阅读说明：本技术 铁-镍钒双金属氢氧化物及其制备方法和应用 (Iron-nickel-vanadium double metal hydroxide and preparation method and application thereof ) 是由 戴仁童 黎忠耀 庞佳政 张珉熙 邓瑶瑶 柏寄荣 于 2021-06-18 设计创作，主要内容包括：本发明涉及铁-镍钒双金属氢氧化物及其制备方法和应用,制备方法是：(1)将镍源和钒源溶于水中,加入形貌控制剂和有机碱源,混合均匀后,进行水热反应,待水热反应完成后分离、洗涤、干燥得到镍钒双金属氢氧化物；(2)将铁源溶于水中获得含铁溶液,将所述镍钒双金属氢氧化物分散于所述含铁溶液中进行交换反应,待反应完成后分离、洗涤、干燥后制得铁-镍钒双金属氢氧化物。本发明方法制得的产物结构为多孔纳米片构成的花状空心微球,应用于电解水中作为催化剂具有较好的OER电催化活性,具有OER极低的工作过电位(10mA·cm～(-2)时为261mV)和塔菲尔斜率(42.4mV·dec～(-1))。(The invention relates to an iron-nickel-vanadium double metal hydroxide, a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) dissolving a nickel source and a vanadium source in water, adding a morphology control agent and an organic alkali source, uniformly mixing, carrying out hydrothermal reaction, and separating, washing and drying after the hydrothermal reaction is finished to obtain nickel-vanadium double metal hydroxide; (2) dissolving an iron source in water to obtain an iron-containing solution, dispersing the nickel-vanadium double metal hydroxide in the iron-containing solution for exchange reaction, and after the reaction is finished, separating, washing and drying to obtain the iron-nickel-vanadium double metal hydroxide. The product of the process of the inventionThe flower-shaped hollow microsphere with the structure formed by porous nano sheets has better OER (organic electroluminescent) electrocatalytic activity and extremely low OER (overvoltage of 10 mA-cm) when being applied as a catalyst in electrolytic water ‑2 261mV) and Tafel slope (42.4mV dec) ‑1 )。)

1. The preparation method of the iron-nickel-vanadium double metal hydroxide is characterized by comprising the following steps:

(1) dissolving a nickel source and a vanadium source in water, adding a morphology control agent and an organic alkali source, uniformly mixing, carrying out hydrothermal reaction, and separating, washing and drying after the hydrothermal reaction is finished to obtain nickel-vanadium double metal hydroxide;

(2) dissolving an iron source in water to obtain an iron-containing solution, dispersing the nickel-vanadium double metal hydroxide in the iron-containing solution for exchange reaction, and after the reaction is finished, separating, washing and drying to obtain the iron-nickel-vanadium double metal hydroxide.

2. The method for preparing the iron-nickel vanadium double metal hydroxide according to claim 1, wherein the nickel source is one of nickel chloride, nickel sulfate and nickel nitrate; the vanadium source is one of vanadium chloride and vanadium sulfate; the iron source is one of ferric chloride, ferric sulfate and ferric nitrate; the organic alkali source is urea.

3. The method of preparing an iron-nickel vanadium double hydroxide according to claim 2, wherein the nickel source is nickel chloride; the vanadium source is vanadium chloride; the iron source is ferric nitrate.

4. The method of claim 1, wherein the morphology controlling agent is ammonium fluoride.

5. The method for preparing the iron-nickel vanadium double metal hydroxide according to claim 1, wherein the hydrothermal reaction is carried out at a temperature of 100 to 130 ℃ for 10 to 20 hours.

6. The method for preparing the iron-nickel vanadium double metal hydroxide according to claim 1, wherein the temperature of the exchange reaction is 50-70 ℃ and the time is 5-8 h.

7. The method for preparing the iron-nickel vanadium double metal hydroxide according to claim 1, wherein the molar ratio of the nickel source, the vanadium source, the organic base source and the morphology control agent is 1:1 (6-10) to (3-5), preferably 1:1:1.2:8.33: 3.24; the dosage ratio of the nickel source to the water is 1mol: 50L; the dosage ratio of the iron source to the nickel-vanadium double metal hydroxide is (1-2) mol:150 g.

8. The iron-nickel vanadium double hydroxide prepared by the preparation method according to any one of claims 1 to 7, wherein the microstructure of the iron-nickel vanadium double hydroxide is flower-like hollow microspheres composed of nanosheets.

9. Use of the iron-nickel vanadium double hydroxide prepared by the preparation method according to any one of claims 1 to 7 in electrolytic water, characterized in that the iron-nickel vanadium double hydroxide is used as a catalyst in the reaction of electrolytic water, and the catalyst is attached to the surface of an electrode.

Technical Field

The invention relates to the technical field of material preparation, in particular to iron-nickel-vanadium double metal hydroxide and a preparation method and application thereof.

Background

The challenges of the energy crisis and global warming have prompted scientific exploration of the water splitting process. Among them, Oxygen Evolution Reaction (OER) is a bottleneck of electrochemical water splitting due to kinetic retardation caused by its complicated four-electron transfer process. Therefore, the development of cost-effective electrocatalysts with excellent performance to reduce the high overpotentials and associated energy losses in OER processes has been the focus of research.

Layered Double Hydroxides (LDHs) have attracted considerable attention in recent years as OER electrocatalysts due to their remarkable tunability in morphology, structure and composition. To date, extensive efforts have focused on the synthesis and application of low density polyethylene for OER by optimizing the metal composition and proportions in the bulk layer, exfoliation into monolayer nanosheets, or in combination with specific functional materials. Although the developed lactate dehydrogenase-based catalysts showed satisfactory activity at OER, inefficient exposure of the active site and poor electron/ion transport capability of the lactate dehydrogenase powder samples tended to result in poor OER performance. To address these problems, it is highly desirable to have an optimized structure that maximizes active site exposure, easy electron/ion transport, and rapid gas evolution. Nanostructured materials having a hierarchical structure (e.g., core-shell or hollow microspheres) are reported to have interesting electrochemical properties compared to their low-dimensional counterparts.

Disclosure of Invention

In order to solve the technical problem of poor catalytic performance of the existing layered double-metal oxide OER electrocatalyst, the iron-nickel-vanadium double-metal hydroxide, the preparation method and the application thereof are provided. According to the method, iron ions are exchanged between the nickel-vanadium double metal hydroxide, so that the iron-nickel-vanadium double metal hydroxide with the hollow nanometer flower-like structure and composed of porous nanosheets can be obtained, more active sites are exposed due to the exchange between iron and the nickel-vanadium double metal hydroxide, and the OER performance is improved.

In order to achieve the purpose, the invention is realized by the following technical scheme:

the preparation method of the iron-nickel-vanadium double metal hydroxide comprises the following steps:

(1) dissolving a nickel source and a vanadium source in water, adding a morphology control agent and an organic alkali source, uniformly mixing, carrying out hydrothermal reaction, and separating, washing and drying after the hydrothermal reaction is finished to obtain nickel-vanadium double metal hydroxide;

(2) dissolving an iron source in water to obtain an iron-containing solution, dispersing the nickel-vanadium double metal hydroxide in the iron-containing solution for exchange reaction, and after the reaction is finished, separating, washing and drying to obtain the iron-nickel-vanadium double metal hydroxide.

Further, the nickel source is one of nickel chloride, nickel sulfate and nickel nitrate; the vanadium source is one of vanadium chloride and vanadium sulfate; the iron source is one of ferric chloride, ferric sulfate and ferric nitrate; the organic alkali source is urea.

Preferably, the nickel source is nickel chloride; the vanadium source is vanadium chloride; the iron source is ferric nitrate.

Further, the morphology controlling agent is ammonium fluoride.

Further, the temperature of the hydrothermal reaction is 100-130 ℃, and the time is 10-20 h.

Further, the temperature of the exchange reaction is 50-70 ℃, and the time is 5-8 h.

Further, the molar ratio of the nickel source to the vanadium source to the organic alkali source to the morphology control agent is 1:1 (6-10) to (3-5), preferably 1:1:1.2:8.33: 3.24; the dosage ratio of the nickel source to the water is 1mol: 50L; the dosage ratio of the iron source to the nickel-vanadium double metal hydroxide is (1-2) mol:150 g.

The invention also provides the iron-nickel-vanadium double metal hydroxide prepared by the method, and the microstructure of the iron-nickel-vanadium double metal hydroxide is flower-shaped hollow microspheres formed by porous nanosheets.

In a final aspect of the present invention, there is provided the use of the iron-nickel vanadium double hydroxide prepared by the above preparation method as a catalyst in an electrolytic water reaction, the catalyst being attached to the surface of an electrode, in electrolytic water.

The beneficial technical effects are as follows:

the method firstly synthesizes nickel-vanadium hydroxide, takes the nickel-vanadium hydroxide as a template, and carries out cation exchange reaction on iron and the nickel-vanadium hydroxide to obtain the iron-nickel-vanadium double metal hydroxide, the product structure prepared by the method is a flower-shaped hollow microsphere formed by porous nano sheets, the nano sheets are porous, the transverse dimension is hundreds of nanometers, the thickness is about 10 nanometers, the porous nano sheets are stacked together to form a flower-shaped hollow microsphere structure, more exposed active sites are arranged on the nano sheets, and the structure can provide enough space for the permeation and diffusion of electrolyte in electrolytic water. When used as an electrocatalyst for OER in alkaline solution (1.0M potassium hydroxide), the Fe-Ni-V double hydroxide has good catalytic activity and very low over-potential (10mA cm) of OER^-2261mV) and Tafel slope (42.4mV dec)^-1). In addition, the material of the invention has better long-term stability when used as a catalyst. The method further optimizes the nickel-based hydroxide material, obtains better electrolytic water catalysis effect, can replace noble metal catalysts, and has better application prospect.

Drawings

FIG. 1 is the SEM images of NiV LDH and Fe-NiV LDH prepared in example 1, wherein (a) and (b) are the SEM images of NiV LDH, and (c) and (d) are the SEM images of Fe-NiV LDH.

FIG. 2 is a transmission electron microscopy morphology of NiV LDH and Fe-NiV LDH in example 1; wherein (a) (b) is a transmission electron micrograph of the NiV LDH, and (c) (d) is a transmission electron micrograph of the Fe-NiV LDH.

FIG. 3 is a scanning electron microscopy topography of NiFeV LDH in comparative example 1.

FIG. 4 is an X-ray diffraction pattern of NiV LDH, Fe-NiV LDH in example 1.

FIG. 5 is a photoelectron spectroscopy XPS plot of Fe-NiV LDH in example 1.

FIG. 6 is a comparison of polarization curves in the electrolytic water oxygen evolution reaction of NiV LDH, Fe-NiV LDH in example 1 and NiFeV LDH in comparative example 1.

FIG. 7 is a graph of the constant voltage v-t of Fe-NiV LDH in example 1.

NiV LDH represents the nickel vanadium double hydroxide in example 1; Fe-NiV LDH represents the iron-nickel vanadium double hydroxide of example 1; NiFeV LDH represents the product obtained in the one-step process of comparative example 1.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention and the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Unless specifically stated otherwise, the numerical values set forth in these examples do not limit the scope of the invention. Techniques, methods known to those of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values.

Example 1

The preparation method of the iron-nickel-vanadium double metal hydroxide comprises the following steps:

(1) synthesis of NiV-LDH

Weighing 1mmol of NiCl₂·6H₂O and VCl₃In 50mLStirring in deionized water for 30min to dissolve, and adding 120mg NH respectively₄F and 500mg of urea are stirred until the solution is completely dissolved, the solution is transferred to a hydrothermal kettle to react for 16h at 120 ℃, the solution is cooled to room temperature, the product is centrifugally separated and taken out, the product is washed for 2 times by distilled water and ethanol, and then the product is placed in a vacuum drying oven at 60 ℃ for 12h to obtain nickel-vanadium double metal hydroxide expressed by NiV LDH;

(2) synthesis of Fe-NiV LDH

First, 20mmol/L Fe (NO) is prepared₃)₃Taking 60mL of the solution, then weighing 150mg of NiV LDH, putting the NiV LDH into a reaction kettle, and adding the prepared Fe (NO)₃)₃Adding the solution into a reaction kettle; the reaction vessel was then placed in an oven at a constant temperature of 60 ℃ for 6h, and after cooling the reaction mixture to room temperature, the product was collected by centrifugation, washed with deionized water and ethanol, and dried in an oven at 60 ℃ for 10h to give iron-nickel vanadium double metal hydroxide, expressed as Fe-NiV LDH.

When the NiV LDH prepared in step 1 of this example is observed by a scanning electron microscope, SEM images are shown in fig. 1(a) and (b), and it can be seen from fig. 1(a) and (b) that the NiV LDH has uniform morphology, and the NiV LDH is assembled into flower-like hollow nanospheres from NiV two-dimensional nanosheets, and the particle size is about 4 μm. When the NiV LDH prepared in step 2 of this example is observed by a scanning electron microscope, SEM images are shown in fig. 1(c) and (d), and as can be seen from fig. 1(c) and (d), after iron is ion-exchanged with the NiV LDH, obvious pore-like defects are formed on the nanosheets, so that a porous structure is generated, the overall shape and appearance of the flower-like hollow nanospheres are not changed, and the average thickness of the nanosheets is between 10-15 nm.

The products of step 1 and step 2 in this example were observed by a projection electron microscope, respectively, to further observe the morphology and three-dimensional layered nanostructure of the products. The results are shown in FIG. 2. Fig. 2a and 2b are transmission electron micrographs of NiV LDH at low and high power, respectively, and clearly show the high density nanosheet array-like structure perpendicular to the x-axis. FIGS. 2c and 2d are transmission electron micrographs of Fe-NiV LDH at low and high power, respectively, again demonstrating that Fe-NiV LDH is also a flower-like nano hollow microsphere assembled from ultrathin nanosheets; in FIG. 2dHigh resolution transmission electron microscopy due to Ni (OH)₂The (101) plane of (2) has lattice fringes with an interlayer spacing of 0.232nm, more importantly Fe³⁺The etching-induced local disordered lattice structure appears on the Fe-NiV LDH nano-sheet, and a rich crystalline-amorphous phase interface is formed.

The invention prepares NiV LDHs through hydrothermal reaction. Metal cation (Ni)²⁺And V³⁺) And reacts with the hydrolysis product of urea to generate hydroxide. Under hydrothermal conditions (optimum 120 ℃ C., 16h), urea gradually decomposed to provide NH₃Then, NH₃Hydrolyzing to generate a large amount of hydroxyl; the NiV LDH nano-sheet grows along with the passage of time, and finally forms a flower-shaped nano hollow microsphere structure under the action of a morphology control agent ammonium fluoride; subsequently, mixing NiV LDH as a template with a solution containing iron ions to perform ion exchange, wherein part of Ni is²⁺Quilt Fe³⁺And (4) substituting to form a stable LDH structure.

The product obtained by the invention is a highly open structure of flower-shaped nano hollow microspheres, and the structure mainly comes from recrystallization of nano sheets growing at an early stage. Notably, the vertically arranged arrays intersect and penetrate each other, forming a 3D highly porous network-like heterostructure. Holes are generated on the surfaces of the Fe-NiV LDH product nano sheets after iron ion exchange, obvious defects are formed, but the form of the integral highly-open structure is well maintained, and no obvious change exists, which shows that the structure is good in stability, and the filling of the nano sheets becomes more compact with the addition of iron. This unique porous structure may provide advanced features of more open coordination sites, efficient diffusion rates of electrolyte ions and electrons at the interface, and full internal surface accessibility for electrochemical reactions.

The products of step 1 and step 2 of this example were subjected to X-ray diffraction analysis, respectively, and the XRD patterns are shown in FIG. 4, and it can be seen from FIG. 4 that Fe-NiV LDH has the same hexagonal phase structure as NiVL DH; diffraction peaks near 11.5 °, 33.7 ° and 59.9 ° in the XRD profile of Fe-NiV LDH correspond to (003), (101) and (110) planes, respectively, indicating that the crystal structure remains good after iron cation exchange.

Fig. 5 shows the photoelectron spectrum of Fe-NiV LDH, with all peaks labeled and revealing the presence of nickel, vanadium, iron and oxygen.

Example 2

This example was the same as the preparation method of comparative example 1, except that the temperature of the hydrothermal reaction in step 1 was 130 ℃ and the time was 12 hours; the temperature of the exchange reaction in the step 2 is 50 ℃ and the time is 8 h.

In this embodiment, the product structures of step 1 and step 2 are the same as those of embodiment 1, and are flower-like hollow microspheres composed of porous nanosheets.

Example 3

This example was the same as the preparation method of comparative example 1, except that the hydrothermal reaction in step 1 was carried out at a temperature of 110 ℃ for 18 hours; the temperature of the exchange reaction in the step 2 is 70 ℃ and the time is 5 h.

In this embodiment, the product structures of step 1 and step 2 are the same as those of embodiment 1, and are flower-like hollow microspheres composed of porous nanosheets.

Comparative example 1

This comparative example is a one-step synthesis product, expressed as NiFeV LDH. The preparation method comprises the following steps:

1.0mmol of nickel chloride hexahydrate (NiCl)₂·6H₂O), 1.0mmol of vanadium chloride (VCl)₃) 1.0mmol of ferric chloride (FeCl)₃) Dissolving in 50ml deionized water, magnetically stirring for 30min, and adding 8.33mmol of urea (CO (NH) respectively₂)₂) And 3.24mmol of ammonium fluoride (NH)₄F) Magnetically stirring for 30min to obtain clear solution; then transferring the solution into a hydrothermal kettle, heating the solution in an oven at 120 ℃ for 16h, cooling the solution to room temperature after heating, centrifuging the reacted solution to obtain a product, and washing the product for 2 times by using water and ethanol respectively; and (3) placing the washed product in a vacuum drying oven at 60 ℃ for drying for 12h to obtain a NiFeV LDH sample.

The product of the comparative example was observed by a scanning electron microscope, and the result is shown in fig. 3, which shows that the product synthesized by one step by a hydrothermal method has a diameter of about 2 μm and a microscopic morphology of flower-like hollow microspheres.

Application example 1

The product NiV LDH of step 1 of example 1, the product Fe-NiV LDH of step 2, and the product NiFeV LDH of comparative example 1 were used as catalysts on working electrodes in an electrolytic water system, respectively. Electrochemical performance was determined using a conventional three-electrode system: Ag/AgCl is used as a reference electrode, a Pt wire is used as an auxiliary electrode, and a glassy carbon electrode modified with a catalyst is used as a working electrode. Firstly, a working electrode is prepared, 5mg of the three samples, 5mg of carbon black, 970 mu L of isopropanol and 30 mu L of naphthol are mixed and ultrasonically treated for 1h to form a uniform mixed solution. And (3) dropwise adding 21 mu L of the mixed solution on the surface of the glassy carbon electrode, and naturally drying to obtain the working electrode. The electrochemical performance tests were carried out using an electrochemical workstation (Shanghai Chenghua) of type CHI 760E. Electrical polarity test at a fixed scan rate (10mV s) in a 1.0M KOH solution^-1) The process is carried out as follows.

The linear sweep voltammograms of the three samples are shown in FIG. 6, and it can be seen from FIG. 6 that the linear sweep voltammograms are at 10mA cm^-2The overpotential of Fe-NiV LDH is 261mV, the overpotential of NiV LDH is 358mV, and the overpotential of NiFeV LDH is 387.4 mV. The result shows that the electrocatalytic activity is reduced due to the doping of the third element in the one-step method, and compared with the NiFeV LDH synthesized in the one-step method, the defects of the material are increased along with the introduction of Fe in the two-step method synthesis process, so that more active sites are exposed, and the electrocatalytic performance is greatly improved.

Fe-NiV LDH of example 1 as a catalyst, when the electrolytic water performance of Fe-NiV LDH was tested in a 1.0M KOH solution, the current density was 10mA cm^-2Compared with the reported related documents, the overpotential of the material is 261.4mV, and the material has good oxygen evolution performance in water electrolysis, thereby proving that the material can be used as an effective electrocatalyst for water electrolysis.

In practical application, the stability of the electrocatalyst is another important measure. The Fe-NiV LDH samples of example 1 were tested using the chrono-voltage method. At a current density of 10mA cm^-2Was tested for 7h and the OER potential was recorded as a function of time, as shown in FIG. 7, with little overpotential of the catalystThe large change indicates that the Fe-NiV LDH has good stability under long-term operation.

The method further optimizes the nickel-based hydroxide material, obtains better electrolytic water catalysis effect, can replace noble metal catalysts, and has better application prospect.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.