Ni-doped nanoflower structure Ni-V2O5@NC, and preparation method and application thereof

Abstract

Ni-doped nano-flower structure Ni-V2O5@NC and a preparation method and application thereof belong to the technical field of water electrolysis oxygen production, and the specific steps are as follows: ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate are sequentially added into deionized water, stirred until dissolved, and nano-flower structure Ni-V2O5@NC is obtained through hydrothermal and carbonization treatment. The present application utilizes the method of Ni doping to inhibit the agglomeration phenomenon of V2O5, thereby providing high specific surface area and rich active sites; Ni doping optimizes the defect structure of V2O5, which is conducive to exciting active sites so that the catalyst has high reaction activity. Ni has high conductivity, and after doping V2O5, the conductivity of the material is improved. In addition, Ni doping helps to form a more stable oxidation state, thereby improving the crystallinity and stability. Based on the above advantages, Ni-V2O5@NC exhibits good electrochemical performance in the oxygen evolution reaction (OER).

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrolytic water oxygen production, in particular to a Ni-doped nano-flower structure Ni-V2O5@NC and a preparation method and application thereof. BACKGROUND

[0002] Due to the increase in consumption of fossil fuels, environmental pollution is caused, and people have carried out in-depth research on clean renewable resources. Water electrolysis is a process of converting electrical energy into chemical energy by decomposing water into hydrogen and oxygen. Water electrolysis includes anode oxygen evolution reaction (OER) and cathode hydrogen evolution reaction (HER). Among them, OER is the rate-controlling step of water decomposition reaction, which needs to overcome a high overpotential, involves a four-electron transfer reaction mechanism and the generation of intermediate species, resulting in slow kinetics. Therefore, a high-activity electrocatalyst is needed to improve the efficiency of OER. Among existing catalysts, RuO2 and IrO2 exhibit high OER catalytic activity, but due to poor stability, high price, rarity and short service life, they cannot meet the needs of practical applications. Therefore, it is still a challenge to develop a new type of electrocatalyst with high activity, strong conductivity and good stability.

[0003] Vanadium-based catalysts have good catalytic performance in the process of water electrolysis. Among them, as a relatively stable phase of vanadium, V2O5 has high activity in a wider pH range. The V element in V2O5 has multiple oxidation states and rich V=O, which can enrich the active intermediate (*OOH) by adjusting the electronic structure of the V element ([Ar]3d 3 4s 2 ) in the atomic network, promote the intermediate reaction and thus reduce the reaction barrier. Specifically, V2O5 obtained by annealing ammonium metavanadate can drive a current density of 10 mA·cm -2 at an overpotential of 410 mV in OER, and the Tafel slope is 44 mV·dec -1 . V2O5 nanorod structure is obtained by using polyvinyl alcohol assisted solution synthesis technology, and the polymer oxidation causes the generation of voids. The V2O5 nanorod structure is coated on a foam nickel, and the overpotential is 310 mV at a current density of 10 mA·cm -2 . V2O5 nanorods synthesized by hydrothermal method using ammonium metavanadate and nitric acid also exhibit good catalytic activity (442 mV@10 mA·cm -2 , Tafel slope is 135 mV·dec -1 ). Doping active metal elements (such as Ni, Fe, Co, etc.) as a promoter can improve the OER catalytic performance of V2O5. Building high dispersity Co(OH)2 grown on V2O5 nanoflower can provide a low overpotential of 320 mV at a current density of 10 mV·cm -2 .

[0004] However, V2O5 has some defects, 1) easy agglomeration leading to low catalytic activity: V2O5 synthesized conventionally is easy to agglomerate and form large particles, resulting in low porosity, small specific surface area and few active sites, thereby reducing the catalytic activity. 2) Poor electrical conductivity: V2O5 has a high ionic bond density, and the mobility of electrons in the energy band formed by the d orbit is limited, reducing the electron freedom within the material, thereby exhibiting low electrical conductivity. 3) Poor stability: in alkaline OER, V metal will dissolve and be over-oxidized, thereby destroying the structure of the catalyst and reducing the stability. Therefore, relying solely on V2O5 itself, improving its electrocatalytic efficiency is still a major obstacle. SUMMARY

[0005] The technical problem solved: In view of the problems of easy agglomeration leading to low catalytic activity, poor electrical conductivity and poor stability of the V2O5 catalyst in the prior art, the present application proposes a Ni-doped nanoflower structure Ni-V2O5@NC and its preparation method and application. The Ni-doped V2O5 nanoflower structure is formed by directly mixing ammonium metavanadate, oxalic acid and nickel nitrate. The V2O5 nanoflower structure after doping Ni has a high active specific surface area, and the overall electrical conductivity of the material can be effectively improved after doping Ni, and the number of oxygen vacancies of V2O5 can be reduced, so that the prepared Ni-doped nanoflower structure Ni-V2O5 catalyst has higher catalytic activity and electrical conductivity and better stability.

[0006] Technical solution: The first object of the present application is to provide a preparation method of a Ni-doped nanoflower structure Ni-V2O5@NC, the steps are as follows:

[0007] Step one, ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate are added to water, and stirring treatment is carried out at room temperature, and then a mixed solution is obtained;

[0008] Step two, the mixed solution obtained in step one is subjected to hydrothermal reaction, washing and drying;

[0009] Step three, the dried sample is subjected to annealing treatment under argon atmosphere to obtain the Ni-doped nanoflower structure Ni-V2O5@NC.

[0010] Preferably, the mass ratio of ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate in step one is 1:2.1:0.1-1:2.1:0.4, and the concentration of the mixed solution formed by adding ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate to deionized water is 0.016g·mL -1 -0.0175g·mL -1 . In this process, the addition amount of nickel nitrate hexahydrate needs to be controlled, and when a small amount or too much nickel nitrate hexahydrate is added, the electrochemical performance and structural stability of the composite are poor.

[0011] Preferably, the mass ratio of ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate in step one is 1:2.1:0.3, and the concentration of ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate in the mixed solution formed by adding deionized water is 0.017 g·mL -1 .

[0012] Preferably, the stirring treatment temperature in step one is 15℃-25℃, and the treatment time is 1h-2h.

[0013] Preferably, the temperature of the hydrothermal reaction in step two is 150℃-200℃, and the treatment time is 18h-24h.

[0014] Preferably, the annealing treatment in step three is carried out in an argon atmosphere, and the conditions are as follows: annealing treatment at 500℃±50℃ for 3h in an argon atmosphere, the heating rate is 2℃·min -1 .

[0015] The second object of the present application is to provide a Ni-doped nanoflower structure Ni-V2O5@NC prepared based on the above method.

[0016] The third object of the present application is to provide the application of the above-mentioned Ni-doped nanoflower structure Ni-V2O5@NC as a catalyst for electrolytic water to produce oxygen.

[0017] Advantages:

[0018] (1) Ni-doped V2O5 forms a nanoflower structure, which has a high active specific surface area. The introduction of Ni not only increases the number of active centers on the surface of the catalyst, but also improves the contact efficiency of the catalyst with the reactants, thereby improving the OER catalytic activity. Among them, the Ni-doped nanoflower structure Ni-V2O5@NC catalyst prepared by the present application has an overpotential of 292-366mV at a current density of 10mA·cm -2 , and the catalyst Ni-60-V2O5@NC has an overpotential of only 292mV at a current density of 10mA·cm -2 ; The prepared catalyst exhibits a low Tafel slope (53.2-88.2mV·dec -1 ), and in particular, the Tafel slope of the Ni-60-V2O5@NC catalyst is 53.2mV·dec -1 , indicating that the Ni-doped nanoflower structure Ni-V2O5@NC prepared by the present application has good reaction kinetics.

[0019] (2) Ni has high electrical conductivity, and after doping, the overall conductivity of the material can be effectively improved, the electron flow path in the material is improved, the resistance is reduced, and the electron quickly transfers on the surface of the catalyst. In addition, the d orbit of Ni interacts with the d orbit of V atom to form strong electron coupling, promote electron delocalization, and improve the conductivity. The charge transfer resistance value of the Ni-doped nanoflower structure Ni-V2O5@NC catalyst prepared by the application is 24.4-60Ω, and the charge transfer resistance value of Ni-60-V2O5@NC is the lowest, only 24.4Ω. The results show that the electron transfer rate of Ni-60-V2O5@NC catalyst in OER is faster, which further shows that the increase of Ni doping will improve the conductivity.

[0020] (3) Ni helps to form a more stable oxidation state. Ni doping reduces the number of oxygen vacancies of V2O5, optimizes the V2O5 lattice structure, and reduces the catalyst deactivation caused by structural changes during the catalytic process. The catalyst Ni-60-V2O5@NC prepared by the application is tested at a constant scanning rate of 50mV·s -1 -1 under a constant scanning rate of 50mV·s -2 -1 under a constant scanning rate of 50mV·s BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The scanning electron microscope (SEM) image of Ni-V2O5@NC synthesized in Example 1.

[0022] Figure 2 The transmission electron microscope (TEM) image of Ni-V2O5@NC synthesized in Example 1.

[0023] Figure 3 The high-resolution transmission electron microscope (HRTEM) image of Ni-V2O5@NC synthesized in Example 1.

[0024] Figure 4 The mapping image of Ni-V2O5@NC synthesized in Example 1, and (j) is the photoelectron diffraction image of Ni-60-V2O5@NC, wherein C, N, O, V and Ni are EDS mapping images of corresponding elements.

[0025] Figure 5 The energy dispersive spectroscopy (EDS) image of Ni-V2O5@NC synthesized in Example 1.

[0026] Figure 6 The Raman spectrum (Raman) image of Ni-V2O5@NC synthesized in Examples 1, 2, 3 and 4.

[0027] Figure 7X-ray diffraction (XRD) pattern of Ni-V2O5@NC synthesized for Example 1, 2, 3, 4.

[0028] Figure 8 Electron paramagnetic resonance (EPR) pattern of Ni-V2O5@NC synthesized for Example 1, 2, 3, 4.

[0029] Figure 9 X-ray photoelectron spectroscopy (XPS) pattern of Ni-V2O5@NC prepared for Example 1.

[0030] Figure 10 Thermogravimetric analysis (TGA) pattern of Ni-V2O5@NC prepared for Example 1.

[0031] Figure 11 Fourier transform infrared spectroscopy (FT-IR) pattern of Ni-V2O5@NC prepared for Example 1, 2, 3, 4.

[0032] Figure 12 Linear sweep voltammetry (LSV) plot of oxygen evolution reaction of Ni-V2O5@NC catalyst prepared for Example 1, 2, 3, 4.

[0033] Figure 13 Tafel slope plot of oxygen evolution reaction of Ni-V2O5@NC catalyst prepared for Example 1, 2, 3, 4.

[0034] Figure 14 Electrochemical impedance spectroscopy (EIS) plot of oxygen evolution reaction of Ni-V2O5@NC catalyst prepared for Example 1, 2, 3, 4.

[0035] Figure 15 Electrochemical active surface area (ECSA) plot of Ni-V2O5@NC catalyst prepared for Example 1, 2, 3, 4.

[0036] Figure 16 Cycling stability plot of Ni-60-V2O5@NC catalyst prepared for Example 1. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions, and advantages of the present application clearer, the present application will be described in detail below with reference to the accompanying drawings and examples.

[0038] In view of the problems existing in V2O5, in the work of the application, we design and prepare Ni-doped V2O5 nanoflower, and use the excellent conductivity and activity of transition metal element Ni to dope Ni into V2O5 nanoflower, and also dope nitrogen and carbon to form stable nanoflower Ni-V2O5@NC. The material has the following advantages: 1) high activity: Ni element is uniformly doped into V2O5, and the nanoflower structure formed has larger active specific surface area, which provides more active sites for OER, thereby increasing the reaction activity. 2) high conductivity: the conductivity of Ni is high, and after doping, the overall conductivity of the material can be effectively improved, the chemical environment around the atoms in the original catalyst material crystal is changed, the electron flow path in the material is optimized, and the electron is quickly transmitted on the surface of the catalyst. In addition, the d orbitals of Ni and V atoms interact with each other, promote electron delocalization, and thus improve the conductivity. 3) good stability: the structure stability of V2O5 is poor, and after Ni doping, the crystal structure is optimized, thereby improving the OER stability of the catalyst.

[0039] The drugs used in the application are purchased from Aladdin Reagent Co., Ltd. and can be used without further purification.

[0040] The preparation method of the Ni-doped V2O5 nanoflower of the application is as follows:

[0041] 1) 0.2g ammonium metavanadate, 0.42g oxalic acid dihydrate and 0.02g-0.08g nickel nitrate hexahydrate are added to 40mL deionized water, stirred at 15℃-25℃ for 1h-2h, and the mass ratio of ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate is 1:2.1:0.1-1:2.1:0.4; the concentration of the mixed solution formed by adding ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate into deionized water is 0.016g·mL -1 -0.0175g·mL -1 .

[0042] 2) the prepared ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate solution is hydrothermally treated at 150℃-200℃ for 18h-24h, centrifuged and dried;

[0043] 3) the obtained solid is annealed at 500℃±50℃ under argon atmosphere for 3h to obtain Ni-doped V2O5 nanoflower structure Ni-V2O5@NC, wherein the heating rate is 2℃·min -1 .

[0044] The specific implementation is as follows:

[0045] Example 1

[0046] The embodiment provides a preparation method of Ni-doped nanoflower structure Ni-V2O5@NC, and steps are as follows:

[0047] 1) 0.2 g of ammonium metavanadate, 0.42 g of oxalic acid dihydrate and 0.06 g of nickel nitrate hexahydrate were weighed into 40 mL of deionized water, and stirred at room temperature for 1 h to form a mixed solution;

[0048] 2) The obtained solution was transferred to a 100 mL high-pressure reaction kettle, and hydrothermal treatment was carried out at 200 DEG C for 24 h. After cooling to room temperature, the sample was obtained by centrifugation, washing and drying;

[0049] 3) The dried sample was annealed at 500 DEG C for 3 h in argon to prepare Ni-doped V2O5 nanoflower structure Ni-60-V2O5@NC, wherein the heating rate was 2 DEG C·min -1 .

[0050] Figure 1 It is an SEM image of the Ni-V2O5@NC catalyst synthesized in the embodiment. It can be observed from the figure that the Ni-V2O5@NC nanoflower formed by the relatively uniform distribution of the sheet structure after Ni doping.

[0051] Figure 2 It is a TEM image of the Ni-V2O5@NC synthesized in the embodiment. It can be observed from the figure that the nanoflower structure of the Ni-V2O5@NC does not occur agglomeration.

[0052] Figure 3 It is an HRTEM image of the Ni-V2O5@NC catalyst synthesized in the embodiment. It can be observed from the figure that the interplanar spacing of the Ni-V2O5@NC is 0.35 nm (110).

[0053] Figure 4 It is a Mapping image of the Ni-V2O5@NC synthesized in the embodiment. Figure 4 It can be seen that: the material surface is distributed with C, N, O, V and Ni elements, and the distribution is the same, indicating that the Ni, N and C are uniformly doped.

[0054] Figure 5 It is an EDS spectrum of the Ni-V2O5@NC synthesized in the embodiment. Figure 5 It can be seen that Cu, C, N, O, V and Ni elements are contained, wherein the Cu element comes from the copper mesh, that is, the material contains C, N, O, V and Ni elements, and the mass content is 8.56%, 0.01%, 14.04%, 74.96% and 2.43% respectively.

[0055] Figure 9 It is an XPS element electron spectrum of the Ni-V2O5@NC catalyst prepared in embodiment 1. Figure 9It can be seen that the prepared material is mainly composed of elements of C, N, O, V and Ni.

[0056] Figure 10 The TGA graph of the Ni-V2O5@NC catalyst synthesized in Example 1 is shown in the figure. It can be observed from the figure that there is a small amount of loss of Ni-V2O5@NC during the temperature rising process from room temperature to 900℃, indicating that the C content is 8.01%.

[0057] Example 2

[0058] The same as Example 1, except that in this example, the amount of nickel nitrate hexahydrate added is 0.02g, and the specific process is as follows:

[0059] 1) 0.2g of ammonium metavanadate, 0.42g of oxalic acid dihydrate and 0.02g of nickel nitrate hexahydrate were weighed into 40mL of deionized water, and stirred at room temperature for 1h to form a mixed solution;

[0060] 2) The same as step 2) of Example 1;

[0061] 3) The same as step 3) of Example 1. Finally, Ni-doped V2O5 nanoflower structure Ni-20-V2O5@NC was obtained.

[0062] The Raman, XRD, EPR and FT-IR graphs of the product obtained in this example are shown in Figure 6 、 7 , 8, 11. The Raman and FT-IR peaks of Ni-20-V2O5@NC are at the same positions, and the intensity is lower than that of Ni-60-V2O5@NC, and the XRD peak intensity is also lower than that of Ni-60-V2O5@NC, which is attributed to the fact that Ni doping improves the crystallinity of V2O5. The oxygen vacancy content is higher than that of Ni-60-V2O5@NC, indicating that Ni doping optimizes the crystal structure.

[0063] Example 3

[0064] The same as Example 1, except that in this example, the amount of nickel nitrate hexahydrate added is 0.04g, and the specific process is as follows:

[0065] 1) 0.2g of ammonium metavanadate, 0.42g of oxalic acid dihydrate and 0.04g of nickel nitrate hexahydrate were weighed into 40mL of deionized water, and stirred at room temperature for 1h to form a mixed solution;

[0066] 2) The same as step 2) of Example 1;

[0067] 3) The same as step 3) of Example 1. Finally, Ni-doped V2O5 nanoflower structure Ni-40-V2O5@NC was obtained.

[0068] The Raman spectrum, XRD spectrum, EPR spectrum and FT-IR spectrum of the product obtained in this example are shown in Figures 1-4, respectively. Figure 6 、 7 , 8, 11.

[0069] Example 4

[0070] The same as Example 1, except that in this example, the amount of nickel nitrate hexahydrate added is 0.08 g, and the details are as follows:

[0071] 1) 0.2 g of ammonium metavanadate, 0.42 g of oxalic acid dihydrate and 0.08 g of nickel nitrate hexahydrate were weighed into 40 mL of deionized water, and stirred at room temperature for 1 h to form a mixed solution;

[0072] 2) The same as step 2) of Example 1;

[0073] 3) The same as step 3) of Example 1. Finally, the Ni-doped V2O5 nanoflower structure Ni-80-V2O5@NC was obtained.

[0074] The Raman spectrum, XRD spectrum, EPR spectrum and FT-IR spectrum of the product obtained in this example are shown in Figures 1-4, respectively. Figure 6 、 7 , 8, 11. The Raman peaks and FT-IR peaks of Ni-80-V2O5@NC are at the same positions, but the intensity is lower than that of Ni-60-V2O5@NC, and the XRD peak intensity is also lower than that of Ni-60-V2O5@NC, which is attributed to the increase in disorder of the V2O5 crystal structure caused by excessive Ni doping. In addition, the oxygen vacancy content is higher than that of Ni-60-V2O5@NC, and excessive Ni doping promotes the formation of oxygen vacancies, resulting in lattice defects.

[0075] Figure 6 The Raman spectrum of the Ni-V2O5@NC synthesized in Examples 1-4 is shown in Figure 5. Figure 6 It can be seen that there are V=O, V-O, O-V-O and O-V=O groups in the prepared Ni-V2O5@NC.

[0076] Figure 7 The XRD spectrum of the Ni-V2O5@NC synthesized in Examples 1-4 is shown in Figure 6. Figure 7 It can be seen that the product prepared in Example 1 contains (001), (110), (002), (003) and (312) characteristic peaks, which correspond to the standard diffraction peaks of VO2 (PDF # 31-1438), which is due to the decrease in the valence state of V caused by the introduction of Ni.

[0077] Figure 8 The EPR spectrum of the Ni-V2O5@NC synthesized in Examples 1-4 is shown in Figure 7. Figure 8It can be seen that Ni doping leads to a significant reduction in the number of oxygen vacancies, and the oxygen vacancies in Ni-V2O5@NC decrease with increasing Ni content, proving that the incorporation of Ni optimizes the defect structure of V2O5. The oxygen vacancies of Ni-60-V2O5@NC are the least, and its EPR curve presents a slant line. The addition of Ni causes the oxygen vacancies to be a slant line, which is due to the shift of spectral absorption caused by Ni atomic doping.

[0078] Figure 11 The FT-IR graph of Ni-V2O5@NC prepared in Examples 1-4 is prepared. From the FT-IR graph of Ni-V2O5@NC prepared in Examples 1-4, it can be seen that the prepared Ni-V2O5@NC has rich functional groups (O-H, C=O, C-O, V=O, V-O and V-O-V). Figure 11

[0079] Application Example

[0080] Parallel tests were carried out on the catalysts prepared in Examples 1-4:

[0081] OER: 5 mg of catalyst was uniformly dispersed in a mixed solution of 950 μL of anhydrous ethanol and 50 μL of Nafion solution (5 wt%), and then 5 μL of catalyst ink was added on the surface of a glassy carbon electrode. Before the electrochemical experiment, the electrolyte was purged with pure nitrogen for 30 minutes. Then, the freshly prepared working electrode was immersed in the electrolyte. The electrochemical performance test was completed in a typical three-electrode system at room temperature (about 25°C). The electrochemical performance of the oxygen evolution reaction was tested with a glassy carbon electrode (GCE, diameter: 3 mm, area: 0.07 cm 2 ) as the working electrode, a graphite rod as the counter electrode and Hg / HgO as the reference electrode. All reported potentials were converted to the reversible hydrogen electrode (RHE) using the following formula: E (RHE) = E (Hg / HgO) + 0.0591*pH+0.098V. All electrochemical tests were carried out on a CHI660E electrochemical workstation (Shanghai). The polarization curve was obtained by LSV scanning at a voltage range of 0-0.8V at room temperature, with a scanning rate of 5 mV s -1 . The overpotential value was defined by the Tafel equation: η = a + blog|j|, where η (V) is the overpotential, j (mA cm -2 ) is the current density, and B (mV dec -1 ) represents the Tafel slope.

[0082] The electrochemical surface area (ECSA) was evaluated by the double-layer capacitance (C dl , in mF): ECSA = C dl / C s ​Cyclic voltammetry (CV) was performed at -0.1V to 0.1V in 1 mol / L KOH at a rate of 20 mV / s. -1 40mV s -1 60mV s -1 80mV s -1 and 100mV s -1 ECSA was determined by scanning rate. C was determined by fitting 0V vs. RHE and the slope Δj = (ja-jc) / 2 at different scanning rates. dl Assuming the specific capacitance of a flat surface is 40 μF cm⁻¹ -2 (C s ECSA is achieved by normalizing the double-layer capacitor to a standard specific capacitance.

[0083] EIS records within a frequency range of 1000 kHz to 10 mHz, testing 10 points every 10 times the frequency. The amplitude of the sinusoidal potential signal is 5 mV. Measurements are taken at 50 mV s. -1 The stability of the catalyst was tested for 1000 cycles at a constant scan rate. The polarization curves were compared with the initial curves to evaluate the catalyst stability after 1000 cycles.

[0084] Figure 12 The LSV curves for the oxygen evolution reaction of the Ni-V₂O₅@NC catalysts prepared in Examples 1, 2, 3, and 4 are shown. Figure 12 It can be seen that: with Ni-20-V2O5@NC(366mV@10mA·cm) -2 ), Ni-40-V2O5@NC(343mV@10mA·cm -2 ) and Ni-80-V2O5@NC(357mV@10mA·cm -2 In comparison, the Ni-60-V2O5@NC prepared in Example 1 only requires 292mV to reach 10mA·cm. -2 Current density.

[0085] Figure 13 The images show the Tafel slopes of the Ni-V₂O₅@NC catalysts prepared in Examples 1, 2, 3, and 4. Figure 13 It can be seen that: with Ni-20-V2O5@NC (74.5mV·dec) -1 Ni-40-V2O5@NC (88.2mV·dec) -1 Ni-80-V2O5@NC (77.7mV·dec) -1 Compared to the Ni-60-V2O5@NC (53.2mV·dec) prepared in Example 1, -1 The small Tafel slope indicates that its catalyst has high OER activity.

[0086] Figure 14 EIS plots of Ni-V2O5@NC catalysts prepared for Example 1, 2, 3, 4 were obtained. From Figure 14 It can be seen that Ni-60-V2O5@NC (24.4 Ω) has a lower charge transfer resistance compared with Ni-20-V2O5@NC (57.7 Ω), Ni-40-V2O5@NC (60.0 Ω), Ni-80-V2O5@NC (44.4 Ω), indicating that Ni-60-V2O5@NC catalyst has high conductivity.

[0087] Figure 15 ECSA plots of Ni-V2O5@NC catalysts prepared for Example 1, 2, 3, 4 were obtained. From Figure 15 It can be seen that Ni-60-V2O5@NC (2.66 cm-2) has a larger electrochemical active specific surface area compared with Ni-20-V2O5@NC (2.31 cm-2), Ni-40-V2O5@NC (2.57 cm-2) and Ni-80-V2O5@NC (2.54 cm-2), indicating that Ni-60-V2O5@NC has better catalytic activity. -2 -2 -2 -2

[0088] Figure 16 Cycle stability plots of Ni-V2O5@NC catalyst prepared for Example 1 were obtained. From Figure 16 It can be seen that the current density after cycling only increases 5 mV compared with the initial curve, indicating its good catalytic stability. -2

[0089] ​​​​​In summary, we successfully synthesized a new type of catalyst Ni-V2O5@NC with high stability and high activity, which exhibits good electrochemical performance in OER. Specifically, by doping Ni into V2O5, we formed a nanoflower structure of Ni-V2O5@NC with stable crystal structure. This material has the following advantages: 1) high reaction activity: the formation of nanoflower structure of Ni-V2O5@NC increases the number of active sites on the surface, reduces the adsorption energy of the reaction transition state on the active center, thereby increasing the catalytic reaction activity of OER. In addition, Ni as a good catalyst material provides additional active sites for OER. 2) large electrical conductivity: the interaction between the d orbitals of the doped Ni and V atoms promotes electron delocalization, improves the electron flow path in the material, and reduces the charge transfer resistance, so that electrons can quickly transport on the surface of the catalyst, improving the electrical conductivity. 3) strong stability: Ni doping inhibits the stacking and agglomeration of the V2O5 sheet structure, maintains the activity and structural integrity of the catalyst, and improves the stability of the catalyst. Based on the above advantages, Ni-V2O5@NC exhibits good electrochemical performance in OER (low overpotential: 292 mV @ 10 mA·cm -2 ).

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can modify the technical solutions described in the foregoing embodiments, or make equivalent replacements to some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing Ni-doped Ni-V2O5@NC with nanoflower structure, characterized in that, The steps are as follows: Step one, ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate are added to water, stirred at room temperature, and then a mixed solution is obtained, wherein the mass ratio of ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate is 1:2.1:0.1 ~ 1:2.1:0.4, and the concentration of the mixed solution formed by adding ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate into deionized water is 0.016 g·mL -1 ~ 0.0175 g·mL -1 ; Step two, the mixed solution obtained in step one is subjected to hydrothermal reaction, washed and dried; Step three, the dried sample is annealed under argon atmosphere to obtain the Ni-doped nanoflower structure Ni-V2O5@NC, and the annealing conditions are as follows: annealing at 500 ℃±50 ℃ for 3 h under argon atmosphere, and the heating rate is 2 ℃·min -1 .

2. The preparation method of the Ni-doped nanoflower structure Ni-V2O5@NC according to claim 1, characterized in that, The mass ratio of ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate in step one is 1:2.1:0.3, and the concentration of ammonium metavanadate, oxalic acid dihydrate and nickel nitrate hexahydrate added into deionized water to form a mixed solution is 0.017 g·mL -1 .

3. The preparation method of the Ni-doped nanoflower structure Ni-V2O5@NC according to claim 1, characterized in that, The stirring treatment temperature in step one is 15-25 DEG C, and the treatment time is 1-2 hours.

4. The preparation method of the Ni-doped nanoflower structure Ni-V2O5@NC according to claim 1, characterized in that, The hydrothermal reaction temperature in step two is 150-200 DEG C, and the treatment time is 18-24 hours.

5. A Ni-doped nanoflower structure Ni-V2O5@NC prepared based on the method according to any one of claims 1-4.

6. Application of the Ni-doped nanoflower structure Ni-V2O5@NC according to claim 5 to water electrolysis for oxygen production as a catalyst.

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