CN114635148B

CN114635148B - Layered metal hydroxide array material with multilevel structure, preparation method and application thereof

Info

Publication number: CN114635148B
Application number: CN202210320340.7A
Authority: CN
Inventors: 钱国栋; 陈义; 崔元靖; 杨雨
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2022-03-29
Filing date: 2022-03-29
Publication date: 2023-06-20
Anticipated expiration: 2042-03-29
Also published as: CN114635148A

Abstract

The invention discloses a layered metal hydroxide array material with a multilevel structure, a preparation method and application thereof, wherein the microstructure is a three-dimensional multilevel array structure, the thickness of a primary nano sheet of the array is 30-80 nm, and the thickness of a secondary nano sheet of the array is 1-30 nm. The preparation method comprises (1) mechanically mixing monovalent, divalent and/or trivalent metal salts, heating and stirring to form molten salt solution. (2) And cleaning the substrate by using hydrochloric acid, ethanol and deionized water in sequence, and drying. (3) Placing the cleaned substrate into the molten salt in the step (1), taking out after the reaction, and obtaining a primary product. (4) And washing the preliminary product with deionized water, and drying to obtain the product. The preparation method is simple, low in cost and short in time consumption, is beneficial to large-scale preparation, and the catalyst prepared by the method is excellent in performance and superior to noble metal and most of Ni and Fe-based catalysts at present. The material of the invention can be used as an electrolytic water catalyst and has great industrial value.

Description

Layered metal hydroxide array material with multilevel structure, preparation method and application thereof

Technical Field

The invention belongs to the technical field of metal hydroxide preparation, and relates to a layered metal hydroxide array material with a multi-stage structure, a preparation method and application.

Background

Layered Double Hydroxides (LDHs) are also known asIs hydrotalcite, is a novel nano inorganic functional material with a layered structure, and the chemical composition of the material can be expressed as [ M ] ²⁺ _1–x M ³⁺ _x (OH) ₂ ][A ^n– ] _x/n ·zH ₂ O, where M ²⁺ Is Ni ²⁺ 、Co ²⁺ An isodivalent metal cation; m is M ³⁺ Is Ni ³⁺ 、Fe ³⁺ An aliovalent metal cation; a is that ^n- Being anionic, e.g. CO ₃ ^2- .NO ₃ -inorganic, organic ions.

The structure and composition of the LDHs can be regulated and controlled to change the electronic structure of the LDHs by regulating divalent and trivalent ions of the laminate and anions between the laminates. Because of the high selectivity of metal ions and interlayer anions, the catalyst has rich adjustability and is widely applied to the fields of catalysis, adsorption, environment, medicine, nano materials, functional polymer materials and the like. In particular in the field of electrocatalytic oxygen evolution, the performance of the catalyst can even be comparable to that of noble metal catalysts. Thus, the preparation of LDHs with high catalytic properties by simple steps is of great importance.

Currently, LDHs are usually prepared by conventional methods such as coprecipitation, sol-gel, hydrothermal, calcination recovery, and ion exchange methods (adv. Energy Mater.2021,2102141; adv.Mater.2021,33,2100745;J.Mater.Chem.A,2021,9,1456). Also, for example, a method for synthesizing LDHs is disclosed in chinese patent document with application publication number CN 108531938A, and a three-dimensional multi-stage cobalt-nickel-aluminum ternary metal electrocatalyst is synthesized by using ZIF-67 as a precursor. The method is suitable for preparing LDHs containing cobalt, and the synthesis step needs two steps of hydrothermal reaction.

The hydroxides prepared by the method have good crystallinity. However, for electrocatalysis, it is desirable to have enough active sites, i.e., defect sites, including point defects and one-dimensional defects (dislocations, etc.). Such defects often need to be introduced by additional preparation methods on the basis of the above-mentioned synthetic materials. However, these methods have difficulty in controlling the quality and quantity of defect generation, and in generating an array having a good multi-level spatial structure, even with damage to the original spatial structure. If the layered double hydroxide with a three-dimensional multistage structure can be rapidly prepared in one step, the damage of complicated reaction process to the space structure can be avoided, and meanwhile, the self-supporting structure is also beneficial to rapid transmission of electrons and transfer of reactive substances and products. In addition, although the conventional molten salt method can rapidly prepare materials, it is limited to oxides, nitrides, etc., and hydroxides are difficult to be suitably prepared by the conventional molten salt method because they are easily damaged at high temperatures.

Therefore, a simple and rapid method for preparing the layered metal hydroxide with the three-dimensional multi-stage structure with universality is developed, and the method has great significance for design and performance optimization of electrocatalytic materials.

Disclosure of Invention

The invention aims to overcome the problems and the defects of the prior art and provide a preparation method of a three-dimensional multi-stage structure layered metal hydroxide with universality, which can prepare a series of catalysts, and the prepared catalysts show very excellent catalytic performance.

In order to achieve the technical effects, the invention adopts the following technical scheme:

according to a specific embodiment of the invention, the preparation method of the layered metal hydroxide array with the multi-stage structure comprises the following steps:

(1) Different monovalent, divalent and/or trivalent metal salt solid powders are mechanically mixed, and different metal salts can be selected according to the prepared product. After mechanical mixing, the mixture is transferred to a crucible for heating and stirring to form a uniform molten salt solution.

(2) The foam nickel is cleaned by hydrochloric acid, ethanol and deionized water in sequence and dried. The foam nickel can also be a metal framework or a metal sheet such as foam iron, foam copper and the like as a substrate;

(3) The washed foam nickel is put into the molten salt solution in the step (1), and is taken out after the reaction, thus obtaining the primary product.

(4) Washing the preliminary product with deionized water, and drying to obtain a product, namely the layered metal hydroxide array material with the multi-stage structure;

the material is characterized in that a primary nano-sheet array structure grows on a substrate, and a secondary nano-sheet grows on the primary nano-sheet; the whole structure forms a three-dimensional multi-stage structure; wherein the thickness of the primary nano-sheet is 30-80 nm, and the thickness of the secondary nano-sheet is 1-30 nm; the material contains abundant crystal defects such as dislocation, vacancy and the like; can be used as an electrolytic water catalyst with excellent catalytic performance.

Further, the monovalent, divalent, trivalent metal salts in the step (1) are K respectively ⁺ 、Na ⁺ ，Ni ²⁺ 、Co ²⁺ 、Fe ²⁺ 、Mn ²⁺ 、Cu ²⁺ 、Zn ²⁺ ，Fe ³⁺ 、Al ³⁺ With CO ₃ ^2- 、SO ₄ ^2- 、Cl ^- 、F-、Br ^- Any one or more of the salts respectively formed.

Further, in the step (2), the foam nickel is ultrasonically cleaned in 3 mol/L hydrochloric acid for 15 minutes, and then sequentially transferred to ethanol and deionized water for respectively ultrasonically cleaning for 15 minutes. And (5) putting the cleaned foam nickel into a vacuum oven for drying at 30 ℃ for 6 hours.

In one embodiment of the present invention, the metal salt in step (1) is ferric nitrate and nickel nitrate in a mass ratio of 1:1.

Further, the heating temperature in the step (3) is 150 ℃, and the reaction time is 7 minutes.

Further, in the step (4), the obtained primary product is directly washed by flowing deionized water, and after washing is finished, the final product can be obtained by natural drying; the final product finally obtained is FeNi LDH.

The invention also provides other layered metal hydroxide three-dimensional multilevel arrays obtained by the preparation method, including NiNi LDH, niCo LDH, feCoNi LDH and the like.

LDHs are believed to be very advanced non-noble metal water catalysts, but LDHs prepared by conventional methods have only a single array structure. Meanwhile, a great deal of research shows that the introduction of defects and stress fields in the catalyst can improve the catalytic activity of the catalyst. However, since LDHs are inherently relatively sensitive and are easily destroyed during post-treatment, how to efficiently introduce defects and stresses into LDHs is an important method for adjusting the free energy of adsorption of reactive intermediates. In addition, the preparation process of the conventional method is time-consuming. Typical hydrothermal reactions require long and high temperature and high pressure reactor conditions, which greatly increase unsafe factors.

Therefore, the LDHs electrochemical catalyst with a multi-stage array is successfully prepared by adopting a molten salt method, and the prepared catalyst is rich in dislocation defects, can introduce stress fields, improves the adsorption free energy of the catalyst and improves the catalytic performance. Meanwhile, the method overcomes the defect that the traditional molten salt method can only prepare oxides, and can play a role in the process of preparing hydroxides.

Compared with the prior art, the method has the following beneficial effects: the invention adopts simple and easy-to-operate fused salt to prepare the three-dimensional multilevel array which is rich in crystal defects such as dislocation and the like. Compared with the prior method, the method has lower cost and shorter synthesis time. Compared with the traditional hydrothermal method, the synthesis conditions are safer. The overpotential for oxygen production under alkaline conditions is only 200mV (current density of 10mA cm ^-2 ) Is superior to other Fe and Ni-based catalysts reported in the prior art. The preparation method of the invention is simple, has universality and is suitable for industrial production.

Drawings

FIG. 1 is a schematic diagram of a catalyst preparation technique route (taking NiNi LDH, foam nickel substrate as an example);

FIG. 2 is a comparison of XRD patterns (NiNi LDH-HT) of example 1 and those synthesized by conventional hydrothermal methods;

FIG. 3 is an SEM and TEM image of example 1;

FIG. 4 is a TEM of example 1 and a corresponding Fourier transform plot;

FIG. 5 is a linear sweep voltammogram (reverse sweep) of example 1 tested in alkaline electrolyte

FIG. 6 is the XRD patterns of examples 2 and 3;

FIG. 7 is an SEM and TEM image of example 2

FIG. 8 is a TEM of example 2 and a corresponding Fourier transform plot;

FIG. 9 is a linear sweep voltammogram (reverse sweep) of example 2 tested in alkaline electrolyte.

FIG. 10 is a linear sweep voltammogram (reverse sweep) of examples 3,4 tested in alkaline electrolyte.

Detailed Description

The invention is further illustrated and described below in connection with specific examples, but embodiments of the invention are not limited thereto.

Example 1

A preparation method of a layered metal hydroxide array material comprises the following specific steps:

20g KNO ₃ ，10g Ni(NO ₃ ) ₂ ·6H ₂ O, mechanically mixing, transferring the mixture into a crucible after mixing, and placing the crucible in a muffle furnace for heating to 150 ℃, and stirring to form a uniform molten salt solution.

The nickel foam was ultrasonically cleaned with 3.0 moles per liter of hydrochloric acid, ethanol, deionized water for 15 minutes each, and placed in a vacuum oven for 6 hours at 30 ℃.

Immersing the cleaned foam nickel in the molten salt in the step 1, reacting for 7 minutes, and taking out to obtain a primary product.

And (3) cleaning the preliminary product by using flowing deionized water, and naturally drying to obtain the product, namely the layered metal hydroxide electrolyzed water catalyst NiNi LDH. In fig. 3, a and b can be seen that the composite material has a three-dimensional array structure, and c can be seen that the material has a large number of lattice defects. It can be seen further in fig. 4 that there are a large number of dislocations in the material. Fig. 5 is a graph showing the electrocatalytic oxygen evolution reaction performance, and it can be seen that the catalyst (NiNi LDH) prepared by the method has better performance than the traditional hydrothermal method (NiNi LDH-HT).

Example 2

20g KNO ₃ ，15g Ni(NO ₃ ) ₂ ·6H ₂ O，15g Fe(NO ₃ ) ₃ ·9H ₂ O is mechanically mixed, after which the mixture is transferred to a crucible and the crucible is placed in a muffle furnace and heated to 150 ℃ and stirred to form a uniform molten salt solution.

And (3) cleaning the preliminary product by using flowing deionized water, and naturally drying to obtain the product, namely the layered metal hydroxide electrolyzed water catalyst FeNi LDH. Fig. 7 shows that the composite material has an array structure, and has a number of structural defects. It is evident from fig. 8 that the material has a large number of dislocations. Fig. 9 is a graph showing the performance comparison of the method (FeNi LDH) and FeNi LDH-HT prepared by conventional hydrothermal methods, and it can be seen that the material prepared by the method has more excellent catalytic performance.

Example 3

20g KNO ₃ ，15g Ni(NO ₃ ) ₂ ·6H ₂ O, and 15g Co (NO) ₃ ) ₂ ·6H ₂ O is mechanically mixed, after which the mixture is transferred to a crucible and the crucible is placed in a muffle furnace and heated to 150 ℃ and stirred to form a uniform molten salt solution.

And (3) cleaning the preliminary product by using flowing deionized water, and naturally drying to obtain the product, namely the layered metal hydroxide electrolyzed water catalyst NiCo LDH. Fig. 10 is a graph of the performance of the present process (NiCo LDH).

Example 4

20g KNO ₃ ，10g Ni(NO ₃ ) ₂ ·6H ₂ O，10g Fe(NO ₃ ) ₃ ·9H ₂ O and 10g Co (NO) ₃ ) ₂ ·6H ₂ O is mechanically mixed, after which the mixture is transferred to a crucible and the crucible is placed in a muffle furnace to be heated to 150 ℃ and stirred to form a uniform molten salt solution.

And (3) cleaning the preliminary product by using flowing deionized water, and naturally drying to obtain the product, namely the layered metal hydroxide electrolyzed water catalyst FeCoNi LDH. FIG. 10 is a graph showing the performance of the method (FeCoNi LDH).

Example 5

20g KNO ₃ ，10g Ni(Cl) ₂ ·6H ₂ O, and 10g Co (Cl) ₂ ·6H ₂ O is mechanically mixed, after which the mixture is transferred to a crucible and the crucible is placed in a muffle furnace for heating to 600 c and stirring to form a uniform molten salt solution.

Immersing the cleaned foam nickel in the molten salt in the step 1, reacting for 15 seconds, and taking out to obtain a primary product.

And (3) cleaning the preliminary product by using flowing deionized water, and naturally drying to obtain the product, namely the layered metal hydroxide electrolyzed water catalyst.

Although the invention has been described herein with reference to the above-described illustrative embodiments thereof, the above-described embodiments are merely preferred embodiments of the present invention, and the embodiments of the present invention are not limited by the above-described embodiments, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope and spirit of the principles of this disclosure.

Claims

1. A layered metal hydroxide array material with a multi-stage structure is characterized in that the metal is Ni ²⁺ 、Co ² ⁺ 、Fe ²⁺ 、Mn ²⁺ 、Cu ²⁺ 、Zn ²⁺ 、Fe ³⁺ 、Al ³⁺ The material is one or more of a primary nano-sheet array structure grown on a substrate or a secondary nano-sheet also grown on the primary nano-sheet; the whole three-dimensional multilevel structure is formed, and the preparation method of the material comprises the following steps:

to monovalent inorganic salts M ⁺ Y, with divalent inorganic salts M ²⁺ Y or trivalent inorganic salts M ³⁺ One or more of the Y are uniformly mixed, and the mixture is transferred into a crucible for heating, wherein the heating temperature range is 100-800 ℃ according to the difference of molten salt addition, so that the mixed salt forms uniform molten solution; immersing the cleaned substrate into the molten solution, taking out a preliminary product after reacting for 1-30 minutes, cleaning with flowing deionized water, and drying to obtain a layered metal hydroxide array material with a multi-stage structure; wherein M in monovalent inorganic salts ⁺ For K ⁺ 、Na ⁺ The method comprises the steps of carrying out a first treatment on the surface of the M in divalent inorganic salt ²⁺ Is Ni ²⁺ 、Co ²⁺ 、Fe ²⁺ 、Mn ²⁺ 、Cu ²⁺ Or Zn ²⁺ Any one or more of the following; m in trivalent inorganic salts ³⁺ Is Fe ³⁺ 、Al ³⁺ The method comprises the steps of carrying out a first treatment on the surface of the Y is CO ₃ ^2- 、SO ₄ ^2- 、Cl ^- 、F ^- 、Br ^- Any one of the following.

2. The layered metal hydroxide array material having a multi-stage structure according to claim 1, wherein the thickness of the primary nanoplatelets is 30 to 80nm and the thickness of the secondary nanoplatelets is 1 to 30nm.

3. The layered metal hydroxide array material having a multi-stage structure according to claim 1, wherein the substrate is a foam metal substrate or a corresponding sheet.

4. A method for preparing a layered metal hydroxide array material having a multi-stage structure according to any of claims 1 to 3, wherein the multi-stage layered metal hydroxide array grown in situ on a substrate is obtained by a one-step molten salt synthesis method.

5. The method for preparing a layered metal hydroxide array material having a multi-stage structure according to claim 4, comprising the steps of:

6. Use of a layered metal hydroxide array material having a multi-stage structure according to any of claims 1-3 as a catalyst for the electrolysis of water.