A preparation method of a modified carbon felt negative electrode of a zinc-bromine flow battery and a carbon felt negative electrode prepared by the method

Abstract

The application discloses a preparation method of a modified zinc-bromine flow battery carbon felt negative electrode and a carbon felt negative electrode prepared by the method, and belongs to the field of zinc-bromine flow batteries. In the method, copper organic precursor is heated and gasified in a double-temperature-zone tubular furnace, and the gasified copper organic precursor molecules are carried to the position of the carbon felt by hydrogen and adsorbed on the carbon felt, so that the copper organic precursor reacts with the hydrogen to form copper single elements, and the copper single elements are attached to the surface of the carbon felt to form a load, thereby achieving the purpose of loading the copper single elements on the modified carbon felt. The method overcomes the obstruction of low conductivity of the loaded oxide to the electron transfer in the zinc deposition / peeling process, avoids the inactivation caused by the reaction of the loaded metal active sites and acidic components of the electrolyte, eliminates the problem that the internal fibers of the carbon felt are difficult to uniformly load the metal single elements or oxide particles due to the high surface tension between the metal salt solution and the carbon felt, realizes the efficient and uniform loading of the copper single elements on the carbon felt, and significantly improves the negative electrode performance of the zinc-bromine flow battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of zinc-bromine flow battery, and particularly relates to a preparation method of a modified carbon felt negative electrode of zinc-bromine flow battery and the carbon felt negative electrode prepared by the method. BACKGROUND

[0002] Zinc-bromine flow battery is expected to become a large-scale energy storage system technology route for promoting efficient use of renewable energy due to its low cost, high energy density, safety features and long cycle life. When zinc-bromine flow battery operates as a hybrid flow battery system, it stores energy in the form of metal zinc at the negative electrode and bromine / polybromine phase at the positive electrode. Like other flow batteries, zinc-bromine flow battery is mainly composed of electrolyte, positive and negative electrodes, separator, external storage tank and the like. As one of the key materials of flow battery, electrode provides a reaction site for the oxidation-reduction reaction in the charging and discharging process and provides a channel for the transmission of internal active substances. The performance of electrode material directly affects the electrochemical reaction rate, internal resistance of the battery and electrolyte transmission process, so electrode material is of great significance to improve the energy efficiency, power density, operation efficiency and service life of flow battery and reduce the system cost. At present, the electrode material used in flow battery is mainly carbon felt, which has the characteristics of low cost, adjustable structure and good stability, but also has problems such as incompatibility of solid-liquid interface, few active sites and large mass transfer resistance, which will cause mass transfer polarization and uneven mass transfer, and further cause zinc dendrite growth. Zinc dendrites will puncture the separator and reduce the coulombic efficiency, increase the risk of self-discharge, short circuit and battery polarization of flow battery, thereby limiting the improvement of battery energy density. Since the physicochemical properties of carbon felt electrode directly affect the rate and reversibility of the oxidation-reduction reaction of active substances in the charging and discharging process, therefore, modification of the negative carbon felt electrode is of great importance to promote the industrialization of zinc-bromine flow battery.

[0003] To improve the solid-liquid interface compatibility between the electrolyte and the carbon felt electrode, increase the active sites for zinc deposition on the carbon felt, thereby forming a uniform zinc deposition layer and inhibiting zinc dendrite formation, researchers have employed modification methods by loading metal elements or oxides onto the carbon felt. Chinese patent document CN117832517A discloses a method for loading metal oxides such as nickel, tin, and cobalt onto the surface of a carbon felt using high-temperature heat treatment. This metal oxide loading modification treatment of the carbon felt electrode significantly improves the electrochemical performance, power density, energy efficiency, and cycle stability of the zinc-bromine flow battery. However, the loaded metal oxides have low conductivity, and as active sites for electrochemical reactions between the carbon felt and the zinc deposition layer, they hinder electron transfer during zinc deposition / stripping. Chinese patent document CN106159286A discloses a method for electrodepositing tin on the surface of carbon felt using a slightly alkaline electrolyte. Through this electrodeposition process, tin is uniformly deposited onto the carbon fiber surface, which not only reduces the nucleation overpotential of Zn but also increases the hydrogen evolution overpotential. This helps prevent the formation of zinc dendrites under high areal capacity conditions, thereby improving the cycle life and reliability of the battery. However, the tin deposited on the carbon felt surface is relatively chemically reactive. During battery charging and discharging, acidic substances in the electrolyte react with the tin, causing the active sites of the zinc-deposited tin to become ineffective. Furthermore, this technical solution requires immersing the carbon felt in a corresponding metal salt solution. Due to the relatively poor hydrophilicity of carbon felt, there is a relatively large surface tension at the solid-liquid interface between the metal salt solution and the carbon felt. Therefore, the internal pores of the carbon felt are not completely wetted, which prevents the corresponding elemental metal or oxide particles from being loaded onto the fibers inside the carbon felt. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a modified carbon felt negative electrode for a zinc-bromine flow battery, which can solve the problem in the prior art where the low conductivity of the oxides loaded on the carbon felt surface affects electron transfer during zinc deposition / stripping; solve the problem where the loaded metal active sites react with acidic substances in the electrolyte, causing the active sites to fail; and solve the problem where the relatively large surface tension at the solid-liquid interface between the metal salt solution and the carbon felt prevents the corresponding metal element or oxide particles from being loaded onto the fibers inside the carbon felt.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for preparing a modified carbon felt negative electrode for a zinc-bromine flow battery, comprising the following steps:

[0006] (1) The cleaned carbon felt is vacuum dried to obtain carbon felt A;

[0007] (2) placing the copper organic precursor in the temperature zone A of the gas inlet of the double-temperature-zone tube furnace, placing the carbon felt A in the temperature zone B of the gas outlet, introducing hydrogen, raising the temperature of the temperature zone A to 50-350 DEG C at a rate of 3-9 DEG C / min, raising the temperature of the temperature zone B to 400-900 DEG C at the same rate, and keeping the temperature for 5-15 h to perform the vapor deposition reaction, and then naturally reducing to room temperature to obtain the carbon felt B; the copper organic precursor can form copper atoms under the high-temperature hydrogen atmosphere;

[0008] (3) washing and vacuum drying the carbon felt B to obtain the carbon felt negative electrode of the copper single-element modified zinc-bromine flow battery.

[0009] Preferably, in step (1), the temperature of the vacuum drying is 60-190 DEG C, and the time is 8-22 h.

[0010] Preferably, in step (2), the copper organic precursor is one of bis(hexafluoroacetylacetone) copper (II), copper acetylacetonate and bis(dimethylamino-2-propoxy) copper (II); and the mass ratio of the copper organic precursor to the carbon felt A is 1-10:1.

[0011] Preferably, in step (2), the flow rate of the hydrogen is 50-200 ml / min.

[0012] Preferably, in step (3), the temperature of the vacuum drying is 100-200 DEG C, and the time is 12-24 h.

[0013] The application further provides a carbon felt negative electrode of a copper single-element modified zinc-bromine flow battery, which is prepared by the above method; the carbon felt negative electrode comprises a carbon felt matrix and copper single-element particles loaded on the carbon felt.

[0014] Compared with the prior art, the application has the following beneficial effects:

[0015] (1) The technical solution of this invention loads copper elemental particles onto the carbon felt negative electrode using a vapor deposition process. During this process, the vaporized copper organic precursor is not affected by the surface tension between the solid and liquid phases and can fill all the pores of the carbon felt, thereby ensuring that copper elemental particles are loaded on the surface and internal fibers of the carbon felt. The loaded copper elemental particles have good chemical stability and are not prone to chemical reactions with acidic substances in the electrolyte. This feature effectively avoids the problem of active sites failing due to side reactions during charging and discharging. At the same time, copper has good conductivity. During the electrochemical reaction, the copper elemental particles loaded on the carbon felt serve as active sites for zinc deposition and can quickly transfer electrons between the carbon felt and the zinc deposition layer, which is beneficial to the rapid transfer of electrons during zinc deposition / stripping and effectively reduces the interfacial charge transfer resistance, thus facilitating the electrochemical reaction. In addition, due to the strong electronic coupling between copper atoms and the zinc lattice, copper has zinc affinity. The copper elemental particles loaded on the carbon felt surface can significantly reduce the activation energy required for zinc ion reduction and nucleation and form active sites for electrochemical reactions on the carbon felt surface. The excellent zinc affinity of copper atoms allows zinc to preferentially deposit at active sites formed by copper rather than at already deposited zinc sites, thereby suppressing the further development of uneven zinc deposition during charging and ultimately inhibiting zinc dendrite growth. The zinc-bromine flow battery prepared using copper-modified carbon felt as the negative electrode in Example 1 of this technical solution maintained an energy efficiency of 95.7% and a coulombic efficiency of 94.5% after 1600 cycles, demonstrating excellent cycle performance. This indicates that the copper-loaded material on the carbon felt continuously acts as an active site for zinc deposition during battery cycling.

[0016] (2) The copper-organic precursor used in the technical solution of this invention has a low evaporation temperature and a high saturated vapor pressure, which can ensure that sufficient copper-organic precursor can be transported to the carbon felt and reduced to form copper elemental support, that is, copper atoms are formed under a high-temperature hydrogen atmosphere, thereby forming copper elemental on the carbon felt. The organic ligand byproducts formed by the reaction have good volatility and can be easily discharged from the dual-temperature zone tube furnace, which can effectively avoid the byproducts affecting the deposited copper elemental particles.

[0017] (3) The technical scheme of the present application significantly improves the performance of zinc-bromine flow battery by precisely regulating key process parameters. First, the mass ratio of copper organic precursor to carbon felt A needs to be controlled, which affects the number of copper single particle loaded on the carbon felt. The inventor found that if the ratio is too small, the number of copper single particles loaded on the carbon felt is too small, which cannot effectively increase the active sites for zinc deposition; if the ratio is too large, the number of copper single particles loaded on the carbon felt is too large, which blocks the pore structure of the carbon felt, affects the transmission of electrolyte inside the carbon felt, and reduces the available space position for zinc deposition; therefore, a suitable mass ratio of copper organic precursor to carbon felt A can not only introduce enough copper single zinc deposition active sites on the carbon felt, but also avoid the blockage of the pore structure of the carbon felt by copper single. Second, the hydrogen flow rate plays a key role in reaction equilibrium and product discharge. The inventor found that too fast hydrogen flow rate will blow out more copper organic precursor and hydrogen gas reaction to form copper single from the double-temperature zone tube furnace, which is not conducive to the loading of copper single on the carbon felt, causing waste of copper organic precursor; too slow hydrogen flow rate cannot take out volatile organic ligand formed by the reaction of copper organic precursor and hydrogen gas from the double-temperature zone tube furnace, which interferes with the copper deposition process; therefore, a suitable hydrogen flow rate can achieve efficient delivery of the precursor and timely discharge of by-products. Third, the temperature and holding time of each temperature zone also need to be controlled well. The inventor found that a suitable temperature in temperature zone A can ensure that the copper organic precursor can be vaporized and gasified without decomposition; a suitable temperature in temperature zone B can ensure that the copper deposited on the carbon felt has high crystallinity and high bonding strength between the carbon felt, avoiding the falling off of the copper loading; a suitable holding time in the two temperature zones can ensure that the reaction is completely carried out, while controlling the particle size of copper particles, further improving the crystallinity of copper single and the bonding strength between copper loading and carbon felt. In summary, due to the synergistic optimization of the above parameters, efficient and uniform loading of copper single is achieved, which lays the foundation for the improvement of battery performance.

[0018] (4) The present application significantly improves the performance of zinc-bromine flow battery by loading copper single particles on the carbon felt negative electrode through the vapor deposition process. Experimental results show that under the conditions of current density of 60 mA / cm 2 , specific capacity of 40 mAh / cm 2 , the zinc-bromine flow battery with the copper single modified carbon felt prepared by the present technical scheme as the negative electrode can achieve a coulombic efficiency of up to 95.0-97.4%, a voltage efficiency of 82.6-85.3%, and an energy efficiency of 78.5-83.1%. The zinc-bromine flow battery with the copper single modified carbon felt prepared in Example 1 as the negative electrode has a retention rate of energy efficiency and coulombic efficiency of 95.7% and 94.5% respectively after 1600 cycles, showing excellent cycle performance. The negative electrode material has good chemical and electrochemical stability, and has wide application prospect, which will make the zinc-bromine flow battery have better electrochemical performance and longer service life in practical application. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The constant current charge-discharge curve of the copper elemental modification carbon felt prepared by the embodiment 1 of the present application and the carbon felt of the comparative example 1 as the negative electrode of the zinc-bromine flow battery for electrochemical performance test is shown in the following figure;

[0020] Figure 2 The cycle curve of the copper elemental modification carbon felt prepared by the embodiment 1 of the present application as the negative electrode of the zinc-bromine flow battery for electrochemical performance test is shown in the following figure;

[0021] Figure 3 The cycle curve of the carbon felt of the comparative example 1 as the negative electrode of the zinc-bromine flow battery for electrochemical performance test is shown in the following figure;

[0022] Figure 4 The X-ray diffraction (XRD) diagram of the copper elemental modification carbon felt prepared by the embodiment 1 of the present application and the unmodified carbon felt is shown in the following figure;

[0023] Figure 5 The scanning electron microscope (SEM) diagram of the copper elemental modification carbon felt prepared by the embodiment 1 of the present application is shown in the following figure;

[0024] Figure 6 The scanning electron microscope (SEM) diagram of the carbon felt of the comparative example 1 of the present application is shown in the following figure;

[0025] Figure 7 The electron diagram collected when the energy dispersive X-ray spectroscopy analysis is performed on the copper elemental modification carbon felt prepared by the embodiment 1 of the present application is shown in the following figure;

[0026] Figure 8 The Figure 7 selected area energy dispersive X-ray spectroscopy diagram (EDS) is shown in the following figure. DETAILED DESCRIPTION

[0027] In order to make the present application more obvious and easy to understand, the technical solutions of the present application are further described and explained by the following examples combined with the drawings, but are not used to limit the protection scope of the present application.

[0028] The double-temperature zone tube furnace used in the present application is OTF-1200X-II, which is purchased from Hefei Kexing Material Technology Co., Ltd.; the three copper organic precursor of bis(hexafluoroacetylacetone) copper (II), copper acetylacetonate and bis(dimethylamino-2-propoxy) copper (II) are purchased from Gede Chemical Network; other medicines and reagents are purchased from Aladdin Network or China Reagent Network. Example 1

[0029] The carbon felt is cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt is placed in a vacuum oven and dried at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) is placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A is placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, and the mass ratio of the copper organic precursor to the carbon felt A is 5:1, hydrogen is introduced to replace the air in the double temperature zone tube furnace, and then the flow rate of the hydrogen is adjusted to 125ml / min, temperature zone A is heated to 200°C at a rate of 6°C / min, and temperature zone B is heated to 650°C at the same heating rate, and after the temperature of the two temperature zones reaches the set temperature, the gas phase deposition reaction is carried out for 10h, and after the heat preservation is completed, the double temperature zone tube furnace is naturally cooled to room temperature, and hydrogen is introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, and then the carbon felt is taken out to obtain carbon felt B; the obtained carbon felt B is washed with deionized water and ethanol, and the washed carbon felt is vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0030] During the reaction process, the copper organic precursor bis(hexafluoroacetylacetone) copper (II) placed in temperature zone A is gasified during heating, and part of the gasified bis(hexafluoroacetylacetone) copper (II) molecules are carried by hydrogen to temperature zone B and adsorbed on the carbon felt, and bis(hexafluoroacetylacetone) copper (II) reacts with hydrogen to form copper single element and organic ligand byproduct. The organic ligand byproduct is discharged from the double temperature zone tube furnace with the gas after the reaction. The copper single element adheres to the surface of the carbon felt to form a load, thereby achieving the purpose of loading modification of the carbon felt by copper single element.

[0031] The loading modification method adopts a gas deposition process. Compared with other liquid processes, in the process of the gas deposition process, the vaporized copper organic precursor is not affected by the surface tension between solid and liquid, and is filled in all pores of the carbon felt, which is conducive to loading copper elemental particles on the surface and internal fibers of the carbon felt. The copper elemental particles loaded on the surface of the carbon felt have stable chemical properties and are not easy to react with acid. This can avoid the reaction with acidic substances in the electrolyte during the charging and discharging process, thereby avoiding the failure of the active sites for zinc deposition. Copper has good electrical conductivity. During the electrochemical reaction process, the copper elemental particles loaded on the carbon felt act as active sites for zinc deposition, can quickly transfer electrons between the carbon felt and the zinc deposition layer, is conducive to the rapid transfer of electrons during the zinc deposition / peeling process, effectively reduces the interface charge transfer resistance, and is conducive to the electrochemical reaction. In addition, due to the strong electronic coupling between copper atoms and zinc lattices, copper has a zinc affinity. The copper elemental particles loaded on the surface of the carbon felt can significantly reduce the activation energy required for the reduction of zinc ions to nucleate and form active sites for electrochemical reaction on the surface of the carbon felt. The good zinc affinity of copper atoms can make zinc preferentially deposit on the active sites formed by copper rather than the deposited zinc sites, thereby inhibiting the further development of the non-uniform zinc deposition during the charging process, and finally achieving the inhibition of zinc dendrite growth. Example 2

[0032] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven at 100°C for 18h to obtain carbon felt A; the copper organic precursor copper acetylacetonate was placed in temperature zone A close to the gas inlet of the double-temperature-zone tubular furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double-temperature-zone tubular furnace, the mass ratio of the copper organic precursor to the carbon felt A was 6:1, hydrogen was introduced to replace the air in the double-temperature-zone tubular furnace, then the flow rate of hydrogen was adjusted to 150ml / min, temperature zone A was heated to 220°C at a rate of 7°C / min, and temperature zone B was heated to 660°C at the same heating rate, after the temperature of both temperature zones reached the set temperature, the gas deposition reaction was carried out for 9h, after the heat preservation was completed, the double-temperature-zone tubular furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stages, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 140°C for 19h to obtain the copper elemental modified carbon felt negative electrode for zinc-bromine flow battery. Example 3

[0033] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 150°C for 12 hours to obtain carbon felt A. The copper organic precursor bis(dimethylamino-2-propoxy)copper(II) was placed in temperature zone A near the inlet of the dual-temperature zone tube furnace, and carbon felt A was placed in temperature zone B near the outlet of the dual-temperature zone tube furnace. The mass ratio of the copper organic precursor to carbon felt A was 4:1. Hydrogen gas was introduced to replace the air in the dual-temperature zone tube furnace, and the hydrogen flow rate was adjusted to 100 ml / min. The temperature was increased to 180℃ at a rate of 5℃ / min, and temperature zone B was increased to 640℃ at the same rate. After both temperature zones reached the set temperature, they were held for 11 hours for vapor deposition reaction. After the holding period, the dual-temperature zone tubular furnace was allowed to cool to room temperature naturally. During the holding and cooling stages, hydrogen gas was introduced at the same flow rate as during the heating stage. Then, the carbon felt was removed to obtain carbon felt B. The carbon felt B was washed with deionized water and ethanol. The washed carbon felt was then vacuum dried at 160℃ for 17 hours to obtain the copper element modified zinc bromine flow battery carbon felt anode. Example 4

[0034] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 80°C for 20 hours to obtain carbon felt A. The copper-organic precursor bis(hexafluoroacetylacetone)copper(II) was placed in temperature zone A near the inlet of the dual-temperature zone tube furnace, and carbon felt A was placed in temperature zone B near the outlet of the dual-temperature zone tube furnace. The mass ratio of the copper-organic precursor to carbon felt A was 3:1. Hydrogen gas was introduced to replace the air in the dual-temperature zone tube furnace, and the hydrogen flow rate was adjusted to 80 ml / min. Temperature zone A was then... The temperature was increased to 100℃ at a rate of 4℃ / min, and then increased to 500℃ in temperature zone B at the same rate. After both temperature zones reached the set temperature, they were held for 13 hours for vapor deposition reaction. After the holding period, the dual-temperature zone tubular furnace was allowed to cool naturally to room temperature. During the holding and cooling stages, hydrogen gas was introduced at the same flow rate as during the heating stage. Then, the carbon felt was removed to obtain carbon felt B. The carbon felt B was washed with deionized water and ethanol. The washed carbon felt was then vacuum dried at 120℃ for 21 hours to obtain the copper-modified zinc-bromine flow battery carbon felt anode. Example 5

[0035] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 170°C for 10h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone)copper(II) was placed in temperature zone A close to the gas inlet of the double-temperature-zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double-temperature-zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 8:1, hydrogen was introduced to replace the air in the double-temperature-zone tube furnace, then the flow rate of hydrogen was adjusted to 180ml / min, temperature zone A was heated to 300°C at a heating rate of 8°C / min, and temperature zone B was heated to 800°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 7h, after the heat preservation was completed, the double-temperature-zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 180°C for 15h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element. Example 6

[0036] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 60°C for 22h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone)copper(II) was placed in temperature zone A close to the gas inlet of the double-temperature-zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double-temperature-zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 1:1, hydrogen was introduced to replace the air in the double-temperature-zone tube furnace, then the flow rate of hydrogen was adjusted to 50ml / min, temperature zone A was heated to 50°C at a heating rate of 3°C / min, and temperature zone B was heated to 400°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 15h, after the heat preservation was completed, the double-temperature-zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 200°C for 12h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element. Example 7

[0037] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven and dried at 190°C for 8h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, and the mass ratio of the copper organic precursor to the carbon felt A was 10:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, and then the flow rate of hydrogen was adjusted to 200ml / min, temperature zone A was heated to 350°C at a rate of 9°C / min, and temperature zone B was heated to 900°C at the same heating rate, and the temperature of the two temperature zones was maintained at the set temperature for 5h to carry out the vapor deposition reaction, and after the temperature maintaining was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the temperature maintaining and cooling stages, and then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 100°C for 24h to obtain the carbon felt negative electrode of the copper single-element modified zinc-bromine flow battery. Comparative Example 1

[0038] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven and dried at 125°C for 15h to obtain carbon felt A; the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, hydrogen was introduced to replace the air in the double temperature zone tube furnace, and then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A close to the gas inlet was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, and the temperature of the two temperature zones was maintained at the set temperature for 10h, and after the temperature maintaining was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the temperature maintaining and cooling stages, and then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery.

[0039] The difference from Example 1 is that in the process of Comparative Example 1, no copper organic precursor was placed in the double temperature zone tube furnace, only the carbon felt was simply heat treated, and no copper single-element was loaded on the carbon felt. Comparative Example 2

[0040] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 15:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0041] The difference from Example 1 is that the mass ratio of the copper organic precursor to the carbon felt A in Comparative Example 2 is 15:1, which is higher than the value of this process parameter in all examples. Comparative Example 3

[0042] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 0.2:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0043] The difference from Example 1 is that the mass ratio of the copper organic precursor to the carbon felt A in Comparative Example 3 is 0.2:1, which is lower than the value of this process parameter in all examples. Comparative Example 4

[0044] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 125°C for 15 hours to obtain carbon felt A. The copper-organic precursor bis(hexafluoroacetylacetone)copper(II) was placed in temperature zone A near the inlet of the dual-temperature zone tube furnace, and carbon felt A was placed in temperature zone B near the outlet of the dual-temperature zone tube furnace. The mass ratio of the copper-organic precursor to carbon felt A was 5:1. Hydrogen gas was introduced to replace the air in the dual-temperature zone tube furnace, and the hydrogen flow rate was adjusted to 10 ml / min. Temperature zone A... The temperature was increased to 200℃ at a rate of 6℃ / min, and then increased to 650℃ in temperature zone B at the same rate. After both temperature zones reached the set temperature, they were held for 10 hours for vapor deposition reaction. After the holding period, the dual-temperature zone tubular furnace was allowed to cool naturally to room temperature. During the holding and cooling stages, hydrogen gas was introduced at the same flow rate as during the heating stage. Then, the carbon felt was removed to obtain carbon felt B. The carbon felt B was washed with deionized water and ethanol. The washed carbon felt was then vacuum dried at 150℃ for 18 hours to obtain the copper-modified zinc-bromine flow battery carbon felt anode.

[0045] The difference from Example 1 is that the hydrogen flow rate in Comparative Example 4 is 10 ml / min, which is lower than the process parameter value in all examples. Comparative Example 5

[0046] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 125°C for 15 hours to obtain carbon felt A. The copper-organic precursor bis(hexafluoroacetylacetone)copper(II) was placed in temperature zone A near the inlet of the dual-temperature zone tube furnace, and carbon felt A was placed in temperature zone B near the outlet of the dual-temperature zone tube furnace. The mass ratio of the copper-organic precursor to carbon felt A was 5:1. Hydrogen gas was introduced to replace the air in the dual-temperature zone tube furnace, and the hydrogen flow rate was adjusted to 300 ml / min. Temperature zone A... The temperature was increased to 200℃ at a rate of 6℃ / min, and then increased to 650℃ in temperature zone B at the same rate. After both temperature zones reached the set temperature, they were held for 10 hours for vapor deposition reaction. After the holding period, the dual-temperature zone tubular furnace was allowed to cool naturally to room temperature. During the holding and cooling stages, hydrogen gas was introduced at the same flow rate as during the heating stage. Then, the carbon felt was removed to obtain carbon felt B. The carbon felt B was washed with deionized water and ethanol. The washed carbon felt was then vacuum dried at 150℃ for 18 hours to obtain the copper-modified zinc-bromine flow battery carbon felt anode.

[0047] The difference from Example 1 is that the flow rate of hydrogen in Comparative Example 5 is 300 ml / min, which is higher than the process parameter value in all examples. Comparative Example 6

[0048] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 30°C at a rate of 6°C / min, and temperature zone B was heated to 360°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0049] The difference from Example 1 is that the heat preservation temperature of temperature zone A of Comparative Example 6 is 30°C, and the heat preservation temperature of temperature zone B is 360°C, which is lower than the value of this process parameter in all examples. Comparative Example 7

[0050] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 400°C at a rate of 6°C / min, and temperature zone B was heated to 1000°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0051] The difference from Example 1 is that the heat preservation temperature of temperature zone A of Comparative Example 7 is 400°C, and the heat preservation temperature of temperature zone B is 1000°C, which is higher than the value of this process parameter in all examples. Comparative Example 8

[0052] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 1h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element.

[0053] The difference from Example 1 is that the holding time of Comparative Example 8 is 1h, which is lower than the value of this process parameter in all examples. Comparative Example 9

[0054] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 20h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element.

[0055] The difference from Example 1 is that the holding time of Comparative Example 9 is 20h, which is higher than the value of this process parameter in all examples. Comparative Example 10

[0056] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis (hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, and the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, and then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, and after the temperature of the two temperature zones reached the set temperature, the temperature was kept for 9h, then the hydrogen was replaced by air and the flow rate was kept at 125ml / min, and the gas phase deposition reaction was continued at 650°C for 1h, after the temperature keeping ended, the double temperature zone tube furnace was naturally cooled to room temperature, and air was introduced at the same flow rate as the heating stage during the temperature keeping and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain a carbon felt negative electrode modified by a copper and copper oxide composite for a zinc-bromine flow battery.

[0057] The difference from example 1 is that in the gas phase deposition reaction stage of keeping at 650°C, the gas passed in the first nine hours is hydrogen, and the hydrogen is replaced by air in the tenth hour, and part of the copper loaded on the carbon felt is oxidized to copper oxide. Comparative example 11

[0058] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis (hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, and the mass ratio of the copper organic precursor to the carbon felt A was 5:1, the flow rate of air was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, and after the temperature of the two temperature zones reached the set temperature, the temperature was kept for 10h to carry out the gas phase deposition reaction, after the temperature keeping ended, the double temperature zone tube furnace was naturally cooled to room temperature, and air was introduced at the same flow rate as the heating stage during the temperature keeping and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain a carbon felt negative electrode modified by a copper and copper oxide composite for a zinc-bromine flow battery.

[0059] The difference from example 1 is that in the gas phase deposition reaction stage of keeping at 650°C for 10h, the gas passed is air, and the copper loaded on the carbon felt is oxidized to copper oxide. Comparative example 12

[0060] To remove impurities from the carbon felt surface, the cleaned carbon felt was dried in a vacuum oven at 125°C for 15 hours to obtain carbon felt A. Carbon felt A was then soaked in a 3% nickel acetate aqueous solution for 5 hours to obtain carbon felt B, with the mass ratio of nickel acetate to carbon felt A in the solution controlled at 5:1. Carbon felt B was then dried in a vacuum oven at 150°C for 18 hours to obtain carbon felt C. Carbon felt C was placed in an atmosphere tube furnace, and hydrogen gas was introduced to replace the air in the atmosphere tube furnace. The flow rate of hydrogen gas was then adjusted to 125 ml / min, and the atmosphere tube furnace was heated to 650°C at 6°C / min and held at that temperature for 10 hours. After the holding period, the atmosphere tube furnace was allowed to cool naturally to room temperature. During the holding and cooling stages, hydrogen gas was introduced at the same flow rate as during the heating stage. The carbon felt was then removed to obtain carbon felt D. Carbon felt D was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18 hours to obtain the nickel-modified zinc-bromine flow battery carbon felt negative electrode.

[0061] The difference from Example 1 is that Comparative Example 12 uses a liquid phase impregnation process to load elemental nickel onto carbon felt.

[0062] Electrochemical performance tests were conducted on a zinc-bromine flow battery assembled from the samples prepared in the examples and comparative examples. The battery used carbon felt as the negative electrode, unmodified carbon felt as the positive electrode, and a microporous membrane as the separator. The electrolytes for both the positive and negative electrodes consisted of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 M tetramethylammonium bromide, and 0.2 M tetrabutylammonium bromide. The effective area of ​​both the positive and negative carbon felt electrodes was 3 cm × 3 cm.

[0063] The electrochemical performance of the zinc-bromine flow battery was tested using a constant current charge-discharge mode. During the test, the electrolytes at both the positive and negative electrodes flowed at 35 mL / min, initially at 60 mA / cm². 2 The battery was charged at a constant current for 40 minutes (charged area specific capacity of 40 mAh / cm²), and then discharged at the same constant current until the voltage reached 0.6V. Based on the battery charge-discharge curves, the electrochemical performance indicators such as coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were calculated.

[0064] The electrochemical performance results of each material in the first charge-discharge test are shown in Table 1.

[0065]

[0066] The electrochemical performance data of Table 1 shows that when the copper-loaded modified carbon felt prepared by Examples 1-7 is used as the negative electrode material of the zinc-bromine flow battery, the zinc-bromine flow battery is significantly superior to the zinc-bromine flow battery using the carbon felt of Comparative Examples 1-12 in terms of three key indicators, namely, coulombic efficiency, voltage efficiency and energy efficiency. This result confirms that loading copper elemental particles on the surface of the carbon felt can effectively improve the electrochemical performance of the carbon felt as the negative electrode of the zinc-bromine flow battery. It is worth noting that among the modified materials of Examples 1-7, Example 1 developed with the optimal process parameters exhibits the best overall performance, with the three efficiency parameters reaching the highest level. As the process parameter range gradually increases, the three key indicators, namely, coulombic efficiency, voltage efficiency and energy efficiency of Examples 2-7 have a decreasing trend. The coulombic efficiency, voltage efficiency and energy efficiency of Example 1 are 97.4%, 85.3% and 83.1%, respectively; while the coulombic efficiency, voltage efficiency and energy efficiency of Example 7 are 95.0%, 82.6% and 78.5%, respectively. This can indicate that the copper organic precursor type, the mass ratio of the copper organic precursor to carbon felt A, the hydrogen flow rate, the holding temperature and the holding time of the two temperature zones and other process parameters need to be optimized and combined to significantly improve the electrochemical performance of the zinc-bromine flow battery.

[0067] Under the condition of constant charging capacity, higher coulombic efficiency directly reflects that the zinc-bromine flow battery can release more effective discharge capacity. The experimental data (Table 1) show that the coulombic efficiency of Examples 1-7 is not less than 95%, which is higher than the numerical level of Comparative Examples 1-12 (<87%). This result verifies that the copper-loaded modified carbon felt can significantly improve the reversible release capacity of electric charge, and the mechanism mainly reflects the following aspects: first, the copper nanoparticles loaded on the surface of the carbon felt have excellent zinc affinity, effectively reducing the activation energy of zinc deposition nucleation, and at the same time, increasing the number of surface active sites to improve the electrochemical activity of the carbon felt; second, the strong interaction force between copper-zinc interface can guide the uniform deposition / stripping of zinc ions on the electrode surface, and inhibit the formation of zinc dendrites.

[0068] Voltage efficiency reflects the ratio of average discharge voltage to average charge voltage during the charging and discharging process of the battery, and the size of this parameter is directly affected by the polarization during the charging and discharging process of the battery. In terms of voltage efficiency, the values of the batteries of Examples 1-7 are stable at more than 82%, which shows a certain advantage over Comparative Examples 1-12 (≤81%). The improvement of voltage efficiency is mainly due to the high conductivity of copper, which as an electrochemical active site can quickly transfer electrons between the carbon felt and the zinc deposition layer, effectively reducing the interface charge transfer resistance, thereby effectively reducing the voltage loss during the charging and discharging process.

[0069] Energy efficiency, as a result of the synergy of coulombic efficiency and voltage efficiency, is an evaluation index for evaluating the electric energy conversion efficiency of the battery in the charging and discharging process. The energy efficiency of Examples 1-7 reaches a high level of more than 78%, while that of Comparative Examples 1-12 does not exceed 70%. The performance improvement of the energy efficiency of the examples is due to the triple optimization effect of the copper-modified carbon felt: the zinc nucleation barrier is reduced by the zincophilic property of copper particles; the interface charge transfer resistance is reduced by the high electrical conductivity of copper particles, reducing polarization; and the uniform deposition / stripping of zinc is achieved by the strong interfacial interaction between copper and zinc. The synergistic effect of these beneficial effects significantly improves the energy conversion efficiency of the examples.

[0070] As can be seen from Comparative Example 1 and Comparative Example 1, the performance indicators of Example 1 are much better than those of Comparative Example 1. This can indicate that simple heat treatment of carbon felt without loading copper single substance cannot achieve the purpose of improving the electrochemical performance of carbon felt.

[0071] As can be seen from Comparative Example 1 and Comparative Examples 2 and 3, the mass ratio of copper organic precursor to carbon felt A affects the number of copper single substance particles loaded on the carbon felt. If the ratio is too large, too many copper single substance particles are loaded on the carbon felt, blocking the pore structure of the carbon felt, affecting the transport of electrolyte inside the carbon felt, and reducing the available space for zinc deposition; if the ratio is too small, too few copper single substance particles are loaded on the carbon felt, which cannot effectively increase the active sites for zinc deposition; therefore, a suitable mass ratio of copper organic precursor to carbon felt A not only introduces enough copper single substance zinc deposition active sites on the carbon felt, but also avoids the blockage of the pore structure of the carbon felt by copper single substance.

[0072] As can be seen from Comparative Example 1 and Comparative Examples 4 and 5, the hydrogen flow rate plays a key role in the reaction equilibrium and product discharge. If the hydrogen flow rate is too slow, the volatile organic ligand formed by the reaction of the copper organic precursor with hydrogen cannot be carried out of the double-temperature zone tube furnace, interfering with the copper deposition process; if the hydrogen flow rate is too fast, more copper organic precursors will react with hydrogen to form copper single substance and be blown out of the double-temperature zone tube furnace, which is not conducive to the loading of copper single substance on the carbon felt, resulting in waste of copper organic precursors; therefore, a suitable hydrogen flow rate can achieve efficient delivery of the precursors and timely discharge of by-products.

[0073] As can be seen from Comparative Example 1 and Comparative Examples 6 and 7, a suitable temperature in temperature zone A can ensure that the copper organic precursor is vaporized and gasified without decomposition; a suitable temperature in temperature zone B can ensure that the copper deposited on the carbon felt has high crystallinity and high bonding force with the carbon felt, avoiding the shedding of the copper loading; a suitable holding time in the two temperature zones can ensure that the loading process is complete, control the particle size of the loaded copper single substance particles, and improve the crystallinity of the copper loading and the bonding force between the copper loading and the carbon felt.

[0074] As can be seen from Comparative Example 1 and Comparative Examples 8 and 9, the appropriate holding time can ensure that the reaction is completely carried out, while controlling the particle size of the copper particles, further improving the crystallinity of the copper element and the bonding strength between the copper-loaded material and the carbon felt.

[0075] In summary, through the synergistic optimization of the above parameters, efficient and uniform loading of copper element is achieved, which lays a foundation for performance improvement of zinc-bromine flow batteries.

[0076] In Comparative Example 10, the gas used in the gas-phase deposition reaction stage at 650°C is hydrogen for the first nine hours, and air is used instead of hydrogen in the tenth hour. Part of the copper element loaded on the carbon felt is oxidized to copper oxide, and the loaded material is a composite of copper and copper oxide. In Comparative Example 11, the gas used in the gas-phase deposition reaction is air, which makes the loaded material on the carbon felt copper oxide. As can be seen from Comparative Example 1 and Comparative Examples 10 and 11, the material loaded on the carbon felt according to the technical solution of the present application is only copper element particles, and its performance indicators are much better than those of Comparative Example 10 loaded with a composite of copper and copper oxide and Comparative Example 11 loaded with copper oxide. Compared with the composite of copper and copper oxide and copper oxide, the copper element loaded on the carbon felt has extremely high electrical conductivity, which can quickly transfer electrons between the carbon felt and the zinc deposition layer, is conducive to the rapid transfer of electrons during the zinc deposition / peeling process, and can effectively reduce the interface charge transfer resistance.

[0077] As can be seen from Comparative Example 1 and Comparative Example 12, the performance indicators of Example 1 are much better than those of Comparative Example 12. This is because when the carbon felt is soaked in the nickel acetate solution, the nickel acetate solution cannot completely fill all the pores of the carbon felt due to the influence of the surface tension between the solid and the liquid, and the nickel particles cannot be loaded on the surface and internal carbon fibers of the carbon felt. In addition, after 600 cycles, the Coulomb efficiency, voltage efficiency and energy efficiency of Comparative Example 12 are reduced to 65.2%, 67.8% and 44.2%, respectively. This is because the nickel element loaded on the carbon felt has a relatively active chemical property, which is easy to react with acidic substances in the electrolyte, thereby causing the nickel active site for zinc deposition to be ineffective.

[0078] Figure 1The constant current charge-discharge curves are used to test the electrochemical performance of the copper-modified carbon felt prepared in Example 1 and the carbon felt in Comparative Example 1 as negative electrodes of a zinc-bromine flow battery. The difference between Comparative Example 1 and Example 1 is that no copper organic precursor was placed in the dual-temperature zone tube furnace in Comparative Example 1; only simple heat treatment was performed on the carbon felt, and no copper element was loaded onto the carbon felt. In the constant current charge-discharge test, the electrolyte flow rate was controlled at 35 mL / min, and the battery was charged at a constant current density of 60 mA / cm² for 40 minutes, followed by discharge at the same current density until the termination voltage of 0.6 V. As shown in the figure, the discharge areal specific capacity of the copper-modified carbon felt negative electrode obtained in Example 1 is 38.96 mAh / cm². 2 It is 5.28 mAh / cm² higher than that of Comparative Example 1. 2 Thanks to the increased discharge area specific capacity, the coulombic efficiency of the carbon felt obtained in Example 1 reached 97.4%, which is about 13.2% higher than that of Comparative Example 1. During the constant current charging stage, the voltage plateau curves of Example 1 and Comparative Example 1 showed a high degree of agreement, but the discharge voltage of the copper-modified carbon felt negative electrode was approximately 1.69V, about 130mV higher than that of Comparative Example 1. Thanks to the increased discharge voltage, the voltage efficiency of the carbon felt obtained in Example 1 was 85.3%, about 6% higher than that of Comparative Example 1. Thanks to the combined effect of coulombic efficiency and voltage efficiency, the energy efficiency of the carbon felt obtained in Example 1 was 83.1%, 16.5% higher than that of Comparative Example 1. The above comparisons demonstrate that the copper loaded on the carbon felt surface, through a synergistic effect of multiple mechanisms such as reducing the activation energy required for zinc nucleation, increasing the reactive sites on the carbon felt surface, and reducing polarization, ultimately significantly improves the three key indicators of the zinc-bromine flow battery: coulombic efficiency, voltage efficiency, and energy efficiency.

[0079] Figure 2 and Figure 3 The comparison shows the cycle performance test results of using the copper-modified carbon felt of Example 1 and the carbon felt of Comparative Example 1 as the negative electrode of a zinc-bromine flow battery under the same test conditions. After 1600 cycles, the copper-modified carbon felt negative electrode of Example 1 showed coulombic efficiency and energy efficiency of 93.2% and 78.5%, respectively, with retention rates of 95.7% and 94.5%, respectively. In contrast, the carbon felt negative electrode of Comparative Example 1 showed greater fluctuations during cycling; after only 130 cycles, its coulombic efficiency and energy efficiency decreased to 58.4% and 46.4%, respectively, with retention rates of 69.4% and 69.7%, respectively. The fluctuations and retention rates of coulombic efficiency and energy efficiency during cycling are related to zinc dendrite formation. Through comparison, the beneficial effect of the copper-modified carbon felt prepared using the technical solution of this invention in suppressing zinc dendrite formation is obvious.

[0080] Figure 4X-ray diffraction (XRD) patterns of the copper elemental modified carbon felt prepared in Example 1 and the unmodified carbon felt are shown for comparison. By X-ray diffraction (XRD) analysis, the modified carbon felt obtained in Example 1 is detected to have copper elemental (111), (200) and (220) characteristic diffraction peaks at diffraction angle positions of 43.5°, 50.6° and 74.3°, respectively. This observation clearly indicates that under the process conditions of Example 1, copper elemental has been successfully loaded on the surface of the carbon felt substrate material. The appearance of each diffraction peak not only verifies the presence of copper crystals, but also reflects the integrity of its crystal structure. Further by comparing the X-ray diffraction patterns of the copper modified carbon felt prepared in Example 1 and the unmodified carbon felt, it can be known that in addition to the copper elemental characteristic peaks, the remaining diffraction peak positions and intensities of the two samples are basically consistent. This can first indicate that the loading material introduced on the carbon felt by the modification process of Example 1 is only copper elemental, without copper oxide, cuprous oxide and other copper compounds; secondly, it can be indicated that the modification process adopted in Example 1 does not significantly affect the crystal structure of the carbon felt, and the modification method better retains the original crystal phase characteristics of the carbon felt while loading copper elemental particles on the surface of the carbon felt.

[0081] Figure 5 and Figure 6 are scanning electron microscope (SEM) images of the copper elemental modified carbon felt prepared in Example 1 and the carbon felt of Comparative Example 1, respectively. By comparing the microstructures of Figure 5 and Figure 6 , it can be found that the surface of the copper elemental modified carbon felt prepared in Example 1 is uniformly distributed with a large number of nanoparticles Figure 5 , while the surface of the carbon fiber of the carbon felt of Comparative Example 1 Figure 6 is smooth and no obvious particles are observed. This difference can directly prove that the gas phase deposition process adopted in Example 1 loads nanoparticles on the surface of the carbon fiber of the carbon felt.

[0082] Figure 7 is an electron map collected when energy dispersive X-ray spectroscopy analysis is performed on the copper elemental modified carbon felt prepared in Example 1. Figure 8 shows the energy dispersive X-ray spectroscopy data of the selected region. Figure 7 In addition to observing the characteristic signals of carbon (C) and oxygen (O), the characteristic peak of copper (Cu) element is clearly detected in the spectrum, indicating the presence of copper element distribution in the region. Combined with the X-ray diffraction (XRD) patterns of Figure 7 , Figure 8 and Figure 4 , it can be clearly determined that the nanoparticles attached to the surface of the carbon fiber of the carbon felt in Figure 5 are copper elemental. This can further indicate that copper elemental particles are loaded on the carbon felt by the technical solution of Example 1.

[0083] The above detailed description has shown, among other things, specific embodiments of the application. However, these particular embodiments do not describe the only way(s) of practicing the application. Any and all equivalents or modifications, now known or later developed, which would be within the scope of the present application are intended to be included as an equivalent to the claims.

Claims

1. A method of preparing a modified zinc-bromine flow battery carbon felt negative electrode, characterized in that, The method comprises the following steps: (1) vacuum drying the cleaned carbon felt to obtain carbon felt A; (2) placing copper organic precursor in temperature zone A of the gas inlet of a double-temperature-zone tube furnace, placing carbon felt A in temperature zone B of the gas outlet, introducing hydrogen, raising the temperature of temperature zone A to 50-350 DEG C at a rate of 3-9 DEG C / min, raising the temperature of temperature zone B to 400-900 DEG C at the same rate, and performing gas phase deposition reaction for 5-15 h, and then naturally reducing to room temperature to obtain carbon felt B; (3) washing and vacuum drying carbon felt B to obtain the carbon felt negative electrode of the modified zinc-bromine flow battery; In step (2), the copper organic precursor is one of bis(hexafluoroacetylacetone)copper(II), copper acetylacetonate, and bis(dimethylamino-2-propoxy)copper(II); the mass ratio of the copper organic precursor to carbon felt A is 1-10:1; the temperature in temperature zone A ensures that the copper organic precursor can be evaporated and gasified without decomposition; and the hydrogen flow rate is 50-200 ml / min.

2. The method of making a modified zinc-bromine flow battery carbon felt negative electrode according to claim 1, wherein, In step (1), the temperature of vacuum drying is 60-190 DEG C, and the time is 8-22 h.

3. The method of making a modified zinc-bromine flow battery carbon felt negative electrode of claim 1, wherein, In step (3), the temperature of vacuum drying is 100-200 DEG C, and the time is 12-24 h.

4. A modified zinc-bromine flow battery carbon felt negative electrode, characterized by, The modified zinc-bromine flow battery carbon felt negative electrode is prepared by the method of any one of claims 1-3, and the carbon felt negative electrode comprises a carbon felt matrix and copper single-element particles loaded on the carbon felt.

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