TWI556501B - Method of direct electrochemical oxidation for enhancing effectiveness of carbon felt of flow battery - Google Patents

Description

Method for directly improving the efficiency of carbon felt in liquid flow battery by direct electrochemical oxidation

The invention relates to a method for directly electrochemically oxidizing the performance of a carbon felt of a liquid flow battery, in particular to a direct voltage-to-cell reactor for redox reaction, so that the carbon felt in the battery stack can be uniformly contacted with the electrolyte. The electrochemical reaction is carried out, in particular, a direct electrochemical oxidation modification method for forming an oxygen-containing functional group (-COOH, -OH) on the surface of the carbon felt to achieve the purpose of upgrading.

Electrochemical Flow Cell, also known as Redox Flow Battery, is an electrochemical energy storage device. Among them, the vanadium salt solution used for both positive and negative electrodes is also called Vanadium Redox Flow Battery, because the all-vanadium redox flow battery has excellent charge and discharge performance, long cycle life and low cost. The characteristics, and its manufacturing, use and disposal process do not produce harmful substances, and become an ideal green energy storage device.

Generally, a method of electrochemically reacting is generally carried out, and the flow is as shown in FIG. 4, and a three-electrode electrode arrangement method is used to carry out a redox reaction by a voltage. The steps are as follows:

Step s21: using an unmodified carbon felt as a negative electrode, a titanium plate (or graphite plate) as a positive electrode, an electrolyte solution of 1 M sulfuric acid aqueous solution, and conducting a voltage or current for electrochemical oxidation reaction;

Step s22: the reaction time is from several minutes to one hour;

Step s23: after deionized water washing, vacuum drying at a temperature of 120 ° C for 5 hours;

Step s24: assembling into a battery stack as an electrode material;

Step s25: by pumping in 1M to 3M vanadyl sulfate and 1M to 5M sulfuric acid (or hydrochloric acid or nitric acid or phosphoric acid) aqueous solution, enter through the anode and cathode inlet of the battery stack and uniformly contact with the carbon felt, the flow rate is controlled at 20 Between 100mL/min, after being collected into the electrolyte storage tank through the anode and cathode outlets of the battery stack, the cathode and anode inlets recycled to the battery stack are driven into the battery stack until the air in the battery stack is completely discharged;

Step s26: The positive and negative poles are connected to the external power supply system, and the current is supplied in the constant current mode to carry out the charge and discharge reaction of the battery of the flow battery, and the process is repeated.

However, the conventional process uses a precious metal titanium plate, and the electrode material cost is high. The process time required for completing the single cell (single cell) in the above steps s21 to s23 is long (about 6 hours), and the battery is assembled into a battery by 10 single cells. In the case of a stack, the above steps need to be repeated 10 times, which is quite time consuming. Since the method is only used in a single cell, each single cell obtained by repeated cycles is susceptible to external factors and has a reaction consistency. The problem is good, so the process is complicated and cannot be effectively commercialized. In addition, the conventional general electrochemical oxidation system cannot completely make the carbon felt completely in contact with the electrolyte, because when immersed in the electrolyte, a side reaction of the electrolyzed water may be generated, and the electrolyzed water generates bubbles such as hydrogen and oxygen at the electrode. On the surface, due to the carbon felt-based porous material, some regions cannot be uniformly contacted with the electrolyte for electrochemical reaction, and thus the efficiency of the flow battery cannot be effectively improved. Therefore, the user-like users cannot meet the needs of the user in actual use.

The main object of the present invention is to overcome the above problems encountered in the prior art and to provide a direct pass voltage to the redox reaction in the stack, so that the carbon felt in the stack can be uniformly contacted with the electrolyte and electrochemically The reaction is carried out to form an oxygen-containing functional group (-COOH, -OH) on the surface of the carbon felt, thereby achieving a direct electrochemical oxidation modification method.

The secondary object of the present invention is to provide a process that is simple and quick to process, easy to control experimental parameters, and replaces experimental conditions without re-disassembly, the device can withstand a wide range of voltages and currents, and can be modified without high temperature treatment. A direct electrochemical oxidation modification method with high quality and low cost.

Another object of the present invention is to provide a direct electrochemical oxidative upgrading method which can increase the efficiency value (Coulomb efficiency, energy efficiency, and voltage efficiency) of a battery.

It is still another object of the present invention to provide a direct electrochemical oxidation modification method that can be applied to a combination of a plurality of single cells into a battery stack.

For the purpose of the above, the present invention is a method for directly electrochemically oxidizing the performance of a carbon felt of a liquid flow battery, comprising at least the following steps: (A) assembling an unmodified carbon felt as an electrode material into a battery stack; B) by pumping the prepared electrolyte, which enters through the cathode anode inlet of the stack and is in uniform contact with the carbon felt, and the flow rate is controlled between 20 and 100 mL/min through the anode and cathode of the stack. After the outlet flow is collected into the electrolyte storage tank, the anode and cathode inlets recycled to the battery stack are driven into the battery stack until the air in the battery stack is completely discharged; (C) the positive and negative electrodes are connected to an external power supply system. , the voltage is applied in a constant voltage mode to perform an electrochemical redox reaction; (D) after the energization time is completed, the pump enters the air through the anode and cathode inlets of the battery stack, and the flow rate is controlled at 20 to 100 mL/min. And then discharge through the anode and cathode outlets of the battery stack and completely discharge the electrolyte in the original battery stack to the electrolyte storage tank; (E) replace the electrolyte with 1M to 3M vanadyl sulfate and 1M to 5M inorganic The aqueous solution enters through the cathode anode inlet of the battery stack and is uniformly contacted with the carbon felt, and the flow rate is controlled between 20 and 100 mL/min, and is collected and discharged to the electrolyte storage tank through the cathode anode outlet of the battery stack, and then recycled to the solution. The cathode anode inlet of the battery stack is driven into the stack until the air in the stack is completely discharged; and (F) the positive and negative electrodes are connected to the external power supply system, and the current is supplied to the current supply mode to 40 mA/cm ^{2 .} At a current of 80 mA/cm ² , the battery stack charge and discharge reaction of the flow battery is performed, and the charge and discharge process is repeated until the end of charging.

In the above embodiment of the present invention, the structure of the battery stack of the step (A) comprises: a separator; two spacers sandwiching the separator; and two electrodes sandwiching the two gaskets, the two electrodes respectively For the positive and negative electrodes, the unmodified carbon felt is used as the electrode material; the two flow plates are sandwiched between the two electrodes, and one of the flow plates has a cathode inlet and an anode inlet, and the other flow plate is The utility model has a cathode outlet and an anode outlet, and a two-end plate for clamping the two flow plates.

In the above embodiment of the present invention, the electrolyte of the step (B) is 0.1M to 5M sulfuric acid, 0.1M to 5M hydrochloric acid, 0.1M to 5M nitric acid, or 0.1M to 5M phosphoric acid.

In the above embodiment of the present invention, the step (C) is to apply a voltage of 1.5 V/cell to 2.5 V/cell.

In the above embodiment of the invention, the step (C) is performed for a power-on time of 5 minutes to 20 minutes.

In the above embodiment of the invention, the step (C) is an operating temperature of between 20 ° C and 30 ° C.

In the above embodiment of the present invention, the inorganic acid of the step (E) is sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid.

In the above embodiment of the present invention, the direct electrochemical oxidation method for improving the performance of the carbon felt of the flow battery is suitable for combining a plurality of single cells into a battery stack.

(part of the invention)

100‧‧‧ flow battery

1‧‧‧Battery stack

11‧‧‧Isolation film

12, 13‧‧‧ shims

14, 15‧‧‧ positive and negative electrodes

16‧‧‧ flow board

161‧‧‧cathode inlet

162‧‧‧Anode inlet

17‧‧‧ flow board

171‧‧‧ Cathode exit

172‧‧‧Anode exit

18, 19‧‧‧ end plates

2, 3‧‧‧ pump

4, 5‧‧‧ electrolyte storage tank

6‧‧‧External power supply system

S11 ~ s16‧‧‧ steps

(customized part)

S21～s26‧‧‧Steps

Fig. 1 is a schematic flow chart of the present invention.

Fig. 2 is a schematic view showing the structure of the battery stack of the present invention.

Fig. 3 is a schematic view showing the structure of a preferred embodiment of the flow battery of the present invention.

Figure 4 is a schematic flow diagram of a general electrochemical oxidation process.

Please refer to FIG. 1 to FIG. 3, which are schematic diagrams of the flow of the present invention, a schematic structural view of the battery stack of the present invention, and a schematic structural view of a preferred embodiment of the flow battery of the present invention. As shown in the figure: The present invention is a method for directly electrochemically oxidizing the performance of a carbon felt of a liquid flow battery, comprising at least the following steps:

Step s11: assembling the battery stack 1 with the unmodified carbon felt as the electrode 14, 15 material, as shown in FIG. 2, comprising a separator 11; sandwiching the spacer 12 of the separator 11 13; sandwiching the two electrodes 14, 15 of the two electrodes 12, 13 respectively, the positive and negative electrodes 14, 15, respectively, sandwiching the flow electrodes 16, 17 of the two electrodes 14, 15, one of the flow The plate 16 has a cathode inlet 161 and an anode inlet 162, and the other flow plate 17 has a cathode outlet 171 and an anode outlet 172; and two end plates 18 and 19 sandwiching the two flow plates 16, 17. Constitute

Step s12: The prepared electrolyte is pumped through the pumps 2, 3, and enters through the cathode and anode inlets 161, 162 of the stack 1 and is in uniform contact with the carbon felt (ie, the positive and negative electrodes 14, 15). The flow rate is controlled between 20 and 100 mL/min, and is discharged to the electrolyte storage tanks 4 and 5 through the cathode and anode outlets 171 and 172 of the battery stack 1, and is recycled to the cathode and anode inlets 161 of the battery stack 1. , 162 is driven into the battery stack 1 until the air in the battery stack 1 is completely discharged, wherein the electrolyte is 0.1M to 5M sulfuric acid, 0.1M to 5M hydrochloric acid, 0.1M to 5M nitric acid, or 0.1M to 5M phosphoric acid. Ren Yi;

Step s13: the positive and negative electrodes 14, 15 are connected to an external power supply system 6, and a voltage of 1.5 V/cell to 2.5 V/cell is applied in a constant voltage mode to perform an electrochemical redox reaction, and the power-on time is 5 minutes. 20 minutes, the operating temperature is 20 ° C to 30 ° C;

Step s14: After the energization time is completed, the air is pumped through the anodes and the anode inlets 161 and 162 of the battery stack 1 by the pump 2, 3, and the flow rate is controlled between 20 and 100 mL/min, and then the battery stack 1 is passed. The cathode and anode outlets 171, 172 are discharged and completely discharge the electrolyte in the original stack 1 to the electrolyte reservoirs 4, 5;

Step s15: replacing the electrolyte with 1M to 3M vanadyl sulfate and 1M to 5M inorganic acid aqueous solution, and enter and join the carbon felt (ie, the positive and negative electrodes 14, 15) through the cathode and anode inlets 161, 162 of the battery stack 1. Uniform contact, the flow rate is controlled between 20 and 100 mL/min, and flows out through the cathode and anode outlets 171 and 172 of the battery stack 1 to be collected into the electrolyte storage tanks 4 and 5, and is recycled to the cathode and anode of the battery stack 1. The inlets 161, 162 are driven into the stack 1 until the air in the stack 1 is completely discharged, wherein the inorganic acid is sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid;

Step s16: the positive and negative electrodes 14, 15 are connected to the external power supply system 6, and a current of 40 mA/cm ² to 80 mA/cm ² is supplied in a constant current mode to perform a charge and discharge reaction of the battery stack 1 of the flow battery 100. The charging and discharging process is repeated until the end of charging. If so, a new method for directly electrochemically oxidizing the performance of the carbon felt of the flow battery is constructed by the above disclosed process.

When used, the present invention uses GFD2.5 carbon felt as an electrode material, and uses Nafion 117 as a separator to be modified by direct electrochemical oxidation, and a voltage of 2 V/cell is applied in a constant voltage mode. At 25 ° C operating temperature, 5, 10, and 20 minutes of electrochemical redox reaction was carried out to complete the carbon felt modification. Then, the above-mentioned single cell with electrochemical oxidation modified carbon felt was subjected to charge and discharge test, and the operating conditions were industrial grade vanadium oxysulfate as an electrolyte, and the flow rate was 50 mL/min, and the temperature was 25 ° C, and 40 mA was introduced. /cm ² current density. The test results of the single cell of the electrochemical oxidation modified carbon felt are shown in Table 1. It can be seen that the efficiency value of the battery is obviously increased by the direct electrochemical oxidation modification method of the present invention, especially the electrochemical treatment time is 5 The coulombic efficiency, energy efficiency, and voltage efficiency obtained in minutes are optimal.

Table I

Therefore, the present invention utilizes a direct electrochemical oxidation reforming method to directly pass a voltage to a stack to perform a redox reaction, so that the carbon felt in the stack can be uniformly contacted with the electrolyte and electrochemically reacted to make the surface of the carbon felt. An oxygen-containing functional group (-COOH, -OH) is formed to achieve the purpose of upgrading. Thereby, the invention has the advantages of simple and rapid process operation, easy adjustment of experimental parameters and replacement of experimental conditions without re-disassembly, the device can withstand a wide range of voltages and currents, can be modified without high temperature treatment, and has low cost. Advantage.

In summary, the present invention is a method for directly electrochemically oxidizing the carbon felt of a liquid flow battery, which can effectively improve various disadvantages of the conventional use, and directly converts the voltage into the battery stack by using a direct electrochemical oxidation modification method. The carbon felt in the stack can be uniformly contacted with the electrolyte and electrochemically reacted to form an oxygen-containing functional group on the surface to achieve the purpose of upgrading, and the process is simple and rapid, and the experimental parameters are easily adjusted and the experimental conditions are replaced. There is no need to re-disassemble, the device can withstand a wide range of voltages and currents, and the advantages of low-cost treatment can be obtained without high-temperature treatment, so that the invention can be more advanced, more practical, and more suitable for users. It must have met the requirements of the invention patent application and filed a patent application according to law.

However, the above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto; therefore, the simple equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the invention are modified. All should remain within the scope of the invention patent.

S11~s16‧‧‧step

Claims (7)

A method for directly electrochemically oxidizing the performance of a carbon felt of a liquid flow battery, comprising at least the following steps: (A) assembling an unmodified carbon felt as an electrode material into a battery stack; (B) preparing by a pump a good electrolyte, which enters through the cathode anode inlet of the battery stack and is in uniform contact with the carbon felt, and the flow rate is controlled between 20 and 100 mL/min, and is collected through the anode and cathode outlets of the battery stack and collected into the electrolyte storage tank. Recirculating the cathode anode inlet of the stack into the stack until the air in the stack is completely exhausted; (C) the positive and negative electrodes are connected to an external power supply system to apply voltage in a constant voltage mode, Conducting an electrochemical redox reaction with an energization time of 5 minutes to 20 minutes; (D) after the energization time is completed, air is pumped through the anode and cathode inlet of the stack by the pump, and the flow rate is controlled at 20 to 100 mL/min. And then discharge through the anode and cathode outlets of the battery stack and completely discharge the electrolyte in the original battery stack to the electrolyte storage tank; (E) replace the electrolyte with 1M to 3M vanadyl sulfate and 1M to 5M inorganic acid aqueous solution, Via the battery The cathode inlet of the cathode enters and is in uniform contact with the carbon felt, and the flow rate is controlled between 20 and 100 mL/min, and is collected and discharged to the electrolyte reservoir through the anode and cathode outlets of the battery stack, and recycled to the anode and cathode of the battery stack. The inlet enters the stack until the air in the stack is completely exhausted; and (F) the positive and negative electrodes are connected to the external power supply system, and a current of 40 mA/cm ² to 80 mA/cm ² is supplied in a constant current mode. The battery stack charge and discharge reaction of the flow battery is performed, and the charge and discharge process is repeated until the end of charging. The method for directly improving the performance of the carbon felt of the liquid flow battery according to the first aspect of the patent application, wherein the structure of the battery stack of the step (A) comprises: a separator; a separator; the two electrodes sandwich the two gaskets, wherein the two electrodes are positive and negative electrodes respectively, and the unmodified carbon felt is used as an electrode material; and the two flow plates sandwich the two electrodes, and wherein A flow plate has a cathode inlet and an anode inlet, another flow plate has a cathode outlet and an anode outlet, and two end plates sandwich the two flow plates. The method for directly improving the performance of the carbon felt of a liquid flow battery according to the first aspect of the patent application, wherein the electrolyte of the step (B) is 0.1 M to 5 M sulfuric acid, 0.1 M to 5 M hydrochloric acid, 0.1 M. Up to 5M nitric acid, or 0.1M to 5M phosphoric acid. The method for directly improving the performance of a carbon felt of a liquid flow battery according to the first aspect of the patent application, wherein the step (C) is to apply a voltage of 1.5 V/cell to 2.5 V/cell. The method for directly improving the performance of a carbon felt of a liquid flow battery according to the first aspect of the patent application, wherein the step (C) is an operating temperature of between 20 ° C and 30 ° C. The method for directly improving the performance of a carbon felt of a liquid flow battery according to the first aspect of the patent application, wherein the inorganic acid of the step (E) is sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid. The method for directly improving the performance of the carbon felt of the flow battery according to the first aspect of the patent application is applicable to the combination of a plurality of single cells into a battery stack.