A method for preparing a cobalt tungstate electrode based on gas phase replacement, electrode and use
By preparing cobalt tungstate electrodes on conductive substrates via gas-phase displacement, the problems of morphological controllability and weak binding force of CoWO4 electrocatalysts were solved, forming a multi-level nanostructure, which improved electrocatalytic activity and electrode stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2026-05-26
- Publication Date
- 2026-06-23
AI Technical Summary
Existing CoWO4 electrocatalysts suffer from poor morphology controllability, weak binding force, and simple structure during preparation, which limits their electrode cycle life and electrocatalytic activity.
Cobalt tungstate electrodes were fabricated on a conductive substrate using a gas-phase displacement method. By reacting at the solid-gas interface, a multi-level nanostructure was formed, which combined with a tightly packed cobalt tungstate nanoarray, preventing structural collapse and increasing active sites.
A multi-level structure with high specific surface area was achieved, which improved the electrocatalytic activity and electrode cycle life, and showed good electrochemical performance and stability.
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Figure CN122257015A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrocatalytic material preparation technology. Specifically, it relates to a method for preparing a cobalt tungstate (CoWO4) multi-level nanosheet array electrode with a multi-level structure grown in situ on a conductive substrate, and the application of the electrode in alkaline medium electrocatalytic oxygen evolution (OER). Background Technology
[0002] CoWO4, as a transition metal tungstate, exhibits good chemical stability and electrochemical catalytic activity under alkaline conditions, and has broad application prospects in fields such as hydrogen production through water electrolysis and fuel cells. Traditional CoWO4 electrocatalysts are mainly prepared by hydrothermal methods, co-precipitation methods, or sol-gel methods. However, existing liquid-phase synthesis methods have the following limitations: (1) Poor morphology controllability: The crystal growth rate in liquid-phase reactions is relatively fast, which easily leads to severe agglomeration, resulting in the active sites being encapsulated and unable to be fully exposed. (2) Weak bonding force: The catalyst layer obtained by physical coating or in-situ liquid-phase growth is prone to detaching from the conductive substrate under long-term high-current operation, affecting the cycle life of the electrode. (3) Simple structure: It is difficult to further construct a multi-level rough structure that can enhance mass transfer and electrochemical area while maintaining the original high specific surface area morphology of the precursor. Therefore, developing a CoWO4 electrode preparation process that can maintain a high specific surface area morphology, has a multi-level structure, and is firmly bonded to the substrate is of great practical significance for improving the efficiency of water electrolysis. Summary of the Invention
[0003] To address the technical challenges in the preparation of traditional CoWO4 electrocatalysts, this invention provides a method for preparing cobalt tungstate electrodes based on gas-phase displacement, the resulting electrode, and its applications. The preparation method of this invention is simple, highly controllable, and the prepared electrode perfectly inherits the array structure of the precursor and forms a unique multi-level rough surface, significantly enhancing electrocatalytic activity.
[0004] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:
[0005] According to one aspect of the present invention, a method for preparing a cobalt tungstate electrode based on gas-phase displacement is provided, comprising:
[0006] S1. A tungsten source precursor solution is deposited on the surface of a conductive substrate, and a WO3 seed layer is formed after drying and heat treatment.
[0007] S2. The conductive substrate with the WO3 seed layer obtained in S1 is placed in a hydrothermal reaction solution containing tungstate to carry out a hydrothermal reaction. After cleaning and drying, it is annealed to obtain a WO3 nanosheet array on the conductive substrate.
[0008] S3. The conductive substrate with WO3 nanosheet arrays obtained in S2 is subjected to a gas-phase cation exchange reaction with a volatile cobalt source under a protective atmosphere and negative pressure to obtain a cobalt tungstate multi-level nanostructure electrode. In the gas-phase cation exchange reaction, the volatile cobalt source is placed upstream of the gas flow, and the conductive substrate with WO3 nanosheet arrays is placed downstream of the gas flow. The reaction temperature is 450 ~ 600 ℃.
[0009] Preferably, in S1, the tungsten source precursor solution is a solution formed by dissolving tungsten hexachloride (WCl6) in N,N-dimethylformamide (DMF).
[0010] Preferably, in step S1, the heat treatment temperature is 450~550 ℃ and the time is 1~2 hours.
[0011] Preferably, in S2, the hydrothermal reaction solution includes sodium tungstate (Na2WO4), hydrochloric acid (HCl), and ammonium acetate (CH3COONH4).
[0012] Preferably, in S2, the temperature of the hydrothermal reaction is 100~140 ℃, and the reaction time is 8~16 hours.
[0013] Preferably, in S2, the annealing process is carried out in an air atmosphere at a temperature of 400-550°C for 1-2 hours.
[0014] Preferably, in S3, the volatile cobalt source is anhydrous cobalt chloride (CoCl2).
[0015] Preferably, in S3, the protective atmosphere is nitrogen or argon.
[0016] Preferably, in S3, the air pressure range of the negative pressure condition is 0.5 ~ 2 Torr.
[0017] Preferably, in step S3, the heating rate of the gas-phase cation exchange reaction is controlled to be 5 ~ 20 °C·min. -1 .
[0018] More preferably, in S3, the reaction temperature is 550 °C.
[0019] Preferably, in S3, the heat preservation time is 10 to 60 minutes.
[0020] Preferably, in S3, the distance between the volatile cobalt source and the FTO substrate on which the WO3 nanosheet array is grown is 0 ~ 10 cm.
[0021] According to another aspect of the present invention, a cobalt tungstate electrode prepared by the above-described method for preparing a cobalt tungstate electrode based on gas phase displacement is provided, comprising an FTO substrate and a CoWO4 nanoarray grown in situ on the surface of the FTO substrate, wherein the nanoarray is a sheet-like structure and nanoparticles are distributed on the surface of the sheet-like structure.
[0022] According to another aspect of the present invention, the above-described cobalt tungstate electrode is provided for use in the electrocatalytic water splitting oxygen evolution reaction (OER).
[0023] The beneficial effects of this invention are:
[0024] (i) The present invention adopts the gas phase displacement method, the reaction process is carried out at the solid-gas interface, the electrode does not require a binder, and can perfectly inherit the two-dimensional nanosheet array structure of the WO3 precursor, avoiding structural collapse; at the same time, during the exchange process, due to the change of lattice volume, a large number of fine nanoparticles are generated in situ on the surface of the nanosheet, forming a multi-level structure and increasing the specific surface area.
[0025] (ii) In this invention, CoWO4 nanoarrays are grown in situ on FTO substrate. The nanoarrays maintain the sheet-like structure of the precursor, and nanoparticles are distributed on the surface of the sheet-like structure. Therefore, the multi-level structure constructed by this invention effectively exposes more active sites and accelerates the charge transfer process. Experimental results show that in 1 M KOH solution, the electrode exhibits a lower overpotential and a higher current density.
[0026] (III) The gas-phase displacement method used in this invention can achieve precise control of product composition and microstructure by adjusting temperature, pressure and time, and is suitable for large-scale preparation. Attached Figure Description
[0027] Figure 1 The image shows the SEM morphology of the WO3 nanosheet array precursor prepared in Example 1; where a is the WO3 nanosheet before hydrothermal reaction and b is the WO3 nanosheet after annealing.
[0028] Figure 2 The images show a comparison of the SEM morphology of the CoWO4 electrodes prepared in Examples 1, 3, 4, and 5; where a represents 450 ℃, b represents 500 ℃, c represents 550 ℃, and d represents 580 ℃.
[0029] Figure 3 Comparison of XRD diffraction patterns of the WO3 precursors prepared in Examples 1-4 and the CoWO4 electrode.
[0030] Figure 4The image shows a comparison of the EDS spectra of the WO3 precursor prepared in Example 1 and the CoWO4 electrode obtained after displacement at 500 °C; where a is the WO3 precursor and b is the CoWO4 electrode.
[0031] Figure 5 TEM image of the WO3 electrode prepared in Example 1.
[0032] Figure 6 Comparison of LSV polarization curves of the WO3 precursor and CoWO4 electrode prepared in Examples 1-3 in 1 M KOH solution. Detailed Implementation
[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.
[0034] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.
[0035] Example 1
[0036] This embodiment provides a cobalt tungstate hierarchical nanostructure electrode grown in situ on an FTO substrate. The specific preparation steps are as follows:
[0037] (1) Preparation of WO3 seed layer:
[0038] Cut the FTO conductive glass to a suitable size, and ultrasonically clean it sequentially in acetone, anhydrous ethanol, and deionized water for 20 minutes each, then dry it with nitrogen gas for later use. Weigh 2 g of tungsten hexachloride (WCl6) and dissolve it in 10 mL of N,N-dimethylformamide, stirring until homogeneous to prepare a transparent tungsten precursor solution.
[0039] The tungsten precursor solution prepared above was dropped onto a clean FTO substrate and spin-coated using a spin coater at 3000 rpm for 30 s. After spin-coating, the FTO substrate was placed in a muffle furnace and annealed at 500 °C for 1 hour in air. After natural cooling, a tightly bonded WO3 seed layer was formed on the surface of the FTO substrate.
[0040] (2) Growth of WO3 nanosheet array:
[0041] Preparation of hydrothermal reaction precursor solution: Weigh 0.25 g sodium tungstate (Na2WO4·2H2O) and dissolve it in 100 mL deionized water. Add 8 mL hydrochloric acid (3 M HCl), followed by 0.2 g ammonium acetate (CH3COONH4) as a structure directing agent. Stir for 30 minutes until the solution is clear.
[0042] The FTO substrate treated in step (1) was placed tilted in a polytetrafluoroethylene liner, and the prepared hydrothermal reaction precursor solution was poured in. The mixture was then sealed in a stainless steel reactor. The reactor was placed in an oven and kept at 120°C for 12 hours. After the reaction, the sample was removed, rinsed repeatedly with deionized water and ethanol, and dried at 60°C. Subsequently, the sample was placed in a muffle furnace and annealed at 500°C at a rate of 10°C / min in air atmosphere for 1 hour. After natural cooling, a well-crystallized WO3 nanosheet array was obtained.
[0043] (3) Preparation of CoWO4 hierarchical structure by gas-phase cation exchange:
[0044] Gas-phase replacement was performed using a dual-temperature zone or single-temperature zone tube furnace capable of negative pressure extraction. Sample loading: 0.5 g of anhydrous cobalt chloride (CoCl2) powder was weighed and placed in a ceramic boat A, positioned upstream of the gas flow direction in the tube furnace; the WO3 nanosheet array sample obtained in step (2) was placed in a ceramic boat B, positioned downstream of the gas flow direction. The center-to-center distance between the two ceramic boats was adjusted to 5 cm. Atmosphere and pressure control: The furnace tube was sealed, and the vacuum pump was started to extract the pressure inside the tube to 1 Torr. Nitrogen gas was introduced as the carrier gas at a flow rate of 30-200 sccm, and the pump was continuously evacuated to maintain the pressure inside the tube at 1 Torr during the reaction. Heat treatment: The tube furnace heating program was set at 10 ℃·min. -1 The temperature was increased to 500℃ at a controlled heating rate and held at this temperature for 30 minutes. Cooling: After the reaction was complete, heating was stopped, and the sample was allowed to cool naturally to room temperature under nitrogen protection and negative pressure. The resulting product is a cobalt tungstate hierarchical nanostructure electrode.
[0045] Example 2
[0046] This embodiment examines the displacement effect in the low-temperature range. The only difference from Example 1 is the gas-phase reaction parameters in step (3); the remaining steps remain the same. In step (3): the distance between the volatile cobalt source and the FTO substrate is set to 5 cm. The pressure inside the tube is controlled at 1 Torr. The heating rate is set to 10 °C·min. -1 The reaction temperature was set to 400℃, and the holding time was 30 min.
[0047] Result: No significant transformation to CoWO4 occurred at this temperature, and the crystal structure of WO3 was retained.
[0048] Example 3
[0049] This embodiment examines the displacement effect in the low-temperature range. The only difference from Example 1 is the gas-phase reaction parameters in step (3); the remaining steps remain the same. In step (3): the distance between the volatile cobalt source and the FTO substrate is set to 5 cm. The pressure inside the tube is controlled at 1 Torr. The heating rate is set to 10 °C·min. -1 The reaction temperature was set to 450℃, and the holding time was 30 min.
[0050] Results: At this temperature, the conversion from WO3 to CoWO4 can still be achieved, and the multi-level structure remains intact.
[0051] Example 4
[0052] This embodiment examines the displacement effect in the intermediate temperature range. The only difference from Example 1 is the gas-phase reaction parameters in step (3); the remaining steps remain the same. In step (3): the distance between the volatile cobalt source and the FTO substrate is set to 5 cm. The pressure inside the tube is controlled at 1 Torr. The heating rate is set to 10 °C·min. -1 The reaction temperature was set at 550℃, and the holding time was 30 min.
[0053] Results: At this temperature, the conversion from WO3 to CoWO4 can still be achieved, and the multi-level structure remains intact.
[0054] Example 5
[0055] This embodiment examines the displacement effect in the high-temperature range. The only difference from Example 1 is the gas-phase reaction parameters in step (3); the remaining steps remain the same. In step (3): the distance between the volatile cobalt source and the FTO substrate is set to 5 cm. The pressure inside the tube is controlled at 1 Torr. The heating rate is set to 10 °C·min. -1 The reaction temperature was set to 580℃, and the holding time was 30 min.
[0056] Results: At this temperature, the conversion from WO3 to CoWO4 can still be achieved, and the multi-level structure remains intact.
[0057] Characterization and testing
[0058] The WO3 and CoWO4 samples prepared in Example 1 were analyzed by scanning electron microscopy (SEM). Figure 1 As shown, the WO3 obtained after the hydrothermal reaction has a smooth surface and exhibits a nanosheet array structure. After annealing, the WO3 nanosheets did not undergo significant morphological changes and still maintained the nanosheet array structure.
[0059] Figure 2 The image shows SEM images of CoWO4 samples obtained at different gas-phase cation exchange temperatures. It can be observed that the samples after gas-phase exchange at different temperatures all inherited the nanosheet array structure of the precursor without structural collapse. At the same time, a large number of fine nanoparticles grew in situ on the nanosheet surface, forming a multi-level rough structure.
[0060] X-ray diffraction (XRD) analysis was performed on the WO3 and CoWO4 samples prepared in Examples 1-4. Figure 3 As shown, at 400℃, the lower substitution temperature cannot effectively achieve the conversion of WO3 to CoWO4. However, as the temperature increases, the diffraction peaks of the samples at other temperatures all match the standard card of CoWO4 well. The absence of diffraction peaks corresponding to WO3 indicates that the precursor has been completely converted into single-crystal CoWO4 with good crystallinity.
[0061] Energy dispersive spectroscopy (EDS) analysis was performed on the WO3 and CoWO4 samples prepared in Example 1. As shown in Figure 4a, the WO3 sample showed the presence of W and O elements; simultaneously... Figure 4 Figure b shows the presence of Co, W, and O elements in the CoWO4 sample, proving the successful conversion from WO3 to CoWO4.
[0062] The WO3 sample prepared in Example 1 was analyzed by transmission electron microscopy (TEM). Figure 5 As shown, the WO3 sample exhibits a crystal plane spacing of 3.84 Å, corresponding to the (002) crystal plane of WO3. The clear lattice fringes indicate that the obtained WO3 has a good crystal structure and high crystallinity.
[0063] Electrochemical performance tests were performed on the CoWO4 samples prepared in Examples 1-4 using a three-electrode system. The prepared electrode was used as the working electrode, the carbon rod as the counter electrode, and the mercury / mercury oxide electrode as the reference electrode. The electrolyte solution was a 1 mol / L NaOH aqueous solution. A KOSTER electrochemical workstation was used. The testing method was linear scan cyclic voltammetry at a scan rate of 10 mV / s. -1 .
[0064] Figure 6 The JV curves for the WO3 precursor and CoWO4 electrode samples prepared in Examples 1-3 are shown. Compared to the WO3 electrode, the CoWO4 electrode exhibits significantly higher current density and significantly lower overpotential at the same overpotential. The optimal replacement temperature for the CoWO4 electrode is 550 °C, achieving a current density of 10 mA·cm⁻¹. -2 The voltage at the current density is only 2.33 V.
[0065] In summary, this invention utilizes the characteristics of gas-phase reactions to construct a hierarchical rough morphology in situ, building upon the two-dimensional array structure of the precursor. This electrode exhibits excellent catalytic activity in the electrocatalytic oxygen evolution reaction in alkaline media, with a simple process and controllable parameters, demonstrating promising application prospects.
[0066] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many specific modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and these modifications all fall within the scope of protection of the present invention.
Claims
1. A method for preparing cobalt tungstate electrodes based on gas-phase displacement, characterized in that, include: S1. A tungsten source precursor solution is deposited on the surface of a conductive substrate, and a WO3 seed layer is formed after drying and heat treatment. S2. The conductive substrate with the WO3 seed layer obtained in S1 is placed in a hydrothermal reaction solution containing tungstate to carry out a hydrothermal reaction. After cleaning and drying, it is annealed to obtain a WO3 nanosheet array on the conductive substrate. S3. The conductive substrate with WO3 nanosheet arrays obtained in S2 is subjected to a gas-phase cation exchange reaction with a volatile cobalt source under a protective atmosphere and negative pressure to obtain a cobalt tungstate multi-level nanostructure electrode. In the gas-phase cation exchange reaction, the volatile cobalt source is placed upstream of the gas flow, and the conductive substrate with WO3 nanosheet arrays is placed downstream of the gas flow. The reaction temperature is 450 ~ 600 ℃.
2. The method for preparing cobalt tungstate electrode based on gas-phase displacement according to claim 1, characterized in that, In S1, the tungsten source precursor solution is a solution formed by dissolving tungsten hexachloride in N,N-dimethylformamide; the heat treatment temperature is 450~550 ℃ and the time is 1~2 hours.
3. The method for preparing a cobalt tungstate electrode based on gas-phase displacement according to claim 1, characterized in that, In S2, the hydrothermal reaction solution includes sodium tungstate, hydrochloric acid, and ammonium acetate; the temperature of the hydrothermal reaction is 100-140 °C, and the reaction time is 8-16 hours.
4. The method for preparing a cobalt tungstate electrode based on gas-phase displacement according to claim 1, characterized in that, In S2, the annealing process is carried out in an air atmosphere at a temperature of 400-550°C for 1-2 hours.
5. The method for preparing a cobalt tungstate electrode based on gas-phase displacement according to claim 1, characterized in that, In S3, the volatile cobalt source is anhydrous cobalt chloride; the protective atmosphere is nitrogen or argon.
6. The method for preparing a cobalt tungstate electrode based on gas-phase displacement according to claim 1, characterized in that, In S3, the air pressure range of the negative pressure condition is 0.5 ~ 2 Torr.
7. The method for preparing a cobalt tungstate electrode based on gas-phase displacement according to claim 1, characterized in that, In S3, the heating rate of the gas-phase cation exchange reaction is controlled at 5 ~ 20 ℃·min. -1 The reaction temperature is 550℃, and the holding time is 10 to 60 minutes.
8. The method for preparing a cobalt tungstate electrode based on gas-phase displacement according to claim 1, characterized in that, In S3, the distance between the volatile cobalt source and the FTO substrate on which the WO3 nanosheet array is grown is 0 ~ 10 cm.
9. A cobalt tungstate electrode obtained by the method for preparing a cobalt tungstate electrode based on gas-phase displacement as described in any one of claims 1-8, characterized in that, It includes an FTO substrate and a CoWO4 nanoarray grown in situ on the surface of the FTO substrate. The nanoarray has a sheet-like structure and nanoparticles are distributed on the surface of the sheet-like structure.
10. The application of the cobalt tungstate electrode as described in claim 9 in the electrocatalytic water splitting and oxygen evolution reaction.