A high-capacity ferroferric oxide electrode and a preparation method and application thereof

Abstract

The application belongs to the technical field of electrode materials, and provides a preparation method of a high-capacity ferroferric oxide electrode, which comprises the following steps: placing iron source salt solution and a carbon cloth substrate into a reaction kettle, and then placing the reaction kettle in an oven to perform a hydrothermal reaction; after the hydrothermal reaction is completed, Fe2O3@CC precursors are obtained, and the Fe2O3@CC precursors are cleaned and dried; taking the Fe2O3@CC precursors as a working electrode, taking a platinum sheet and a calomel electrode as a counter electrode and a reference electrode respectively, taking potassium hydroxide solution as an electrolyte, performing an electrochemical oxidation-reduction process on the working electrode by using a cyclic voltammetry method or a constant-current charging and discharging method until the Fe2O3@CC precursors are completely converted into Fe3O4@CC active substances, taking out the Fe3O4@CC active substances, cleaning and drying the Fe3O4@CC active substances, and thus a high-capacity ferroferric oxide electrode is obtained. The application further provides a high-capacity ferroferric oxide electrode and an application thereof. The Fe3O4@CC material is synthesized by using a hydrothermal method and an electrochemical conversion method, and thus a super-high specific capacitance close to a theoretical capacity is achieved, and the specific capacitance reaches about 1000 F / g.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode materials, and particularly relates to a high-capacity ferroferric oxide electrode and a preparation method and application thereof. BACKGROUND

[0002] With the decreasing reserves of traditional energy and the serious pollution of the environment caused by the combustion products of traditional energy, the development and utilization of clean energy are imminent. Supercapacitors and batteries are two typical electrochemical energy storage devices, which have the advantages of high power density, good cycle stability and low maintenance cost. However, the lower energy density limits the further development of supercapacitors. The capacity of the positive electrode material of the supercapacitor is mostly 1000-2000 F / g, while the capacity of the negative electrode material is only 100-500 F / g. In order to improve the energy density of the energy storage device, the specific capacity of the negative electrode material must be improved.

[0003] At present, the commercially available negative electrode material is mainly multifunctional carbon material, but its specific capacity is low (about 150 F / g), which greatly reduces the overall performance of the energy storage device and limits its application. The traditional iron-based oxide (ferric oxide, hydroxyl ferric oxide) negative electrode relies on the faradic reaction to significantly improve the specific capacity (about 300 F / g), but there is still a large gap with the theoretical capacity (1060 F / g). In the prior art, the negative electrode material is mostly prepared by hydrothermal / solvothermal method, electrodeposition method, electrochemical oxidation method, molten salt method and electrostatic spinning method. In the hydrothermal / solvothermal synthesis process, it is not easy to control the particle size and loading amount, and the size of the obtained particles is not uniform due to the influence of temperature and concentration. Different morphologies of metal oxide materials are also obtained due to factors such as salt solution and substrate. In the electrodeposition method, metal hydroxide (hydroxyl oxide) is deposited on the substrate by means of high-potential faradic reaction. The active material is deposited unevenly due to the hydrophilic and hydrophobic properties of the substrate, and the deposition current that is too large or too small can affect the morphology and deposition loading amount. In the electrochemical oxidation method, the precursor sample is electrochemically converted into the target active material by cyclic voltammetry or constant current charge and discharge method. However, different activation methods result in different crystal phases or morphologies of the active material sample. In the molten salt method, the concentration of the active component on the carrier is not uniform due to the movement of the active material to the outer surface, which reduces the concentration of the active material on the inner surface. The active material synthesized by the electrostatic spinning method often has large size and low structural strength, and cannot make the active material fully participate in the energy storage reaction. SUMMARY

[0004] The purpose of the embodiment of the application is to provide a preparation method of a high-capacity ferroferric oxide electrode, which aims to solve the problems in the background art.

[0005] The embodiment of the application is implemented as follows. A preparation method of a high-capacity ferroferric oxide electrode comprises the following steps:

[0006] (1) Put the iron source salt solution and carbon cloth substrate into the reaction kettle together, and then put it into the oven for hydrothermal reaction, and after the hydrothermal reaction is completed, Fe2O3@CC precursor is obtained, and it is washed and dried;

[0007] (2) Fe2O3@CC precursor is used as a working electrode, platinum sheet and mercury electrode are used as counter electrode and reference electrode respectively, potassium hydroxide solution is used as electrolyte, and the working electrode is subjected to electrochemical oxidation and reduction process by cyclic voltammetry or constant current charging and discharging method until Fe2O3@CC precursor is completely converted into Fe3O4@CC active material, and then it is washed and dried, and high-capacity ferroferric oxide electrode is obtained.

[0008] Preferably, in step (1), the preparation method of the iron source salt solution comprises the following steps: mixing 3mmol of Fe(NO3)3 or FeCl3 with 40mL of deionized water and stirring uniformly to obtain a clear solution.

[0009] Preferably, in step (1), the temperature of the hydrothermal reaction is 120℃, and the time is 24h.

[0010] Preferably, in step (2), the parameters of the cyclic voltammetry are 2mV / s scan rate, 10 cycles or 4mV / s, 20 cycles or 8mV / s, 50 cycles or 20mv / s, 100 cycles, and the potential window is-1.2-0V.

[0011] Preferably, in step (2), the parameters of the constant current charging and discharging method are current density 30A / g.

[0012] Preferably, in steps (1) and (2), the washing and drying are as follows: washed with deionized water, and then dried in an oven at 60℃.

[0013] Another object of the embodiment of the application is to provide a high-capacity ferroferric oxide electrode prepared by the above preparation method.

[0014] Another object of the embodiment of the application is to provide a high-capacity ferroferric oxide electrode in the preparation of supercapacitors.

[0015] The embodiment of the present application provides a preparation method of a high-capacity ferroferric oxide electrode, Fe3O4@CC materials are synthesized through a hydrothermal method and an electrochemical conversion method, oxygen functional groups on a surface of a carbon cloth substrate are used as nucleation sites of iron oxide nanoparticles, grain growth is uniform and no agglomeration occurs at a relatively low temperature (120 DEG C), and the uniformity of particle size is greatly improved; during an electrochemical activation process, +3 valence state Fe is partially reduced to +2 valence through a reduction reaction near-1.1V, then an oxidation reaction near-0.7V loses part of electrons, and after multiple activation, a relatively stable electrochemical state is reached, and crystal phase conversion is completed, that is, iron oxide is converted into ferroferric oxide, in a subsequent charging and discharging process, the Fe3O4@CC negative electrode realizes super-high specific capacitance close to a theoretical capacity, and the specific capacitance reaches about 1000 F / g due to the unique inverse spinel structure, the characteristics of iron atoms in multiple valence states and easy electron loss, and sufficient Faraday reactions caused by particle size. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The XRD pattern and SEM morphology of the Fe2O3@CC precursor provided by the embodiment of the present application are shown in the following figure;

[0017] Figure 2 The XRD pattern and SEM morphology of the Fe3O4@CC active material provided by the embodiment of the present application are shown in the following figure;

[0018] Figure 3 The cyclic voltammogram of the Fe2O3@CC precursor provided by the embodiment of the present application through electrochemical conversion by a cyclic voltammetry method is shown in the following figure;

[0019] Figure 4 The charge-discharge curve of the Fe2O3@CC precursor provided by the embodiment of the present application without electrochemical activation directly for charging and discharging test is shown in the following figure;

[0020] Figure 5 The XRD pattern and SEM morphology of the mixture FeOOH+Fe3O4@CC provided by the embodiment of the present application are shown in the following figure;

[0021] Figure 6 The cyclic voltammogram of the Fe3O4@CC active material provided by the embodiment of the present application is shown in the following figure;

[0022] Figure 7 The constant-current charge-discharge curve of the Fe3O4@CC active material provided by the embodiment of the present application is shown in the following figure;

[0023] Figure 8 The EIS pattern of the Fe3O4@CC active material provided by the embodiment of the present application is shown in the following figure;

[0024] Figure 9The cyclic voltammogram of the mixture FeOOH+Fe3O4@CC provided by the embodiment of the present application;

[0025] Figure 10 The constant current charge-discharge curve of the mixture FeOOH+Fe3O4@CC provided by the embodiment of the present application;

[0026] Figure 11 The rate performance of the mixture FeOOH+Fe3O4@CC provided by the embodiment of the present application;

[0027] Figure 12 The chemical performance comparison results of the Fe3O4@CC active material and RuO2·xH2O, AC provided by the embodiment of the present application;

[0028] Figure 13 The specific capacitance and working potential window of the Fe3O4@CC active material applied in different types of aqueous electrolyte provided by the embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0030] The specific implementation of the present application is described in detail below in combination with specific embodiments.

[0031] Embodiment 1, a high-capacity magnetite electrode, the preparation method comprises the following steps:

[0032] (1) 3 mmol of Fe(NO3)3 medicine is mixed with 40 mL of deionized water and stirred uniformly to obtain a clear solution, a commercial carbon cloth CC (the carbon cloth is not limited to the brand, and can be used carbon can carbon cloth, Hesen carbon cloth, Toray carbon cloth, etc.; the hydrophilic carbon cloth can be directly used, or the raw carbon cloth can be pretreated with concentrated acid, plasma etching, high-temperature annealing, etc. to increase the number of surface oxygen functional groups) of appropriate size (2 cm*3 cm) is cut, the solution and the carbon cloth are put into a 50 mL reaction kettle, and placed in a 120°C oven for 24 h, and after natural cooling, the iron oxide loaded carbon cloth sample is taken out, washed with deionized water and dried in a 60°C oven, and is recorded as Fe2O3@CC precursor;

[0033] (2) The Fe2O3@CC precursor sample is cut into a suitable size (1 cm*1.5 cm), and a water-based alkaline three-electrode electrochemical system is prepared, with the Fe2O3@CC precursor as the working electrode, a platinum sheet as the counter electrode, a mercury-mercury electrode as the reference electrode, 2M potassium hydroxide solution as the electrolyte, cyclic voltammetry as the activation method, the scanning speed set to 2mV / s, the number of cycles set to 10, and the potential window set to-1.2-0V. The Fe2O3@CC precursor is completely electrochemically converted until no obvious redox peak appears. The electrode sheet is taken out, washed with deionized water, and dried in a 60°C oven. The product is denoted as Fe3O4@CC active material.

[0034] Performance test:

[0035] The Fe2O3@CC precursor synthesized in Example 1 is analyzed by XRD diffractometer and scanning electron microscope. The XRD pattern and SEM morphology diagram are shown in Figure 1 According to Figure 1 It can be seen that the Fe2O3@CC precursor is an α-Fe2O3 crystal phase, and the particle size is uniform, with a particle size of about 40nm;

[0036] The Fe3O4@CC active material prepared in Example 1 is analyzed by XRD diffractometer and scanning electron microscope. The XRD pattern and SEM morphology diagram are shown in Figure 2 According to Figure 2 It can be seen that the Fe3O4@CC active material is a cubic crystal system inverse spinel structure, and the particle size changes little compared with the particle size before conversion;

[0037] The cyclic voltammetry curve of the electrochemical conversion of the Fe2O3@CC precursor by cyclic voltammetry is shown in Figure 3 , that is, the process of electrochemical conversion of α-Fe2O3 crystal phase into Fe3O4;

[0038] The Fe2O3@CC precursor synthesized in Example 1 is directly subjected to charge and discharge test without electrochemical activation (current density is 2A / g). The charge and discharge curve is shown in Figure 4 According to Figure 4 It can be seen that there is an obvious charge and discharge platform. During this platform stage, part of the precursor iron oxide is converted into hydroxyl ferric oxide, and another part is converted into ferric oxide. The reaction is irreversible, which is a side reaction in the charge and discharge process. After about 10 cycles of charge and discharge, the side reaction ends. The hydroxyl ferric oxide hardly provides pseudo-capacitance, greatly reducing the capacitance of the electrode material;

[0039] The mixture FeOOH+Fe3O4@CC generated during the charge and discharge test is analyzed. The XRD pattern and SEM morphology diagram are shown in Figure 5It can be seen that two crystal phases coexist obviously, in which Fe3O4 is cubic inverse spinel structure and FeOOH is hexagonal crystal system, and the particles change greatly after conversion, and the original particle morphology is difficult to distinguish, and more are irregular nanosheets and nanorods.

[0040] The electrochemical performance test of the Fe3O4@CC active substance prepared in Example 1 is carried out, and the cyclic voltammogram (different scan rate) is as shown in Figure 6 The constant current charge-discharge curve (different current density) is as shown in Figure 7 The electrochemical impedance spectrum (EIS spectrum) is as shown in Figure 8 It can be calculated that the Fe3O4@CC active substance has a specific capacity of up to 1230 F / g at a current density of 1 A / g, and has a very small mass transfer resistance, which also reflects its high and fast charge transfer capacity.

[0041] The electrochemical performance test of the mixture FeOOH+Fe3O4@CC is carried out, and the cyclic voltammogram (different scan rate) is as shown in Figure 9 The constant current charge-discharge curve (different current density) is as shown in Figure 10 The rate performance is as shown in Figure 11 It can be calculated that the mixture FeOOH+Fe3O4@CC has a specific capacity of up to 776 F / g at a current density of 1 A / g, which is much lower than that of the Fe3O4@CC active substance after electrochemical oxidation activation.

[0042] The performance test of the Fe3O4@CC active substance prepared in Example 1 and the typical supercapacitor electrode material RuO2·xH2O, AC is carried out, and the results are as shown in Figure 12 The AC active carbon only shows a specific capacity of about 150 F / g, but has excellent cycle life, and can retain 98.6% of the original capacity after 10000 charge-discharge cycles; RuO2·xH2O only shows a specific capacity of about 600 F / g, and rapidly decays, and only retains 61.1% of the original capacity after 10000 charge-discharge cycles; and the Fe3O4@CC active substance prepared in the embodiment of the application not only shows a specific capacity of up to about 1200 F / g, but also has excellent cycle life, and can retain 97.4% of the original capacity after 10000 charge-discharge cycles.

[0043] The Fe3O4@CC active substance prepared in Example 1 is applied in different types of aqueous electrolyte, and the specific capacity size and working potential window are as shown in Figure 13 It can be seen that the Fe3O4@CC active substance of the embodiment of the application can be applied in alkaline, neutral and acidic electrolyte systems, and can well adapt to multivalent metal ions such as Mg 2+ , Al3+ In addition to the above, the redox electrolyte still has good capacitance performance.

[0044] The above merely provides the preferred embodiments of the present application, but not for limiting the present application. Any modification, equivalent replacement, and improvement made in the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a high-capacity ferroferric oxide electrode, characterized in that: The following steps are involved: (1) placing the iron source salt solution and the carbon cloth substrate into a reactor, and then placing them in an oven for hydrothermal reaction. After the hydrothermal reaction is completed, a Fe2O3@CC precursor is obtained, which is then cleaned and dried; (2) The Fe2O3@CC precursor is used as the working electrode, the platinum sheet and the calomel electrode are used as the counter electrode and the reference electrode respectively, and the potassium hydroxide solution is used as the electrolyte. The working electrode is subjected to an electrochemical redox process using cyclic voltammetry or constant current charge-discharge method until the Fe2O3@CC precursor is completely converted into the Fe3O4@CC active substance. After taking it out, it is cleaned and dried to obtain a high-capacity ferroferric oxide electrode.

2. The method for preparing a high-capacity ferroferric oxide electrode according to claim 1, wherein: In step (1), the method for preparing the iron source salt solution includes the following steps: mixing 3 mmol of Fe(NO3)3 or FeCl3 with 40 mL of deionized water and stirring uniformly to obtain a clear solution.

3. The method for preparing a high-capacity ferroferric oxide electrode according to claim 1, wherein: In step (1), the temperature of the hydrothermal reaction is 120° C. and the time is 24 h.

4. The method for preparing a high-capacity ferroferric oxide electrode according to claim 1, wherein: In step (2), the parameters of the cyclic voltammetry are 2 mV / s scan rate, 10 cycles or 4 mV / s, 20 cycles or 8 mV / s, 50 cycles or 20 mV / s, 100 cycles, and the potential window is -1.2-0 V.

5. The method for preparing a high-capacity ferroferric oxide electrode according to claim 1, wherein: In step (2), the parameter of the constant current charge and discharge method is a current density of 30 A / g.

6. The method for preparing a high-capacity ferroferric oxide electrode according to claim 1, wherein: In step (1) and step (2), the cleaning and drying are specifically as follows: cleaning with deionized water and then drying in an oven at 60°C.

7. A high-capacity ferroferric oxide electrode, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the high-capacity ferrosoferric oxide electrode according to claim 7 in preparing a supercapacitor.

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