CN115662800A

CN115662800A - Mo-doped CoWO 4 Electrode material and preparation method and application thereof

Info

Publication number: CN115662800A
Application number: CN202211217067.1A
Authority: CN
Inventors: 张伟; 黄成相; 郑伟涛
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2022-09-30
Filing date: 2022-09-30
Publication date: 2023-01-31

Abstract

The invention provides a high-performance CoWO ₄ Electrode material and method for preparing the same, coWO ₄ The electrode material is effectively doped with Mo, molybdenum atoms partially replace tungsten, the coordination symmetry of a cobalt center is destroyed, the polarity of a cobalt active center is enhanced, and CoWO is effectively improved ₄ The electrochemical activity of the electrode material; when the electrode is used for an SC electrode, coWO is effectively improved ₄ For example, the discharge capacity is improved by 1.6 times or more.

Description

Mo-doped CoWO 4 Electrode material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of material synthesis, and relates to Mo-doped CoWO ₄ A method for preparing the material.

Background

Due to their high power density, fast charging capability, long life, excellent safety and environmental friendliness, supercapacitors (SCs) are receiving wide worldwide attention as efficient, sustainable, high-performance electrochemical energy storage and power supply devices. However, low specific capacitance and small operating voltage windows limit their widespread use in high energy density devices. The asymmetric super capacitor is assembled by using the battery type anode and the carbon-based cathode material, is an effective method, can improve the working voltage window and the specific capacitance, improves the energy density, and is used as an energy storage device in practical application. Although a great deal of research has been conducted in the field of supercharge, there is still enough room to further improve the electrochemical performance of supercharge. In this case, many of the reported polyelectrodes show low energy density, poor rate performance and poor cycling stability due to the structural misdesign of the electrode material. Furthermore, there is a trade-off between energy and power density. The most challenging task is to produce high performance pseudocapacitive electrode materials that can increase the energy density of the supercharge without affecting other electrochemical properties (cycle life).

Transition metal oxides and their derivatives, typically based on Mn, co, ni, mn, W, fe, zn etc. and their derivatives, are very valuable candidates for energy storage applications due to their rich earth properties, environmental friendliness, low cost effectiveness and rich redox chemistry. CoWO (cobalt oxide) ₄ Is a bimetallic oxide containing tungsten metal ions and has obvious characteristics in the energy storage technology. Co ²⁺ /Co ³⁺ The redox couple is responsible for charge storage and the W atom for transfer 10 ^-7 -10 ^-2 Scm ^-2 Electrical conductivity of a magnitude. However, since CoWO ₄ The development of electrochemical applications is hampered by inherent properties, such as poor conductivity and agglomeration of nanoparticles. Therefore, there is a need to develop a simple and sustainable method to enhance CoWO ₄ Electrochemical properties of the electrode material.

The introduction of the heteroatom through the coprecipitation method is the simplest method for modifying the surface electronic state of the electrode material so as to improve the electrochemical performance of the electrode material. Among the numerous heteroatoms, mo is considered to be particularly promising for enhancing the electrochemical properties of the electrode material by modifying the conductivity, wettability and reactivity of the electrode material with electrolyte ions.

For example, CN202111397586.6 utilizes the high valence state of Mo to inhibit the dissolution of Mn and thereby increase MnO ₂ The cycle performance of the manganese-based material zinc ion battery is improved. CN202011495200.0 doping Mo to NiCo ₂ O ₄ Partial substitution of Co in the lattice ³⁺ Doped to NiCo ₂ O ₄ The lattice forms the trimetal oxide, which not only makes the chemical element composition of the material complex, but also makes the ion composition of the doped material more complex due to the multiple oxidation states of Mo, forms rich defect sites, and simultaneously, the Ni, the Co and the Mo have synergistic effect, thereby leading the Mo to be doped into the NiCo ₂ O ₄ The material has excellent electrochemical performance, and Mo is mainly utilized to have multiple oxidation states, so that the ion composition of the doped material is more complex, and abundant defect sites are formed.

However, against CoWO ₄ The system, on the one hand, does not present the problem of dissolution and the person skilled in the art would not use Mo on CoWO based on the teaching of CN202111397586.6 ₄ Doping is carried out; on the other hand, coWO ₄ With the valence of the metal being singly fixed, without NiCo ₂ O ₄ The multiple oxidation states of Mo to CoWO ₄ Will not contribute and therefore those skilled in the art will not adopt Mo to CoWO based on the teaching of CN202011495200.0 ₄ And (6) doping.

Disclosure of Invention

The invention aims to provide high-performance CoWO ₄ Electrode material, the CoWO ₄ The electrode material is effectively doped with Mo, molybdenum atoms partially replace tungsten, the coordination symmetry of a cobalt center is destroyed, the polarity of a cobalt active center is enhanced, and CoWO is effectively improved ₄ Electrochemical activity of the electrode material.

In the present invention, effective doping of Mo means: moO ₆ Octahedral substitution of one WO attached to Co ₆ Octahedral ligands, thereby destroying CoWO ₄ The symmetry of (a).

The invention also provides the Mo-doped CoWO ₄ The preparation method of the electrode material comprises the steps of firstly obtaining Co-Mo-W precursor powder by a coprecipitation method; calcining Co-Mo-W precursor powder for 3-5h at the temperature of 450-550 ℃ to obtain Mo-doped CoWO ₄ An electrode material.

In order to ensure sufficient eccentric doping, the cobalt acetate, sodium molybdate and sodium tungstate should be mixed according to a molar ratio of 10:1-3:9-7 and mixing.

In certain embodiments of the invention, the following scheme is employed: 3mmol of cobalt acetate tetrahydrate was weighed out and dissolved in 50mL of deionized water, and stirred at 70 ℃ for 20min, and labeled as solution A. In addition, 0.6mmol of sodium molybdate dihydrate and 2.4mmol of sodium tungstate dihydrate were weighed and dissolved in 30mL of deionized water with stirring to form a homogeneous solution, which was labeled as solution B. Then, the solution B was dropwise added to the solution A, and after completion of the dropwise addition, the mixed solution was stirred for 4 hours while maintaining the temperature of 70 ℃.

In certain embodiments of the invention, the Co-Mo-W precursor powder is calcined in a muffle furnace at 500 ℃ for 3 hours.

The invention also provides the Mo-doped CoWO ₄ The application of the electrode material is used for the electrode material of a super capacitor.

All reagents used in the experiment are analytically pure and are commercially available.

The invention has the beneficial effects that:

(1) According to the invention, based on the fact that W and Mo have different d electronic structures and electronegativity, mo replaces W to realize a more controllable electronic structure, molybdenum atoms partially replace tungsten to destroy the coordination symmetry of a cobalt center, enhance the polarity of a cobalt active center, and effectively promote CoWO ₄ For example, the discharge capacity is improved by 1.6 times or more.

Therefore, the invention provides a reasonable strategy for enhancing the pseudo-capacitance reaction. In particular, the coordination symmetry is destroyed by heteroatom substitution, so that an innovative and feasible way is provided for further modulating the electronic structure of the pseudocapacitance active center.

(2) The invention designs and synthesizes the Mo-doped CoWO with a particle stacking structure by a simple method and with simple cost ₄ The synthesized material has a bright particle structure and a good appearance, is suitable for being used as an electrode material of a super capacitor, and is easy for industrial production.

Drawings

FIG. 1 is an example CoWO ₄ (a) And CoWO with different Mo doping ratios (10% -b,20% -c,30% -d) ₄ SEM images of the samples;

FIG. 2 shows example CoWO ₄ And XRD patterns of the cooh 4 samples with different Mo doping ratios (10%, 20%, 30%); wherein, the doping proportion of Mo 10% is marked as Mo-CoWO ₄ -1; the doping proportion of Mo 20% is marked as Mo-CoWO ₄ -2; the doping proportion of Mo 30% is marked as Mo-CoWO ₄ -3；

FIG. 3 is an example CoWO ₄ And CoWO with different Mo doping ratios (10%, 20%, 30%) (Co-O) ₄ EELS plot of the sample; wherein, the doping proportion of Mo 10% is marked as Mo-CoWO ₄ -1; the doping proportion of Mo 20% is marked as Mo-CoWO ₄ -2; the doping proportion of Mo 30% is marked as Mo-CoWO ₄ -3；

FIG. 4 at 10mV s ^-1 Cyclic Voltammetry (CV) curves for CW and MCW-1/-2/-3 electrodes at scan rates of (a); coWO (cobalt oxide) ₄ Expressed by CW, the doping proportion of Mo 10% is marked MCW-1; the doping proportion of Mo of 20% is marked as MCW-2; the doping proportion of Mo 30% is marked as MCW-3;

FIG. 5 shows a current density of 1A g ^-1 Constant current charge and discharge (GCD) curves for CW and MCW-1/-2/-3 electrodes. CoWO (cobalt oxide) ₄ Expressed by CW, the doping proportion of Mo 10% is marked MCW-1; the doping proportion of Mo 20% is marked as MCW-2; the doping proportion of Mo 30% is marked MCW-3.

Detailed Description

To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description of the embodiments, structures, features and effects according to the present invention will be made with reference to the accompanying drawings and preferred embodiments.

Example 1

(1) The Co-Mo-W precursor is prepared by coprecipitation method, firstly 3mmol cobalt acetate tetrahydrate is weighed and dissolved in 50mL deionized water, and stirred for 20min at 70 ℃, and marked as solution A. In addition, 0.3mmol sodium molybdate dihydrate and 2.7mmol sodium tungstate dihydrate were weighed and dissolved in 30mL deionized water with stirring to form a homogeneous solution, which was labeled as solution B. Then, the solution B was dropwise added to the solution A, and after completion of the dropwise addition, the mixed solution was stirred for 4 hours while maintaining the temperature of 70 ℃. And after stirring, centrifuging and washing to obtain Co-Mo-W precursor powder.

(2) And (3) putting a certain amount of Co-Mo-W precursor powder into a muffle furnace, and calcining for 3h at 500 ℃. The sample was then removed for collection.

Example 2

(1) The Co-Mo-W precursor is prepared by coprecipitation method, firstly 3mmol cobalt acetate tetrahydrate is weighed and dissolved in 50mL deionized water, and stirred for 20min at 70 ℃, and marked as solution A. In addition, 0.9mmol of sodium molybdate dihydrate and 2.1mmol of sodium tungstate dihydrate were weighed and dissolved in 30mL of deionized water with stirring to form a homogeneous solution, which was labeled as solution B. Then, the solution B was dropwise added to the solution A, and after completion of the dropwise addition, the mixed solution was stirred for 4 hours while maintaining the temperature of 70 ℃. And after stirring, washing to obtain the Co-Mo-W precursor.

(2) And (3) putting a certain amount of Co-Mo-W precursor into a muffle furnace, and calcining for 3h at 500 ℃. Then, the sample was removed for collection.

Example 3

(1) The Co-Mo-W precursor is prepared by coprecipitation method, firstly 3mmol cobalt acetate tetrahydrate is weighed and dissolved in 50mL deionized water, and stirred for 20min at 30 ℃, and marked as solution A. In addition, 0.6mmol of sodium molybdate dihydrate and 2.4mmol of sodium tungstate dihydrate were weighed and dissolved in 30mL of deionized water with stirring to form a homogeneous solution, which was labeled as solution B. Then, the solution B was dropwise added to the solution A, and after completion of the dropwise addition, the mixed solution was stirred for 4 hours while maintaining the temperature of 70 ℃. And after stirring, washing to obtain the Co-Mo-W precursor.

(2) And (3) putting a certain amount of Co-Mo-W precursor into a muffle furnace, and calcining for 3h at 500 ℃. The sample was then removed for collection.

In the above examples, mo was doped at 10% (example 1), 20% (example 3) and 30% (example 2), respectively, and the SEM of the product is shown in FIG. 1, from which it can be seen that MCW-2 nanoparticles are uniformly densely aggregated and form nanoparticle clusters. Notably, the original CoWO ₄ And Mo-substituted CoWO ₄ The comparison between them clearly shows that the morphology of MCW-2 inherits the nanoparticle morphology well.

FIG. 2 is a CoWO ₄ Different Mo doping ratio from the above examples(10％，20％，30％)CoWO ₄ XRD pattern of the sample; it can be seen from the figure that all XRD patterns can be well ascribed to Shan Xiexiang CoWO ₄ (JCPDS No. 15-0867), which means that Mo substitution does not cause phase change and no additional phase is detected. However, it is similar to original CoWO ₄ The latter showed broadened and attenuated diffraction peaks compared to the Mo-substituted samples, which were associated with induced grain refinement.

FIG. 3 is CoWO ₄ CoWO with different Mo doping ratios (10%, 20%, 30%) from the above examples ₄ EELS pattern of samples, verifying Mo substitution in CoWO ₄ Use of EELS to study CoWO after Mo substitution ₄ Electron transfer of (3). As can be seen in FIG. 3, the EELS Co L of samples from CW to MCW-3 _2,3 -a change in edge. Here, co L _2,3 The edge is due to the transition from the 2p state to the highly localized 3d state closer to the fermi level. As observed, for CW samples, L of Co ₃ The edges maintain a good peak on the lower energy loss side. However, as Mo substitution increases, the low energy loss characteristics change dramatically: at Co L ₃ A significant shift to higher energy loss is observed at the edges, indicating an increase in the polarity of the cobalt active center. This means that a WO is attached to Co ₆ Octahedral ligand MoO ₆ The octahedron is effectively substituted to form a symmetrical break in the crystal structure. In addition to such chemical shifts, the valence state of the transition metal may also be determined by using the white line intensity ratio (L) ₃ /L ₂ ) And (5) further confirming. According to some previous reports, L ₃ /L ₂ Represents the valence state of the metal: a decrease in the ratio of Co ions means an increase in the oxidation state. Co L edge Spectrum shows Co L ₃ /L ₂ The intensity ratio of the features decreases from CW to MCW-3 samples. This strength ratio decays with increasing Mo substitution, confirming the increased polarity of the cobalt active center.

Example 4

(1) The Co-Mo-W precursor is prepared by coprecipitation method, firstly 3mmol cobalt acetate tetrahydrate is weighed and dissolved in 100mL deionized water, and stirred for 30min at 100 ℃, and is marked as solution A. In addition, 0.6mmol of sodium molybdate dihydrate and 2.7mmol of sodium tungstate dihydrate were weighed and dissolved in 30mL of deionized water with stirring to form a homogeneous solution, which was labeled as solution B. Then, the solution B was dropwise added to the solution A, and after completion of the dropwise addition, the mixed solution was stirred for 5 hours while maintaining the temperature of 100 ℃. And after stirring, washing to obtain the Co-Mo-W precursor.

(2) And (3) putting a certain amount of Co-Mo-W precursor into a muffle furnace, and calcining for 5h at 550 ℃. The sample was then removed for collection.

This example, in which the respective products of examples 1-3 above were stirred into a slurry and then uniformly applied to foamed nickel for three-electrode performance testing, we evaluated and compared the electrochemical performance of CW and MCW-1/-2/-3 electrodes in a three-electrode system using 2M KOH aqueous solution as the electrolyte. FIG. 4 depicts s at 10mV ^-1 The Cyclic Voltammetry (CV) curves of the CW and MCW-1/-2/-3 electrodes at the scan rate of (a). Notably, all electrodes showed one reduction peak and two oxidation peaks therein. CV curves, indicating that charge storage is a typical battery-type reaction. As observed, it can be seen that MCW-1/-2/-3 exhibits a larger closed CV curve area than CW, indicating that the MCW-1/-2/-3 electrode has excellent electrochemical reactivity; particularly, the MCW-2 electrode is more remarkable. It is apparent that the redox peak is positively shifted with an increase in the substitution amount of Mo. This oxidation peak shift can be attributed to the change in the filled-in anti-bonding state of the cobalt-oxygen bond caused by the induction effect associated with Mo substitution.

FIG. 5 shows a discharge current density of 1A g ^-1 Constant current charge and discharge (GCD) curves for CW and MCW-1/-2/-3 electrodes. It is clear that MCW-1/-2/-3 exhibits longer discharge times than CW. Of these electrodes, the MCW-2 electrode was found to provide the longest discharge time, exhibiting the highest specific capacitance.

This charge-discharge comparison shows that Mo substitution effectively promotes OH in the electrolyte ^- And (4) adsorbing ions. Based on Mo in CoWO ₄ The specific effects at different substitution levels in (b) revealed: due to the introduction of Mo, the original crystal structure is symmetrically broken, so that the electron transfer between transition metals is activated, and high-valence Co is induced to be used as an electrochemical active site. As inAs expected, coWO ₄ The electrochemical performance of the medium Mo substitution is better than that of the original CoWO ₄ Thus proving the improvement of the electrochemical performance after Mo doping.

Example 5

(1) The Co-Mo-W precursor is prepared by coprecipitation method, firstly 3mmol cobalt acetate tetrahydrate is weighed and dissolved in 100mL deionized water, and stirred for 40min at 70 ℃, and marked as solution A. In addition, 0.3mmol of sodium molybdate dihydrate and 2.1mmol of sodium tungstate dihydrate were weighed and dissolved in 30mL of deionized water with stirring to form a homogeneous solution, which was labeled as solution B. Then, the solution B was dropwise added to the solution A, and after completion of the dropwise addition, the mixed solution was stirred for 3 hours while maintaining the temperature of 70 ℃. And after stirring, washing to obtain the Co-Mo-W precursor.

(2) And (3) putting a certain amount of Co-Mo-W precursor into a muffle furnace, and calcining for 3h at the temperature of 450 ℃. The sample was then removed for collection.

The electrochemical performance test was performed with reference to example 4, and the discharge capacity was measured, compared to CoWO ₄ The improvement is 1.62 times.

Example 6

(1) The Co-Mo-W precursor is prepared by coprecipitation method, firstly 3mmol cobalt acetate tetrahydrate is weighed and dissolved in 100mL deionized water, and stirred for 30min at 90 ℃, and marked as solution A. In addition, 0.6mmol of sodium molybdate dihydrate and 2.7mmol of sodium tungstate dihydrate were weighed and dissolved in 30mL of deionized water with stirring to form a homogeneous solution, which was labeled as solution B. Then, the solution B was dropwise added to the solution A, and after completion of the dropwise addition, the mixed solution was stirred for 4 hours while maintaining the temperature of 90 ℃. And after stirring, washing to obtain the Co-Mo-W precursor.

(2) And (3) putting a certain amount of Co-Mo-W precursor into a muffle furnace, and calcining for 5 hours at 480 ℃. The sample was then removed for collection.

The electrochemical performance test was performed with reference to example 4, and the discharge capacity was measured, compared to CoWO ₄ The improvement is 1.66 times.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. Mo-doped CoWO ₄ Electrode material, characterized in that MoO ₆ Octahedral substitution of one WO attached to Co ₆ Octahedral ligands, disruption of CoWO ₄ The symmetry of (a).

2. The Mo-doped CoWO of claim 1 ₄ The preparation method of the electrode material is characterized by comprising the following steps:

dropwise adding the cobalt acetate solution into a mixed solution of sodium molybdate and sodium tungstate, stirring for 3-5h at the temperature of 70-100 ℃, centrifuging, and washing to obtain Co-Mo-W precursor powder; calcining Co-Mo-W precursor powder for 3-5h at the temperature of 450-550 ℃ to obtain Mo-doped CoWO ₄ An electrode material.

3. The method according to claim 2, wherein the ratio of cobalt acetate, sodium molybdate and sodium tungstate is 10:1-3:9-7 and mixing.

4. The preparation method of claim 3, wherein 3mmol of cobalt acetate tetrahydrate is weighed and dissolved in 50mL of deionized water, and stirred at 70 ℃ for 20min to obtain solution A. In addition, 0.6mmol of sodium molybdate dihydrate and 2.4mmol of sodium tungstate dihydrate were weighed and dissolved in 30mL of deionized water with stirring to form a homogeneous solution, which was labeled as solution B. Then, the solution B was dropwise added to the solution A, and after completion of the dropwise addition, the mixed solution was stirred for 4 hours while maintaining the temperature of 70 ℃.

5. The preparation method according to claim 2, wherein the Co-Mo-W precursor powder is placed in a muffle furnace and calcined at 500 ℃ for 3h.

6. The Mo-doped CoWO of claim 1 ₄ The application of the electrode material is characterized in that: the method is used for an electrode material of a super capacitor.