Preparation method and application of heteroatom-rich cobaltosic oxide modified electrode
By introducing heteroatoms into the cobalt tetroxide electrode and regulating the electronic structure using hydrothermal reaction and pyrolysis processes, the electrochemical inert problem of existing electrode materials is solved, and the catalytic effect with high activity and high stability is achieved, and the performance of the flow battery is improved.
Patent Information
- Application Number
- CN202510022424.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-07
- Publication Date
- 2025-05-13
AI Technical Summary
Existing liquid flow battery electrode materials, especially graphite felt, are electrochemically inert and are difficult to provide highly active catalytic sites, which seriously hinders the improvement of battery power performance.
Through hydrothermal reaction and pyrolysis processes, heteroatoms are targeted and anchored into the oxygen vacancy of cobalt tetroxide to regulate the electronic structure in the oxide, and achieve high activity and high stability catalysis.
The catalytic activity and stability of the tri-cobalt oxide electrode are improved, and the energy efficiency and cycle stability of the flow battery are improved.
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Figure CN119994079A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of electrodes for liquid flow batteries, and in particular to a preparation method and application of a cobalt tetroxide-modified electrode rich in heteroatoms. Background Art
[0002] Under the background of "dual carbon", large-scale access of new energy to the power grid has become an inevitable trend. However, short-term energy storage technology is difficult to meet the energy storage needs of the power system in scenarios across days, months and even years, which puts forward urgent requirements for long-term energy storage technology with a storage time of more than 4 hours. Liquid flow batteries have become an important development direction in the field of large-scale energy storage due to their high safety, design flexibility, and long cycle life. Electrodes, as the core material of liquid flow battery power units, directly determine the realization and breakthrough of high-power battery technology. At present, carbon-based fiber materials represented by graphite felt have become the first choice for commercial electrodes due to their low cost and strong corrosion resistance. However, the degree of graphitization of graphite felt is very high (>99%), which is electrochemically inert and difficult to provide highly active catalytic sites. Studies have shown that the activation polarization caused by electrode catalytic behavior accounts for only nearly 50% of the total polarization of the battery, which seriously hinders the improvement of battery power performance.
[0003] Transition metals have unfilled valence d orbitals, and their oxides exhibit good intrinsic catalytic activity. In early studies, "Novel catalytic effects of Mn3O4 for all vanadium redox flowbatteries. Chem. Commun., 2012, 48: 5455-5457" used a hydrothermal method for the first time to uniformly introduce Mn3O4 with controllable particle size onto the surface of carbon felt, which promoted the application of transition metal oxides in the field of all-vanadium redox flow battery catalysis. In order to fully stimulate the catalytic activity of transition metal oxides, researchers have conducted regulatory studies on the electronic structure of oxides, including element doping, heterojunction design, and oxygen vacancy engineering. Compared with other electronic regulation methods, the construction of oxygen vacancies is simple and easy, and has stronger universality. A variety of metal oxides containing vacancies have been successfully applied in the field of all-vanadium redox flow batteries, such as CeO 2-x 、Ti4O7、W 18 O 49 、Co3O 4-xEtc. Using a reducing agent to construct oxygen vacancies is a typical strategy. For example, in the literature [Oxygen-vacancy-rich cubic CeO2 nanowires as catalysts for vanadium redox flow batteries. ACSSustainable Chem. Eng., 2020, 8: 16757-16765], CeO2 nanowires were grown on the surface of carbon felt by hydrothermal reaction, and oxygen vacancy defects were further introduced by hydrogen thermal reduction technology to increase the catalytic activity of the oxide. However, it is not easy to control the vacancy concentration by the reduction method to construct oxygen vacancies, which makes it difficult to effectively regulate the catalytic activity. Among many transition metal oxides, cobalt-based oxides (such as CoO, Co3O4) are widely used due to their abundant crustal reserves, adjustable electronic structure and excellent acid resistance. For example, the literature [Investigation of advanced catalytic effect of Co3O4nanosheets modified carbon felts as vanadium flow battery electrodes. J. Power Sources, 2021, 494: 229775] prepared Co3O4 nanosheets with rich lattice defects. Compared with the hydrothermal method, pulse electrodeposition can introduce more vacancy defects, but it still cannot achieve effective regulation of vacancy defects. Moreover, although the introduction of oxygen vacancies can improve the local electronic structure of metal oxides, metal oxides containing vacancy defects are always in a thermodynamically metastable state. Under the strong acid and strong oxidation conditions of all-vanadium liquid flow batteries, it is extremely challenging to maintain the stability of oxygen vacancies and their electronic structures during the long-term service of the battery.
[0004] In summary, how to effectively regulate the oxygen vacancy state to directionally control the electronic structure and thereby achieve long-term catalysis of highly active transition metal oxides has become a limiting factor and key issue in the development of high-power all-vanadium liquid flow battery catalytic systems. Summary of the invention
[0005] The object of the present invention is to provide a method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms and its application for liquid flow batteries. Based on the oxygen vacancy filling strategy, heteroatoms are targeted and anchored into some oxygen vacancies of metal oxides through hydrothermal reaction and subsequent pyrolysis process. The degree of crystallization of the precursor (basic cobalt carbonate), the type of heteroatoms and the filling ratio are used to regulate the chemical environment of heteroatoms in the oxide to achieve precise modulation of the electronic structure. The introduced heteroatoms not only optimize the local electronic state, but also reduce the oxygen vacancy formation energy, thereby achieving high activity and high stability electronic modulation of oxygen vacancies.
[0006] The technical solution of the present invention is as follows: a method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms, and the specific preparation steps are as follows:
[0007] Step (1), activation pretreatment of the porous carbon fiber electrode: the porous carbon fiber electrode is heated at 2 to 10 ° C min in an air atmosphere. -1 The temperature is heated to 350-500°C at a rate of 10000°C and kept at this temperature for 5-10 hours to obtain an activated pretreated electrode;
[0008] Step (2), in-situ hydrothermal growth of basic cobalt carbonate on the surface of the activated pretreated electrode: dissolving cobalt salt and urea in deionized water to prepare a solution; vertically immersing the activated pretreated electrode in the solution, and performing a hydrothermal reaction at 90 to 120° C. for 4 to 8 hours; after the hydrothermal reaction, a basic cobalt carbonate array is in-situ grown on the surface of the activated pretreated electrode to obtain a basic cobalt carbonate modified electrode;
[0009] Step (3), preparation of cobalt tetroxide modified electrode: the basic cobalt carbonate modified electrode was heated at 2-5°C min in air atmosphere. -1 The temperature is heated to 350-450°C at a heating rate of 10000 °C and kept at this temperature for 2-5 hours, so that the basic cobalt carbonate grown in situ is thermally decomposed into cobalt tetroxide containing oxygen vacancy defects, thereby obtaining a cobalt tetroxide modified electrode;
[0010] Step (4), preparation of a cobalt tetroxide-modified electrode rich in heteroatoms: calcining the cobalt tetroxide-modified electrode and the heteroatom compound under an argon atmosphere, with the heteroatom compound placed at the upwind side of the airflow direction, and the argon flow rate of 20 to 50 ml min -1 , calcination temperature 700~900℃, heating rate 2~5℃min -1 , keep warm for 3 to 6 hours, the heteroatom compound decomposes under heat, so that the heteroatoms are filled into some of the existing oxygen vacancy defects of cobalt oxide, and finally a cobalt oxide modified electrode rich in heteroatoms is obtained.
[0011] Furthermore, the temperature of the hydrothermal reaction in step (2) is 90°C.
[0012] The porous carbon fiber electrode is graphite felt, carbon felt or carbon cloth.
[0013] The cobalt salt is one of cobalt nitrate, cobalt sulfate and cobalt chloride, and the concentration of the aqueous solution of the cobalt salt is 0.05-0.2 molL -1 .
[0014] The concentration of urea in the solution is 0.2-1.0 mol L -1 .
[0015] The heteroatom compound is one of sodium hypophosphite, diammonium hydrogen phosphate, urea, melamine, sodium thiosulfate and ammonium fluoride, and its mass is 2 to 5 times that of the porous carbon fiber electrode.
[0016] The heteroatom-rich cobalt tetroxide modified electrode prepared according to the preparation method can be applied to all-vanadium liquid flow batteries and iron-based liquid flow batteries.
[0017] Compared with the prior art, the present invention has the following beneficial effects:
[0018] (1) A simple and efficient method for regulating the oxygen vacancy concentration in cobalt tetroxide is proposed. By controlling the hydrothermal reaction temperature, the crystallization degree of the precursor (basic cobalt carbonate) is controlled, thereby achieving controllable regulation of the oxygen vacancy concentration in the metal oxide.
[0019] (2) Based on the oxygen vacancy filling strategy, heteroatoms are targeted and anchored into some oxygen vacancies of metal oxides. The oxygen vacancy concentration, heteroatom type and filling ratio are used to synergistically optimize the electronic structure of cobalt tetroxide to improve the catalytic activity. At the same time, based on the bonding between heteroatoms and cobalt tetroxide lattice atoms, the oxygen vacancy formation energy is reduced to improve the catalytic stability. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 The present invention is a process flow chart for preparing a cobalt tetroxide-modified electrode rich in heteroatoms.
[0021] Figure 2 The following are scanning electron microscope images of the N-doped cobalt tetroxide modified graphite felt prepared in the present invention and commercial graphite felt. (a) is commercial graphite felt, and (b) is N-doped cobalt tetroxide modified graphite felt.
[0022] Figure 3 This is a transmission electron microscope image of N-doped cobalt tetroxide prepared in the present invention.
[0023] Figure 4 This is a comparison chart of the BET specific surface areas of the N-doped cobalt tetroxide-modified graphite felt prepared in the present invention, commercial graphite felt, and cobalt tetroxide-modified graphite felt.
[0024] Figure 5 This is a comparison chart of the rate performance of the N-doped cobalt tetroxide modified graphite felt prepared in the present invention, commercial graphite felt, and cobalt tetroxide modified graphite felt.
[0025] Figure 6 This is a comparison chart of the charge and discharge cycle performance of the N-doped cobalt tetroxide modified graphite felt prepared in the present invention after the first charge and discharge cycle and after replacing the electrolyte and the diaphragm after 500 cycles. DETAILED DESCRIPTION
[0026] The present invention provides a method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms, which method is as follows: (1) activation pretreatment of a porous carbon fiber electrode; (2) in-situ hydrothermal growth of basic cobalt carbonate on the surface of the porous carbon fiber electrode; (3) thermally decomposing the in-situ grown basic cobalt carbonate into cobalt tetroxide containing oxygen vacancy defects under air atmosphere; (4) utilizing thermal decomposition of heteroatom compounds to directionally fill heteroatoms into existing oxygen vacancy defects of cobalt tetroxide, thereby finally obtaining a cobalt tetroxide-modified electrode rich in heteroatoms.
[0027] The following are specific examples to describe the present invention in detail. The examples are provided to facilitate understanding of the present invention and are by no means intended to limit the present invention.
[0028] Example 1
[0029] In this embodiment, a method for preparing an N-doped cobalt tetroxide-modified graphite felt electrode comprises the following steps:
[0030] (1) Activation pretreatment of graphite felt electrode: Place the graphite felt electrode in a muffle furnace and heat it at 5℃ min in air atmosphere. -1 The electrode was heated to 450°C at a heating rate of 100 °C and taken out after keeping the temperature for 6 h.
[0031] (2) In-situ hydrothermal growth of basic cobalt carbonate on the graphite felt electrode surface: Cobalt nitrate and urea were dissolved in 50 mL of deionized water to obtain a 0.1 mol L -1 Cobalt nitrate and 0.5 mol L -1 An aqueous solution of urea; subsequently, the above solution is poured into a hydrothermal reactor, and the activated pretreated graphite felt electrode is vertically immersed therein, and the hydrothermal reaction is carried out at 90°C for 6 hours; after the hydrothermal reactor is naturally cooled to room temperature, the sample is taken out for cleaning and vacuum drying, so that a basic cobalt carbonate array is in situ grown on the surface of the graphite felt electrode to obtain a basic cobalt carbonate modified electrode;
[0032] (3) Preparation of cobalt tetroxide modified graphite felt electrode: The basic cobalt carbonate modified electrode obtained in step (2) was placed in a tube furnace and heated at 2°C min in air atmosphere. -1 The temperature was raised to 400°C at a rate of 100°C and kept at this temperature for 3 hours, so that the basic cobalt carbonate grown in situ on the surface of the graphite felt electrode was decomposed into cobalt tetroxide containing oxygen vacancy defects by heat, thereby obtaining a cobalt tetroxide modified electrode;
[0033] (4) Preparation of heteroatom-rich cobalt tetroxide-modified graphite felt electrode: The cobalt tetroxide-modified electrode obtained in step (3) is placed in a tubular furnace, and melamine with a mass three times that of the graphite felt is placed at the upwind direction of the air flow direction, and calcined together with the cobalt tetroxide-modified electrode in an argon atmosphere at an argon flow rate of 40 ml min -1 , calcination temperature 800℃, heating rate 5℃min-1 , and keep warm for 4h, finally obtaining N-doped cobalt tetroxide modified graphite felt electrode.
[0034] In this embodiment, the temperature of the hydrothermal reaction is regulated to control the crystallization degree of the precursor (basic cobalt carbonate) so as to ensure the concentration of oxygen vacancies generated subsequently.
[0035] Table 1: Comparison of atomic fractions of N-doped cobalt tetroxide modified graphite felt prepared in Example 1, commercial graphite felt, and cobalt tetroxide modified graphite felt
[0036] C 1s O 1s N 1s 2p Commercial graphite felt 99.4％ 0.6％ Cobalt Tetroxide Modified Graphite Felt 81.0％ 14.7％ 4.3％ Example 1 81.2％ 12.9％ 1.7％ 4.2％
[0037] like Figure 1 As shown, the N-doped cobalt tetroxide modified graphite felt electrode is mainly prepared through hydrothermal reaction, thermal decomposition, pyrolysis treatment and other steps. The method has high integration and strong controllability, and is easy to achieve large-scale production.
[0038] like Figure 2 As shown, a large number of one-dimensional nanorod arrays grew on the surface of the prepared N-doped cobalt tetroxide modified graphite felt electrode, which had a more complex interface structure than graphite felt.
[0039] like Figure 3 As shown, the nanorods grown on the surface of the N-doped cobalt tetroxide modified graphite felt electrode have a diameter of about 70 nm and are composed of a large number of nanocrystals.
[0040] like Figure 4 As shown in the figure, the prepared N-doped cobalt tetroxide modified graphite felt electrode has a greatly improved BET specific surface area (9.36 m 2 g -1 ).
[0041] like Figure 5 As shown in the figure, the all-vanadium liquid flow battery assembled with the prepared N-doped cobalt tetroxide modified graphite felt electrode has greatly improved the battery energy efficiency compared with commercial graphite felt, 300mA cm -2 The energy efficiency is 77.8%.
[0042] like Figure 6 As shown, 300mA cm -2 After 500 cycles, the battery's separator and electrolyte were replaced, and the battery energy efficiency could be restored to 76.9%, indicating that the prepared N-doped cobalt tetroxide modified graphite felt electrode has good cycle stability.
[0043] Example 2
[0044] In this embodiment, a method for preparing an N-doped cobalt tetroxide-modified graphite felt electrode comprises the following steps:
[0045] (1) Activation pretreatment of graphite felt electrode: Place the graphite felt electrode in a muffle furnace and heat it at 5℃ min in air atmosphere. -1 The electrode was heated to 450°C at a heating rate of 100 °C and taken out after keeping the temperature for 6 h.
[0046] (2) In-situ hydrothermal growth of basic cobalt carbonate on the graphite felt electrode surface: Cobalt nitrate and urea were dissolved in 50 mL of deionized water to obtain a 0.1 mol L -1 Cobalt nitrate and 0.5 mol L -1 An aqueous solution of urea; subsequently, the above solution is poured into a hydrothermal reactor, and the activated pretreated graphite felt electrode is vertically immersed therein, and the hydrothermal reaction is carried out at 120°C for 6 hours; after the hydrothermal reactor is naturally cooled to room temperature, the sample is taken out for cleaning and vacuum drying, so that a basic cobalt carbonate array is in situ grown on the surface of the graphite felt electrode to obtain a basic cobalt carbonate modified electrode;
[0047] (3) Preparation of cobalt tetroxide modified graphite felt electrode: The basic cobalt carbonate modified electrode obtained in step (2) was placed in a tube furnace and heated at 2°C min in air atmosphere. -1 The temperature was raised to 400°C at a rate of 100°C and kept at this temperature for 3 hours, so that the basic cobalt carbonate grown in situ on the surface of the graphite felt electrode was decomposed into cobalt tetroxide containing oxygen vacancy defects by heat, thereby obtaining a cobalt tetroxide modified electrode;
[0048] (4) Preparation of heteroatom-rich cobalt tetroxide-modified graphite felt electrode: The cobalt tetroxide-modified electrode obtained in step (3) is placed in a tubular furnace, and melamine with a mass three times that of the graphite felt is placed at the upwind direction of the air flow direction, and calcined together with the cobalt tetroxide-modified electrode in an argon atmosphere at an argon flow rate of 40 ml min -1 , calcination temperature 800℃, heating rate 5℃min -1 , and heat preservation for 4 hours, finally obtaining an N-doped cobalt tetroxide modified graphite felt electrode. The all-vanadium liquid flow battery assembled with the N-doped cobalt tetroxide modified graphite felt electrode prepared in this embodiment has a high current density of 300 mA cm -2 The energy efficiency is 73.1%. The battery prepared at the hydrothermal temperature in this embodiment has good performance, but is slightly inferior to that in Example 1, mainly because the hydrothermal reaction temperature in this embodiment is relatively high, resulting in high crystallinity of the basic cobalt carbonate obtained, which reduces the oxygen vacancy concentration in the cobalt oxide after pyrolysis.
[0049] Example 3
[0050] In this embodiment, a method for preparing a P-doped cobalt tetroxide-modified carbon felt electrode comprises the following steps:
[0051] (1) Activation pretreatment of carbon felt electrode: Place the carbon felt electrode in a muffle furnace and heat it at 8℃ min in air atmosphere. -1The electrode was heated to 400°C at a heating rate of 100°C and taken out after keeping the temperature for 8 hours;
[0052] (2) In-situ hydrothermal growth of basic cobalt carbonate on the carbon felt electrode surface: Cobalt chloride and urea were dissolved in 50 mL of deionized water to obtain a 0.15 mol L -1 Cobalt chloride and 0.8 mol L -1 An aqueous solution of urea; subsequently, the above solution is poured into a hydrothermal reactor, and the activated pretreated carbon felt electrode is vertically immersed therein, and the hydrothermal reaction is carried out at 100°C for 5 hours; after the hydrothermal reactor is naturally cooled to room temperature, the sample is taken out for cleaning and vacuum drying, so that a basic cobalt carbonate array is in situ grown on the surface of the carbon felt electrode to obtain a basic cobalt carbonate modified electrode;
[0053] (3) Preparation of cobalt tetroxide modified carbon felt electrode: The basic cobalt carbonate modified electrode obtained in step (2) was placed in a tube furnace and heated at 5°C min in air atmosphere. -1 The temperature was raised to 450°C at a rate of 100°C and kept at this temperature for 4 hours, so that the basic cobalt carbonate grown in situ on the surface of the carbon felt electrode was decomposed into cobalt tetroxide containing oxygen vacancy defects by heat, thereby obtaining a cobalt tetroxide modified electrode;
[0054] (4) Preparation of heteroatom-rich cobalt tetroxide-modified carbon felt electrode: The cobalt tetroxide-modified electrode obtained in step (3) is placed in a tubular furnace, and sodium hypophosphite with a mass four times that of the carbon felt is placed at the upwind direction of the air flow direction, and calcined together with the cobalt tetroxide-modified electrode in an argon atmosphere at an argon flow rate of 30 ml min -1 , calcination temperature 700℃, heating rate 5℃min -1 , and heat preservation for 5 hours, finally obtaining a P-doped cobalt tetroxide-modified carbon felt electrode. The all-vanadium redox flow battery assembled with the P-doped cobalt tetroxide-modified carbon felt electrode prepared in this embodiment has a high current density of 300 mA cm -2 The energy efficiency is 76.2%.
[0055] Example 4
[0056] In this embodiment, a method for preparing a S-doped cobalt tetroxide-modified carbon felt electrode comprises the following steps:
[0057] (1) Activation pretreatment of carbon felt electrode: Place the carbon felt electrode in a muffle furnace and heat it at 2℃min in air atmosphere. -1 The temperature was raised to 500°C at a rate of 100°C and the electrode was taken out after keeping the temperature for 5 hours.
[0058] (2) In-situ hydrothermal growth of basic cobalt carbonate on the carbon felt electrode: Cobalt sulfate and urea were dissolved in 50 mL of deionized water to obtain a 0.2 mol L -1 Cobalt sulfate and 1.0 mol L -1An aqueous solution of urea; subsequently, the above solution is poured into a hydrothermal reactor, and the activated pretreated carbon felt electrode is vertically immersed therein, and the hydrothermal reaction is carried out at 110°C for 8 hours; after the hydrothermal reactor is naturally cooled to room temperature, the sample is taken out for cleaning and vacuum drying, so that a basic cobalt carbonate array is in situ grown on the surface of the carbon felt electrode to obtain a basic cobalt carbonate modified electrode;
[0059] (3) Preparation of cobalt tetroxide modified carbon felt electrode: The basic cobalt carbonate modified electrode obtained in step (2) was placed in a tube furnace and heated at 2°C min in air atmosphere. -1 The temperature was raised to 350°C at a rate of 100°C and kept at this temperature for 5 hours, so that the basic cobalt carbonate grown in situ on the surface of the carbon felt electrode was decomposed into cobalt tetroxide containing oxygen vacancy defects by heat, thereby obtaining a cobalt tetroxide modified electrode;
[0060] (4) Preparation of heteroatom-rich cobalt tetroxide-modified carbon felt electrode: The cobalt tetroxide-modified electrode obtained in step (3) was placed in a tubular furnace, and sodium thiosulfate with a mass 5 times that of the carbon felt was placed at the upwind direction of the air flow, and calcined together with the cobalt tetroxide-modified electrode in an argon atmosphere at an argon flow rate of 20 ml min -1 , calcination temperature 900℃, heating rate 2℃min -1 , and heat preservation for 5h, finally obtaining S-doped cobalt tetroxide modified carbon felt electrode. The all-vanadium liquid flow battery assembled with the S-doped cobalt tetroxide modified carbon felt electrode prepared in this embodiment has a high current density of 300mA cm -2 The energy efficiency is 75.0%.
[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.
[0062] Comparative Example 1
[0063] In this comparative example, a method for preparing an N-doped cobalt tetroxide-modified graphite felt electrode comprises the following steps:
[0064] Except that the hydrothermal reaction temperature in step (2) is 180°C;
[0065] The rest are the same as in Example 1.
[0066] The BET specific surface area of the modified electrode prepared in this comparative example is 4.25 m 2 g -1 .
[0067] The all-vanadium liquid flow battery assembled with the modified electrode prepared in this comparative example has a high current density at 300 mA cm -2 The energy efficiency is 70.5%.
[0068] The poor battery performance is mainly due to the high hydrothermal reaction temperature in this comparative example, which results in high crystallinity of the obtained basic cobalt carbonate and almost no oxygen vacancies in the cobalt oxide after pyrolysis.
[0069] Comparative Example 2
[0070] In this comparative example, a method for preparing an N-doped cobalt tetroxide-modified graphite felt electrode comprises the following steps:
[0071] Except that in step (4), the amount of melamine used is 10 times that of graphite felt;
[0072] The rest are the same as in Example 1.
[0073] The all-vanadium liquid flow battery assembled with the modified electrode prepared in this comparative example has a high current density at 300 mA cm -2 The energy efficiency is 70.9%.
[0074] The poor performance of the battery is mainly due to the excessively high content of heteroatom compounds in this comparative example, which leads to an increase in the heteroatom filling ratio in cobalt tetroxide, affecting the lattice structure in the metal oxide and causing excessive lattice distortion.
[0075] Comparative Example 3
[0076] In this comparative example, a method for preparing a P-doped cobalt tetroxide-modified carbon felt electrode comprises the following steps:
[0077] Except that the holding temperature in air atmosphere in step (3) is 300° C.;
[0078] The rest are the same as in Example 2.
[0079] The all-vanadium liquid flow battery assembled with the modified electrode prepared in this comparative example has a high current density at 300 mA cm -2 The energy efficiency is 68.9%.
[0080] Comparative Example 4
[0081] In this comparative example, a method for preparing a cobalt tetroxide-modified carbon felt electrode comprises the following steps:
[0082] Except that step (4) is not performed;
[0083] The rest is the same as in Example 3, so that the cobalt tetraoxide grown on the surface of the carbon felt does not contain heteroatoms.
[0084] The all-vanadium liquid flow battery assembled with the modified electrode prepared in this comparative example has a high current density at 300 mA cm -2 The energy efficiency is 69.1% at 300mA cm -2After 500 cycles, the battery's separator and electrolyte were replaced, and the battery energy efficiency decayed to 60.9%.
Claims
1. A method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms, characterized in that: The specific preparation steps are as follows: Step (1), activation pretreatment of the porous carbon fiber electrode: the porous carbon fiber electrode is heated at 2 to 10 ° C min in an air atmosphere. -1 The temperature is heated to 350-500°C at a rate of 10000°C and kept at this temperature for 5-10 hours to obtain an activated pretreated electrode; Step (2), in-situ hydrothermal growth of basic cobalt carbonate on the activation pretreatment electrode surface: dissolving cobalt salt and urea in deionized water to prepare a solution; The activated pretreated electrode is vertically immersed in the solution and subjected to a hydrothermal reaction at 90 to 120° C. for 4 to 8 hours; after the hydrothermal reaction, a basic cobalt carbonate array is in situ grown on the surface of the activated pretreated electrode to obtain a basic cobalt carbonate modified electrode; Step (3), preparation of cobalt tetroxide modified electrode: the basic cobalt carbonate modified electrode was heated at 2-5°C min in air atmosphere. -1 The temperature is heated to 350-450°C at a heating rate of 10000 °C and kept at this temperature for 2-5 hours, so that the basic cobalt carbonate grown in situ is thermally decomposed into cobalt tetroxide containing oxygen vacancy defects, thereby obtaining a cobalt tetroxide modified electrode; Step (4), preparation of a cobalt tetroxide-modified electrode rich in heteroatoms: calcining the cobalt tetroxide-modified electrode and the heteroatom compound under an argon atmosphere, with the heteroatom compound placed at the upwind side of the airflow direction, and the argon flow rate of 20 to 50 ml / min -1 , calcination temperature 700~900℃, heating rate 2~5℃min -1 , keep warm for 3 to 6 hours, the heteroatom compound decomposes under heat, so that the heteroatoms are filled into some of the existing oxygen vacancy defects of cobalt oxide, and finally a cobalt oxide modified electrode rich in heteroatoms is obtained.
2. The method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step (2) is 90°C.
3. The method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms according to claim 1 or 2, characterized in that: The porous carbon fiber electrode is graphite felt, carbon felt or carbon cloth.
4. The method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms according to claim 1 or 2, characterized in that: The cobalt salt is one of cobalt nitrate, cobalt sulfate and cobalt chloride, and the concentration of the aqueous solution of the cobalt salt is 0.05-0.2 molL -1 .
5. The method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms according to claim 1 or 2, characterized in that: The concentration of urea in the solution is 0.2-1.0 mol L -1 .
6. The method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms according to claim 1 or 2, characterized in that: The heteroatom compound is one of sodium hypophosphite, diammonium hydrogen phosphate, urea, melamine, sodium thiosulfate and ammonium fluoride, and its mass is 2 to 5 times that of the porous carbon fiber electrode.
7. An application of a cobalt tetroxide-modified electrode rich in heteroatoms, wherein the electrode is prepared by the method for preparing a cobalt tetroxide-modified electrode rich in heteroatoms according to any one of claims 1 to 6, characterized in that: The electrode is applied to all-vanadium liquid flow batteries and iron-based liquid flow batteries.