

[0014] Furthermore, the positive electrode active material of the organic aqueous phase flow battery is 0.2-0.4 mol / L TEMPO, the negative electrode active material is 0.2-0.4 mol / L methyl viologen (MV), the supporting electrolyte is 1.5-2 mol / L NaCl solution, and the battery separator is an anion exchange membrane.

[0015] Compared with existing technologies, the present invention has the following beneficial effects:

[0016] The manganese dioxide used in this invention is the most common and polymorphically diverse of manganese oxides, and is also one of the most widely studied. Due to its diverse structure, abundant sources, and environmental friendliness, it has attracted much attention and is widely used in energy-related fields such as supercapacitors and alkaline liquid batteries. By confining highly catalytically active manganese dioxide nanoparticles within porous carbon fibers of graphite felt electrode material, the designed heterostructure possesses abundant hierarchical pores and a high specific surface area, increasing the number of active sites on the graphite felt electrode surface and significantly improving the electrochemical activity of the graphite felt electrode. The assembled organic aqueous flow battery exhibits good electrochemical performance. Applying this modified graphite felt electrode, with manganese dioxide nanoparticles confined within carbon fibers, to organic aqueous flow batteries can significantly optimize the battery's energy efficiency, coulombic efficiency, and voltage efficiency. The electrode modification method of this invention has the following advantages:

[0017] (1) The present invention uses an electrochemical method to introduce a three-dimensional pore structure on the surface of graphite felt carbon fiber. The operation process is simple and easy to control. It can introduce pores on the surface and inside of carbon fiber texture, and can also avoid carbon fiber breakage.

[0018] (2) The present invention proposes to confine MnO2 nanoparticles in the three-dimensional pores of carbon fiber. This heterostructure breaks through the limitations of traditional heat treatment, acid treatment, doping and carbon material modification, which can only be carried out on the surface of carbon fiber. It extends the modification treatment of graphite felt electrode material to three-dimensional space and can greatly improve the electrochemical performance of graphite felt electrode.

[0019] (3) MnO2 can be further doped and modified to introduce more electrochemical active sites and improve its conductivity, thereby further improving the electrochemical performance of the electrode; or other nanoparticles can be introduced to form a confined structure to explore the influence of other types of nanoparticles on the electrochemical performance of graphite felt electrodes.

[0020] (4) The raw materials used in this invention are low in cost, the process is simple and easy to control, and it is easy to promote industrialization, which is conducive to promoting the industrialization of organic aqueous phase flow batteries. Attached Figure Description

[0021] Figure 1This is a scanning electron microscope image of the three-dimensional porous graphite felt prepared in this invention;

[0022] Figure 2 Scanning electron microscope image of the manganese dioxide nanoparticle modified graphite felt electrode prepared in this invention;

[0023] Figure 3 The graph shows the current-voltage cycle test results of the graphite felt electrode before and after modification in Example 1 of this invention.

[0024] Figure 4 This is a comparison chart showing the efficiency of the modified graphite felt electrode and the untreated graphite felt electrode in an organic aqueous phase flow battery in Example 1 of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] This invention provides a method for modifying graphite felt electrodes with manganese dioxide nanoparticles, with the optimization objectives of each step as follows:

[0028] (1) Prepare an ammonium sulfate electrolyte of a certain concentration, place two graphite felts as the positive and negative electrodes of the reaction in the ammonium sulfate electrolyte, apply a certain voltage to the two ends of the electrodes, and perform electrolytic pretreatment on the graphite felts for 2 minutes; after the electrolytic pretreatment is completed, rinse with deionized water and then place in an oven to dry for later use.

[0029] This step aims to alter the surface roughness of the graphite felt, thereby changing its wettability. This ensures that the DMF dispersion of graphene can fully contact the carbon fiber surface constituting the graphite felt during the subsequent etching process, promoting the etching reaction. The key control parameters for the surface roughness of the graphite felt in this step are the electrolyte concentration and the applied voltage range. Lower electrolyte concentrations and lower applied voltages do not significantly change the roughness of the graphite felt. However, higher electrolyte concentrations and higher applied voltages can easily lead to deep cracks on the surface of the carbon fibers constituting the graphite felt, affecting its intrinsic properties. After parameter optimization, the ammonium sulfate electrolyte concentration was set at 0.1–0.4 mol / L, and the applied voltage across the electrodes was 5–10 V. Placing the cleaned sample in an oven removes surface moisture. The experimental values ​​were: drying temperature 80℃ and drying time 24 hours.

[0030] (2) Prepare a DMF dispersion of graphene with a certain concentration, place the positive and negative graphene felt electrodes after electrolytic pretreatment in the DMF dispersion of graphene, apply a certain voltage to both ends of the electrodes, and perform electrochemical etching treatment on the graphene felt for a certain time of 3 to 100 min; after the electrochemical etching treatment is completed, rinse with deionized water and then place in an oven to dry, thereby obtaining a three-dimensional porous graphene felt for later use.

[0031] This step involves obtaining a three-dimensional porous graphite felt through electrochemical etching. The number, shape, size, depth, and uniformity of the pores are all affected by the concentration of the graphene dispersion, the applied voltage, and the processing time. Therefore, through parameter optimization, the concentration of the graphene DMF dispersion is 0.05–0.2 mg / mL; the voltage applied across the electrodes is 5–10 V; and the processing time is 3–100 min. The washed sample is placed in an oven to remove moisture from the sample surface. The experimental values ​​are: drying temperature in the oven is 80 °C; and drying time is 24 h.

[0032] (3) Take an appropriate amount of KMnO4 and dissolve it in 65 mL of deionized water. Stir until completely dissolved, then continuously add anhydrous ethanol and stir until uniform. Place the electrochemically etched graphite felt in a polytetrafluoroethylene liner. At the same time, place the aforementioned mixed solution of KMnO4 and anhydrous ethanol in a 100 mL polytetrafluoroethylene liner. Place the polytetrafluoroethylene liner in a reaction vessel and place it in an oven. Keep it warm for a certain time to obtain a porous carbon fiber confined manganese dioxide nanoparticle modified graphite felt electrode.

[0033] This step aims to grow a certain number of MnO2 nanoparticles in situ on the surface of three-dimensional porous carbon fibers. The quantity and morphology of MnO2 are mainly controlled by the amount of manganese source KMnO4, the amount of reducing agent anhydrous ethanol, and the conditions of the hydrothermal reaction (temperature and time). After parameter optimization, the amount of KMnO4 is 0.1-0.4 g, the amount of anhydrous ethanol added dropwise is 2-5 mL, the oven temperature is 150-180℃, and the holding time is 10-20 h.

[0034] Example 2

[0035] A method for modifying graphite felt electrodes with manganese dioxide nanoparticles specifically includes the following steps:

[0036] Step 1: Prepare an ammonium sulfate electrolyte with a concentration of 0.2 mol / L. Place two graphite felts in the ammonium sulfate electrolyte as the positive and negative electrodes, respectively. Apply a voltage of 10V across the electrodes and pre-treat the graphite felts for 2 minutes to increase their surface roughness. After the pre-treatment, rinse with deionized water and then dry in an oven at 80℃ for 24 hours for later use.

[0037] Step 2: Prepare a DMF dispersion of graphene with a concentration of 0.05 mg / mL. Place the pre-treated positive and negative graphene felt electrodes in the DMF dispersion and apply a 7V voltage across the electrodes for electrochemical etching for 20 min. After electrochemical etching, rinse thoroughly with deionized water and then dry in an oven at 80℃ for 24 h to obtain a three-dimensional porous graphene felt (see appendix for details). Figure 1 ),spare;

[0038] Step 3: Dissolve 0.2g of KMnO4 in 65mL of deionized water, stir until completely dissolved, then continuously add 3mL of anhydrous ethanol, stirring until homogeneous. Place the electrochemically etched graphite felt in a polytetrafluoroethylene (PTFE) liner, and simultaneously place the entire KMnO4 and anhydrous ethanol mixture into a 100mL PTFE liner. Place the PTFE liner in a reaction vessel and in an oven at 160℃ for 15 hours to obtain a porous carbon fiber confined manganese dioxide nanoparticle modified graphite felt electrode (see appendix for details). Figure 2 ).

[0039] The porous carbon fiber-confined manganese dioxide nanoparticle-modified graphite felt electrode obtained by the above method was assembled in an organic aqueous flow battery. The positive electrode active material was 0.4 mol / L LTEMPO, the negative electrode active material was 0.4 mol / L methyl viologen (MV), the supporting electrolyte was a 2 mol / L NaCl solution, and an anion exchange membrane was selected as the battery separator. The battery was operated at a current density of 40 mA / cm². 2 At that time, the coulombic efficiency was 98.88%, the voltage efficiency was 73.50%, and the energy efficiency was 70.39% (see appendix for details). Figure 3 and 4 ).

[0040] Example 3

[0041] A method for modifying graphite felt electrodes with manganese dioxide nanoparticles specifically includes the following steps:

[0042] Step 1: Prepare an ammonium sulfate electrolyte with a concentration of 0.1 mol / L. Place two graphite felts in the ammonium sulfate electrolyte as the positive and negative electrodes, respectively. Apply a voltage of 5V to both ends of the electrodes and perform electrolytic pretreatment on the graphite felts for 2 minutes to increase the surface roughness of the graphite felts. After the electrolytic pretreatment is completed, rinse with deionized water and then place in an oven at 80℃ to dry for 24 hours for later use.

[0043] Step 2: Prepare a DMF dispersion of graphene with a concentration of 0.1 mg / mL. Place the pre-treated positive and negative graphene felt electrodes in the DMF dispersion and apply a voltage of 5V across the electrodes to perform electrochemical etching on the graphene felt for 3 min. After the electrochemical etching is completed, rinse with deionized water and then dry in an oven at 80℃ for 24 h to obtain a three-dimensional porous graphene felt for later use.

[0044] Step 3: Dissolve 0.1g of KMnO4 in 65mL of deionized water and stir until completely dissolved. Then, continuously add 2mL of anhydrous ethanol and stir until homogeneous. Place the electrochemically etched graphite felt in a polytetrafluoroethylene (PTFE) liner. At the same time, place the entire KMnO4 and anhydrous ethanol mixture in a 100mL PTFE liner. Place the PTFE liner in a reaction vessel and put it in an oven at 150℃ for 10 hours to obtain a porous carbon fiber confined manganese dioxide nanoparticle modified graphite felt electrode.

[0045] The porous carbon fiber-confined manganese dioxide nanoparticle-modified graphite felt electrode obtained by the above method was assembled in an organic aqueous flow battery. The positive electrode active material was 0.2 mol / L LTEMPO, the negative electrode active material was 0.2 mol / L methyl viologen (MV), the supporting electrolyte was 1.5 mol / L NaCl solution, and an anion exchange membrane was selected as the battery separator. The battery was operated at a current density of 20 mA / cm². 2 At that time, the coulombic efficiency was 95.44%, the voltage efficiency was 83.03%, and the energy efficiency was 80.94%.

[0046] Example 4

[0047] A method for modifying graphite felt electrodes with manganese dioxide nanoparticles specifically includes the following steps:

[0048] Step 1: Prepare an ammonium sulfate electrolyte with a concentration of 0.4 mol / L. Place two graphite felts in the ammonium sulfate electrolyte as the positive and negative electrodes, respectively. Apply a voltage of 7V across the electrodes and pre-treat the graphite felts for 2 minutes to increase their surface roughness. After the pre-treatment, rinse with deionized water and then dry in an oven at 80℃ for 24 hours for later use.

[0049] Step 2: Prepare a DMF dispersion of graphene with a concentration of 0.2 mg / mL. Place the pre-treated positive and negative graphene felt electrodes in the DMF dispersion and apply a voltage of 10 V across the electrodes to perform electrochemical etching on the graphene felt for 100 min. After the electrochemical etching is completed, rinse thoroughly with deionized water and then dry in an oven at 80℃ for 24 h to obtain a three-dimensional porous graphene felt for later use.

[0050] Step 3: Dissolve 0.4g of KMnO4 in 65mL of deionized water and stir until completely dissolved. Then, continuously add 5mL of anhydrous ethanol and stir until homogeneous. Place the electrochemically etched graphite felt in a polytetrafluoroethylene (PTFE) liner. At the same time, place the entire KMnO4 and anhydrous ethanol mixture in a 100mL PTFE liner. Place the PTFE liner in a reaction vessel and put it in an oven at 180℃ for 20 hours to obtain a porous carbon fiber confined manganese dioxide nanoparticle modified graphite felt electrode.

[0051] The porous carbon fiber-confined manganese dioxide nanoparticle-modified graphite felt electrode obtained by the above method was assembled in an organic aqueous flow battery. The positive electrode active material was 0.3 mol / L LTEMPO, the negative electrode active material was 0.3 mol / L methyl viologen (MV), the supporting electrolyte was a 2 mol / L NaCl solution, and an anion exchange membrane was selected as the battery separator. The battery was operated at a current density of 30 mA / cm². 2 At that time, the coulombic efficiency was 96.34%, the voltage efficiency was 72.09%, and the energy efficiency was 67.87%.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a manganese dioxide nanoparticle modified graphite felt electrode, characterized in that, Specifically, the steps include the following: Step 1: Prepare an ammonium sulfate electrolyte of a certain concentration, place two graphite felts as the positive and negative electrodes of the reaction in the ammonium sulfate electrolyte, apply a certain voltage to the two ends of the electrodes, and perform electrolytic pretreatment on the graphite felts for 2 minutes. After the electrolytic pretreatment is completed, rinse it with deionized water and then place it in an oven to dry for later use. Step 2: Prepare a DMF dispersion of graphene with a certain concentration. Place the pre-treated positive and negative graphene felt electrodes in the DMF dispersion of graphene. Apply a certain voltage to both ends of the electrodes and perform electrochemical etching on the graphene felt for a certain time of 3 to 100 minutes. After the electrochemical etching is completed, rinse with deionized water and then dry in an oven to obtain a three-dimensional porous graphene felt for later use. Step 3: Dissolve an appropriate amount of KMnO4 in 65 mL of deionized water, stir until completely dissolved, and then continuously add anhydrous ethanol while stirring until homogeneous. Place the electrochemically etched graphite felt in a polytetrafluoroethylene (PTFE) liner, and simultaneously place the entire KMnO4 and anhydrous ethanol mixture in a 100 mL PTFE liner. Place the PTFE liner in a reaction vessel and then in an oven for a certain period of time to obtain a porous carbon fiber confined manganese dioxide nanoparticle modified graphite felt electrode.

2. The method for preparing a manganese dioxide nanoparticle modified graphite felt electrode according to claim 1, characterized in that, In step 1, the concentration of ammonium sulfate electrolyte is 0.1–0.4 mol / L; the voltage applied across the electrodes is 5–10 V; the drying temperature in the oven is 80 °C, and the drying time is 24 h.

3. The method for preparing a manganese dioxide nanoparticle-modified graphite felt electrode according to claim 1, characterized in that, In step 2, the concentration of the DMF dispersion of graphene is 0.05–0.2 mg / mL; the voltage applied across the electrodes is 5–10 V; the processing time is 3–100 min; the drying temperature in the oven is 80 °C; and the drying time is 24 h.

4. The method for preparing a manganese dioxide nanoparticle-modified graphite felt electrode according to claim 1, characterized in that, In step 3, the amount of KMnO4 used is 0.1-0.4g, and the amount of anhydrous ethanol added dropwise is 2-5mL; the oven temperature is 150-180℃, and the holding time is 10-20h.

5. Use of manganese dioxide nanoparticles modified graphite felt electrode, characterized in that, The manganese dioxide nanoparticle-modified graphite felt electrode is prepared by any one of the methods in claims 1-4, and the manganese dioxide nanoparticle-modified graphite felt electrode is used in organic aqueous flow batteries.

6. The use of a manganese dioxide nanoparticle modified graphite felt electrode according to claim 5, characterized in that, The positive electrode active material of the organic aqueous phase flow battery is 0.2-0.4 mol / L TEMPO, the negative electrode active material is 0.2-0.4 mol / L methyl viologen, the supporting electrolyte is 1.5-2 mol / L NaCl solution, and the battery separator is an anion exchange membrane.

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