A method for electrochemical redox activation of graphite felt electrodes for vanadium redox flow batteries

Abstract

The present invention provides a method for electrochemical redox activation of graphite felt electrodes for vanadium flow batteries. The activated graphite felt electrodes are obtained through two electrochemical activations. The anodic oxidation activation and cathodic electrochemical activation in each electrochemical activation are performed in the same electrolytic cell, where the anodic and cathodic half-cells are separated by an ion-selective exchange membrane. The anolyte is selected from a sulfuric acid solution, and the catholyte is selected from one or two of ferrous sulfate, nickel sulfate, nickel nitrate, manganese sulfate, bismuth-containing hydrochloric acid solution, and tungsten-containing hydrofluoric acid solution. Compared to traditional activation methods, the present invention combines the beneficial effects of electrochemical oxidation and electrochemical reduction on graphite felt electrodes, and can continuously perform oxidation and reduction activation treatments on the graphite felt.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage, and in particular relates to a method for activating electrode materials of a liquid flow battery. Background Art

[0002] As the proportion of renewable energy (wind, solar, etc.) in global power generation continues to increase, the instability of renewable energy (intermittent and volatile power generation due to environmental factors) has become increasingly prominent, resulting in low overall energy utilization. To improve the stability and energy utilization of renewable energy, a supporting energy storage system is needed. Vanadium flow batteries, due to their unique advantages (high efficiency, flexible control of capacity and power, deep, high-current discharge capability, short response time, long life, renewable active materials, and safe operation), are currently the largest, most technologically mature, and most promising energy storage technology. They can be applied to renewable energy peak regulation, distributed power stations, and other fields.

[0003] As a core component of vanadium flow batteries, polyacrylonitrile-based graphite felt cannot be used directly as an electrode material at high operating current densities. This is because the electrochemical activity and reversibility of the graphite felt do not meet the application requirements, resulting in high activation polarization. Therefore, polyacrylonitrile-based graphite felt needs to be modified to improve its hydrophilicity and electrochemical activity, resulting in electrodes with high catalytic activity, good electrochemical reversibility, suppressed side reactions, and stable properties that can withstand multiple charge and discharge cycles. Currently, methods for modifying graphite felt mainly include surface functionalization, increasing the active area, and loading electrocatalysts.

[0004] Surface functionalization primarily involves introducing active functional groups onto the surface of graphite felt. Among various functional groups, oxygen- and nitrogen-containing groups have been shown to improve the hydrophilicity of graphite felt, enhance its adsorption capacity for electrolytes, and serve as reactive sites, increasing the electrocatalytic activity of electrode materials and accelerating electrochemical reaction rates. The introduction of oxygen-containing functional groups primarily involves chemical or electrochemical oxidation of the graphite felt, partially oxidizing the carbon atoms on its surface. This increases the number of oxygen-containing functional groups, such as carbonyl, carboxyl, and phenolic hydroxyl groups, on the surface, improving the hydrophilicity of the carbon fibers and catalyzing redox reactions at both the positive and negative electrodes. In 2007, Li et al. reported electrochemical oxidation of graphite felt in their article "Characteristics of graphite felt electrode electrochemically oxidized for vanadium redox battery application." The authors used graphite felt as anode and Ti plate as cathode, and placed them in 1 mol / L sulfuric acid solution. The voltage was controlled at 5-15V, and the degree of oxidation was controlled by adjusting the time. The specific surface area of ​​the graphite felt before and after treatment increased from 0.33m 2 / g increased to 0.49m 2 / g, the O / C atomic ratios on the graphite felt surface were 0.085 and 0.15 respectively, and the added O mainly existed in the form of -COOH functional groups. Cyclic voltammetry studies have shown that the treated graphite felt significantly improved the positive electrode charge of the all-vanadium redox flow battery VO 2+ / VO2 + Electrochemical activity and reversibility. At 30mA / cm 2 Under the condition of 100 ℃ and 100 ℃, the coulombic efficiency and voltage efficiency of the battery are 94% and 85% respectively. The characteristics of electrochemical oxidation are mild oxidation process conditions and controllable oxidation degree of graphite felt. In 2013, Zhang et al. published the article "Electrochemical activation of graphite felt electrode for VO 2+ / VO2 + In the paper "Redox Couple Application", the graphite felt was also electrochemically oxidized by electrochemical oxidation, and the performance of the single cell was significantly improved. For traditional graphite felt electrode materials, since the diameter of the carbon fiber is usually 10 to 20 μm and the fiber surface is smooth and dense, their specific surface area is very low, only 0.1 to 1 m 2 / g. Increasing the specific surface area of ​​electrode materials, especially the electrochemically effective specific surface area, is an effective method for improving electrochemical catalytic activity and reducing electrochemical polarization. Some researchers have attempted to activate carbon fiber electrode materials using physical or chemical activation methods, creating pores on the carbon fiber surface and increasing its specific surface area. However, these modification methods have been difficult to scale up industrially. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a method for electrochemical redox activation of graphite felt electrodes for vanadium redox flow batteries.

[0006] The technical solution for achieving the above-mentioned purpose of the present invention is:

[0007] A method for electrochemical redox activation of a graphite felt electrode for a vanadium flow battery, comprising the following steps:

[0008] (1) The first graphite felt which has not been activated is used as a cathode and immersed in a cathode tank filled with a cathode electrolyte. Meanwhile, the second graphite felt which has not been activated is used as an anode and immersed in a cathode tank filled with an anolyte. The third graphite felt which has not been treated is used as the original graphite felt for the next oxidation.

[0009] (2) After preparation, power is turned on to perform the first electrochemical activation: the first graphite felt in the cathode electrolytic cell is subjected to cathode reduction, and the second graphite felt in the anode electrolytic cell is subjected to anodic oxidation activation;

[0010] (3) After the first electrochemical activation, the second graphite felt is cleaned and then placed in the cathode tank of the electrolytic cell, the third graphite felt that has not been treated in any way is placed in the anode tank of the electrolytic cell, and the fourth graphite felt that has not been treated in any way is used as the original graphite felt for the next oxidation;

[0011] (4) After preparation, power is turned on to perform a second electrochemical activation, wherein the third graphite felt in the anode electrolytic cell is subjected to anodic oxidation activation, and the second graphite felt in the cathode electrolytic cell is subjected to cathode reduction;

[0012] (5) After the second electrochemical activation, the obtained second graphite felt is washed and dried to obtain a prepared graphite felt electrode that can be used in a liquid flow battery;

[0013] (6) performing a third electrochemical activation, placing the third graphite felt in a cathode electrolytic cell for cathode reduction, and placing the fourth graphite felt in an anode electrolytic cell for anodic oxidation. After the electrochemical activation is completed, the obtained third graphite felt is washed and dried, and can be used as a graphite felt electrode for a liquid flow battery;

[0014] The above operation is continued to carry out continuous electrochemical activation of the graphite felt. The anode oxidation activation and cathode electrochemical activation are carried out in the same electrolytic cell. The anode half cell and cathode half cell of the electrolytic cell are separated by an ion exchange membrane.

[0015] The anolyte is selected from one of sulfuric acid, sodium hydroxide, and potassium hydroxide solutions, and the concentration of the anolyte is 1 to 3 mol / L; the catholyte is made of one or two of ferrous sulfate, nickel sulfate, nickel nitrate, manganese sulfate, and bismuth salt dissolved in acid, and the concentration of the solute ranges from 0.2 mol / L to 2.5 mol / L; the acid is sulfuric acid or hydrochloric acid, and the concentration of the acid is 1 to 3 mol / L.

[0016] A direct current is applied between the positive and negative electrodes of the electrolytic cell, and the current density of the direct current is 5 mA / cm 2 ~40mA / cm 2 The current is applied for 0.5h to 3h.

[0017] Wherein, the activation temperature range is 25°C to 40°C.

[0018] Preferably, the activation time is 1.8 to 2.2 hours, and the activation temperature is 20°C to 30°C.

[0019] More preferably, the catholyte is made of ferrous sulfate and nickel sulfate dissolved in acid, wherein the concentrations of ferrous sulfate and nickel sulfate are independently 0.8 mol / L to 1.2 mol / L, and the concentration of the acid is 1.8 to 2.2 mol / L. For example, the catholyte can be composed of 1.0 M ferrous sulfate + 1.0 M nickel sulfate + 2 M sulfuric acid.

[0020] Furthermore, the graphite felt after the electrochemical treatment is ultrasonically cleaned with deionized water, and then dried at 35-45° C. for 6-10 hours.

[0021] The method of the present invention can realize continuous large-scale production, which can use industrial production equipment. The following is the production equipment scheme proposed by the present invention.

[0022] The method described herein adopts an activation system comprising two electrolytic cells, one electrolytic cell connected to the positive pole of a power supply as an anode electrolytic cell, and the other connected to the negative pole of a power supply as a cathode electrolytic cell; the activation system comprises an activation fixture, and the activation fixture comprises three parts: a graphite felt fixture, a fixture transport mechanism, and an electric clamping mechanism; the first part is the graphite felt fixture used during electrochemical activation, and the second part is used to transport the fixture during the transport process after activation is completed; the third part, the electric clamping mechanism, is connected to a power supply.

[0023] The activation system used in the method further comprises two electrolytic cells, one electrolytic cell is connected to the positive electrode of the power supply as an anode electrolytic cell, and the other electrolytic cell is connected to the negative electrode of the power supply as a cathode electrolytic cell.

[0024] Among them, the graphite felt fixture includes a frame base plate, a graphite plate, and a hollow frame panel. The hollow part of the frame panel is the area for placing the graphite felt; the graphite plate is provided with a grid and a protrusion for connecting the electrode (the grid enables the graphite felt to contact the electrolyte); the frame base plate, graphite plate, frame panel and graphite felt are combined and fixed on the four sides with split horizontal clips, long horizontal clips and vertical clips.

[0025] The electric clamp mechanism includes an electric clamp drive mechanism, an electric clamp transmission mechanism, an electric clamp plate connecting rod, an electric clamp plate, and wires. The electric clamp drive mechanism is installed in the central motor compartment of the main frame, and the electric clamp transmission mechanism is installed on the lower side of the central motor compartment. The bottom end of the output shaft at the bottom of the electric clamp transmission mechanism is connected to the driving bevel gear, and the driving bevel gear engages with two driven bevel gears. (The electric clamp transmission mechanism and the electric clamp plate connecting rod are connected by the driving bevel gear and the two driven bevel gears.) When the driving bevel gear rotates, it drives the driven bevel gears to rotate, and the two driven bevel gears rotate in opposite directions, thereby realizing the rotation of the electric clamp plate connecting rod around the output shaft axis. When the electric clamp plate connecting rod rotates, the end electric clamp plate and the graphite plate are tightly attached and loosened. After the attachment, the wires led out through the electric clamp plate are connected to the power supply.

[0026] Specifically, the bottom of the connecting rod is connected to an electric splint, and the electric splint leads out electric wires. After the main body bracket is fixed, the electric wires are led out along the mechanical arm to the power supply.

[0027] The invention provides a method for electrochemical oxidation-reduction activation of a graphite felt electrode and application of the method in a vanadium redox flow battery.

[0028] The electrocatalyst is loaded on the surface of the graphite felt by introducing highly active components on the surface of the carbon fiber through methods such as ion exchange, impregnation-reduction, chemical vapor deposition or electrochemical deposition, thereby enhancing the electrochemical reaction activity of the electrode. The introduction of these electrocatalysts not only improves the electrical conductivity of the graphite felt, but also acts as an electrocatalyst by changing the reaction pathway and accelerating the reaction rate. In the present invention, the electrochemical oxidation of the graphite felt occurs at the anode, while the cathode is also undergoing reduction, and the metal ion catalyst is loaded, achieving a single electrolysis to prepare a graphite felt electrode that originally required two electrochemical reactions. In addition to containing oxygen-containing functional groups on the surface of the activated graphite felt of the present invention, the surface modification of the graphite felt can also be achieved, nano-scale metal particles can be deposited, the active sites of the graphite felt electrode can be effectively increased, and the effective area of ​​the electrochemical reaction of the graphite felt can be increased, thereby improving the electrochemical activity of the graphite felt. This method saves energy and can perform continuous electrochemical treatment on the graphite felt.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The activated graphite felt electrode prepared by the method of the present invention has a large number of oxygen-containing functional groups and metal doping on the electrode surface, which further increases the electrochemical activity of the graphite felt electrode, reduces the charge transfer resistance, and improves the voltage efficiency and energy efficiency of the all-vanadium liquid flow battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a process flow chart for electrochemically activated graphite felt;

[0032] Figure 2 It is a graphite felt fixture 110; Figure 2 (a) shows the clamping position and locking direction during assembly, and (b) is a diagram of the various components.

[0033] Figure 3 A fixture transfer mechanism 120;

[0034] Figure 4 is an electric clamping mechanism 130;

[0035] Figure 5 Schematic diagram of the transfer of the fixture.

[0036] Figures 2 to 4 The corresponding relationship between parts and numbers is:

[0037] Graphite felt fixture 110, frame bottom plate 111, graphite plate 112, frame panel 113, graphite felt 114, frame pressure plate 115, split horizontal buckle 116, long horizontal buckle 117, vertical buckle 118,

[0038] The clamp transfer mechanism 120, the main body support 121, the transmission mechanism 122, the drive mechanism 123, the clamping claw 124, the transmission rod 127, the connecting rods 128 and 129;

[0039] Electric clamp mechanism 130 , electric clamp driving mechanism 131 , electric clamp transmission mechanism 132 , electric clamp plate connecting rod 133 , electric clamp plate 134 , wire 135 , output shaft 136 , driving bevel gear 137 , first driven bevel gear 138 , second driven bevel gear 139 . DETAILED DESCRIPTION

[0040] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0041] Unless otherwise specified, the methods used in the specification are all technical methods known in the art. The materials used are commercially available or prepared by methods known in the art.

[0042] In order to further illustrate the performance of the graphite felt electrode prepared by the present invention, performance tests were carried out on the prepared graphite felt.

[0043] The test method is as follows:

[0044] 1. Electrochemical activity:

[0045] Using an electrochemical workstation, perform cyclic voltammetry on the sample. Read the peak potential and peak current of the oxidation peak and reduction peak from the cyclic voltammetry curve, and then calculate the peak position difference and peak current ratio. Cyclic voltammetry tests use a three-electrode system. Working electrode: electrode area 1cm 2 (1cm×1cm). Counter electrode: Graphite plate (32×47mm). Reference electrode: Saturated calomel electrode (SCE).

[0046] Positive electrolyte: contains 0.05M VO 2+ , 0.05M VO2 + and 3M H2SO4

[0047] Negative electrolyte: contains 0.05MV 2+ , 0.05MV 3+ and 3M H2SO4

[0048] Test conditions: scan rate 5mv / s, positive electrode electrolyte scan range 0.2~1.6V(SCE), negative electrode electrolyte scan range -1.0~0.2V(SCE).

[0049] During testing, the amount of electrolyte should be no less than 100ml. When testing in the negative electrolyte, the test process must be carried out under inert gas protection. Take three samples of each graphite felt for testing and take the average value for comparative analysis.

[0050] 2. Constant current charge and discharge: Charge at 2A to a voltage ≥1.7V; discharge at 2.5A to a voltage ≤0.7V. Single cell assembly: 5cm×5cm graphite felt electrodes, a cation exchange membrane, graphite plates as current collectors, and 80ml of 2M vanadium electrolyte for each positive and negative electrode. Perform 10 charge and discharge cycles.

[0051] Example 1:

[0052] See also Figure 2 The graphite felt fixture 110 is composed of a frame bottom plate 111, a graphite plate 112, a frame panel 113, a graphite felt 114, a frame pressure plate 115, a horizontal clip 116, a horizontal clip 117, and a vertical clip 118. Figure 2(b) Arrange as shown. When installing, first place the graphite plate 112 in the corresponding position of the frame bottom plate 111, then install the frame panel 113 to sandwich the graphite plate 112 between them, and glue the three together to form a whole. Place the graphite felt 114 in the groove of the panel 113, install the pressure plate to press the graphite felt 114, and then use the fastening clips 116, 117, and 118 to fix it. Push the clips until they reach the limit. The installation position and locking direction are shown in the figure. Figure 2 (a).

[0053] Example 2:

[0054] The fixture transfer mechanism 120 is composed of a main frame 121, a transmission mechanism 122, a drive mechanism 123 and a clamping claw 124. The graphite felt is transferred and rotated by clamping the transverse buckle 116. The drive mechanism 123 is fixed in the motor compartments on both sides of the main frame 121; the transmission mechanism 122 is installed at the corresponding positions on the two inner sides below the main frame 121, and the transmission rod 127 extends into the upper motor compartment and is connected to the internal drive mechanism; the clamping claw 124 is connected to the main frame 121 and the transmission mechanism 122 through an axis to achieve the clamping and loosening actions, such as Figure 3 (a).

[0055] The output shaft of the driving mechanism 123 drives the transmission rod 127 to move upward or downward, and the clamping and releasing actions of the clamping claw 124 are realized through the transmission mechanism 122. The principle diagram is shown in FIG. Figure 3 (b) In the figure, shafts 125 and 126 are fixed to the main frame 121, and the clamping jaws 124 rotate around the shafts 125 and 126; when the transmission rod 127 moves downward, the connecting rods 128 and 129 are pushed to the sides, causing the clamping jaws 124 to clamp the horizontal buckle 116, and vice versa when 127 moves upward.

[0056] Example 3:

[0057] The electric clamp mechanism 130 is composed of an electric clamp drive mechanism 131, an electric clamp transmission mechanism 132, an electric clamp plate connecting rod 133, an electric clamp plate 134, and an electric wire 135. The electric clamp drive mechanism 131 is installed in the central motor compartment of the main frame 121, and the electric clamp transmission mechanism 132 is installed on the lower side. The shaft extending from the bottom is connected to the electric clamp plate connecting rod 133. The bottom of the connecting rod is connected to the electric clamp plate 134. The electric clamp plate leads to the electric wire 135. After the main frame is fixed, the extension arm leads to the power supply. Figure 4 As shown in (a).

[0058] The output shaft 136 of the electric clamp driving mechanism 131 drives the driving bevel gear 137 at its end to rotate, and then drives the first driven bevel gear 138 and the second driven bevel gear 139 arranged 180 degrees apart. The two driven bevel gears are fixed relatively and concentrically to the lower side electric clamp connecting rod. The principle diagram is as follows Figure 4(b) When driving bevel gear 137 rotates, it drives bevel gears 138 and 139, with the two driven bevel gears rotating in opposite directions. This causes the electrical clamping plate connecting rod 133 to rotate about the output shaft axis. Rotation of the electrical clamping plate connecting rod 133 allows the end electrical clamping plate 134 to be pressed against and released from the graphite plate. After pressing against the graphite plate, the wire 135 extending from the electrical clamping plate 134 is connected to a power source.

[0059] The transfer of the fixture is completed by the robotic arm. It can be transferred from the electrolytic cell to the cleaning cell, or from the cleaning cell to the electrolytic cell. The movement trend diagram is as follows: Figure 5 shown.

[0060] Example 4:

[0061] The following example provides a method for electrochemical redox activation of graphite felt electrodes for vanadium flow batteries, using the apparatus of Examples 1-3 and two electrolytic cells, one connected to the positive electrode of a power supply as an anode electrolytic cell, and the other connected to the negative electrode of a power supply as a cathode electrolytic cell; forming a continuously operating activation system.

[0062] The method comprises the operations of:

[0063] (1) The first graphite felt which has not been activated is used as a cathode and immersed in a cathode tank filled with a cathode electrolyte. Meanwhile, the second graphite felt which has not been activated is used as an anode and immersed in a cathode tank filled with an anolyte. The third graphite felt which has not been treated is used as the original graphite felt for the next oxidation.

[0064] (2) After preparation, power is turned on to perform the first electrochemical activation: the first graphite felt in the cathode electrolytic cell is subjected to cathode reduction, and the second graphite felt in the anode electrolytic cell is subjected to anodic oxidation activation;

[0065] (3) After the first electrochemical activation, the second graphite felt is cleaned and then placed in the cathode tank of the electrolytic cell, the third graphite felt that has not been treated in any way is placed in the anode tank of the electrolytic cell, and the fourth graphite felt that has not been treated in any way is used as the original graphite felt for the next oxidation;

[0066] (4) After preparation, power is turned on to perform a second electrochemical activation, wherein the third graphite felt in the anode electrolytic cell is subjected to anodic oxidation activation, and the second graphite felt in the cathode electrolytic cell is subjected to cathode reduction;

[0067] (5) After the second electrochemical activation, the obtained second graphite felt is washed and dried to obtain a prepared graphite felt electrode that can be used in a liquid flow battery;

[0068] (6) performing a third electrochemical activation, placing the third graphite felt in a cathode electrolytic cell for cathode reduction, and placing the fourth graphite felt in an anode electrolytic cell for anodic oxidation. After the electrochemical activation is completed, the obtained third graphite felt is washed and dried, and can be used as a graphite felt electrode for a liquid flow battery;

[0069] Continue the above operation to carry out continuous electrochemical activation of graphite felt. For the process, refer to Figure 1 The anode oxidation activation and cathode electrochemical activation are carried out in the same electrolytic cell, and the anode half cell and cathode half cell of the electrolytic cell are separated by an ion exchange membrane.

[0070] Specifically in this embodiment,

[0071] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm sizes, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1, graphite felt 2, and graphite felt 3. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in a cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in an anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 1.8A (current density is 2mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0072] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0073] Example 5:

[0074] Specifically in this embodiment,

[0075] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm sizes, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1, graphite felt 2, and graphite felt 3. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 4.5A (current density is 5mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0076] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0077] Example 6:

[0078] Specifically in this embodiment,

[0079] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm sizes, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1, graphite felt 2, and graphite felt 3. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in a cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in an anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 9A (current density is 10mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0080] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0081] Example 7:

[0082] Specifically in this embodiment,

[0083] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm pieces, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1, graphite felt 2, and graphite felt 3. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 18A (current density is 20mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0084] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0085] Example 8:

[0086] Specifically in this embodiment, the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm was cut into a size of 300×300 mm, and a total of 4 pieces were cut, which were numbered as graphite felt 0, graphite felt 1, graphite felt 2, and graphite felt 3. The original graphite felt 0 was used as the cathode, clamped in a fixture, and immersed in a cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). The original graphite felt 1 was used as the anode, clamped in a fixture, and immersed in an anode tank filled with anolyte (2.5M sulfuric acid). The graphite felt 2 that had not been treated was used as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 27A (current density is 30mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0087] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0088] Example 9:

[0089] Specifically in this embodiment,

[0090] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm sizes, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1 and graphite felt 2. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 36A (current density is 40mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0091] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0092] Example 10:

[0093] Specifically in this embodiment,

[0094] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm sizes, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1 and graphite felt 2. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 45A (current density is 50mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0095] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0096] Example 11:

[0097] Specifically in this embodiment,

[0098] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm pieces, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1, graphite felt 2, and graphite felt 3. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 27A (current density is 30mA / cm 2 ), the electrolysis time is set to 3 hours, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0099] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0100] Example 12:

[0101] Specifically in this embodiment,

[0102] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm sizes, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1 and graphite felt 2. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 27A (current density is 30mA / cm 2 ), the electrolysis time is set to 1 hour, the electrolytic cell temperature is controlled at 20°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hour, and the graphite felt 1 is taken out and dried.

[0103] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0104] Example 13:

[0105] Specifically in this embodiment,

[0106] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm pieces, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1, graphite felt 2, and graphite felt 3. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 27A (current density is 30mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 30°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0107] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0108] Example 14:

[0109] Specifically in this embodiment,

[0110] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm sizes, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1 and graphite felt 2. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with cathode electrolyte (1.0M ferrous sulfate + 1.0M nickel sulfate + 2M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Use the graphite felt 2 that has not been treated as the standby graphite felt for the next electrochemical treatment. Turn on the power supply and set the current to 27A (current density is 30mA / cm 2 ), the electrolysis time is set to 2 hours, the electrolytic cell temperature is controlled at 40°C, and the first electrochemical activation is carried out. The graphite felt 0 in the cathode electrolytic cell is subjected to cathode reduction activation, and the graphite felt 1 in the anode electrolytic cell is subjected to anodization. The electrochemically treated graphite felt 1 is cleaned, clamped with a clamp, and then placed in the cathode cell of the electrolytic cell. The graphite felt 2 that has not been treated is clamped with a clamp and placed in the anode cell of the electrolytic cell. The graphite felt 3 is used as the standby graphite felt for the next electrolysis. The current, electrolysis time, and electrolytic cell temperature are set to be the same as the previous electrolysis conditions. After the electrolysis is completed, the graphite felt 1 is cleaned with deionized water in an ultrasonic cleaning machine (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and the graphite felt 1 is taken out and dried.

[0111] Clean graphite felt 2 with deionized water, clamp it with a clamp, and place it in the cathode tank of the electrolytic cell. Clamp the untreated graphite felt 3 with a clamp and place it in the anode tank of the electrolytic cell. Use graphite felt 4 as the standby graphite felt for the next electrolysis. Set the current, electrolysis time, and electrolytic cell temperature to the same conditions as the previous electrolysis. After the electrolysis is completed, clean graphite felt 2 with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours, and take out graphite felt 2 for drying. Put graphite felt 1 and graphite felt 2 into an oven together and air-dry them at 40°C for 8 hours. The dried graphite felt 1 and graphite felt 2 are used as electrochemically activated graphite felt electrodes and used as electrodes of the all-vanadium liquid flow battery. Samples are taken for CV testing, and single cells are assembled for charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0112] Comparative Example 1:

[0113] Cut the original polyacrylonitrile-based graphite felt with a thickness of 4.5 mm into 300×300 mm dimensions, and cut a total of 4 pieces, numbered as graphite felt 0, graphite felt 1, and graphite felt 2. Use the original graphite felt 0 as the cathode, clamp it in a fixture, and immerse it in the cathode tank filled with catholyte (2.5M sulfuric acid). Use the original graphite felt 1 as the anode, clamp it in a fixture, and immerse it in the anode tank filled with anolyte (2.5M sulfuric acid). Turn on the power supply and set the current to 27 A (current density is 30 mA / cm 2 ), the electrolysis time was set to 2 hours, and the electrolytic cell temperature was controlled at 20°C. The first electrochemical activation process was performed: Graphite Felt 0 in the cathode electrolytic cell underwent cathodic reduction activation, while Graphite Felt 1 in the anode electrolytic cell underwent anodic oxidation. After the electrolysis was completed, the electrochemically treated Graphite Felt 1 was cleaned. Graphite Felt 0 and Graphite Felt 1 were cleaned with deionized water in an ultrasonic cleaner (F-330A, Shenzhen Fuyang Technology Group Co., Ltd.) for 0.5 hours. Graphite Felt 0 and Graphite Felt 1 were then removed and placed in an oven at 40°C for 8 hours with forced air drying. The dried Graphite Felt 0 and Graphite Felt 1 were used as electrodes in the all-vanadium redox flow battery.

[0114] Samples were taken for CV testing. Graphite felt 0 was used as the negative electrode of the all-vanadium redox flow battery, and graphite felt 1 was used as the positive electrode of the all-vanadium redox flow battery. A single cell was assembled and subjected to charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0115] Comparative Example 2:

[0116] The graphite felt 0 in comparative example 1 was used as the positive electrode of the all-vanadium redox flow battery, and the graphite felt 1 was used as the negative electrode of the all-vanadium redox flow battery. Single cells were assembled and charge and discharge cycles were performed to examine energy efficiency and voltage efficiency.

[0117] Comparative Example 3:

[0118] Two pieces of graphite felt 1 in Comparative Example 1 were cut and used as the positive electrode and negative electrode of the all-vanadium liquid flow battery respectively. Single cells were assembled and subjected to charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0119] Comparative Example 4:

[0120] Two pieces of graphite felt 0 in Comparative Example 1 were cut and used as the positive electrode and negative electrode of the all-vanadium redox flow battery, respectively. Single cells were assembled and subjected to charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0121] Comparative Example 5:

[0122] The electrically activated graphite felt 1 in Example 11 was cut into corresponding sizes and used as the positive electrode of the all-vanadium redox flow battery; the electrically activated graphite felt 1 in Comparative Example 1 was cut into corresponding sizes and used as the negative electrode of the all-vanadium redox flow battery. Single cells were assembled and charge and discharge cycles were performed to examine energy efficiency and voltage efficiency.

[0123] Comparative Example 6:

[0124] The electrically activated graphite felt 1 in Example 11 was cut into corresponding sizes and used as the positive electrode of the all-vanadium redox flow battery; the electrically activated graphite felt 0 in Comparative Example 1 was cut into corresponding sizes and used as the negative electrode of the all-vanadium redox flow battery. Single cells were assembled and charge and discharge cycles were performed to examine energy efficiency and voltage efficiency.

[0125] Comparative Example 7:

[0126] The electrically activated graphite felt 1 in Example 11 was cut into corresponding sizes and used as the negative electrode of the all-vanadium redox flow battery; the electrically activated graphite felt 1 in Comparative Example 1 was cut into corresponding sizes and used as the positive electrode of the all-vanadium redox flow battery. Single cells were assembled and charge and discharge cycles were performed to examine energy efficiency and voltage efficiency.

[0127] Comparative Example 8:

[0128] The electrically activated graphite felt 1 in Example 11 was cut into corresponding sizes and used as the negative electrode of the all-vanadium redox flow battery; the electrically activated graphite felt 0 in Comparative Example 1 was cut into corresponding sizes and used as the positive electrode of the all-vanadium redox flow battery. Single cells were assembled and charge and discharge cycles were performed to examine energy efficiency and voltage efficiency.

[0129] Comparative Example 9:

[0130] CV testing was performed on raw graphite felt samples. Single cells were constructed using the raw graphite felt and subjected to charge and discharge cycles to examine energy efficiency and voltage efficiency.

[0131] Table 1 Test data comparison

[0132]

[0133]

[0134] From the comparison of Examples 4 to 10, it can be seen that the current density is 30 mA / cm 2 When electrolysis is carried out at 100°C, the peak position difference of CV of the obtained graphite felt is small, the electrochemical activity is high, the energy efficiency and voltage efficiency are the highest, and the comprehensive performance is the best; from the comparison between Example 11 and Example 12, it can be seen that with the increase of electrolysis time, the electrochemical activity of the graphite felt increases, while the energy efficiency and voltage efficiency do not show advantages; from the comparison between Example 13 and Example 14, it can be seen that increasing the temperature is conducive to the increase of the electrochemical activity of the graphite felt, but the energy efficiency and voltage efficiency do not show advantages; from the comparison between Comparative Examples 1 to Comparative Examples 9 and Example 8, it can be seen that the performance of the graphite felt after secondary electrochemical activation is the best.

Claims

1. A method for electrochemical redox activation of graphite felt electrodes for vanadium redox flow batteries, characterized in that: Includes operations: (1) A first graphite felt which has not undergone any activation treatment is used as a cathode and immersed in a cathode electrolytic cell filled with a cathode electrolyte. A second graphite felt which has not undergone any activation treatment is used as an anode and immersed in an anode electrolytic cell filled with an anode electrolyte. A third graphite felt which has not undergone any treatment is used as an original graphite felt for the next oxidation; the anode electrolyte is selected from one of sulfuric acid, sodium hydroxide, and potassium hydroxide solution, and the concentration of the anode electrolyte is 1 to 3 mol / L; the cathode electrolyte is prepared by dissolving one or two of ferrous sulfate, nickel sulfate, nickel nitrate, manganese sulfate, and bismuth salt in an acid, and the concentration of the solute is in the range of 0.2 mol / L to 2.5 mol / L; the acid is sulfuric acid or hydrochloric acid, and the concentration of the acid is 1 to 3 mol / L; (2) After preparation, power is turned on to perform the first electrochemical activation: the first graphite felt in the cathode electrolytic cell is subjected to cathode reduction, and the second graphite felt in the anode electrolytic cell is subjected to anodic oxidation activation; (3) After the first electrochemical activation, the second graphite felt is cleaned and then placed in the cathode electrolytic cell of the electrolytic cell, the third graphite felt that has not been treated in any way is placed in the anode electrolytic cell of the electrolytic cell, and the fourth graphite felt that has not been treated in any way is used as the original graphite felt for the next oxidation; (4) After preparation, power is turned on to perform a second electrochemical activation, wherein the third graphite felt in the anode electrolytic cell is subjected to anodic oxidation activation, and the second graphite felt in the cathode electrolytic cell is subjected to cathode reduction; (5) After the second electrochemical activation, the obtained second graphite felt is washed and dried to obtain a prepared graphite felt electrode that can be used in a liquid flow battery; (6) performing a third electrochemical activation, placing the third graphite felt in a cathode electrolytic cell for cathode reduction, and placing the fourth graphite felt in an anode electrolytic cell for anodic oxidation. After the electrochemical activation is completed, the obtained third graphite felt is washed and dried, and can be used as a graphite felt electrode for a liquid flow battery; The above operation is continued to perform continuous electrochemical activation of the graphite felt. The anode oxidation activation and cathode electrochemical activation are carried out in the same electrolytic cell. The anode half cell and cathode half cell of the electrolytic cell are separated by an ion exchange membrane. A direct current is applied between the positive and negative electrodes of the electrolytic cell. The current density of the direct current is 5 mA / cm 2 ~40mA / cm 2 The time of each electrochemical activation is 1.8 to 2.2 hours, and the activation temperature is 20°C to 30°C.

2. The method according to claim 1, characterized in that The cathode electrolyte is prepared by dissolving ferrous sulfate and nickel sulfate in acid, wherein the concentrations of ferrous sulfate and nickel sulfate are independently 0.8 mol / L to 1.2 mol / L; and the concentration of the acid is 1.8 to 2.2 mol / L.

3. The method according to claim 1, wherein the graphite felt after electrochemical treatment is ultrasonically cleaned with deionized water and then dried at 35-45°C for 6-10 hours.

4. The method according to any one of claims 1 to 3, characterized in that The activation system adopted in the method includes an activation fixture, which includes three parts: a graphite felt fixture, a fixture transfer mechanism and an electric clamp mechanism. The first part is the graphite felt fixture used during electrochemical activation, the second part is used to transfer the fixture during the transfer process after activation is completed; the third part, the electric clamp mechanism, is connected to a power supply.

5. The method according to claim 4, characterized in that The graphite felt fixture includes a frame base plate, a graphite plate, and a hollow frame panel. The hollow part of the frame panel is the area for placing the graphite felt. The graphite plate is provided with a grid and a protrusion for connecting the electrodes. After the frame base plate, graphite plate, frame panel and graphite felt are combined, they are fixed on the four sides using split horizontal clips, long horizontal clips and vertical clips.

6. The method according to claim 4, characterized in that The electric clamp mechanism includes an electric clamp driving mechanism, an electric clamp transmission mechanism, an electric clamp plate connecting rod, an electric clamp plate, and an electric wire; the electric clamp driving mechanism is installed in the central motor compartment of the main body bracket, and the electric clamp transmission mechanism is installed on the lower side of the central motor compartment. The bottom end of the output shaft at the bottom of the electric clamp transmission mechanism is connected to the active bevel gear, and the active bevel gear engages with two driven bevel gears. When the active bevel gear rotates, it drives the driven bevel gears to rotate, and the rotation directions of the two bevel gears are opposite, so as to realize the rotation of the electric clamp plate connecting rod around the axis of the output shaft; after the electric clamp plate connecting rod rotates, the end electric clamp plate and the graphite plate are tightly attached and loosened; after being tightly attached, the electric wire led out through the electric clamp plate is connected to the power supply.

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