CN112501650A

CN112501650A - Multi-vacancy transition metal layered dihydroxy compound, preparation method and application

Info

Publication number: CN112501650A
Application number: CN202011232643.0A
Authority: CN
Inventors: 杨世和; 王亚琼
Original assignee: Peking University Shenzhen Graduate School
Current assignee: Peking University Shenzhen Graduate School
Priority date: 2020-11-06
Filing date: 2020-11-06
Publication date: 2021-03-16
Anticipated expiration: 2040-11-06
Also published as: CN112501650B

Abstract

The invention relates to the technical field of new energy and electrocatalytic materials, and discloses a multi-vacancy transition metal layered dihydroxy compound, a preparation method and application thereof. The preparation method anchors TM LDH by using organic micromolecules which have continuous double bond functional groups and the tail ends of which can be coordinated with transition metals, so that the TM LDH with multiple vacant sites is formed. The invention also discloses the prepared multi-vacancy TM LDH and application thereof, and a water decomposition anode and a water decomposition three-electrode system which take the multi-vacancy TM LDH as a catalyst. The water decomposition anode is applied to the electric decomposition of water, and compared with the traditional foam nickel electrode, the water decomposition anode shows lower overpotential and Tafel slope, greatly improves the water decomposition capability and reduces the cost of hydrogen production by water decomposition.

Description

Multi-vacancy transition metal layered dihydroxy compound, preparation method and application

Technical Field

The invention relates to the technical field of new energy, in particular to a multi-vacancy transition metal layered dihydroxy compound, a preparation method and application.

Background

With the increasing number of global population and the rapid development of the modernization process of human society, the demand of energy as an important material basis of national economy is increasing greatly on the global scale, and the following environmental problems are becoming prominent. The current global energy consumption is reported to be mostly dependent on traditional fossil energy, such as coal, petroleum, natural gas and the like, and accounts for about 87.9%, while the national fossil energy consumption proportion is as high as 93.8%. Tradition ofIs a non-renewable resource with limited reserves on earth. The rapid development of economy and the increasing population have led to a continuous increase in energy demand and consumption, resulting in a continuous decrease in fossil energy reserves. If developed at present, resource exhaustion, greenhouse effect and environmental pollution become inevitable problems for human beings. Hydrogen is a novel clean energy which is expected to replace the traditional fossil energy. The hydrogen energy has abundant sources, high combustion energy density, no pollution of combustion products, easy storage and transportation and wide application range, is widely researched in the last 30 years, is considered as the most ideal green energy in the 21 st century and is the most promising green energy for replacing the traditional fossil fuel. Efficient, cheap and pollution-free hydrogen (H) production₂) Is the basis for realizing large-scale production and utilization of hydrogen energy. The application of electrocatalysis water cracking reaction to prepare hydrogen is efficient and safe, and is considered to be the most practical application in the future and can be used for preparing high-purity H on a large scale₂The main route of (1).

The hydrogen production by water decomposition is to prepare hydrogen by decomposing water by electricity or light, and the chemical reaction formula is 2H₂O→2H²⁺O₂. The reaction process includes a cathodic Hydrogen Evolution Reaction (HER) and an anodic Oxygen Evolution Reaction (OER). The reaction kinetics of the anode oxygen production reaction is very slow, and the process of hydrogen production by water decomposition is greatly limited. The price of hydrogen production by water electrolysis is higher than that of hydrogen production by natural gas steam conversion and hydrogen production by methanol cracking at present. Therefore, the development of the efficient and cheap water decomposition catalyst, the reduction of the energy barrier of the OER reaction and the reduction of the energy consumption required by hydrogen production through water decomposition are of great importance for the large-scale preparation of high-purity hydrogen, the development of new energy, the promotion of the development of fields such as hydrogen energy automobiles and the like and the alleviation of environmental pollution.

Layered Double Hydroxides (LDHs) are composed of a positively charged main plate layer of metal ions and hydroxyl ligands and interlayer anions for charge compensation. Transition metal-based layered double hydroxide (TM LDH) is an LDH in which metal ions in the main plate layer are transition metal ions. In recent years, TM LDH has been inThe application of the field of hydrogen production by water decomposition is greatly developed. The catalytic oxygen production activity and stability of the TM LDH are close to those of a noble metal oxygen production catalyst iridium oxide (IrO)₂) And ruthenium oxide (RuO)₂). And the reserves of non-noble metals such as transition metals on the earth are abundant, so that the non-noble metal water decomposition catalyst such as TM LDH has larger application potential compared with a noble metal catalyst.

The TM LDH may be optimized to further improve its catalytic performance. The presence of vacancies in the catalyst can significantly adjust the local atomic structure, thereby adjusting the electronic configuration of the surface and creating an unsaturated coordination geometry. The combination of anionic and cationic complex ions often produces a synergistic effect, enhancing electrochemical activity, as compared to the anionic or cationic vacancies alone. For example, Wang and colleagues first exfoliated the CoFe bulk LDH with Ar-plasma and then created multiple vacancies (including O, Co and Fe vacancies) on ultra-thin 2D nanosheets. Recently, new technologies, such as lasers and flames, have shown their potential to create vacant applications. However, the fundamental principle of creating the vacancy is still unknown and cannot be quantitatively controlled. Zhang et al prepared a single layer NiFe LDH with various Ni, Fe and O vacancies at high concentrations of salt at pH 10, resulting in higher conductivity, larger electrochemical surface area (ECSA) and faster charge transfer than LDH.

However, some methods of complex dialysis are random and limited to single-layer LDHs. Furthermore, few methods consider multilayer materials and produce multiple vacancies in the plane of the substrate, and a specific method of activating the substrate face of the layered material is required to take full advantage of conventional LDH materials.

Disclosure of Invention

The invention aims to anchor organic small molecules of a transition metal layered double hydroxyl compound (TM LDH for short) to obtain the TM LDH with multiple vacancies, which can be used as a catalyst of an oxygen generation reaction in a water decomposition reaction to improve the hydrogen production performance by water decomposition.

Accordingly, a first aspect of the invention provides a method for the preparation of an organic small molecule anchored TM LDH, the method comprising the steps of:

(1) uniformly dispersing TM LDH in a polar solvent to obtain a TM LDH suspension, wherein the transition metal is any combination of divalent and trivalent transition metal ions;

(2) and (2) adding an appropriate amount of organic micromolecules for activation reaction into the suspension liquid obtained in the step (1), and performing activation reaction to obtain the TM LDH treated by the organic micromolecules.

(3) Washing the TM LDH treated by the organic micromolecules in the step (2) with an organic solvent, and drying to obtain the multi-vacancy TM LDH.

In a preferred embodiment of the first aspect of the invention, the atomic ratio of the divalent/trivalent transition metal ions is between 3 and 10:1, more preferably between 4 and 8:1, still more preferably between 5 and 6: 1.

In a preferred embodiment of the first aspect of the invention, any component of the transition metal ion specifically refers to Ni²⁺/Fe³⁺Combination, Ni²⁺/Co³⁺Combinations or Co²⁺/Fe³⁺In combination, more preferably Ni²⁺/Fe³⁺And (4) combining.

In a preferred embodiment of the first aspect of the invention, in step (1), the weight to volume ratio of the TM LDH to the polar solvent is 0.5-2mg:1ml, i.e. the weight (mg) of TM LDH to volume of polar solvent (ml) is 0.5-2:1, more preferably 0.8-1.8mg:1ml, still more preferably 1.0-1.5mg:1 ml.

In a preferred embodiment of the first aspect of the present invention, in step (1), the polar solvent is deionized water or ethanol or a mixed solvent thereof.

In a preferred embodiment of the first aspect of the present invention, in the step (2), the small organic molecule is a small organic molecule having a continuous double bond functional group and a terminal capable of coordinating with a transition metal, and includes not only methyl isothiocyanate (CH)₃NCS), methyl isocyanate (CH)₃NCO)。

In a preferred embodiment of the first aspect of the invention, a suitable final concentration of the small organic molecules used in step (2) is 0.01-1.0M.

In a preferred embodiment of the first aspect of the present invention, the reaction temperature of the anchoring reaction is 60 to 100 ℃ and the reaction time is 0.5 to 10 hours, more preferably, the reaction temperature is 70 to 90 ℃ and the reaction time is 1 to 5 hours.

In a preferred embodiment of the first aspect of the present invention, in step (3), the organic solvent used is a polar organic solvent, including not only ethanol, acetonitrile, methanol or any mixture thereof.

In a particularly preferred embodiment of the first aspect of the invention, the preparation process comprises the following specific steps:

(1) ni in an atomic ratio of 3-10:1²⁺/Fe³⁺、Ni²⁺/Co³⁺Or Co²⁺/Fe³⁺Uniformly dispersing TM LDH in deionized water or ethanol or a mixed solvent thereof, wherein the weight-volume ratio of the TM LDH to the polar solvent is 0.5-2mg:1ml, and uniformly dispersing the TM LDH by ultrasonic vibration and stirring to obtain a TM LDH suspension;

(2) adding CH with final concentration of 0.01-1.0M into the suspension of the step (1)₃NCS is stirred and dispersed evenly under the stirring speed of 400-1000rpm, then reacts for 0.5-10 hours under the reaction temperature of 60-100 ℃ and the stirring speed of 700-1000rpm, after the mixture is naturally cooled to room temperature, a proper amount of absolute ethyl alcohol is added as a washing solvent, the mixture is centrifugally washed for three times under 6000-8000rpm, each time for 5-10 minutes, and then vacuum drying is carried out for 3-6 hours, so as to obtain the multi-vacancy TM LDH.

In the above particularly preferred embodiment of the first aspect of the invention, the weight to volume ratio of the TM LDH to the polar solvent is more preferably 0.8-1.8mg:1ml, still more preferably 1.0-1.5mg:1 ml.

In the above-mentioned specifically preferred embodiment of the first aspect of the present invention, in step (2), the CH₃The final concentration of NCS is more preferably 0.05-0.07M; the reaction temperature of the reaction is more preferably 70 to 90 ℃ and the reaction time is more preferably 3 to 8 hours.

In a second aspect the invention provides a multi-vacancy TM LDH (multi-vacancy TM LDH is referred to as v-TM LDH) electrode, which is prepared by the preparation method of the first aspect of the invention.

A third aspect of the invention provides the use of the v-TM LDH of the second aspect of the invention as an oxygen-producing catalyst for a water-splitting anode.

A fourth aspect of the invention provides a water-splitting anode comprising a foamed nickel, carbon cloth or iron substrate and a v-TM LDH electrode coated on the foamed nickel, carbon cloth or iron substrate. The v-TM LDH acts as an oxygen production catalyst for the water splitting anode.

The water-splitting anode can be prepared by the following steps: taking 1-2mg of the v-TM LDH catalyst, placing the v-TM LDH catalyst in 1ml of absolute ethyl alcohol, and performing strong ultrasonic dispersion to obtain a catalyst dispersion liquid. Uniformly mixing 200-500 mu L of catalyst dispersion liquid prepared with PTFE aqueous solution with the mass fraction of 4-8% according to the volume ratio of 1-3:1, and performing ultrasonic dispersion. And uniformly coating the obtained mixed dispersion liquid on a foamed nickel, carbon cloth or iron substrate, and drying in an oven at 40-70 ℃ for 20-40 minutes.

A fifth aspect of the invention provides a water-splitting three-electrode system comprising a water-splitting anode according to the fifth aspect of the invention, Pt wire as a counter electrode, Ag/AgCl as a reference electrode and 0.5-1.5M aqueous potassium hydroxide or sodium hydroxide solution as an electrolyte. Preferably, the electrolyte is a 1M aqueous solution of potassium hydroxide or sodium hydroxide.

The invention has the beneficial effects that:

according to the preparation method of the TM LDH with the multiple vacant sites, the hydroxyl and the metal in the LDH are respectively anchored to act through a nucleophilic addition and coordination reaction mechanism, so that an organic complex is formed. The organic complex is washed away from the etched LDH by washing with a polar organic solvent to form a multi-vacancy TM LDH having both O and M vacancies. The generation of the vacancy is helpful for solving the problem of difficult electron transfer between transition metal ions, solving the condition of non-ideal electron arrangement of the transition metal ions and realizing the optimal electron arrangement of the catalytic active atoms.

The TM LDH with multi-vacancy prepared by the preparation method can be used as a water decomposition anode catalyst, so that efficient and stable oxygen production is realized, and the hydrogen production performance of the catalyst for decomposing water is improved. The water decomposition anode prepared by the multi-vacancy TM LDH is applied to the electrolysis of water, and compared with the traditional foam Nickel (NF) electrode, the water decomposition anode shows lower overpotential and Tafel slope, greatly improves the water decomposition capability and reduces the cost of hydrogen production by water decomposition.

Drawings

FIG. 1 is a washing of CH with ethanol and deionized water₃Schematic representation of NCS-targeted LDH solutions. The washing solution was clear by using deionized water and brown by ethanol.

FIG. 2 is an XRD image of a NiFe LDH and a multi-vacancy v-NiFe LDH in accordance with example 1 of the present invention.

FIG. 3 is a TEM (HRTEM) image of (A-D) NiFe LDH and (E-H) v-NiFe LDH. The red circles in G and H indicate lattice distortion.

FIG. 4 shows the present example in organic CH₃The polarization curve plot of v-NiFe LDH obtained by NCS treatment and washing is compared with that of NiFe LDH. As can be seen from fig. 4, the v-NiFe LDH catalyst has the lowest overpotential, indicating that the catalyst has better electrochemical properties.

FIG. 5 shows the present example in organic CH₃The tafel slope of v-NiFe LDH washed by NCS treatment was compared with that of NiFe LDH. As can be seen from fig. 5, the v-NiFe LDH catalyst has the lowest tafel slope, indicating that the catalyst has better electrochemical properties.

FIG. 6 shows the v-NiFe LDH of this example at 50mA cm^-2A chronopotentiometric test chart at a current density of (1). Where the inset is v-NiFe LDH at 50mA cm^-2A long-time chronopotentiometric test pattern of more than 8 hours at a current density of (a).

FIG. 7 shows the present embodiment in organic CH₃The polarization curve of v-NiCo LDH obtained by NCS treatment and washing is compared with that of NiCo LDH. As can be seen from FIG. 7, the v-NiCo LDH catalyst has the lowest overpotential, indicating that the catalyst has better electrochemical properties.

FIG. 8 shows the present example in organic CH₃The tafel slope of the v-NiCo LDH washed by NCS treatment was compared with that of NiCo LDH. As can be seen from FIG. 8, the v-NiCo LDH catalyst has the lowest Tafel slope, indicating that the catalyst has better electrochemical properties.

FIG. 9 shows the present embodiment in organic CH₃The polarization profile of v-CoFe LDH from NCS treatment washes was compared to CoFe LDH. As can be seen from FIG. 9, the v-CoFe LDH catalyst has the lowest overpotential, indicating that the catalyst has better electrochemical properties.

FIG. 10 shows the present example in organic CH₃The tafel slope of v-CoFe LDH washed by NCS treatment was compared to CoFe LDH. As can be seen from FIG. 10, the v-CoFe LDH catalyst has the lowest Tafel slope, indicating that the catalyst has better electrochemical properties.

FIG. 11 shows the present example in organic CH₃S-CN treatment of the washed CH₃The S-CN-NiFe LDH polarization curve graph is compared with the NiFe LDH. As can be seen from FIG. 11, CH₃The S-CN-NiFe LDH catalyst does not produce multi-vacancies and has inferior performance to NiFe LDH.

FIG. 12 is a schematic structural diagram of a three-electrode system with NiFe LDH as the water electrolysis anode catalyst according to a test example of the present invention, wherein 1 denotes a working electrode, 2 denotes a reference electrode, and 3 denotes a counter electrode.

Detailed Description

The present invention will be described in further detail below with reference to specific embodiments and accompanying drawings.

Examples

Description of the drawings:

examples the following parameters were varied mainly:

the atomic ratio of the divalent/trivalent transition metal ions is (3-10): 1;

the weight-volume ratio of TM LDH to polar solvent (0.5-2) mg:1 ml;

the final concentration of the organic micromolecules is 0.01-1.0M;

the reaction temperature is 60-100 ℃, and the reaction time is 0.5-10 hours.

Example 1: synthesis and characterization of NiFe LDH catalyst (v-NiFe LDH for short) treated by organic small molecules

1.1 Synthesis of NiFe LDH

NiFe LDH nano powder is synthesized by a hydrothermal method, and the specific operation is as follows. 0.725ml of 1M nickel chloride (NiCl) was added in a beaker₂) Aqueous solution and 0.145ml of 1M iron chloride (FeCl)₃) The aqueous solution was mixed with 70.8ml of deionized water. Then 5.6ml of 0.5M aqueous urea solution and 2ml of 0.01M aqueous trisodium citrate solution were added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. After the reaction, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to prepare NiFe LDH nanopowder, which is Ni²⁺/Fe³⁺Transition metal layered dihydroxy compounds.

Synthesis of 1.2 v-NiFe LDH catalyst

Adding 1mg of the NiFe LDH powder prepared in the above step into 10ml of deionized water in a 15ml sealed bottle, and preparing a NiFe LDH suspension by ultrasonic vibration at the vibration frequency of 50KHz and uniformly stirring and dispersing at the stirring speed of 800 rmp. Adding 0.5M of small organic molecule CH into a sealed bottle₃The NCS ethanol reagent is stirred and dispersed evenly at the stirring speed of 500rpm to obtain CH₃The final NCS concentration was 0.05M. The beaker was placed in a 75 ℃ water bath and reacted for 2 hours at a stirring speed of 800 rpm. After the reaction is finished, the reaction product is naturally cooled to room temperature. The organic small molecule treated NiFe LDH was washed separately with water and ethanol as controls and centrifuged at 7000rpm for 10 minutes. Until the wash liquid is clear. And (3) drying the final precipitate for 5 hours in vacuum at the pressure of-100 KPa relative to the atmospheric pressure to obtain the v-NiFe LDH catalyst.

1.3 characterization of the Multi-vacancy NiFe LDH (v-NiFe LDH) catalyst

FIG. 1 is a washing of CH with ethanol and deionized water₃NCS-targeted LDH, then centrifuged. The washing solution was clear by using deionized water and brown by ethanol.

FIG. 2 shows XRD patterns of the present example on NiFe LDH and a multi-vacancy v-NiFe LDH, showing the same characteristic diffraction peaks, indicating that the crystal phase is unchanged and the crystallinity is high.

FIG. 4 shows the present example in organic CH₃The polarization curve plot of v-NiFe LDH obtained by NCS treatment and washing is compared with that of NiFe LDH. As can be seen from fig. 3, the v-NiFe LDH catalyst has the lowest overpotential, indicating that the catalyst has better electrochemical properties.

FIG. 5 shows the present example in organic CH₃The tafel slope of v-NiFe LDH washed by NCS treatment was compared with that of NiFe LDH. As can be seen from fig. 4, the v-NiFe LDH catalyst has the lowest tafel slope, indicating that the catalyst has better electrochemical properties.

FIG. 6 is a graph showing v-NiFe LDH at 50mA cm^-2The current density of (a), wherein the inset is the v-NiFe LDH at 50mA cm^-2A long-time chronopotentiometric test pattern of more than 8 hours at a current density of (a).

Example 2: CH (CH)₃Synthesis of NCS-treated washed NiCo LDH catalyst (v-NiCo LDH)

2.1 Synthesis of NiCo LDH

NiCo LDH nano powder is synthesized by a hydrothermal method, and the specific operation is as follows. 0.435ml of 1M nickel chloride (NiCl) was added in a beaker₂) Aqueous solution and 0.145ml of 1M cobalt chloride (CoCl)₂) The aqueous solution was mixed with 70ml of deionized water. 4.48ml of a 0.5M aqueous urea solution and 1.6ml of a 0.01M aqueous trisodium citrate solution were then added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. After the reaction, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to prepare NiCo LDH nanopowder, which is Ni²⁺/Co³⁺Transition metal layered dihydroxy compounds.

Synthesis of 2.2 v-NiCo LDH catalyst

0.5mg of NiCo LDH powder prepared as described above was added to 1ml of deionized water in a 15ml sealed bottle, and NiMn LD was prepared by ultrasonic vibration at an amplitude of 50KHz and uniformly dispersed by stirring at a stirring speed of 800rmpAnd H, suspending the solution. CH was added to the beaker to a final concentration of 0.05M₃NCS ethanol solution. The beaker was placed in a 80 ℃ water bath and reacted for 10 hours at a stirring speed of 800 rpm. After the reaction, the reaction mixture was cooled to room temperature and centrifuged at 7000rpm to wash the reaction mixture with the organic solvent for 10 minutes. Until the upper layer liquid was clear, a centrifugal washing was performed twice more in the same manner. And (4) drying the final precipitate for 5 hours in vacuum to obtain the v-NiCo LDH catalyst.

Example 3: CH (CH)₃Synthesis of NCS-anchored CoFe LDH catalyst (v-CoFe LDH)

3.1 Synthesis of CoFe LDH

CoFe LDH nanopowder was synthesized by a hydrothermal method, specifically as follows. 0.145ml of 1M cobalt chloride (CoCl) was placed in a beaker₂) Aqueous solution and 1.45ml of 1M iron chloride (FeCl)₃) The aqueous solution was mixed with 70ml of deionized water. Then 11.2ml of 0.5M aqueous urea solution and 4ml of 0.01M aqueous trisodium citrate solution were added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml teflon-lined stainless steel autoclave, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. After the reaction, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to prepare CoFe LDH nanopowder, which is Co²⁺/Fe³⁺Transition metal layered dihydroxy compounds.

Synthesis of 3.2 v-CoFe LDH catalyst

Adding 2mg of CoFe LDH powder prepared above to a 15ml sealed bottleCoFe LDH suspension was prepared by ultrasonic vibration in 10ml of absolute ethanol at an amplitude of 50KHz and uniformly dispersed with stirring at a stirring speed of 800 rmp. CH was added to the beaker to a final concentration of 0.05M₃The NCS ethanol solution was uniformly dispersed with stirring at a stirring speed of 500 rpm. The sealed bottle was placed in a 75 ℃ water bath and reacted for 2 hours at a stirring speed of 800 rpm. After the reaction was completed, it was naturally cooled to room temperature, and centrifuged at 7000rpm for 10 minutes. Until the wash was clear, two more centrifugation washes were performed in the same manner. And (4) drying the final precipitate for 5 hours in vacuum to obtain the v-CoFe LDH catalyst.

Example 4: CH (CH)₃NiFe LDH Catalyst (CH) of S-CN₃Synthesis and characterization of S-CN-NiFe LDH)

4.1 Synthesis of NiFe LDH

NiFe LDH nano powder is synthesized by a hydrothermal method, and the specific operation is as follows. 0.725ml of 1M nickel chloride (NiCl) was added in a beaker₂) Aqueous solution and 0.145ml of 1M iron chloride (FeCl)₃) The aqueous solution was mixed with 70.8ml of deionized water. Then 5.6ml of 0.5M aqueous urea solution and 2ml of 0.01M aqueous trisodium citrate solution were added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. After the reaction, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to prepare NiFe LDH nanopowder, which is Ni²⁺/Fe³⁺Transition metal layered bisA hydroxy compound.

4.2 CH₃Synthesis of S-CN v-NiFe LDH catalyst

Adding 1mg of the NiFe LDH powder prepared in the above step into 10ml of deionized water in a 15ml sealed bottle, and preparing a NiFe LDH suspension by ultrasonic vibration at the vibration frequency of 50KHz and uniformly stirring and dispersing at the stirring speed of 800 rmp. Adding 0.5M of small organic molecule CH into a sealed bottle₃Stirring and dispersing the S-CN ethanol reagent uniformly at the stirring speed of 500rpm to obtain CH₃The final NCS concentration was 0.05M. The beaker was placed in a 75 ℃ water bath and reacted for 2 hours at a stirring speed of 800 rpm. After the reaction is finished, the reaction product is naturally cooled to room temperature. The organic small molecule treated NiFe LDH was washed separately with water and ethanol as controls and centrifuged at 7000rpm for 10 minutes. Until the wash liquid is clear. And (3) drying the final precipitate for 5 hours in vacuum at the pressure of-100 KPa relative to the atmospheric pressure to obtain the v-NiFe LDH catalyst.

4.3 CH₃S-CN-NiFe LDH and CH₃Characterization of the-CN-NiFe LDH catalyst

FIG. 11 shows the present example in organic CH₃S-CN and CH₃CN treatment of the washed CH₃S-CN-NiFe LDH、CH₃The polarization curve of-CN-NiFe LDH is compared with that of NiFe LDH. As can be seen from FIG. 11, CH₃S-CN-NiFe LDH and CH₃the-CN-NiFe LDH catalyst did not produce multi-vacancies, which were not as good as NiFe LDH.

Example 5: CH (CH)₃NiFe LDH catalyst for NCO (v)₁-NiFe LDH) Synthesis

This example was carried out in the same manner as example 1, but using CH at a final concentration of 1M₃NCO, finally to produce v₁-a NiFe LDH catalyst.

Example 6: c₂H₅NiFe LDH catalyst for NCO (v)₂-NiFe LDH) Synthesis

This example was carried out in the same manner as in example 1, but using C at a final concentration of 1M₂H₅NCO, finally to produce v₂-a NiFe LDH catalyst.

Example 7: preparation of catalyst/foamed nickel electrode

The nickel foam was immersed in 1M HCl solution for 10 minutes to remove surface oxides, then washed several times with deionized water and ethanol, and dried in an oven at 60 ℃ until use. 1mg of the H-NiFe LDH catalyst synthesized in example 1 was ultrasonically and uniformly dispersed in 0.25ml of ethanol for 2 hours to obtain a catalyst dispersion. Uniformly mixing 500uL of prepared catalyst dispersion liquid with 5% of PTFE aqueous solution according to the volume ratio of 2:1, and performing ultrasonic dispersion. And uniformly coating the obtained mixed dispersion liquid on a piece of foamed nickel (1cm x 1cm), and drying in an oven at 60 ℃ for 30 minutes to obtain the v-NiFe LDH catalyst/foamed nickel electrode.

Electrodes can be prepared in a similar manner on carbon cloth or iron substrates using the v-NiFe LDH catalyst prepared in example 1. Also, electrodes can be prepared in a similar manner on foamed nickel, carbon cloth or iron substrates using the catalysts prepared in examples 2-10.

Of these, the comparative NiFe LDH was synthesized as described above.

Test example: water splitting catalytic performance of v-NiFe LDH catalyst

Using the v-NiFe LDH catalyst/foamed nickel electrode prepared in example 7 as the water-splitting anode (working electrode), Pt wire as the counter electrode, Ag/AgCl as the reference electrode, and 1M aqueous potassium hydroxide solution as the electrolyte, a water-splitting three-electrode system was constructed, as shown in FIG. 12. A NiFe LDH catalyst/foamed nickel electrode was prepared in the same manner as in example 7, and a water-splitting three-electrode system having the NiFe LDH catalyst/foamed nickel electrode as a working electrode was constructed in the same manner as in this test example. In addition, a water-splitting three-electrode system having a nickel foam electrode as a working electrode was constructed in the same manner as in the present test example.

The three water splitting three-electrode systems constructed above were tested on an EC-lab (Bio-Logic) and a Chi electrochemical workstation (Shanghai Chenghua) to verify the water splitting catalytic performance of the v-NiFe LDH catalyst of the present invention. FIG. 4 shows a comparative plot of the catalytic hydrogen production polarization curves for NiFe LDH and v-NiFe LDH. As can be seen from fig. 4, the activated v-NiFe LDH catalyst has the lowest overpotential, indicating that the same current density is achieved with the lowest energy consumption. FIG. 5 shows a comparative graph of catalytic oxygen production tafel curves for NiFe LDH and v-NiFe LDH. As can be seen from fig. 5, the v-NiFe LDH catalyst after the organic small molecule treatment has the lowest tafel slope, representing the fastest oxygen production reaction rate.

The stability of v-NiFe LDH was tested by chronopotentiometry. FIG. 6 is a graph showing v-NiFe LDH at 50mA cm^-2The current density of (a), wherein the inset is the v-NiFe LDH at 50mA cm^-2A long-time chronopotentiometric test pattern of more than 8 hours at a current density of (a). As can be seen from FIG. 7, the catalyst after generating vacancies has better stability and industrial application prospect.

Thus, the inventors found that in the preparation method of the TM LDH with multiple vacancies of the present invention, the selection and concentration of small organic molecules, the reaction temperature and reaction time, and washing of all organic solvents are of critical importance. Improper selection of organic micromolecules, too low water bath temperature or too short reaction time, difficult reaction or incomplete activation and undesirable catalytic action. If the concentration of the selected organic micromolecules is too low, the generation of vacancies is incomplete, the electrochemical performance cannot reach the best, and if the concentration of the selected organic micromolecules is too high, the anchoring etching cannot be well achieved due to steric hindrance, so that the electrochemical performance is not excellent enough. The selected polar organic solvent is used for cleaning, and if the polar organic solvent is not used for cleaning, the effect of generating multiple vacant sites by etching cannot be achieved.

The present invention has been described above using specific examples, which are only for the purpose of facilitating understanding of the present invention, and are not intended to limit the present invention. Numerous simple deductions, modifications or substitutions may be made by those skilled in the art in light of the teachings of the present invention. Such deductions, modifications or alternatives also fall within the scope of the claims of the present invention.

Claims

1. The preparation method of the multi-vacancy transition metal layered dihydroxy compound is characterized by comprising the following steps of:

(1) uniformly dispersing a transition metal layered dihydroxy compound in a polar solvent to obtain a transition metal layered dihydroxy compound suspension, wherein transition metal in the transition metal layered dihydroxy compound is any combination of divalent and trivalent transition metal ions; preferably, the atomic ratio of the divalent and trivalent transition metal ions is from 3 to 10: 1; preferably, any combination of divalent and trivalent transition metal ions is Ni²⁺/Fe³⁺Combination, Ni²⁺/Co³⁺Combinations or Co²⁺/Fe³⁺Combining;

(2) adding organic micromolecules required by anchoring reaction into the suspension liquid obtained in the step (1), and carrying out activation reaction to obtain a transition metal layered dihydroxy compound treated by the organic micromolecules;

(3) and (3) washing the transition metal layered dihydroxy compound treated by the small organic molecules obtained in the step (2) by using an organic solvent to obtain the multi-vacancy transition metal layered dihydroxy compound.

2. The method according to claim 1, wherein the small organic molecule has a continuous double bond functional group and a terminal end capable of coordinating to a transition metal.

3. The method of claim 2, wherein the small organic molecule is methyl isothiocyanate or methyl isocyanate.

4. The method according to claim 3, wherein the polar solvent comprises one or both of ionic water and ethanol; the organic solvent comprises one or more of ethanol, methanol and acetonitrile.

5. The production method according to claim 4, wherein in the step (1), the ratio of the weight of the transition metal layered double hydroxy compound to the volume of the polar solvent is 0.5-2mg:1 ml; in the step (2), the final concentration of the organic small molecules in the suspension liquid in the step (1) is 0.01-1.0M, and the reaction temperature of the activation reaction is 60-100 ℃.

6. The preparation method according to claim 5, comprising the following specific steps:

(1) ni in an atomic ratio of 3-10:1²⁺/Fe³⁺、Ni²⁺/Co³⁺Or Co²⁺/Fe³⁺Uniformly dispersing a transition metal layered dihydroxy compound in a polar solvent, wherein the ratio of the weight of the transition metal layered dihydroxy compound to the volume of the polar solvent is 0.5-2mg:1ml, and uniformly dispersing by ultrasonic vibration and stirring to obtain a transition metal layered dihydroxy compound suspension;

(2) adding an organic micromolecule solution with the final concentration of 0.01-1.0M into the suspension liquid in the step (1), stirring and dispersing uniformly at the stirring speed of 400-80 rpm, then reacting for 1-5 hours at the reaction temperature of 20-80 ℃ and the stirring speed of 700-1000rpm, and naturally cooling to room temperature to obtain the transition metal layered double-hydroxy compound treated by the organic micromolecules; the organic micromolecule is methyl isothiocyanate or methyl isocyanate;

(3) adding an organic solvent into the transition metal layered double-hydroxy compound obtained in the step (2) for washing, centrifugally washing for three times at 6000-8000rpm, each time for 5-10 minutes, and then vacuum drying for 3-6 hours to obtain the multi-vacancy transition metal layered double-hydroxy compound.

7. A multi-vacancy transition metal layered dihydroxy compound, characterized in that it is produced by the production method according to any one of claims 1 to 6.

8. Use of the multi-vacancy transition metal layered double hydroxy compound according to claim 7 as an oxygen generation catalyst for a water-splitting anode.

9. A water-splitting anode comprising a substrate comprising a foamed nickel, carbon cloth or iron substrate, and the multi-vacancy transition metal layered double hydroxide of claim 7.

10. A water-splitting three-electrode system comprising the water-splitting anode of claim 9, further comprising Pt wire as a counter electrode, Ag/AgCl as a reference electrode, and 0.5-1.5M potassium hydroxide or sodium hydroxide aqueous solution as an electrolyte; preferably, the electrolyte is a 1M aqueous solution of potassium hydroxide or sodium hydroxide.