CN115521476B

CN115521476B - Co-MOFs nano sheet material and application thereof

Info

Publication number: CN115521476B
Application number: CN202211239726.1A
Authority: CN
Inventors: 高山; 孙桂林
Original assignee: Anhui University
Current assignee: Anhui University
Priority date: 2022-10-11
Filing date: 2022-10-11
Publication date: 2023-10-10
Anticipated expiration: 2042-10-11
Also published as: CN115521476A

Abstract

The invention relates to the technical field of synthesis of high-efficiency electrocatalytic water-splitting oxygen-generating catalysts, and discloses a Co-MOFs nano sheet material prepared by a hydrothermal method, which comprises the following steps: and (3) dropwise adding the aqueous solution of cobalt chloride hexahydrate into the aqueous solution of L-cysteine for reaction, centrifugally collecting precipitate, and washing and drying the reaction product. The flaky Co-MOFs and the etched netlike Co-MOFs prepared by the invention show excellent catalytic activity and stability under alkaline conditions by electrocatalytic water decomposition to prepare oxygen; in an alkaline electrolyte of 1.0MKOH, the current density was 10mAcm ^‑2 The overpotential of the thick plate-shaped Co-MOFs is 412mV, the overpotential of the thin plate-shaped Co-MOFs is 220mV, and the overpotential of the net-shaped Co-MOFs after etching is only 90mV, and the overpotential of the net-shaped Co-MOFs after etching is 20mAcm ^‑2 Can be stably maintained for more than 100 hours at the higher current density of (2); the catalyst with good adaptability to the electrolytic environment, high activity and good stability has higher practical application value.

Description

Co-MOFs nano sheet material and application thereof

Technical Field

The invention relates to the technical field of synthesis of high-efficiency electrocatalytic water decomposition oxygen-generating catalysts, in particular to a Co-MOFs nano sheet material and application thereof.

Background

The increase of global economy is limited by the consumption of fossil fuel and the aggravation of environmental problems, and a clean and efficient new energy system is developed, so that the problems of resources, energy and environment can be fundamentally solved; the hydrogen has high combustion heat value, and the combustion product only contains water and cannot produce secondary pollution, so the hydrogen is listed as a new energy source; electrochemical water splitting to produce hydrogen and oxygen using renewable electrical energy has been considered one of the most promising methods.

In the electrocatalytic hydrolysis of hydrogen and oxygen reactions, due to the production ofOxygen reaction (OER) is a thermodynamically unfavorable process that requires overcoming a large overpotential, which would reduce energy conversion efficiency and water separation efficiency, impeding the practical application of electrocatalytic water separation hydrogen production; in order to solve the above problems, it is important to develop an efficient and stable OER electrocatalyst; although some studies have demonstrated noble metal oxide nanomaterials such as IrO ₂ And RuO (Ruo) ₂ Has high electrochemical activity on OER, but the scarcity and high cost of these materials severely limit their large-scale industrial application; therefore, developing an efficient, low-cost, stable OER catalyst has important scientific significance and economic value.

MOFs are periodic structural units formed by coordination bonds between organic ligands and metal atom nodes, have definite chemical structures and are easy to access active sites, and are widely applied to homogeneous and heterogeneous catalytic reactions; in addition, MOFs are highly crystalline solid materials, easy to recycle, and robust against both chemical and physical attack; however, MOFs systems reported so far still have problems of low mass permeability, poor conductivity, annihilation of active metal centers, etc., which greatly limit their application as electrocatalysts; in order to solve the above problems, a new ultra-thin ultrastable structure needs to be developed to provide more reaction sites and good conductivity to improve OER catalytic performance.

Disclosure of Invention

The invention provides a Co-MOFs nano sheet material and application thereof, aiming at solving the application technical problem of MOFs as OER electrocatalyst.

The invention is realized by adopting the following technical scheme: the Co-MOFs nano sheet material is prepared by a hydrothermal method and comprises the following steps: and (3) dropwise adding the aqueous solution of cobalt chloride hexahydrate into the aqueous solution of L-cysteine for reaction, centrifugally collecting precipitate, and washing and drying the reaction product.

As a further improvement of the above scheme, the mass ratio of cobalt chloride hexahydrate to water in the cobalt chloride hexahydrate aqueous solution is: 0.0856-0.1598:1.

as a further improvement of the above scheme, the mass ratio of the L-cysteine aqueous solution to water is: 0.0705-0.0874:1.

as a further improvement of the above scheme, the molar ratio of the L-cysteine to cobalt chloride hexahydrate is 2-5:1.

as a further improvement of the scheme, the hydrothermal reaction is carried out in a constant-temperature water bath reaction tank, the reaction temperature is 10-40 ℃, and the reaction time is 0.5-30min.

As a further improvement of the scheme, the reaction product is washed by water for 2 times and ethanol for 1 time; the drying condition is freeze drying for 10-14h.

As a further improvement of the scheme, the Co-MOFs nano sheet material is added with nitric acid, stirred, centrifugally collected, and then washed and dried.

As a further improvement of the above scheme, the concentration of the nitric acid is 6.5-8.3mol/L.

As a further improvement of the scheme, the mass volume ratio of the Co-MOFs nano-sheet material to the nitric acid is 8-11:5.

the application of the Co-MOFs nano sheet material is that the Co-MOFs nano sheet material is applied to an electrocatalytic water decomposition oxygen production reaction.

Compared with the prior art, the invention has the beneficial effects that:

1. the method for synthesizing the Co-MOFs catalyst by controlling the reaction temperature and time can realize a large amount of synthesis and has a wide application prospect in actual large-scale industrial application;

2. the invention controls the reaction time at a specific temperature to regulate the appearance of the catalyst, synthesizes a thick sheet with short time, a thin sheet with proper time and a catalyst with etching to the thin sheet and sequentially enhanced performance;

3. according to the invention, through the interaction between the ligand and the metal ion, the catalytic activity of the flake Co-MOFs is further enhanced by etching;

4. the flaky Co-MOFs and the etched netlike Co-MOFs prepared by the invention show excellent catalytic activity and stability in alkaline electric power of 1.0MKOH under alkaline condition by electrocatalytic water decomposition oxygen productionIn the solution, the current density is 10mAcm ^-2 At the time, the overpotential of the thick-plate Co-MOFs was 412mV, the overpotential of the thin-plate Co-MOFs was 220mV, and the overpotential of the net-like Co-MOFs after etching was only 90mV, and 20mAcm in the alkaline electrolyte ^-2 Can be stably maintained for more than 100 hours under the condition of larger current density; the catalyst with good adaptability to the electrolytic environment, high activity and good stability has higher practical application value.

Drawings

FIG. 1 is an optical photograph of a device for mass synthesis of a flaky Co-MOFs catalyst prepared in the present invention;

FIG. 2 is an optical photograph of a mass prepared etched reticulated Co-MOFs catalyst of the present invention;

FIG. 3 is an X-ray diffraction pattern of thick plate-like Co-MOFs, flake-like Co-MOFs, and net-like Co-MOFs after etching, prepared according to the present invention;

FIG. 4 is a general IR chart of thick plate-like Co-MOFs, flake-like Co-MOFs, and net-like Co-MOFs after etching prepared by the present invention;

FIG. 5 is a Transmission Electron Microscope (TEM) photograph of thick plate-like Co-MOFs (a), flake-like Co-MOFs (b), and net-like Co-MOFs (c) after etching, which were prepared according to the present invention;

FIG. 6 is a graph of linear voltammograms (LSV) of thick-plate Co-MOFs, flaky Co-MOFs, and etched reticulated Co-MOFs prepared according to the present invention in 1.0MKOH electrolyte;

FIG. 7 is a plot of current density over time (it) of thick-plate Co-MOFs, flaky Co-MOFs, and etched reticulated Co-MOFs prepared according to the present invention in a 1.0MKOH electrolyte;

FIG. 8 is an electrochemical active area (ECSA) graph of thick-plate-like Co-MOFs, flaky Co-MOFs, and net-like Co-MOFs after etching prepared according to the present invention;

FIG. 9 is an impedance (EIS) diagram of thick-plate-like Co-MOFs, flaky Co-MOFs, and net-like Co-MOFs after etching, prepared according to the present invention;

FIG. 10 is a Tafel slope plot of thick-plate-like Co-MOFs, flaky Co-MOFs, and net-like Co-MOFs after etching, prepared according to the present invention.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and detailed description, wherein it is to be understood that, on the premise of no conflict, the following embodiments or technical features may be arbitrarily combined to form new embodiments.

Embodiment one:

pretreatment of carbon paper:

cutting commercial carbon paper into 1X 2cm ² The impurities adsorbed on the surface of the carbon paper were washed with ethanol, and then 30mL of the water containing: concentrated sulfuric acid: and (3) carrying out oil bath heat treatment at 80 ℃ for 24 hours in a mixed solution with the volume ratio of concentrated nitric acid of 1:1:1, and finally carrying out ultrasonic cleaning on the carbon paper for multiple times by using deionized water, washing to be neutral, and storing in the deionized water for standby.

Embodiment two:

thick flake Co-MOFs preparation:

weighing 2.423g of L-cysteine and 2.378g of cobalt chloride hexahydrate, respectively dissolving in 30mL of water and 20mL of water, pouring the L-cysteine aqueous solution into a constant-temperature water bath reaction tank, setting the temperature to 15 ℃, starting stirring, dropwise adding the cobalt chloride hexahydrate aqueous solution into the L-cysteine aqueous solution on the premise that the L-cysteine aqueous solution and the cobalt chloride hexahydrate aqueous solution are both at 15 ℃, starting timing after the addition, centrifugally collecting precipitate after 1min of reaction, washing for 2 times with water and 1 time with ethanol, and freeze-drying for 12h to obtain the cobalt chloride hexahydrate;

wherein, under the condition that the mol ratio of L-cysteine to cobalt chloride hexahydrate is 2:1, the dosage of the L-cysteine to the cobalt chloride hexahydrate is increased, and the thick Co-MOFs is continuously synthesized.

Embodiment III:

preparation of flake Co-MOFs:

weighing 2.423g of L-cysteine and 2.378g of cobalt chloride hexahydrate, respectively dissolving in 30mL of water and 20mL of water, pouring the L-cysteine aqueous solution into a constant-temperature water bath reaction tank, setting the temperature to 15 ℃, starting stirring, dropwise adding the cobalt chloride hexahydrate aqueous solution into the L-cysteine aqueous solution on the premise that the L-cysteine aqueous solution and the cobalt chloride hexahydrate aqueous solution are both at 15 ℃, starting timing after the addition, centrifugally collecting precipitate after the reaction is completed for 25min, washing for 1 time with water and ethanol, and freeze-drying for 12h to obtain the cobalt chloride hexahydrate;

wherein, under the condition that the mol ratio of L-cysteine to cobalt chloride hexahydrate is 2:1, the dosage of the L-cysteine to the cobalt chloride hexahydrate is increased, and the continuous synthesis of the flake Co-MOFs is carried out.

Embodiment four:

preparation of reticular Co-MOFs:

weighing 10mg of the flake-shaped Co-MOF material prepared in the third embodiment, adding 5mL of nitric acid with the concentration of 8mol/L, stirring for 1h at room temperature, centrifuging, collecting precipitate, washing with water for 2 times, washing with ethanol for 1 time, and freeze-drying for 12h, wherein the mass volume ratio of Co-MOFs nano-flake to nitric acid is 10:5, under the condition of increasing the dosage of the two, continuously synthesizing.

Fifth embodiment:

catalytic experiment:

5mg of the thick plate-like Co-MOFs, the flake-like Co-MOFs and the net-like Co-MOFs obtained in examples two, three and four above were weighed and dispersed in 0.5mL of a solution containing absolute ethanol: deionized water: in the mixed solution with the volume ratio of naphthol of 2:1.3:1.7, carrying out ultrasonic dispersion for 30min to obtain uniformly dispersed mixed solution; a solution of 60uL of the uniformly dispersed mixture was applied to an area of 1X 1cm by a pipette with a measuring range of 10uL ² On the pretreated carbon paper, the carbon paper coated with the catalyst is directly used as a working electrode after being dried, and an Ag/AgCl electrode is used as a reference electrode, 1cm x 1cm ² The platinum sheet electrode is used as a counter electrode to form a three-electrode system, and an electrocatalytic water decomposition oxygen production test is carried out on electrolyte of 1.0 MKOH; in the test, a Linear Sweep Voltammetry (LSV) is adopted to explore the electrocatalytic activity of the catalyst, the change of current with time under a fixed potential is tested by a potentiostatic method to show the stability of the catalyst, and the performance of the three catalysts prepared in the invention is compared;

wherein the mass of the catalyst supported on the carbon paper is 0.6mg, and the scanning speed of LSV is 1mVs ^-1 The test current density was 20mAcm ^-2 Is stable.

Example six:

comparative example preparation:

thick flake Co-MOFs were prepared on the basis of example two, with reaction times of 5min, 10min, 15min, 20min, respectively, all other conditions remaining unchanged, with results close to those obtained in examples two to five.

Analysis of results:

the optical photographs shown in figures 1 and 2 are added with the raw materials for preparing the flake Co-MOF catalyst, so that a large amount of catalyst can be obtained, and the method for preparing the flake Co-MOF catalyst and the net Co-MOF catalyst after etching is simple and can realize a large amount of synthesis;

the X-ray diffraction patterns of thick plate-shaped Co-MOFs, flake-shaped Co-MOFs and etched network-shaped Co-MOFs shown in FIG. 3 are consistent, the crystallinity of the etched network-shaped Co-MOFs is poor, but the physical phase is not changed;

FIG. 4 is a general infrared plot of thick-plate Co-MOFs, lamellar Co-MOFs, and net-like Co-MOFs after etching, where the infrared vibration peaks of the thick-plate Co-MOFs, lamellar Co-MOFs, and net-like Co-MOFs are consistent;

FIG. 5 is a low resolution TEM photograph of thick-plate-shaped Co-MOFs, lamellar Co-MOFs, and etched network-shaped Co-MOFs, wherein the Co-MOFs synthesized by 1min of reaction are thick-plate-shaped, the Co-MOFs reacted for 25min are thin-plate-shaped, and the etched Co-MOFs are network-shaped;

FIG. 6 is a graph showing a linear voltammetric scanning curve (LSV) of a thick-plate Co-MOFs, a thin-plate Co-MOFs, and an etched net-like Co-MOFs, wherein the current density reaches 10mAcm when oxygen is generated by electrolysis of water in an alkaline 1.0M KOH electrolyte ^-2 When the required overpotential thick slice Co-MOFs are 412mV, slice Co-MOFs are 220mV, and the net Co-MOFs after etching are only 90mV;

FIG. 7 is a graph showing the current density of thick-plate Co-MOFs, flaky Co-MOFs, and etched net-like Co-MOFs in a 1.0M KOH electrolyte with time (it), and in a 1.0M KOH electrolyte, the current density was 20mAcm ^-2 When the method is used, the current density of the thick-plate-shaped Co-MOFs decays rapidly in a short time, and the stability of the flaky Co-MOFs is far smaller than that of the etched net-shaped Co-MOFs;

FIG. 8 is an electrochemical active area (ECSA) graph of thick plate-like Co-MOFs, flaky Co-MOFs, and etched network Co-MOFs, in alkaline 1.0MKOH electrolyte, with electrochemical active surface area thick plate-like Co-MOFs < flaky Co-MOFs < etched network Co-MOFs;

FIG. 9 is a graph showing the impedance (EIS) of thick-plate Co-MOFs, flaky Co-MOFs, and net-like Co-MOFs after etching, wherein in alkaline 1.0M KOH electrolyte, the impedance of thick-plate Co-MOFs > flaky Co-MOFs > net-like Co-MOFs after etching;

FIG. 10 is a Tafel slope plot of thick-plate Co-MOFs, flaky Co-MOFs, and etched network Co-MOFs in alkaline 1.0M KOH electrolyte.

The method for synthesizing the Co-MOFs catalyst by controlling the reaction temperature and time can realize a large amount of synthesis and has a wide application prospect in actual large-scale industrial application;

controlling the reaction time at a specific temperature to regulate the appearance of the catalyst, and synthesizing a thick sheet with short time, a thin sheet with proper time and a catalyst which etches the thin sheet and has sequentially enhanced performance;

further etching enhances the catalytic activity of the flake Co-MOFs through the interaction between the ligand and the metal ion;

the flaky Co-MOFs and the etched netlike Co-MOFs show excellent catalytic activity and stability under alkaline conditions by electrocatalytic water decomposition to oxygen, and the current density is 10mAcm in an alkaline electrolyte of 1.0MKOH ^-2 When the overpotential of the thick-plate Co-MOFs is 412mV, the overpotential of the lamellar Co-MOFs is 220mV, the overpotential of the net-shaped Co-MOFs after etching is only 90mV, which is lower than most MOFs reported at present, and 20mAcm of the alkaline electrolyte ^-2 Can be stably maintained for more than 100 hours under the condition of larger current density; the catalyst with good adaptability to the electrolytic environment, high activity and good stability has higher practical application value.

The above embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention are intended to be within the scope of the present invention as claimed.

Claims

1. The Co-MOFs nano sheet material is characterized by being prepared by a hydrothermal method, and comprises the following steps: dropwise adding a cobalt chloride hexahydrate aqueous solution into an L-cysteine aqueous solution for reaction, centrifugally collecting precipitates, washing and drying reaction products, adding nitric acid, stirring, centrifugally collecting the precipitates, washing and drying the reaction products to obtain the cobalt chloride hexahydrate aqueous solution;

the concentration of the nitric acid is 6.5-8.3mol/L;

the mass volume ratio of the Co-MOFs nano sheet material to the nitric acid is 8-11:5.

2. the Co-MOFs nanoplatelets of claim 1, wherein the mass ratio of cobalt chloride hexahydrate to water in the aqueous cobalt chloride hexahydrate solution is: 0.0856-0.1598:1.

3. the Co-MOFs nanoplatelets of claim 1, wherein the mass ratio of the aqueous L-cysteine to water is: 0.0705-0.0874:1.

4. the Co-MOFs nanoplatelets of claim 1, wherein the molar ratio of L-cysteine to cobalt chloride hexahydrate is from 2 to 5:1.

5. the Co-MOFs nanosheet material of claim 1, wherein the hydrothermal reaction is performed in a constant temperature water bath reaction tank at a reaction temperature of 10-40 ℃ for a reaction time of 0.5-30min.

6. The Co-MOFs nanoplatelets of claim 1, wherein the reaction product wash is performed 2 times with water and 1 time with ethanol; the drying condition is freeze drying for 10-14h.

7. Use of Co-MOFs nanoplatelets according to any of claims 1-6 for the production of oxygen by electrocatalytic water decomposition.