Vanadium-doped cobalt selenide nanosheet array rich in selenium vacancy as well as preparation method and application of vanadium-doped cobalt selenide nanosheet array

Abstract

The invention provides a vanadium-doped cobalt selenide nanosheet array rich in selenium vacancy as well as a preparation method and application of the vanadium-doped cobalt selenide nanosheet array. The invention provides a preparation method of a vanadium-doped cobalt selenide nanosheet array rich in selenium vacancy, which comprises the following steps: dissolving cobalt salt and 2-methylimidazole in deionized water, adding foamed nickel, and reacting at room temperature to obtain ZIF-L; the method comprises the following steps: dissolving a vanadium source in deionized water, adding ZIF-L, and carrying out hydrothermal reaction to obtain CoV-ZIF; then adding the CoV-ZIF into a selenium source solution, and carrying out selenylation to obtain V-Co9Se8; and finally, soaking in a NaBH4 solution to obtain the nanosheet array. The formed nanosheet structure can provide a larger active specific surface area; the electron transfer rate can be improved through the synergistic effect of Co and V; the introduction of selenium vacancies can enhance the conductivity and active sites. Practice shows that when the Vse-V-Co9Se8 is used as the water electrolysis electrode material, the Vse-V-Co9Se8 shows low overpotential and high cycle stability.

Description

Technical Field

[0001] The present invention belongs to the cross - field of preparation methods of nanomaterials and electrochemical applications, and specifically relates to a selenium - deficient vanadium - doped Co9Se8 nanosheet array, a preparation method thereof, and an application thereof. se -V - Co9Se8 nanosheet array and its preparation method and application. Background Art

[0002] As a green and clean energy source, hydrogen energy has become an excellent substitute for traditional fossil fuels due to its compliance with national energy strategic needs, and its development has received increasing attention. Electrolysis of water is an effective way to obtain high - purity hydrogen energy. The key to improving the efficiency of electrocatalytic water decomposition reaction lies in the development of efficient and stable water - splitting electrocatalysts. Currently, noble - metal - based catalysts such as RuO2, IrO2, and Pt / C have been recognized as commercial single - function benchmark electrocatalysts for OER or HER. However, due to the limitations of noble - metal costs and reserves, industrial production is hindered. Developing bifunctional electrocatalysts with both high activity and excellent stability is the key to breaking through the industrialization bottleneck of electrolytic water technology.

[0003] Transition metal selenides such as Co9Se8 have advantages such as good electrical conductivity and rich reaction valence states, and are considered to be one of the most promising electrode materials. However, the over - potential of unmodified Co9Se8 is still not ideal enough, and it is prone to stacking and agglomeration phenomena in redox reactions, with low electrical conductivity and electrochemical performance, which greatly limits its practical applications. In recent years, studies have shown that metal element doping, defect engineering, morphology control, etc. are effective strategies to improve the performance of Co9Se8 electrode materials. Summary of the Invention

[0004] In order to solve the above - mentioned technical problems, the present invention has realized the preparation of a selenium - vacancy - rich vanadium - doped cobalt selenide nanosheet array by using a simple and low - cost preparation method. In this study, nickel foam is used as the basic framework, vanadium element is used as the doping ion, and ZIF - L is used as the precursor. A selenide is prepared by adjusting the selenization strategy and combining defect engineering. Since ZIF - L as a precursor has adjustable porosity and high specific surface area, it can provide abundant active sites; the dual - metal synergistic effect formed by vanadium ion doping accelerates the electron transfer rate; defect engineering adjusts the electronic structure and optimizes the charge transport channel. The advantages of this study are as follows: (1) Based on the ZIF - L - derived selenide, the porosity and electron transfer efficiency of the material are improved. (2) The dual - metal synergistic effect formed by vanadium metal element doping can increase the electron transfer rate, and its rich oxidation valence states can enhance the charge storage capacity of the material. (3) Defect engineering regulates the electronic structure, optimizes the charge transport channel, and improves the electrochemical activity.

[0005] The present invention provides a preparation method for a selenium - vacancy - rich vanadium - doped cobalt selenide nanosheet array, comprising the following steps:

[0006] (1) Dissolve cobalt nitrate hexahydrate and 2-methylimidazole in deionized water to obtain a reaction solution. Put the cleaned nickel foam into the reaction solution, react at room temperature for 2 h, wash with distilled water, and then dry in a blast drying oven to obtain the ZIF-L precursor;

[0007] (2) Dissolve 0.16 g of vanadium source in 40 mL of deionized water, mix and stir for 30 minutes to obtain a light yellow homogeneous reaction solution. Put the ZIF-L prepared in step (1) into the reaction solution, transfer it to a 100 mL reaction kettle, and obtain CoV-ZIF nanosheet arrays after hydrothermal reaction;

[0008] (3) Dissolve 20 mg of selenium source and 0.1 mol of hydrazine hydrate in 20 mL of deionized water, stir for 20 minutes to obtain a homogeneous transparent solution. Put the CoV-ZIF obtained in step (2) into it and carry out selenization reaction in the reaction kettle. After the reaction is completed, cool to room temperature, wash several times with absolute ethanol, and dry in a constant temperature oven at 60 °C to obtain V-Co9Se8 nanosheet arrays;

[0009] (4) Dissolve 1.25 g of NaBH4 in 20 mL of deionized water, stir until the solution is clear. Put the V-Co9Se8 prepared in step (3) into the solution, soak for a period of time in an open environment, wash and dry to obtain vanadium-doped cobalt selenide nanosheet arrays rich in selenium vacancies, simply referred to as V se -V-Co9Se8.

[0010] In step (1), the type of cobalt salt is not limited, including cobalt chloride, cobalt nitrate, cobalt acetate, etc., but cobalt nitrate hexahydrate is most preferably used;

[0011] In step (1), the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is (1-3):(7-10), but the optimal ratio is 1:4;

[0012] In step (1), the volume of deionized water used is 50-100 mL, but 80 mL is most preferably used;

[0013] In step (2), the type of vanadium source is not limited, including ammonium metavanadate, sodium metavanadate, potassium metavanadate, sodium orthovanadate, etc., or one or more of them, but sodium metavanadate is most preferably used;

[0014] In step (2), the hydrothermal reaction temperature is 100-140 °C and the time is 1-5 hours, but the reaction at 120 °C for 2 hours is most preferred;

[0015] In step (3), the type of selenium source is not limited, including sodium selenide, selenium powder, selenium dioxide, etc., or one or more of them, but selenium dioxide is most preferably used;

[0016] In step (3), the temperature of the selenization reaction is 180 - 230 °C, and the time is 6 - 10 hours, but most preferably, the reaction is carried out at 200 °C for 8 hours;

[0017] In step (4), the soaking time of NaBH4 is 50 - 100 s, but most preferably, it is soaked for 75 s at room temperature.

[0018] In summary, the vanadium-doped cobalt selenide nanosheet array rich in selenium vacancies of the present invention has the following

[0019] beneficial effects:

[0020] (1) The raw material cost for preparing V se -V-Co9Se8 is low, and the synthesis process is simple. It can be synthesized only by the room-temperature in-situ growth method, the hydrothermal method, and the room-temperature soaking method. The ZIF-L template has a high porosity and a large specific surface area, which can increase the redox reaction active sites of the derivative, shorten the ion diffusion path, and inhibit the stacking and aggregation of nanosheets; the metal synergistic effect formed by the doping of vanadium metal elements can improve the electron transfer rate, and its rich oxidation valence states can enhance the charge storage capacity of the material; the introduction of selenium vacancies can improve the conductivity and increase the number of active sites, so the improvement in overpotential and cycle stability can be achieved.

[0021] (2) The V se -V-Co9Se8 nanosheet array prepared by the present invention exhibits a low overpotential and high stability in electrochemical tests. The linear sweep voltammetry curve and the chronopotentiometry curve were measured using a CHI 760E electrochemical workstation. The scanning rate for measuring the linear sweep voltammetry curve is 2 mV s -1 . The double-layer capacitance (C dl ) of the catalyst was calculated from the voltammetric cycle test in the small potential range of the non-Faraday region at a scanning rate of 20 mV s -1 to 100 mV s -1 . To evaluate the long-term stability of the electrocatalyst, the chronopotentiometry was tested for 50 hours at a current density of 100 mA cm -2 , and the scanning rate was 1.0 mV s -1 . Under the evaluation standard of 100 mA cm -2 , the overpotentials of OER and HER are 284 mV and 246 mV respectively. A two-electrode device was assembled to test the overall water splitting performance, and only a driving voltage of 1.91 V is required to reach 100 mA cm -2 . At the same time, at 100 mA cm -2Chronopotentiometry measurements were carried out at a constant current density, and during the 100-hour test cycle, its catalytic performance did not show a significant decline and could be maintained at 94.8% of the original performance. In summary, this electrode material has excellent catalytic performance and high stability.

[0022] (3) The preparation method of the present invention is simple and effective, and the construction of the cobalt vanadium-doped selenium nanosheet array rich in selenium vacancies can be simply extended to construct other transition metal compound nanosheet arrays for electrochemical energy storage and conversion devices. Brief Description of the Drawings

[0023] Figure 1 It is the scanning electron microscope image of the ZIF-L precursor prepared in step (1) of Example 1 of the present invention;

[0024] Figure 2 It is the scanning electron microscope image of the CoV-ZIF nanosheet array prepared in step (2) of Example 1 of the present invention;

[0025] Figure 3 It is the scanning electron microscope image of the V-Co9Se8 nanosheet array prepared in step (3) of Example 1 of the present invention;

[0026] Figure 4 It is the scanning electron microscope image of the V se -V-Co9Se8 nanosheet array prepared in step (4) of Example 1 of the present invention;

[0027] Figure 5 It is the V prepared in step (4) of Example 1 of the present invention se - Electron paramagnetic resonance curve of the V-Co9Se8 nanosheet array prepared in step (4) of Example 1 of the present invention;

[0028] Figure 6 It is the V prepared in step (4) of Example 1 of the present invention se - Linear sweep voltammetry curve of the V-Co9Se8 nanosheet array prepared in step (4) of Example 1 of the present invention, the left figure is for HER and the right figure is for OER;

[0029] Figure 7 It is the V prepared in step (4) of Example 1 of the present invention se - Performance of the full hydrolysis device assembled with the V-Co9Se8 nanosheet array as the electrode material in 1M KOH electrolyte solution, the left figure is the linear sweep voltammetry curve and the right figure is the chronopotentiometry at a constant current density of 100 mA cm -2 ;

[0030] Figure 8 It is the V prepared in step (4) of Example 1 of the present invention se - Double-layer capacitance (C of the V-Co9Se8 nanosheet array as the electrode material in 1M KOH electrolyte solutiondl )。 Detailed implementation manners

[0031] The preferred embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples.

[0032] Example 1

[0033] A preparation method of vanadium-doped cobalt selenide nanosheet arrays rich in selenium vacancies, comprising the following steps:

[0034] (1) Take 0.59 g of cobalt nitrate hexahydrate and 1.32 g of 2-methylimidazole and dissolve them in 80 mL of deionized water to obtain a reaction solution. Put the cleaned nickel foam into the reaction solution, react at room temperature for 2 h, wash with absolute ethanol and distilled water, and then dry in a blast drying oven to obtain a ZIF-L precursor. Its scanning electron microscope is as Figure 1 shown, presenting a triangular nanosheet morphology with a smooth surface and a certain thickness;

[0035] (2) Dissolve 0.16 g of sodium metavanadate in 40 mL of deionized water, mix and stir for 30 minutes to obtain a light yellow homogeneous reaction solution. Put the ZIF-L precursor prepared in step (1) into the reaction solution, transfer it to a 100 mL reaction kettle, and carry out hydrothermal reaction at 120 °C for 2 hours to obtain CoV-ZIF nanosheet arrays. Its scanning electron microscope image is as Figure 2 shown, presenting a porous triangular nanosheet morphology;

[0036] (3) Dissolve 20 mg of SeO2 and 0.1 mol of hydrazine hydrate in 20 mL of deionized water, stir for 20 minutes to obtain a homogeneous transparent solution. Put the CoV-ZIF nanosheet arrays prepared in step (2) into it, carry out hydrothermal reaction at 200 °C for 8 hours in the reaction kettle. After the reaction, cool to room temperature, wash several times with absolute ethanol, and dry in a constant temperature oven at 60 °C to obtain V-Co9Se8 nanosheet arrays. Its scanning electron microscope image is as Figure 3 shown, presenting a nanosheet morphology with a rough surface;

[0037] (4) Take 1.25 g of NaBH4 and dissolve it in 20 mL of deionized water, stir until the solution is clear. Put the V-Co9Se8 prepared in step (3) into the solution, soak it in an open environment for 75 s, then wash and dry to obtain vanadium-doped cobalt selenide nanosheet arrays rich in selenium vacancies, simply referred to as V se -V-Co9Se8. Its scanning electron microscope image is as Figure 4 shown, presenting a nanosheet morphology with a rough surface;

[0038] Use the above-prepared V se -V-Co9Se8 as the electrode material for electron paramagnetic resonance spectroscopy (EPR) testing, as shown in Figure 5As shown, compared with V-Co9Se8, V se -V-Co9Se8 has a stronger resonance signal, indicating that V se -V-Co9Se8 has more selenium vacancies;

[0039] Taking the above-prepared V se -V-Co9Se8 as the electrode material for electrochemical testing, its catalytic performance was tested in a 1M KOH electrolyte solution, and the linear sweep voltammetry curve is as Figure 6 shown. The left figure is for HER and the right figure is for OER. At a current density of 100 mA cm -2 , the overpotentials of HER and OER are 246 mV and 284 mV respectively, both showing excellent electrocatalytic activity;

[0040] Taking the above-prepared V se -V-Co9Se8 as the electrode material, a full water splitting device was assembled, and its catalytic performance was tested in a 1M KOH electrolyte solution, as Figure 7 (left) shown. Only a voltage of 1.92 V is required to reach a current density of 100 mA cm -2 , showing excellent catalytic performance in overall water splitting; Chronopotentiometry was carried out at a constant current density of 100 mA cm -2 , as Figure 7 (right) shown. During the 100-hour test cycle, its catalytic performance did not show an obvious decline and could remain at 94.8% of the original performance, with high stability;

[0041] Taking the materials prepared in the above steps as the electrode materials, their double-layer capacitance (C dl ) at different current densities was tested in a 1M KOH electrolyte solution, as Figure 8 shown. V se -V-Co9Se8 has the largest C dl value, indicating that V se -V-Co9Se8 has a larger electrochemically active surface area.

[0042] Example 2

[0043] (1) 1.18 g of cobalt nitrate hexahydrate and 1.32 g of 2-methylimidazole were dissolved in 80 mL of deionized water to obtain a reaction solution. The cleaned nickel foam was put into the reaction solution, reacted at room temperature for 2 h, washed with absolute ethanol and distilled water, and then dried in a blast drying oven to obtain the ZIF-L precursor;

[0044] (2) Dissolve 0.16 g of sodium metavanadate in 40 mL of deionized water, mix and stir for 30 minutes to obtain a light yellow homogeneous reaction solution. Put the ZIF-L precursor prepared in step (1) into the reaction solution, transfer it to a 100 mL autoclave, and perform a hydrothermal reaction at 120 °C for 2 hours to obtain a CoV-ZIF nanosheet array;

[0045] (3) Dissolve 20 mg of SeO2 and 0.1 mol of hydrazine hydrate in 20 mL of deionized water, stir for 20 minutes to obtain a homogeneous transparent solution. Put the CoV-ZIF nanosheet array prepared in step (2) into it, and perform a hydrothermal reaction at 200 °C in the autoclave for 8 hours. After the reaction is completed, cool it to room temperature, wash it several times with absolute ethanol, and dry it in a constant temperature oven at 60 °C to obtain a V-Co9Se8 nanosheet array;

[0046] (4) Dissolve 1.25 g of NaBH4 in 20 mL of deionized water, stir until the solution is clear. Put the V-Co9Se8 prepared in step (3) into the solution, soak it in an open environment for 75 s, then wash and dry it to obtain a vanadium-doped cobalt selenide nanosheet array rich in selenium vacancies, abbreviated as V se -V-Co9Se8.

[0047] Take the prepared V se -V-Co9Se8 nanosheet array as the electrode material for overall water splitting, and test its cyclic voltammetry curve at a current density of 100 mA cm -2 in a 1 M KOH electrolyte solution. The overpotentials of HER and OER of this electrode material are 255 mV and 292 mV respectively.

[0048] Example 3

[0049] (1) Take 0.59 g of cobalt nitrate hexahydrate and 1.32 g of 2-methylimidazole and dissolve them in 80 mL of deionized water to obtain a reaction solution. Put the cleaned nickel foam into the reaction solution, react at room temperature for 2 h, wash it with absolute ethanol and distilled water, and then dry it in a blast drying oven to obtain a ZIF-L precursor;

[0050] (2) Dissolve 0.16 g of sodium metavanadate in 40 mL of deionized water, mix and stir for 30 minutes to obtain a light yellow homogeneous reaction solution. Put the ZIF-L precursor prepared in step (1) into the reaction solution, transfer it to a 100 mL autoclave, and perform a hydrothermal reaction at 100 °C for 2 hours to obtain a CoV-ZIF nanosheet array;

[0051] (3) Dissolve 20 mg of SeO2 and 0.1 mol of hydrazine hydrate in 20 mL of deionized water, stir for 20 minutes to obtain a homogeneous transparent solution, put the CoV-ZIF nanosheet array prepared in step (2) into it, and carry out a hydrothermal reaction at 200 °C for 8 hours in a reaction kettle. After the reaction is completed, cool it to room temperature, wash it several times with absolute ethanol, and dry it in a constant temperature oven at 60 °C to obtain a V-Co9Se8 nanosheet array;

[0052] (4) Dissolve 1.25 g of NaBH4 in 20 mL of deionized water, stir until the solution is clear, put the V-Co9Se8 prepared in step (3) into the solution, soak it in an open environment for 75 s, then wash and dry it to obtain a vanadium-doped cobalt selenide nanosheet array rich in selenium vacancies, abbreviated as V se -V-Co9Se8.

[0053] Take the prepared V se -V-Co9Se8 nanosheet array as the electrode material for overall water splitting, and test its cyclic voltammetry curve at a current density of 100 mA cm -2 in a 1 M KOH electrolyte solution. The overpotentials of HER and OER for this electrode material are 252 mV and 296 mV respectively.

[0054] Example 4

[0055] (1) Take 0.59 g of cobalt nitrate hexahydrate and 1.32 g of 2-methylimidazole and dissolve them in 80 mL of deionized water to obtain a reaction solution. Put the cleaned nickel foam into the reaction solution, react at room temperature for 2 h, wash it with absolute ethanol and distilled water, and then dry it in a blast drying oven to obtain a ZIF-L precursor;

[0056] (2) Dissolve 0.16 g of sodium metavanadate in 40 mL of deionized water, mix and stir for 30 minutes to obtain a light yellow homogeneous reaction solution. Put the ZIF-L precursor prepared in step (1) into the reaction solution, transfer it to a 100 mL reaction kettle, and carry out a hydrothermal reaction at 120 °C for 2 hours to obtain a CoV-ZIF nanosheet array;

[0057] (3) Dissolve 20 mg of SeO2 and 0.1 mol of hydrazine hydrate in 20 mL of deionized water, stir for 20 minutes to obtain a homogeneous transparent solution, put the CoV-ZIF nanosheet array prepared in step (2) into it, and carry out a hydrothermal reaction at 180 °C for 8 hours in a reaction kettle. After the reaction is completed, cool it to room temperature, wash it several times with absolute ethanol, and dry it in a constant temperature oven at 60 °C to obtain a V-Co9Se8 nanosheet array;

[0058] (4) Dissolve 1.25 g of NaBH4 in 20 mL of deionized water, stir until the solution is clear, put the V-Co9Se8 prepared in step (3) into the solution, soak it for 75 s in an open environment, wash and dry it to obtain a vanadium-doped cobalt selenide nanosheet array rich in selenium vacancies, simply referred to as V se -V-Co9Se8.

[0059] Take the prepared V se -V-Co9Se8 nanosheet array as the electrode material for overall water splitting, and test its cyclic voltammetry curve at a current density of 100 mA cm -2 in a 1 M KOH electrolyte solution. The overpotentials of HER and OER for this electrode material are 259 mV and 303 mV respectively.

[0060] Example 5

[0061] (1) Take 0.59 g of cobalt nitrate hexahydrate and 1.32 g of 2-methylimidazole and dissolve them in 80 mL of deionized water to obtain a reaction solution. Put the cleaned nickel foam into the reaction solution, react at room temperature for 2 h, wash it with absolute ethanol and distilled water, and then dry it in a blast drying oven to obtain a ZIF-L precursor;

[0062] (2) Dissolve 0.16 g of sodium metavanadate in 40 mL of deionized water, mix and stir for 30 minutes to obtain a light yellow homogeneous reaction solution. Put the ZIF-L precursor prepared in step (1) into the reaction solution, transfer it to a 100 mL reaction kettle, and carry out a hydrothermal reaction at 120 °C for 2 hours to obtain a CoV-ZIF nanosheet array;

[0063] (3) Dissolve 20 mg of SeO2 and 0.1 mol of hydrazine hydrate in 20 mL of deionized water, stir for 20 minutes to obtain a homogeneous transparent solution. Put the CoV-ZIF nanosheet array prepared in step (2) into it, carry out a hydrothermal reaction at 180 °C for 8 hours in a reaction kettle. After the reaction, cool it to room temperature, wash it several times with absolute ethanol, and dry it in a constant temperature oven at 60 °C to obtain a V-Co9Se8 nanosheet array;

[0064] (4) Dissolve 1.25 g of NaBH4 in 20 mL of deionized water, stir until the solution is clear, put the V-Co9Se8 prepared in step (3) into the solution, soak it for 90 s in an open environment, wash and dry it to obtain a vanadium-doped cobalt selenide nanosheet array rich in selenium vacancies, simply referred to as V se -V-Co9Se8.

[0065] Take the prepared V se -V-Co9Se8 nanosheet array as the electrode material for overall water splitting, and test its 100 mAcm-2 The cyclic voltammetry curve under current density. For this electrode material, the overpotentials of HER and OER are 250 mV and 305 mV respectively.

[0066] The embodiments described above are detailed descriptions of the technical solutions of the present invention. It should be understood that the specific implementation measures of the present invention do not generalize the present invention. Any modifications, supplements, or substitutions in a similar manner within the scope of the principles of the present invention all fall within the scope of protection that the present invention should enjoy.

Claims

1. A vanadium-doped cobalt selenide nanosheet array rich in selenium vacancies, characterized in that, The preparation method includes the following steps: (1) Dissolve 0.59 g of cobalt nitrate hexahydrate and 1.32 g of 2-methylimidazole in 80 mL of deionized water to obtain a reaction solution. Put the cleaned nickel foam into the reaction solution, react at room temperature for 2 h, wash with distilled water, and then dry in a blast drying oven to obtain a ZIF-L precursor; (2) Dissolve 0.16 g of sodium metavanadate in 40 mL of deionized water, mix and stir for 30 minutes to obtain a light yellow homogeneous reaction solution. Put the ZIF-L precursor prepared in step (1) into the reaction solution, and transfer it to a 100 mL autoclave, and carry out hydrothermal reaction at 120 °C for 2 hours to obtain a CoV-ZIF nanosheet array; (3) Dissolve 20 mg of SeO2 and 0.1 mol of hydrazine hydrate in 20 mL of deionized water, stir for 20 minutes to obtain a homogeneous transparent solution. Put the CoV-ZIF nanosheet array prepared in step (2) into it, carry out hydrothermal reaction at 200 °C for 8 hours in an autoclave. After the reaction is completed, cool to room temperature, wash several times with absolute ethanol, and dry in a constant temperature oven at 60 °C to obtain a V-Co9Se8 nanosheet array; (4) Dissolve 1.25 g of NaBH4 in 20 mL of deionized water and stir until the solution becomes clear. Put the V-Co9Se8 prepared in step (3) into the solution, soak it in an open environment for 75 s, then wash and dry it to obtain a vanadium-doped cobalt selenide nanosheet array rich in selenium vacancies, simply referred to as V se -V-Co9Se8.

2. Use of the selenium vacancy-rich vanadium-doped cobalt selenide nanosheet array prepared by the preparation method according to claim 1 as an electrolytic water electrode material.

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