A method for activating the surface of a graphite felt and removing amorphous carbon using a photothermal effect

Abstract

The present application belongs to the technical field of all-vanadium redox flow battery, and particularly relates to a method for activating the surface of graphite felt and removing amorphous carbon by using photothermal effect, which comprises the following steps: step one, placing the semi-finished graphite felt which has not been activated and is flattened into a transparent container; step two, introducing a required oxidizing gas into the transparent container to adjust the atmosphere in the transparent container to be the atmosphere of the oxidizing gas; step three, setting a light source above the transparent container to irradiate the upper surface of the flattened semi-finished graphite felt, continuously introducing the oxidizing gas into the transparent container, continuously irradiating for a period of time under the condition of maintaining the atmosphere of the oxidizing gas, then stopping the irradiation, removing the amorphous carbon of the graphite felt and realizing the activation of the surface of the graphite felt. The present application realizes the removal of amorphous carbon and the activation of the surface of the graphite felt at the same time, and overcomes the technical problems of the prior art, such as complex process, high energy consumption and pollution caused by the chemical reagents.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of all-vanadium redox flow batteries, and particularly relates to a method for activating the surface of graphite felt and removing amorphous carbon by using photothermal effect. BACKGROUND

[0002] At present, the most widely used electrode material of all-vanadium redox flow batteries is graphite felt, which belongs to a porous felt-like fiber material of carbon fiber weaving, has a wide three-dimensional network structure, a high specific surface area, and good electrical conductivity and electrochemical stability. However, the catalytic activity is limited, and a large electrochemical polarization impedance will be generated.

[0003] The graphite felt is mainly PAN-based pre-oxidized fiber, and is processed into a flat felt with a specific required thickness and good uniformity of square meter gram weight on a high-end non-woven needle punching equipment as a raw material felt. The graphite felt intermediate product with a large number of carbon nanotubes and amorphous carbon deposited on the surface is obtained through carbonization and high-temperature sintering.

[0004] The graphite carbon fiber intermediate product is subjected to oxidation pretreatment through an activation furnace to increase the electrochemical activity of the electrode graphite felt. The activation condition is that water vapor is injected into a quartz tube containing the graphite felt electrode, and the activation treatment is carried out at a temperature of 700 DEG C to increase the surface active groups. In order to increase the number of active sites, Fe and Ni metal catalysts are used, but the metal elements remaining in the electrode may contaminate the electrolyte.

[0005] The amorphous carbon deposited on the surface of the graphite carbon fiber intermediate product increases the energy consumption, cost and time of electrode activation, reduces the porosity of the electrode, hinders the contact between the electrolyte and the electrode, falls off during use, and affects the performance of the electrode and the stability of the system. It has many adverse effects on the "catalytic surface". A large number of carbon nanotubes deposited on the surface of the graphite increase the contact between the fibers, reduce the contact resistance, and improve the conductivity of the "conductive surface", which is beneficial to the system.

[0006] The traditional heat treatment operation is isothermal heating operation on the whole graphite felt. In fact, only the amorphous carbon between the "catalytic active surface" directly contacting the separator needs to be removed, so that the graphite felt surface can be activated while removing the amorphous carbon. However, some existing methods for removing amorphous carbon often need to use chemical reagents with pollution or adopt complex processes, and the overall heating needs to consume high energy consumption, so a processing method with simple process and low energy consumption and pollution is needed. SUMMARY

[0007] The purpose of the present application is to provide a method for activating the surface of graphite felt and removing amorphous carbon by using photothermal effect, which solves the technical problems of complex process, high energy consumption or pollution caused by chemical reagents in the prior art.

[0008] The method for activating the surface of graphite felt and removing amorphous carbon by using the photo-thermal effect comprises the following steps.

[0009] Step one, flatten the semi-finished graphite felt which has not been activated and place it in a transparent container.

[0010] Step two, introduce the required oxidizing gas into the transparent container to adjust the atmosphere in the transparent container to the atmosphere of the oxidizing gas.

[0011] Step three, set a light source above the transparent container to irradiate the upper surface of the flattened semi-finished graphite felt, continuously introduce the oxidizing gas into the transparent container, continuously irradiate for a period of time under the condition of maintaining the atmosphere of the oxidizing gas, then stop the irradiation, remove the amorphous carbon of the graphite felt and achieve the activation of the surface of the graphite felt.

[0012] Preferably, the oxidizing gas comprises one or more of air, oxygen, water vapor and carbon dioxide.

[0013] Preferably, the oxidizing gas comprises air, water vapor and carbon dioxide, wherein the volume ratio of air to carbon dioxide is 1:10-1, and the oxidizing gas contains saturated water vapor.

[0014] Preferably, the light source is a xenon lamp with a condensing accessory, the distance between the xenon lamp and the surface of the graphite felt is 1-20 cm, and the current range of the xenon lamp during irradiation is 16-21 A.

[0015] Preferably, during the irradiation process, when the temperature of the exposed upper surface of the graphite felt rises to a set temperature, maintain the temperature for constant temperature irradiation treatment, and the treatment time of the constant temperature irradiation is 10-30 min.

[0016] Preferably, the set temperature is 800℃.

[0017] Preferably, the thickness of the semi-finished graphite felt is 3 mm.

[0018] The advantages of the present application are as follows:

[0019] 1. The present application can activate the graphite felt under mild conditions by controlling the atmosphere and irradiation conditions, effectively avoiding damage to the structure of the graphite felt.

[0020] 2. The present application has little effect on the overall structure of the graphite felt and only removes the amorphous carbon on the catalytic active surface. In this way, the carbon deposition on the "catalytic surface" can be removed, and the conductivity of the "conductive surface" can be preserved, thus ensuring the performance of the product.

[0021] 3. Utilizing one or more of air, oxygen, water, and carbon dioxide as oxidants, without using strong acids, strong alkalis, or other hazardous chemicals, amorphous carbon impurities on the surface of the graphite felt are removed. This protects the graphite felt structure and avoids potential pollution and hazards from chemical agents.

[0022] 4. No other metal-based catalysts are introduced during the processing of this invention, thus avoiding subsequent contamination of the vanadium electrolyte by metal ions in the electrode.

[0023] 5. The equipment required for implementation of this invention is simple, the equipment requirements are not high, and the operation steps are simple, quick, easy to implement and promote. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of a method for activating the surface of graphite felt and removing amorphous carbon using the photothermal effect according to the present invention. Detailed Implementation

[0025] The following detailed description of the embodiments, with reference to the accompanying drawings, will further illustrate the specific implementation of the present invention, in order to help those skilled in the art to have a more complete, accurate, and in-depth understanding of the inventive concept and technical solution of the present invention.

[0026] like Figure 1 As shown, the present invention provides a method for activating the surface of graphite felt and removing amorphous carbon using photothermal effect, comprising the following steps.

[0027] Step 1: Flatten the unactivated semi-finished graphite felt and place it in a transparent container.

[0028] In this step, commercially available products such as polyacrylonitrile-based acrylic fibers or polyacrylonitrile-based carbon fibers are used as raw materials for preparing graphite felt. The fiber raw materials are woven and needle-punched to form fiber felt, with the felt thickness approximately 3 mm formed by needle punching. The fiber felt is then sent to a pre-oxidation furnace for heat treatment at 150-260℃. The pre-oxidized fiber felt is then sent to a carbonization furnace for carbonization, and then to a graphite mold for graphitization, yielding unactivated semi-finished graphite felt. Finally, the semi-finished graphite felt is flattened and placed in a transparent container.

[0029] Step 2: Introduce the required oxidizing gas into the transparent container to adjust the atmosphere inside the transparent container to an oxidizing gas atmosphere.

[0030] The oxidizing gas includes one or more of air, oxygen, water vapor, and carbon dioxide. In this embodiment, the oxidizing gas includes air, water vapor, and carbon dioxide, wherein the volume ratio of air to carbon dioxide is 1:10 to 1, and the oxidizing gas contains saturated water vapor. The oxidizing gas is introduced into the transparent container to achieve the effect of adjusting the atmosphere in the transparent container to an oxidizing gas atmosphere. Under this mixed oxidizing gas atmosphere, step three is prepared to be performed, and the oxidizing gas is continuously introduced during the treatment process of step three.

[0031] Step three, a light source is arranged above the transparent container to irradiate the upper surface of the exposed semi-finished graphite felt. The transparent container continuously introduces the oxidizing gas, and the irradiation is stopped after a period of time under the condition of maintaining the oxidizing gas atmosphere, thereby removing the amorphous carbon of the graphite felt and achieving the activation of the surface of the graphite felt.

[0032] In this step, the light source uses a xenon lamp with a condensing accessory. The current of the xenon lamp can be adjusted, and the power of the xenon lamp can be selected as 300 W. The distance between the xenon lamp and the surface of the graphite felt is adjusted to 1-20 cm. The current range of the xenon lamp during irradiation is 16-21 A. When the temperature of the exposed upper surface of the graphite felt rises to a set temperature, constant temperature irradiation treatment is maintained at this temperature. The treatment time of constant temperature irradiation is 10-30 min. The aforementioned oxidizing gas is continuously introduced during the irradiation process to maintain the gas atmosphere in the transparent container. After the light source is turned off, the aforementioned oxidizing gas is still continuously introduced for cooling. After the graphite felt cools down, the treated graphite felt is taken out for standby.

[0033] This method controls the intensity, time, and atmosphere conditions (one or more of air, oxygen, water, and carbon dioxide) of the xenon lamp irradiation, utilizes the photo-thermal effect of carbon materials, and makes the amorphous carbon with poor crystallinity on the surface of the graphite felt be oxidized into CO2 or CO. Since the photons can only reach a certain thickness of the graphite felt, the structure of the other side of the graphite felt cannot be damaged, and the conductivity will not be affected. Therefore, this method can remove the carbon deposition on the "catalytic surface" while preserving the conductivity of the "conductive surface". At the same time, only the upper surface of the graphite felt is heated by irradiation. While the upper surface of the graphite felt is heated, the heat is removed by the continuously introduced oxidizing gas to avoid the overall temperature of the graphite felt being too high, thereby avoiding the destruction of the overall structure of the graphite felt at high temperature.

[0034] In the experiment, a temperature sensor for detecting the temperature of the upper surface of the graphite felt is arranged in the transparent container during the process of the method, and the samples of the semi-finished graphite felt before and after the treatment are weighed. Based on the method provided by the application, taking a 10mg sample as an example, the flow rate of the oxidation gas is set to 20mL / min, and the distance between the surface of the graphite felt and the xenon lamp is fixed. When the temperature of the upper surface of the graphite felt rises to 800℃, it is maintained for 10-30min as the light treatment time. The results of different treatment times can be seen in Table 1, and the maintenance times of three experiments are 10min, 20min and 30min respectively. After the experiment, the mass loss of the treated graphite felt accounts for 21.5%, 29.3% and 31.7% of the mass loss of the unactivated semi-finished graphite felt respectively.

[0035] Table 1. Amorphous carbon removal effect of different light treatment times

[0036] Irradiation time / min 10 20 30 Mass loss / % 21.5％ 29.3％ 31.7％

[0037] Using the method, only simple equipment such as a transparent container, a corresponding temperature sensor, a light source and a ventilation device is required, the equipment requirement is not high, and the operation is simple and fast. The method can activate the graphite felt under mild conditions by controlling the atmosphere and light conditions, and effectively avoid damaging the structure of the graphite felt. Therefore, the method has little effect on the overall structure of the graphite felt, and only removes the amorphous carbon on the catalytic active surface, which can remove the carbon deposition on the "catalytic surface" and retain the conductivity of the "conductive surface".

[0038] The application is described above in conjunction with the drawings, and it is obvious that the specific implementation of the application is not limited by the above method. Any non-essential improvement or direct application of the inventive concept and technical solution to other occasions without improvement is within the protection scope of the application.

Claims

1. A method for activating the surface of a graphite felt and removing amorphous carbon using a photothermal effect, characterized by: It comprises the following steps: Step 1, the unactivated semi-finished graphite felt is flattened and placed in a transparent container; Step 2, the required oxidizing gas is introduced into the transparent container to adjust the atmosphere in the transparent container to the atmosphere of the oxidizing gas; Step 3, a light source is arranged above the transparent container to irradiate the exposed upper surface of the flattened semi-finished graphite felt, the transparent container continuously introduces the oxidizing gas, and the graphite felt is activated by removing the amorphous carbon on the surface of the graphite felt under the condition of maintaining the oxidizing gas atmosphere for a period of time, then the irradiation is stopped; The oxidizing gas comprises air, water vapor and carbon dioxide, wherein the volume ratio of air to carbon dioxide is 1:10~1, and the oxidizing gas contains saturated water vapor.

2. The method for activating the surface of a graphite felt and removing amorphous carbon using a photothermal effect according to claim 1, characterized by: The light source is a xenon lamp containing a condensing accessory, the distance between the xenon lamp and the surface of the graphite felt is 1~20 cm, and the current range of the xenon lamp during irradiation is 16~21 A.

3. The method for activating the surface of graphite felt and removing amorphous carbon by using the photothermal effect according to claim 1, characterized in that: During the irradiation process, when the temperature of the exposed upper surface of the graphite felt rises to a set temperature, the constant temperature irradiation treatment is maintained at this temperature, and the treatment time of the constant temperature irradiation is 10~30 min.

4. The method for activating the surface of graphite felt and removing amorphous carbon by using the photothermal effect according to claim 3, characterized in that: The set temperature is 800℃.

5. The method for activating the surface of graphite felt and removing amorphous carbon by using the photothermal effect according to claim 1, characterized in that: The thickness of the semi-finished graphite felt is 3 mm.

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