A method for modifying graphite felt electrode materials based on three-dimensional porous MnO2 and its application

Abstract

This invention relates to a method for modifying graphite felt electrode materials based on three-dimensional porous MnO2, comprising the following steps: pretreating the graphite felt with a single-mode microwave electric field to increase its wettability and surface defects; and performing a redox reaction on the pretreated graphite felt using a potassium permanganate solution under acidic conditions to uniformly grow three-dimensional porous nanostructured MnO2 on the surface of the graphite felt electrode. The catalytic activity of MnO2 and the high specific surface area of ​​the three-dimensional nanostructure increase the reactive sites on the surface of the graphite felt carbon fibers, thereby improving battery efficiency. The graphite felt electrode material obtained by this invention based on three-dimensional porous MnO2 modification possesses rich three-dimensional structure, large specific surface area, high electrode stability, and is easy to operate.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a method for modifying graphite felt electrode material based on three-dimensional porous MnO2 and its application in the preparation of electrodes for organic aqueous flow batteries. Background Technology

[0002] Currently, new energy sources, represented by wind power and photovoltaics, are booming and have already reached a considerable scale. However, solar, wind, and geothermal energy all have significant drawbacks, namely intermittency, uncontrollability, and instability. Developing efficient energy storage technologies has become a necessary support for the efficient utilization of various new energy sources, especially large-scale, high-capacity energy storage systems. Organic aqueous flow batteries, which use organic molecules as battery active materials, show potential application prospects in the field of large-scale energy storage technology because the electrochemical reaction site and the energy storage active material are spatially separated, allowing for independent design of battery power and capacity. Furthermore, organic active materials possess green and environmentally friendly characteristics. Therefore, against the backdrop of the development needs of renewable energy and the construction of smart grids, organic aqueous flow batteries have received widespread attention and rapid development.

[0003] Graphite felt electrode materials possess excellent electrical conductivity and strong oxidation resistance, making them a relatively ideal electrode material. However, when used as electrode materials in flow batteries, they still suffer from drawbacks such as poor hydrophilicity and low electrochemical activity, limiting the improvement of battery energy conversion efficiency and power density. Therefore, modifying graphite felt electrodes is crucial to improving their electrochemical activity and wettability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in order to overcome the shortcomings of the prior art, the present invention provides a method for modifying graphite felt electrode material based on three-dimensional porous MnO2. By utilizing the three-dimensional porous nanostructure of MnO2 and its catalytic activity, the specific surface area and interfacial electrochemical activity of the graphite felt electrode are increased, thereby improving the efficiency and cycle stability of the entire organic aqueous flow battery when it is used as an electrode.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for modifying graphite felt electrode materials based on three-dimensional porous MnO2, comprising the following steps:

[0006] Step 1: Cut the graphite felt into pieces, wash and dry it with deionized water;

[0007] Step 2: Place the graphite felt inside the single-mode microwave reaction cavity and at the position of maximum single-mode microwave electric field intensity, and perform pretreatment at a certain power.

[0008] Step 3: Dissolve an appropriate amount of potassium permanganate in 60 mL of deionized water. After complete dissolution, slowly add acid dropwise to the solution to adjust the pH of the solution.

[0009] Step 4: Place the prepared solution into a water bath. After the temperature stabilizes, place the pretreated graphite felt into the solution and react at a constant temperature for a certain period of time.

[0010] Step 5: Remove the graphite felt from the solution, rinse it with deionized water and dry it.

[0011] in:

[0012] In step 2, the microwave power during preprocessing is 200W-1000W, and the preprocessing time is 1-5 minutes.

[0013] In step 3, the mass of potassium permanganate is 0.03792g-0.22752g; in step 3, the acid added is one of hydrochloric acid, sulfuric acid or nitric acid, preferably hydrochloric acid with a concentration of 0.1-1mol / L, and the pH value of the solution is adjusted to be less than 7.

[0014] In step 4, the temperature of the water bath is 60-80℃, and the constant temperature reaction time is 3-30 minutes.

[0015] An electrode for an organic aqueous flow battery is prepared using a graphite felt electrode material obtained by the above-mentioned modification method based on three-dimensional porous MnO2 graphite felt electrode material.

[0016] This invention employs a single-mode microwave electric field to pretreat the surface of graphite felt electrode materials. Unlike multi-mode microwave heating devices (including household microwave ovens), in single-mode microwave heating devices, standing waves are formed due to the interference of incident and reflected microwave waves. Therefore, the spatial positions of the microwave electric and magnetic fields in the waveguide are fixed. By precisely controlling the position of the sample in the waveguide, heating can be performed at the location where the microwave electric or magnetic field is strongest. The single-mode microwave electric field can induce oscillations of electrons and functional groups within the graphite felt electrode material, thereby altering the surface state of the carbon fiber electrode material. This is beneficial for the subsequent uniform formation of MnO2 in a three-dimensional porous structure on the carbon fiber surface.

[0017] The beneficial effects of this invention are:

[0018] (1) The present invention adopts a single-mode microwave electric field pretreatment method, which is more efficient and consumes less energy compared with the traditional acid and heat treatment methods. Through the electromagnetic oscillation effect with the electrons and functional groups inside the electrode material, the surface state of the electrode material is activated, which is the basis for the uniform generation of three-dimensional porous nanostructure MnO2 on the surface of the electrode material.

[0019] (2) The single-mode microwave electric field pretreatment method adopted in this invention has high safety and avoids the safety hazards such as electric sparks that could damage equipment or cause fires when using a household microwave oven (multi-mode microwave) to process conductive carbon materials.

[0020] (3) The present invention utilizes a one-step reaction method of potassium permanganate with carbon fiber electrode material in an acidic environment to prepare a three-dimensional porous MnO2 nanostructure on the surface of the electrode material. The process is simple and low cost, and MnO2 is directly generated on the surface of carbon fiber and is not easy to fall off.

[0021] (4) The prepared modified graphite felt electrode material has a high specific surface area and the three-dimensional nanostructure MnO2 has good catalytic activity and a high specific surface area, which greatly improves the hydrophilicity and electrochemical reaction activity of the graphite felt electrode. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Figure 1 This is a scanning electron microscope image of the three-dimensional porous MnO2 modified graphite felt electrode in Example 1.

[0024] Figure 2 The cyclic voltammetry curves of the three-dimensional porous MnO2 modified graphite felt electrode and the untreated graphite felt electrode in Example 1 are shown as (a) TEMPO; (b) MV.

[0025] Figure 3 The coulombic efficiency and energy efficiency of the three-dimensional porous MnO2 modified graphite felt electrode and the untreated graphite felt electrode in Example 1 are compared in an organic aqueous phase flow battery. Detailed Implementation

[0026] The following embodiments will further illustrate the present invention, but are not intended to limit the invention.

[0027] Example 1:

[0028] (1) Cut the graphite felt, wash and dry it with deionized water; place the graphite felt in a single-mode microwave reaction cavity and place it at the position with the maximum single-mode microwave electric field intensity, and pre-treat it with microwave power of 800W for 1min; take 0.1896g of potassium permanganate and dissolve it in 60mL of deionized water. After it is completely dissolved, slowly add 1mol / L hydrochloric acid to the solution to adjust the pH of the solution to 1; put the prepared solution into a 70℃ water bath. After the temperature stabilizes, put the pre-treated graphite felt into the solution and react at a constant temperature for 5min; take the graphite felt out of the solution, rinse it with deionized water and dry it.

[0029] Scanning electron microscope images of the modified graphite felt electrode are as follows: Figure 1As shown, the three-dimensional porous MnO2 is uniformly dispersed on the surface of the carbon fiber, and the surface of the smooth carbon fiber after modification exhibits a uniform nano-network structure. This structure of the modified carbon fiber is more porous and looser than the smooth structure of the unmodified sample.

[0030] (2) Cyclic voltammetry tests were performed on the graphite felt electrodes before and after modification. The electrolyte was TEMPO solution. The test results are as follows: Figure 2 As shown, the polarization overpotential of the modified graphite felt electrode is 217.9 mV, which is significantly lower than the polarization overpotential of the unmodified graphite felt electrode, which is 280.4 mV.

[0031] (3) Using modified graphite felt as electrode materials, and TEMPO solution and MV solution as positive and negative electrolytes respectively, organic aqueous phase flow single cells were assembled, and the performance of the two electrode cells was compared. Figure 3 As shown, the single cell assembled with modified graphite felt electrodes exhibits a high coulombic efficiency (~97%). After 100 cycles, the coulombic efficiency and energy efficiency remain essentially unchanged, with the energy efficiency remaining around 70%.

[0032] Example 2:

[0033] (1) Cut the graphite felt, wash and dry it with deionized water; place the graphite felt in a single-mode microwave reaction cavity and place it at the position with the maximum single-mode microwave electric field intensity, and pre-treat it with microwave power of 600W for 2 minutes; take 0.1896g of potassium permanganate and dissolve it in 60mL of deionized water. After it is completely dissolved, slowly add 1mol / L sulfuric acid to the solution to adjust the pH of the solution to 1; put the prepared solution into a 60℃ water bath. After the temperature stabilizes, put the pre-treated graphite felt into the solution and react at a constant temperature for 5 minutes; take the graphite felt out of the solution, rinse it with deionized water and dry it.

[0034] (2) Cyclic voltammetry tests were performed on the graphite felt electrodes before and after modification, using TEMPO solution as the electrolyte. The polarization overpotential of the modified graphite felt electrode was 254.9 mV, which was lower than the polarization overpotential of 280.4 mV of the unmodified graphite felt electrode.

[0035] (3) Using modified graphite felt as electrode materials, and TEMPO solution and MV solution as positive and negative electrolytes respectively, organic aqueous phase flow single cells were assembled, and the performance of the two electrode cells was compared. It can be seen that the coulombic efficiency of the single cell assembled with modified graphite felt electrode is about 96%. After 100 cycles, the coulombic efficiency and energy efficiency remain basically unchanged, and the energy efficiency remains at about 65%.

[0036] Example 3:

[0037] (1) Cut the graphite felt, wash and dry it with deionized water; place the graphite felt in a single-mode microwave reaction cavity and place it at the position with the maximum single-mode microwave electric field intensity, and pre-treat it with microwave power of 400W for 5min; take 0.2275g of potassium permanganate and dissolve it in 60mL of deionized water. After it is completely dissolved, slowly add 0.5mol / L nitric acid to the solution to adjust the pH of the solution to 3; put the prepared solution into a 70℃ water bath. After the temperature stabilizes, put the pre-treated graphite felt into the solution and react at a constant temperature for 5min; take the graphite felt out of the solution, rinse it with deionized water and dry it.

[0038] (2) Cyclic voltammetry tests were performed on the graphite felt electrodes before and after modification, using TEMPO solution as the electrolyte. The polarization overpotential of the modified graphite felt electrode was 262.9 mV, which was lower than the polarization overpotential of 280.4 mV of the unmodified graphite felt electrode.

[0039] (3) Using modified graphite felt as electrode materials, and TEMPO solution and MV solution as positive and negative electrolytes respectively, organic aqueous phase flow single cells were assembled, and the performance of the two electrode cells was compared. It can be seen that the coulombic efficiency of the single cell assembled with modified graphite felt electrode is about 96%. After 100 cycles, the coulombic efficiency and energy efficiency remain basically unchanged, and the energy efficiency remains at about 67%.

[0040] Example 4:

[0041] (1) Cut the graphite felt, wash and dry it with deionized water, place the graphite felt in the single-mode microwave reaction cavity and place it at the position with the maximum single-mode microwave electric field intensity, and pre-treat it with microwave power of 800W for 1min; take 0.0379g of potassium permanganate and dissolve it in 40mL of deionized water. After it is completely dissolved, slowly add 0.5mol / L hydrochloric acid to the solution to adjust the pH of the solution to 5; put the prepared solution into a 70℃ water bath. After the temperature stabilizes, put the pre-treated graphite felt into the solution and react at a constant temperature for 5min; take the graphite felt out of the solution, rinse it with deionized water and dry it.

[0042] (2) Cyclic voltammetry tests were performed on the graphite felt electrodes before and after modification, using TEMPO solution as the electrolyte. The polarization overpotential of the modified graphite felt electrode was 289.3 mV, which was lower than the polarization overpotential of 280.4 mV of the unmodified graphite felt electrode.

[0043] (3) Using modified graphite felt as electrode materials, and TEMPO solution and MV solution as positive and negative electrolytes respectively, organic aqueous phase flow single cells were assembled, and the performance of the two electrode cells was compared. It can be seen that the coulombic efficiency of the single cell assembled with modified graphite felt electrode is about 95%. After 100 cycles, the coulombic efficiency and energy efficiency remain basically unchanged, and the energy efficiency remains at about 64%.

[0044] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for modifying graphite felt electrode materials based on three-dimensional porous MnO2, characterized in that: It includes the following steps: Step 1: Cut the graphite felt into pieces, wash and dry it with deionized water; Step 2: Place the graphite felt in the single-mode microwave reaction cavity and at the position of maximum single-mode microwave electric field intensity, and pre-treat for 1-5 minutes at microwave power of 200W-1000W. Step 3: Dissolve an appropriate amount of potassium permanganate in 60 mL of deionized water. After complete dissolution, slowly add acid dropwise to the solution to adjust the pH of the solution. Step 4: Place the prepared solution into a water bath at a temperature of 60-80℃. After the temperature stabilizes, place the pretreated graphite felt into the solution and react at a constant temperature for 3-30 minutes. Step 5: Remove the graphite felt from the solution, rinse it with deionized water and dry it.

2. The method for modifying graphite felt electrode material based on three-dimensional porous MnO2 as described in claim 1, characterized in that: In step 3, the mass of potassium permanganate is 0.03792g-0.22752g.

3. The method for modifying graphite felt electrode materials based on three-dimensional porous MnO2 as described in claim 2, characterized in that: In step 3, the acid added is one of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 0.1-1 mol / L, and the pH of the solution is adjusted to be less than 7.

4. An electrode for an organic aqueous phase flow battery, characterized in that: The electrode for the flow battery is prepared using the graphite felt electrode material obtained by any one of the graphite felt electrode material modification methods based on three-dimensional porous MnO2 as described in claims 1-3.

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