A Mo-doped CoWO4 electrode material and its preparation method and application

Abstract

The present invention provides a high-performance CoWO4 electrode material and a preparation method thereof. The CoWO4 electrode material is effectively doped with Mo, and molybdenum atoms partially replace tungsten, which destroys the coordination symmetry of the cobalt center, enhances the polarity of the cobalt active center, and effectively improves the electrochemical activity of the CoWO4 electrode material. When used in SC electrodes, the electrochemical performance of CoWO4 is effectively improved, for example, the discharge capacity is increased by more than 1.6 times.

Description

Technical Field

[0001] The invention belongs to the technical field of material synthesis and relates to a method for preparing a Mo-doped CoWO4 material. Background Art

[0002] Supercapacitors (SCs) are attracting significant attention worldwide as efficient, sustainable, and high-performance electrochemical energy storage and power delivery devices due to their high power density, fast charging capability, long lifespan, excellent safety, and environmental friendliness. However, their low specific capacitance and narrow operating voltage window restrict their widespread application in high-energy-density devices. Assembling asymmetric supercapacitors using battery-type cathodes and carbon-based anode materials is a highly effective approach to enhance the operating voltage window and specific capacitance, thereby increasing energy density for practical applications as energy storage devices. Despite extensive research in the field of supercapacitors, ample room remains for further improvement of the electrochemical performance of supercapacitors. In this context, many reported supercapacitors exhibit low energy density, poor rate performance, and poor cycling stability due to inappropriate structural design of electrode materials. Furthermore, there is a trade-off between energy and power density. The most challenging task is to prepare high-performance pseudocapacitive electrode materials that can enhance the energy density of supercapacitors without compromising other electrochemical properties (cycle life).

[0003] Transition metal oxides and their derivatives, usually based on oxides of Mn, Co, Ni, Mn, W, Fe, Zn, etc., are very worthy candidates for energy storage applications due to their abundant earth properties, environmental friendliness, low cost effectiveness and rich redox chemistry. CoWO4 is a bimetallic oxide containing tungsten metal ions, which has obvious characteristics in energy storage technology. 2+ / Co 3+ The redox couple is responsible for charge storage while the W atom is responsible for transfer 10 -7 -10 -2 Scm -2 However, the inherent properties of CoWO4, such as poor conductivity and agglomeration of nanoparticles, have hindered the development of its electrochemical applications. Therefore, it is necessary to develop a simple and sustainable method to improve the electrochemical performance of CoWO4 electrode materials.

[0004] The introduction of heteroatoms via coprecipitation is the best and simplest method for modifying the surface electronic state of electrode materials and thereby improving their electrochemical performance. Among the various heteroatoms, Mo is considered particularly promising for enhancing the electrochemical properties of electrode materials by modifying their conductivity, wettability, and reactivity with electrolyte ions.

[0005] For example, CN202111397586.6 utilizes the high valence characteristics of Mo to inhibit the dissolution of Mn, thereby improving the cycle performance of MnO2, and further improving the overall electrochemical performance of manganese-based zinc ion batteries. CN202011495200.0 dopes Mo into the NiCo2O4 lattice to partially replace Co 3+ , doped into the NiCo2O4 lattice to form a trimetallic oxide, which not only makes the chemical element composition of the material complex, but also because of the multiple oxidation states of Mo, the ion composition of the doped material is more complex, forming abundant defect sites. At the same time, Ni, Co, and Mo work synergistically, so that the material doped with Mo in NiCo2O4 has excellent electrochemical properties. This is mainly due to the fact that Mo has multiple oxidation states, which makes the ion composition of the doped material more complex and forms abundant defect sites.

[0006] However, for the CoWO4 system, on the one hand, there is no dissolution problem, and those skilled in the art will not use Mo to dope CoWO4 based on the inspiration of CN202111397586.6; on the other hand, the metal valence states of CoWO4 itself are single and fixed, and it does not have the metal multi-valence properties of NiCo2O4. The various oxidation states of Mo will not contribute to CoWO4. Therefore, those skilled in the art will not use Mo to dope CoWO4 based on the inspiration of CN CN202011495200.0. Summary of the Invention

[0007] The purpose of the present invention is to provide a high-performance CoWO4 electrode material. The CoWO4 electrode material is effectively doped with Mo, and molybdenum atoms partially replace tungsten, which will destroy the coordination symmetry of the cobalt center, enhance the polarity of the cobalt active center, and effectively improve the electrochemical activity of the CoWO4 electrode material.

[0008] In the present invention, effective doping of Mo means that a MoO6 octahedron replaces a WO6 octahedron ligand connected to Co, thereby destroying the symmetry of CoWO4.

[0009] The present invention also provides a method for preparing the above-mentioned Mo-doped CoWO4 electrode material. The method first uses a coprecipitation method to obtain a Co-Mo-W precursor powder; and calcining the Co-Mo-W precursor powder at 450-550°C for 3-5h to obtain the Mo-doped CoWO4 electrode material.

[0010] In order to ensure sufficient eccentric doping, cobalt acetate, sodium molybdate, and sodium tungstate should be mixed in a molar ratio of 10:1-3:9-7.

[0011] In certain embodiments of the present invention, the following protocol was employed: 3 mmol of cobalt acetate tetrahydrate was weighed and dissolved in 50 mL of deionized water, stirred at 70°C for 20 minutes, and labeled as Solution A. Additionally, 0.6 mmol of sodium molybdate dihydrate and 2.4 mmol of sodium tungstate dihydrate were weighed and dissolved in 30 mL of deionized water, stirred, and dissolved to form a homogeneous solution, labeled as Solution B. Solution B was then added dropwise to Solution A. Upon completion of the addition, the mixed solution was stirred at 70°C for 4 hours.

[0012] In certain embodiments of the present invention, the Co—Mo—W precursor powder is placed in a muffle furnace and calcined at 500° C. for 3 h.

[0013] The present invention also provides an application of the Mo-doped CoWO4 electrode material, which is used as an electrode material for a supercapacitor.

[0014] All reagents used in this experiment were of analytical grade and commercially available.

[0015] The beneficial effects of the present invention are:

[0016] (1) The present invention is based on the fact that W and Mo have different d electron structures and electronegativity. The replacement of W by Mo achieves a more controllable electronic structure. The partial replacement of tungsten by molybdenum atoms will destroy the coordination symmetry of the cobalt center, enhance the polarity of the cobalt active center, and effectively improve the electrochemical performance of CoWO4. For example, the discharge capacity is increased by more than 1.6 times.

[0017] Therefore, the present invention provides a rational strategy for enhancing pseudocapacitive reactions. In particular, breaking the coordination symmetry through heteroatom substitution provides an innovative and feasible approach to further modulate the electronic structure of pseudocapacitive active centers.

[0018] (2) The present invention designs and synthesizes a Mo-doped CoWO4 with a particle stacking structure by a simple method and at a low cost. The synthesized material has a distinct particle structure and good morphology, is suitable as an electrode material for supercapacitors, and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 SEM images of CoWO4 samples in Example (a) and CoWO4 samples with different Mo doping ratios (10%-b, 20%-c, 30%-d);

[0020] Figure 2The following are XRD patterns of CoWO4 samples in Example 1 and CoWO4 samples with different Mo doping ratios (10%, 20%, and 30%); wherein the Mo doping ratio of 10% is marked as Mo-CoWO4-1; the Mo doping ratio of 20% is marked as Mo-CoWO4-2; and the Mo doping ratio of 30% is marked as Mo-CoWO4-3;

[0021] Figure 3 EELS images of CoWO4 in Example 1 and CoWO4 samples with different Mo doping ratios (10%, 20%, 30%) are shown; among them, the Mo doping ratio of 10% is marked as Mo-CoWO4-1; the Mo doping ratio of 20% is marked as Mo-CoWO4-2; and the Mo doping ratio of 30% is marked as Mo-CoWO4-3.

[0022] Figure 4 At 10mVs -1 Cyclic voltammetry (CV) curves of CW and MCW-1 / -2 / -3 electrodes at a scan rate of 100 nm. CoWO4 is represented by CW, and the Mo doping ratio of 10% is marked as MCW-1; the Mo doping ratio of 20% is marked as MCW-2; and the Mo doping ratio of 30% is marked as MCW-3.

[0023] Figure 5 At a current density of 1 A g -1 Galvanostatic charge-discharge (GCD) curves of CW and MCW-1 / -2 / -3 electrodes. CoWO4 is represented by CW, and the Mo doping ratio of 10% is marked as MCW-1; the Mo doping ratio of 20% is marked as MCW-2; and the Mo doping ratio of 30% is marked as MCW-3. DETAILED DESCRIPTION

[0024] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0025] Example 1

[0026] (1) The Co-Mo-W precursor was prepared by coprecipitation. First, 3 mmol of cobalt acetate tetrahydrate was weighed and dissolved in 50 mL of deionized water, stirred at 70 ° C for 20 min, and marked as solution A. In addition, 0.3 mmol of sodium molybdate dihydrate and 2.7 mmol of sodium tungstate dihydrate were weighed and dissolved in 30 mL of deionized water and stirred to form a uniform solution, marked as solution B. Then, solution B was added dropwise to solution A. After the addition was completed, the mixed solution was kept at 70 ° C and stirred for 4 hours. After the stirring was completed, the mixture was centrifuged and washed to obtain a Co-Mo-W precursor powder.

[0027] (2) A certain amount of Co-Mo-W precursor powder was placed in a muffle furnace and calcined at 500°C for 3 h. The sample was then taken out for collection.

[0028] Example 2

[0029] (1) The Co-Mo-W precursor was prepared by coprecipitation. First, 3 mmol of cobalt acetate tetrahydrate was weighed and dissolved in 50 mL of deionized water, stirred at 70 ° C for 20 min, and marked as solution A. In addition, 0.9 mmol of sodium molybdate dihydrate and 2.1 mmol of sodium tungstate dihydrate were weighed and dissolved in 30 mL of deionized water and stirred to form a uniform solution, marked as solution B. Then, solution B was added dropwise to solution A. After the addition was completed, the mixed solution was kept at 70 ° C and stirred for 4 h. After the stirring was completed, it was washed clean to obtain the Co-Mo-W precursor.

[0030] (2) A certain amount of Co-Mo-W precursor was placed in a muffle furnace and calcined at 500°C for 3 h. Then, the sample was taken out and collected.

[0031] Example 3

[0032] (1) The Co-Mo-W precursor was prepared by coprecipitation. First, 3 mmol of cobalt acetate tetrahydrate was weighed and dissolved in 50 mL of deionized water, stirred at 30 ° C for 20 min, and marked as solution A. In addition, 0.6 mmol of sodium molybdate dihydrate and 2.4 mmol of sodium tungstate dihydrate were weighed and dissolved in 30 mL of deionized water and stirred to form a uniform solution, marked as solution B. Then, solution B was added dropwise to solution A. After the addition was completed, the mixed solution was kept at 70 ° C and stirred for 4 h. After the stirring was completed, it was washed clean to obtain the Co-Mo-W precursor.

[0033] (2) A certain amount of Co-Mo-W precursor was placed in a muffle furnace and calcined at 500°C for 3 h. Then, the sample was taken out and collected.

[0034] In the above examples, Mo was doped at 10% (Example 1), 20% (Example 3), and 30% (Example 2), and the SEM images of the products showed that Figure 1 As can be seen from the figure, MCW-2 nanoparticles are uniformly and densely aggregated to form nanoparticle clusters. It is worth noting that the comparison between the original CoWO4 and Mo-substituted CoWO4 clearly shows that the morphology of MCW-2 inherits the nanoparticle morphology of the former very well.

[0035] Figure 2Figure 2 shows the XRD patterns of CoWO4 and samples of CoWO4 with different Mo doping ratios (10%, 20%, and 30%) from the above examples. As can be seen from the figure, all XRD patterns can be well assigned to the monoclinic phase of CoWO4 (JCPDS No. 15-0867), indicating that Mo substitution does not induce a phase transition and no additional phases are detected. However, compared with the original CoWO4 and Mo-substituted samples, the latter exhibits broadened and weakened diffraction peaks, which is associated with induced grain refinement.

[0036] Figure 3 The EELS images of CoWO4 and CoWO4 samples with different Mo doping ratios (10%, 20%, 30%) in the above examples verify the regulatory effect of Mo substitution in CoWO4 and use EELS to study the electron transfer of CoWO4 after Mo substitution. Figure 3 It can be seen that the EELS Co L of the CW to MCW-3 sample 2,3 -Edge changes. Here, Co L 2,3 The L-edge is attributed to the transition from 2p states to highly localized 3d states closer to the Fermi level. As observed, for the CW sample, the Co L3 edge maintains a well-defined peak on the lower energy loss side. However, with increasing Mo substitution, the low-energy loss characteristics change significantly: a significant shift toward higher energy losses is observed at the Co L3 edge, indicating an increase in the polarity of the cobalt active center. This implies that one of the WO6 octahedral ligands attached to the Co phase is effectively replaced by a MoO6 octahedron, resulting in symmetry breaking in the crystal structure. In addition to this chemical shift, the valence state of the transition metal can also be further confirmed using the white line intensity ratio (L3 / L2). According to some previous reports, L3 / L2 represents the valence state of the metal: a decrease in the Co ion ratio indicates an increase in the oxidation state. The Co L-edge spectra show a decrease in the intensity ratio of the Co L3 / L2 features from the CW to the MCW-3 samples. This intensity ratio decays with increasing Mo substitution, confirming the increased polarity of the cobalt active center.

[0037] Example 4

[0038] (1) The Co-Mo-W precursor was prepared by coprecipitation. First, 3 mmol of cobalt acetate tetrahydrate was weighed and dissolved in 100 mL of deionized water, and stirred at 100 ° C for 30 min, which was marked as solution A. In addition, 0.6 mmol of sodium molybdate dihydrate and 2.7 mmol of sodium tungstate dihydrate were weighed and dissolved in 30 mL of deionized water and stirred to form a uniform solution, which was marked as solution B. Then, solution B was added dropwise to solution A. After the addition was completed, the mixed solution was kept at 100 ° C and stirred for 5 h. After stirring, it was washed clean to obtain the Co-Mo-W precursor.

[0039] (2) A certain amount of Co-Mo-W precursor was placed in a muffle furnace and calcined at 550°C for 5 h. The sample was then taken out and collected.

[0040] In this example, the products of Examples 1-3 were stirred into slurries and then evenly applied to nickel foam 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. Figure 4 Depicted at 10mV s -1 Cyclic voltammetry (CV) curves of CW and MCW-1 / -2 / -3 electrodes at a scan rate of 100 nm. It is noteworthy that all electrodes show one reduction peak and two oxidation peaks in the CV curves, indicating that charge storage is a typical battery-type reaction. As observed, MCW-1 / -2 / -3 exhibits a larger closed CV curve area than CW, indicating that the MCW-1 / -2 / -3 electrodes have excellent electrochemical reaction activity; especially the MCW-2 electrode is more significant. Obviously, it can be seen that the redox peak shifts positively with the increase of Mo substitution. This oxidation peak shift can be attributed to the change in the filling anti-bonding state of the cobalt-oxygen bond caused by the inductive effect associated with Mo substitution.

[0041] Figure 5 The discharge current density is 1A g -1 Galvanostatic charge-discharge (GCD) curves of CW and MCW-1 / -2 / -3 electrodes are shown. MCW-1 / -2 / -3 exhibit significantly longer discharge times than CW electrodes. Among these electrodes, MCW-2 exhibits the longest discharge time and the highest specific capacitance.

[0042] This charge-discharge comparison shows that Mo substitution effectively promotes the OH - ion adsorption. Based on the specific role of Mo in CoWO4 at different substitution levels, it is revealed that the introduction of Mo breaks the original crystal structure symmetry, thereby activating electron transfer between transition metals and inducing high-valent Co to serve as electrochemically active sites. As expected, the electrochemical performance of Mo-substituted CoWO4 is superior to that of the original CoWO4, thus demonstrating the improved electrochemical performance after Mo doping.

[0043] Example 5

[0044] (1) The Co-Mo-W precursor was prepared by coprecipitation. First, 3 mmol of cobalt acetate tetrahydrate was weighed and dissolved in 100 mL of deionized water, and stirred at 70 ° C for 40 min, which was marked as solution A. In addition, 0.3 mmol of sodium molybdate dihydrate and 2.1 mmol of sodium tungstate dihydrate were weighed and dissolved in 30 mL of deionized water and stirred to form a uniform solution, which was marked as solution B. Then, solution B was added dropwise to solution A. After the addition was completed, the mixed solution was kept at 70 ° C and stirred for 3 h. After stirring, it was washed clean to obtain the Co-Mo-W precursor.

[0045] (2) A certain amount of Co-Mo-W precursor was placed in a muffle furnace and calcined at 450°C for 3 h. The sample was then taken out and collected.

[0046] The electrochemical performance test was carried out with reference to Example 4, and the discharge capacity was measured to be 1.62 times higher than that of CoWO4.

[0047] Example 6

[0048] (1) The Co-Mo-W precursor was prepared by coprecipitation. First, 3 mmol of cobalt acetate tetrahydrate was weighed and dissolved in 100 mL of deionized water, and stirred at 90 ° C for 30 min, which was marked as solution A. In addition, 0.6 mmol of sodium molybdate dihydrate and 2.7 mmol of sodium tungstate dihydrate were weighed and dissolved in 30 mL of deionized water and stirred to form a uniform solution, which was marked as solution B. Then, solution B was added dropwise to solution A. After the addition was completed, the mixed solution was kept at 90 ° C and stirred for 4 h. After stirring, it was washed clean to obtain the Co-Mo-W precursor.

[0049] (2) A certain amount of Co-Mo-W precursor was placed in a muffle furnace and calcined at 480°C for 5 h. The sample was then taken out and collected.

[0050] The electrochemical performance test was carried out with reference to Example 4, and the discharge capacity was measured to be 1.66 times higher than that of CoWO4.

[0051] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a Mo-doped CoWO4 electrode material, characterized in that: The method is: A mixed solution of sodium molybdate and sodium tungstate is added dropwise to a cobalt acetate solution, stirred at 70-100°C for 3-5 hours, and then centrifuged and washed to obtain a Co-Mo-W precursor powder; the Co-Mo-W precursor powder is calcined at 450-550°C for 3-5 hours to obtain a Mo-doped CoWO4 electrode material; in the Mo-doped CoWO4 electrode material, a MoO6 octahedron replaces a WO6 octahedral ligand connected to Co, destroying the symmetry of CoWO4; cobalt acetate, sodium molybdate, and sodium tungstate are mixed in a molar ratio of 10:1-3:7-9.

2. The preparation method according to claim 1, characterized in that Weigh 3 mmol of cobalt acetate tetrahydrate and dissolve it in 50 mL of deionized water, stir it at 70°C for 20 min, and mark it as solution A. In addition, weigh 0.6 mmol of sodium molybdate dihydrate and 2.4 mmol of sodium tungstate dihydrate and dissolve them in 30 mL of deionized water, stir and dissolve them into a uniform solution, and mark it as solution B. Then, solution B is added dropwise to solution A. After the addition is completed, the mixed solution is stirred at 70°C for 4 h.

3. The preparation method according to claim 1, characterized in that The Co-Mo-W precursor powder was placed in a muffle furnace and calcined at 500 °C for 3 h.

4. Mo-doped CoWO4 electrode material prepared by the method according to claim 1.

5. The use of the Mo-doped CoWO4 electrode material as claimed in claim 4, characterized in that: It is used as an electrode material for supercapacitors.

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