Modification method for carbon felt electrode of all-iron redox flow battery

Abstract

A modification method for a carbon felt electrode of an all-iron redox flow battery, comprising the following steps: 1) placing carbon felt into a tubular furnace for firing; 2) preparing a Fe2(SO 4)3 methanol solution and a dimethylimidazole methanol solution; 3) placing the heat-treated carbon felt into the dimethylimidazole methanol solution, and then pouring the Fe2(SO4)3 methanol solution into the solution; 4) stirring the mixed solution and the carbon felt, and then taking out and drying the mixed solution and the carbon felt; 5) placing the dried carbon felt into the tubular furnace, and firing the dried carbon felt in a nitrogen atmosphere; and 6) taking out the fired carbon felt, cleaning with hydrochloric acid, then cleaning with deionized water, and drying after the cleaning to obtain a modified carbon felt electrode. The method is used for modifying the carbon felt electrode of the all-iron redox flow battery, and the hydrophilicity and the electrochemical activity of the carbon felt electrode can be improved by means of soaking and stirring in the solution and firing in the tubular furnace, effectively improving the voltage efficiency of the all-iron redox flow battery.

Description

A method for modifying carbon felt electrodes for all-iron flow batteries Technical Field

[0001] The present invention belongs to the technical field of liquid flow battery energy storage, and in particular provides a method for modifying a carbon felt electrode of an all-iron liquid flow battery. Background Art

[0002] With the rapid development of the economy, energy consumption is increasing, and the environmental problems caused by the combustion of fossil fuels are unavoidable. Renewable energy sources such as wind and solar energy are effective solutions to this problem. However, wind and solar energy are intermittent and unstable, and directly integrating them into the power grid after generation can easily impact the grid's stable operation. Therefore, there is an urgent need for long-term energy storage systems that operate in conjunction with renewable energy to absorb renewable energy generation and contribute to the goal of "carbon peak and carbon neutrality."

[0003] Among numerous energy storage technologies, flow batteries are a rising star in the long-duration energy storage market due to their inherently aqueous nature. Compared to lithium-ion batteries, they offer no risk of spontaneous combustion, a long service life, and flexible design. All-iron flow batteries are the most mature and commercially available flow battery system. They are primarily used in conjunction with wind and photovoltaic power plants, addressing issues such as unstable and uncertain power generation.

[0004] In a flow battery, electrodes are one of the most critical components, playing the crucial role of providing a reaction site for the positive and negative active materials. Therefore, flow battery electrodes must possess high electrical conductivity, high electrochemical activity, high porosity, and corrosion resistance. Graphite felt is the primary electrode material for flow batteries, due to its low cost, strong corrosion resistance, and high electrical conductivity. However, factory-produced graphite felt also suffers from low electrochemical activity and poor reaction kinetics. These two issues limit the efficiency of flow batteries and make flow battery systems difficult to implement. Summary of the Invention

[0005] In order to solve the problems of low electrode electrochemical activity and poor reaction kinetics in all-iron liquid flow batteries, the present invention provides a method for modifying carbon felt electrodes of all-iron liquid flow batteries.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A method for modifying a carbon felt electrode of an all-iron liquid flow battery, characterized in that it comprises the following steps:

[0007] 1) Place the carbon felt in a tube furnace and fire it in an air atmosphere;

[0008] 2) Prepare Fe2(SO4)3 methanol solution and dimethylimidazole methanol solution with different concentrations;

[0009] 3) Place the heat-treated carbon felt into dimethylimidazole methanol solution, and then pour the Fe2(SO4)3 methanol solution into the dimethylimidazole methanol solution containing the carbon felt;

[0010] 4) Stir the mixed solution and carbon felt and then take them out to dry;

[0011] 5) Place the dried electrode in a tube furnace and sinter in a nitrogen atmosphere;

[0012] 6) Take out the fired carbon felt, wash it with hydrochloric acid first, then with deionized water, and dry it after washing to obtain the modified carbon felt electrode.

[0013] The step 1) specifically comprises: placing the carbon felt in a tubular furnace, heating the tubular furnace at a rate of 1 to 10°C / min, a maximum temperature of 400 to 600°C, and firing and holding for 5 to 7 hours;

[0014] Wherein, step 2) specifically comprises: preparing Fe2(SO4)3 dissolved in methanol solution with a concentration of 0.1 to 0.5 mol / L, and preparing dimethylimidazole dissolved in methanol solution with a concentration of 0.1 to 0.5 mol / L;

[0015] Wherein, step 3) is specifically as follows: immersing the carbon felt in step 1) in the dimethylimidazole methanol solution in step 2) and stirring, and then pouring the Fe2(SO4)3 methanol solution in step 2) into the dimethylimidazole methanol solution containing the carbon felt;

[0016] Specifically, step 4) is as follows: stirring the carbon felt soaked in step 3) for 4 to 6 hours, then taking it out and placing it in a vacuum drying oven at a drying temperature of 80 to 110° C. for 12 to 24 hours.

[0017] Specifically, step 5) comprises taking out the carbon felt dried in step 4) and placing it in a tubular furnace for firing. The heating rate of the tubular furnace is 1 to 10°C / min, the maximum temperature is 600 to 1000°C, and the firing and holding time is 6 to 12 hours.

[0018] Specifically, step 6) comprises: removing the electrode from step 5) and cleaning it with 3-6 mol / L hydrochloric acid, washing it 1-5 times with hydrochloric acid, and washing it 1-5 times with deionized water. After washing, the drying temperature is 80-110° C. for 12-24 hours.

[0019] The advantages of the present invention are: by soaking and stirring in a solution and firing in a tubular furnace, the two shortcomings of the existing carbon felt electrode, namely, poor hydrophilicity and poor electrochemical activity, can be modified in a targeted manner. This method is to improve the performance of the carbon felt electrode by soaking and firing the electrode, wherein the surface morphology and reaction sites of the electrode can be easily regulated by changing the concentration of the soaking solution, soaking time, firing temperature and time, thereby further controlling the performance of the electrode. By firing at high temperature, the modified electrode can effectively improve the voltage efficiency of the all-iron liquid flow battery. This process is simple and easy to implement and can be promoted to other liquid flow battery systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a schematic structural diagram of the all-iron liquid flow battery of the present invention.

[0021] Figure 2 is a test diagram of the contact angle of carbon felt before and after process treatment.

[0022] FIG3 shows the voltage efficiency of the all-iron flow battery assembled with the modified carbon felt in Example 2 in the rate performance test at current densities ranging from 40 to 120.

[0023] Explanation of the serial numbers in the figure: 1 is the positive electrolyte storage tank, 2 is the negative electrolyte storage tank, 3 is the flow battery diaphragm, 4 is the positive electrode, 5 is the negative electrode, 6 is the positive end plate, 7 is the negative end plate, 8 is the positive pump, and 9 is the negative pump. DETAILED DESCRIPTION

[0024] As shown in Figure 1, the all-iron flow battery of the present invention primarily comprises: a positive electrolyte storage tank 1, a negative electrolyte storage tank 2, a flow battery separator 3, a positive electrode 4, a negative electrode 5, a positive terminal plate 6, a negative terminal plate 7, a positive pump 8, and a negative pump 9. The bottom of the positive electrolyte storage tank 1 is connected to the bottom of the positive electrode 4 via a pipeline with the positive pump 8, the top of the positive electrolyte storage tank 1 is connected to the top of the positive electrode 4 via a pipeline, and the positive terminal plate 6 is disposed outside the positive electrode 4, forming the positive electrode portion of the flow battery. The bottom of the negative electrolyte storage tank 2 is connected to the bottom of the negative electrode 5 via a pipeline with the negative pump 9, the top of the negative electrolyte storage tank 2 is connected to the top of the negative electrode 5 via a pipeline, and the negative terminal plate 7 is disposed outside the negative electrode 5, forming the positive electrode portion of the flow battery. The positive electrode 4 and the negative electrode 5 are arranged vertically and parallel to each other, separated by the flow battery separator 3. The negative electrode 4 of the flow battery is equipped with the modified electrode used in the all-iron flow battery according to the present invention, while the positive electrode still uses the untreated original felt as the electrode. The carbon felt electrode has a very large active area. The area of ​​the carbon felt electrode used in the all-iron flow battery is 2×2 cm 2 The battery separator uses the commercial Nafion proton exchange membrane commonly used in flow batteries, and the proton exchange membrane area is 2×2 cm 2And use aluminum alloy end plates (positive end plate 6, negative end plate 7) to clamp each component.

[0025] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or utilized through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. Example 1

[0026] This embodiment provides a method for modifying a carbon felt electrode of an all-iron liquid flow battery, the method comprising the following steps:

[0027] 1) Place the carbon felt in a high-temperature tube furnace and sinter it at high temperature for a certain period of time in an air atmosphere; at room temperature, place the carbon felt in the tube furnace, heat the tube furnace at a rate of 1°C / min, gradually heat it to 400°C, and then maintain it at 400°C for 5 hours;

[0028] 2) Prepare a 0.1 mol / L solution of Fe2(SO4)3 in methanol and a 0.1 mol / L solution of dimethylimidazole in methanol.

[0029] 3) Take out the heat-treated carbon felt and place it in dimethylimidazole methanol solution, and pour the Fe2(SO4)3 methanol solution into the dimethylimidazole methanol mixed solution containing the carbon felt;

[0030] 4) Stir the mixed solution and carbon felt for 4 hours, then remove and dry in a vacuum drying oven at 85°C for 12 hours.

[0031] 5) Take out the dried carbon felt and place it in a tubular furnace for firing. The atmosphere is nitrogen. The heating rate of the tubular furnace is 1 ℃ / min. The temperature is gradually raised from room temperature to 600 ℃ and maintained at 600 ℃. ℃, time is 6 hours;

[0032] 6) Remove the fired carbon felt, wash it with hydrochloric acid first and then with deionized water, and dry it after washing; remove the fired carbon felt and wash it with 3 mol / L hydrochloric acid, wash it once with hydrochloric acid and once with deionized water, and dry it at 80°C for 12 hours. Example 2

[0033] This embodiment provides a method for modifying a carbon felt electrode of an all-iron liquid flow battery, the method comprising the following steps:

[0034] 1) Place the carbon felt in a high-temperature tube furnace and sinter it at high temperature for a certain period of time in an air atmosphere; the carbon felt is placed in the tube furnace at room temperature, and the heating rate of the tube furnace is 5°C / min, gradually increasing the temperature to 500°C, and then maintaining 500°C for 6 hours;

[0035] 2) Prepare a solution of Fe2(SO4)3 dissolved in methanol with a concentration of 0.3 mol / L and a solution of dimethylimidazole dissolved in methanol with a concentration of 0.3 mol / L;

[0036] 3) Take out the heat-treated carbon felt and place it in dimethylimidazole methanol solution, and pour the Fe2(SO4)3 methanol solution into the dimethylimidazole methanol solution containing carbon felt;

[0037] 4) Stir the mixed solution and carbon felt for a certain period of time and then take it out to dry; stir for 5 hours, then take it out and place it in a vacuum drying oven at a drying temperature of 95°C for 18 hours;

[0038] 5) Place the dried carbon felt in a tubular furnace at room temperature in a nitrogen atmosphere. The heating rate of the tubular furnace is 5°C / min, gradually heating to 800°C and maintaining at 800°C. ℃, time is 9 hours;

[0039] 6) The fired carbon felt was removed and cleaned with 4.5 mol / L hydrochloric acid three times and deionized water three times. After cleaning, the drying temperature was 100°C for 18 hours. Example 3

[0040] This embodiment provides a method for modifying a carbon felt electrode of an all-iron liquid flow battery, the method comprising the following steps:

[0041] 1) Place the carbon felt in a high-temperature tube furnace and sinter it at high temperature for a certain period of time in an air atmosphere; the carbon felt is placed in the tube furnace at room temperature, and the heating rate of the tube furnace is 10°C / min, gradually increasing the temperature to 600°C, and then maintaining 600°C for 7 hours;

[0042] 2) Prepare a 0.5 mol / L solution of Fe2(SO4)3 in methanol and a 0.5 mol / L solution of dimethylimidazole in methanol.

[0043] 3) Take out the heat-treated carbon felt and place it in dimethylimidazole methanol solution, and pour the Fe2(SO4)3 methanol solution into the dimethylimidazole methanol solution containing the carbon felt;

[0044] 4) Stir the mixed solution and carbon felt for a certain period of time and then take them out to dry; stir for 6 hours, then take them out and place them in a vacuum drying oven at 105°C for 24 hours;

[0045] 5) Place the dried carbon felt in a tubular furnace at room temperature in a nitrogen atmosphere and heat it up at a rate of 10°C / min to 1000°C, then keep it at 1000°C. ℃, time is 12 hours;

[0046] 6) The fired carbon felt was taken out and cleaned with 6 mol / L hydrochloric acid for 5 times and then with deionized water for 5 times. The drying temperature after cleaning was 110°C for 24 hours.

[0047] Performance test experiment:

[0048] The carbon felt electrode materials modified in the comparative example (carbon felt electrode before modification) and Examples 1-3 were used as the negative electrode of the battery and placed in the aforementioned all-iron liquid flow battery for testing. The positive electrode used the original carbon felt and the perfluorosulfonic acid ion exchange membrane was used as the diaphragm to assemble the all-iron liquid flow battery. The positive electrode electrolyte was 15 mL of 1 mol / L Fe 2+ +3mol / L NH4Cl solution, the negative electrode electrolyte is 15 mL of 0.5mol / L Fe 2+ +3mol / L NH4Cl solution. The battery voltage efficiency is shown in the following table:

[0049] Battery voltage efficiency

[0050] Comparative Example Example 1 Example 2 Example 3 40 Current density 83.1% 86.1% 86.3% 85.9% 60 Current density 79.4% 83.0% 82.9% 82.7% 80 Current density 75.0% 79.3% 79.8% 79.6% 100 Current density 70.8% 76.9% 77.4% 77.0% 120 Current density 64.3% 73.9% 74.0% 74.2%

[0051] As can be seen from the above table, the voltage efficiency of the battery corresponding to the modified carbon felt electrode is significantly improved; the battery voltage efficiency is improved more significantly (10%) at a higher current density, proving that the electrochemical activity of the electrode is significantly improved and the battery polarization is significantly reduced after this treatment method; the battery assembled using the carbon felt electrode treated with this method still has a voltage efficiency of 74% at a current density of 120, which is superior to other material treatment methods in the same field.

[0052] The modified carbon felt electrode materials prepared in the comparative example and Example 2 were tested for hydrophilicity using a contact angle tester, and the comparative test results are shown in Figure 2. As can be seen from Figure 2, the contact angle of the modified carbon felt is much smaller than that of the original felt, indicating that this treatment method can improve the hydrophilicity of the carbon felt, which is beneficial to the diffusion of iron ions on the carbon felt surface, thereby enhancing the electrochemical reaction process.

[0053] The modified carbon felt electrode materials prepared in the comparative example and Example 2 were assembled into an all-iron flow battery and tested. Figure 3 shows the voltage efficiency of the battery test results. This figure is a continuous test result, and each four data points correspond to a current density. For example, the four data points under the number 80 in the figure correspond to 11 to 15 cycles of continuous test charge and discharge, and the current density of the battery is 80 mA / cm -2 The voltage efficiency of the battery using the modified carbon felt is significantly improved. The current density of this battery is 120 (mA / cm -2 ) still has a voltage efficiency of 74%, which compares favorably to other electrode materials in the same field. This process is simple and stable, significantly improving battery performance and can be extended to other flow battery fields.

[0054] The above embodiments are merely illustrative of the spirit and scope of the present invention. Modifications or variations to the above embodiments are permitted. Therefore, any equivalent modifications or variations made by one of ordinary skill in the art without departing from the spirit and technical concepts disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for modifying a carbon felt electrode of an all-iron liquid flow battery, characterized in that: The steps include: 1) Place the carbon felt in a tubular furnace and fire it in an air atmosphere; 2) Prepare Fe2(SO4)3 methanol solution and dimethylimidazole methanol solution; 3) Place the heat-treated carbon felt into a dimethylimidazole methanol solution, and then pour the Fe2(SO4)3 methanol solution into the dimethylimidazole methanol solution containing the carbon felt; 4) Stir the mixed solution and carbon felt and then take them out to dry; 5) placing the dried carbon felt in a tube furnace and firing it in a nitrogen atmosphere; 6) Take out the fired carbon felt, wash it with hydrochloric acid first, then with deionized water, and dry it after washing to obtain the modified carbon felt electrode.

2. The method for modifying the carbon felt electrode of the all-iron liquid flow battery according to claim 1, characterized in that: In step 1), the heating rate of the tubular furnace is 1-10°C / min, the firing temperature is 400-600°C, and the firing and holding time is 5-7 hours.

3. The method for modifying the carbon felt electrode of the all-iron liquid flow battery according to claim 1, characterized in that: In step 2), the concentration of the methanol solution of Fe2(SO4)3 is 0.1-0.5 mol / L, and the concentration of the methanol solution of dimethylimidazole is 0.1-0.5 mol / L.

4. The method for modifying the carbon felt electrode of the all-iron liquid flow battery according to claim 1, characterized in that: In step 4), the stirring time is 4 to 6 hours, the drying temperature is 80 to 110° C., and the drying time is 12 to 24 hours.

5. The method for modifying the carbon felt electrode of the all-iron liquid flow battery according to claim 1, characterized in that: In step 5), the heating rate of the tubular furnace is 1-10°C / min, the firing temperature is 600-1000°C, and the firing and holding time is 6-12 hours.

6. The method for modifying the carbon felt electrode of the all-iron liquid flow battery according to claim 1, characterized in that: In step 6), the concentration of hydrochloric acid is 3-6 mol / L; during the cleaning process, the hydrochloric acid is cleaned 1-5 times, and the deionized water is cleaned 1-5 times. After cleaning, the drying temperature is 80-110° C. and the drying time is 12-24 hours.

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