Disclosure of Invention
In view of the above problems, the technical problem to be solved by the present invention is to provide a method for preparing a nickel-based metal organic framework electrocatalyst with low cost, high performance and high stability, which can be directly used. The method has the advantages of abundant raw material reserves, low price and simple preparation process, and the obtained nickel-based metal organic framework electro-catalysis material has a hierarchical porous structure, has excellent oxygen precipitation electro-catalysis performance, and has certain guiding significance for the commercial application of electrolyzed water.
In order to solve the problem, the invention prepares the bimetallic organic framework electro-catalytic material Ni-M-MOFs (M = Fe, Co, Cu, Mn, Zn), on one hand, the bimetallic synergistic effect is beneficial to increasing the number of active sites and improving the activity of the catalytic active sites; on the other hand, the doping of the metal element can effectively adjust the active site Ni2+With 3d orbital electron arrangement, via bridge O2-Realize the electron transfer of Ni-O-M, thereby improving the activity of the active site. Meanwhile, the formation of a graded porous structure is beneficial to enhancing the adsorption of oxygen-containing intermediates (OH, O and OOH) and oxygen (O)2) The releasing capacity of the catalyst can effectively improve the oxygen evolution reaction performance and the catalytic stability.
In particular, the invention successfully synthesizes a series of nickel-based metal organic framework electrocatalysis materials by adopting a simple interface induction strategy, so that the nickel-based metal organic framework electrocatalysis materials can be directly used as an efficient oxygen precipitation reaction electrocatalyst in an alkaline solution. The technical solution we have designed is mainly based on the following considerations: firstly, the metal organic framework electro-catalytic material has the advantages of higher specific surface area, adjustable chemical environment, abundant active sites, higher porosity and the like; secondly, a simple interface induction synthesis strategy is adopted, different solutions are utilized to have different densities, the diffusion directions of metal ions on the upper layer and ligand molecules on the bottom layer in the solutions on the different layers are different, the diffusion direction of the metal ions on the upper layer is from top to bottom, the diffusion direction of the ligand molecules on the bottom layer is from bottom to top, the metal ions and the ligand molecules are in coordination reaction after being contacted with each other on the middle layer, and the generated metal organic framework electrocatalytic material is precipitated on the bottommost layer by means of gravity. Meanwhile, in the process of further centrifugal collection, redundant ligand molecules and solvent molecules remained in pores of the metal organic framework electro-catalysis material can be removed through the cleaning action of the N, N-dimethylformamide and the trichloromethane, and the formation of a hierarchical pore structure (comprising micropores less than or equal to 2nm, mesopores of 2-50nm and macropores) is facilitated>50 nm) nickel-based metal organic framework electrocatalysisMaterial is changed; the formation of the hierarchical porous morphology is beneficial to the material transmission between the catalyst surface and the electrolyte, enhances the adsorption of oxygen-containing intermediates in the process of the anodic oxygen evolution reaction, obviously reduces the Gibbs free energy of the oxygen evolution reaction, and can accelerate the product (O)2) Thereby improving the catalytic activity and stability of the catalyst. In the process of the anodic oxygen evolution reaction of electrolyzed water, catalysts such as NiFe-MOF, NiCo-MOF and the like prepared by the method show unusual catalytic activity in an alkaline electrolyte system, which is obviously superior to commercial Ru-based catalysts and sheet nickel-based metal organic framework electrocatalytic materials prepared by most of traditional methods, and provides a new concept and approach for rational design and development of novel high-efficiency oxygen evolution reaction electrocatalysts.
Different from the traditional manufacturing method of the sheet nickel-based metal organic framework electro-catalytic material, the hierarchical porous nickel-based metal organic framework electro-catalytic material prepared in the invention enables metal ions on the upper layer and ligand molecules on the bottom layer to perform coordination reaction at the interface of the middle layer by controlling the layering of a liquid phase interface at low temperature and adjusting the solution density between different layers under the action of diffusion control, a reaction product is precipitated at the bottommost layer, and then the metal organic framework electro-catalytic material (Ni-M-MOFs, M = Fe, Co, Cu, Mn and Zn) is obtained by adopting simple centrifugal collection.
By using mixed solvents with different volume ratios, the solution density is different, and the solvent density of the upper layer, the middle layer and the lower layer is different. According to the diffusion law, the solute diffuses from a high-density position to a low-density position under the action of a chemical gradient, so that the diffusion direction of the solute between different layers is adjusted. In order to ensure that the formed porous structure is more uniform and ordered, and the formed porous structure is beneficial to the adsorption and desorption of an oxygen-containing intermediate in the process of anodic oxygen evolution reaction, the diffusion speed of solute is reasonably controlled. Researches find that under different temperatures of low temperature, room temperature, 50 ℃ and 100 ℃, the reaction speed is accelerated when the temperature is too high, which is not beneficial to the coordination reaction between metal ions and ligands; the diffusion speed is slowed down under the low temperature condition, and the formation of the hierarchical porous morphology is facilitated, so that the coordination reaction is carried out under the specific low temperature of-25 ℃. In addition, if the nickel-based metal organic framework electro-catalytic material is prepared in a mode of not adding an intermediate mixed solvent layer, the coordination reaction speed is remarkably increased, and the hierarchical porous morphology is difficult to form. Therefore, the method of adding the intermediate mixed solvent layer can slow down the diffusion speed, and is very favorable for forming the graded porous morphology.
The technical scheme adopted by the invention is as follows: dissolving a proper amount of 1, 4-terephthalic acid ligand powder and metal salt in a mixed solvent of N, N-dimethylformamide and acetonitrile respectively; respectively dripping the prepared solutions with different densities into a glass bottle to form a clear layered interface, standing for reaction to generate a sediment substance at the bottommost layer; and centrifuging the obtained precipitate, drying the precipitate at room temperature, and collecting the precipitate to obtain the nickel-based metal-organic framework electrocatalyst. In particular to a preparation method of a graded porous nickel-based metal organic framework electro-catalytic material, which comprises the following steps:
a) the pretreatment process comprises the following steps: weighing a certain amount of dicarboxylic acid ligand powder, dissolving the dicarboxylic acid ligand powder in a mixed solvent consisting of N, N-dimethylformamide and acetonitrile in a fixed proportion, stirring at room temperature at a certain rotating speed until the dicarboxylic acid ligand powder is completely dissolved, and preparing a solution A with a certain concentration; measuring N, N dimethylformamide and acetonitrile in a fixed proportion, stirring at room temperature at a certain rotating speed, and preparing a solution B; weighing a proper amount of bimetallic salt in proportion, dissolving the bimetallic salt in a mixed solvent consisting of N, N dimethylformamide and acetonitrile, stirring at room temperature at a certain rotating speed until the bimetallic salt is completely dissolved, and preparing a solution C with a certain concentration;
b) and (3) interface induction process: forming a layered solution with a clear interface by controlling the liquid phase density of the solution A, the solution B and the solution C at a low temperature, and precipitating a product at the bottom layer after reaction;
c) and (3) centrifugal collection process: and (c) placing the whole substance after the step (b) in a centrifuge tube, repeatedly centrifuging by using an organic solvent, collecting the centrifuged substance, and placing the centrifuge tube containing the centrifuged substance in a room-temperature environment for standing and drying for a period of time.
Further, in the step (B), a proper amount of the solution A is placed at the bottom of the glass bottle to form a solution bottom layer, a proper amount of the solution B is slowly dripped along the wall of the glass bottle to serve as an intermediate layer solution, a proper amount of the solution C is slowly dripped along the wall of the glass bottle to serve as an upper layer solution to form a layered solution with a clear interface, and the glass bottle is placed at a low temperature and stands for a period of time.
Further, in the step (b), the liquid phase density is controlled at low temperature to form a three-layer solution, the solution density between different layers is adjusted, under the action of diffusion control, ligand molecules on the upper layer and metal ions on the lower layer are subjected to coordination reaction at the interface, and reaction products are precipitated at the bottommost layer.
Further, the volume ratio of the solution A, the solution B and the solution C in the step (B) is 3: 2: 3 respectively; the standing time is 24h, and the standing temperature is-25 ℃.
Further, in the step (a), the volume ratio of N, N-dimethylformamide to acetonitrile in the solution A is 2: 1, the volume ratio of N, N-dimethylformamide to acetonitrile in the solution B is 1: 1, the volume ratio of N, N-dimethylformamide to acetonitrile in the solution C is 1: 2, and the stirring rotation speed is 800 rpm.
Further, in the step (a), the dicarboxylic acid ligand powder is 1, 4-terephthalic acid; the double metal salt is the combination of nickel acetate tetrahydrate and another substance, and the another substance is any one of ferrous acetate, cobalt acetate tetrahydrate, copper acetate monohydrate, manganese acetate tetrahydrate and zinc acetate dihydrate.
Further, in the step (c), the organic solvent is N, N-dimethylformamide and chloroform.
Further, in the step (c), centrifuging three times respectively by using N, N-dimethylformamide and chloroform, wherein the volume of the solvent used in each time is 3 mL; the standing and drying time is 12 h.
Furthermore, the preparation method can obtain NiFe-MOF, NiCo-MOF, NiCu-MOF, NiMn-MOF or NiZn-MOF with graded porous morphology.
Furthermore, the hierarchical porous nickel-based metal organic framework electrocatalysis material prepared by the method can be applied to the anodic oxygen evolution reaction of catalytic electrolysis water.
Compared with the prior art, the invention has the beneficial effects that:
(1) the method is simple and efficient, layering is carried out at a low temperature by controlling a liquid phase interface, solution density between different layers is adjusted, ligand molecules on an upper layer and metal ions on a bottom layer are diffused to an intermediate layer to carry out a coordination reaction under the action of diffusion control, a reaction product is precipitated on the bottom layer, and then the nickel-based metal organic framework electrocatalytic material (Ni-M-MOFs, M = Fe, Co, Cu, Mn and Zn) can be obtained by adopting simple centrifugal collection and can be directly used as an efficient oxygen evolution reaction electrocatalyst in an alkaline environment.
(2) The nickel-based metal organic framework electrocatalysis material with the hierarchical pore structure promotes the adsorption of oxygen-containing intermediates (OH, O and OOH) in the oxygen evolution reaction process, can realize rapid electron transfer and material transmission in an alkaline environment when being applied to the electrolytic water anodic oxygen evolution reaction, reduces the overpotential of the oxygen evolution reaction, and further shows excellent electrocatalysis performance.
(3) The invention has the advantages of low price of raw materials, low production cost and simple preparation process, and is a low-cost preparation method. The Ni-M-MOFs catalyst prepared by the method has the advantages of high specific surface area, excellent hierarchical porous structure and fully exposed active sites, and shows excellent oxygen evolution electrocatalytic activity and stability. The preparation method is simple and convenient to operate, low in cost and universal, and has important significance for promoting high-efficiency utilization of clean and renewable energy sources and reasonably designing devices such as fuel cells, metal-air cells and water electrolysis cells.
Detailed Description
The invention will now be described with reference to the following specific examples, but is not limited to the examples.
Example 1: preparation of NiFe-MOF oxygen evolution catalyst
Weighing 80 mg of 1, 4-terephthalic acid powder, dissolving in a mixed solvent consisting of 16mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring and dissolving at room temperature for 2 hours to obtain a solution A; measuring 8mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring at room temperature for 2h to obtain a solution B; weighing a proper amount of nickel acetate tetrahydrate and ferrous acetate, dissolving the nickel acetate tetrahydrate and the ferrous acetate in a mixed solvent consisting of 8mL of N, N-dimethylformamide and 16mL of acetonitrile, and fully stirring the mixture for 2 hours at room temperature to obtain a solution C. And then in the stirring process, 3mL of the solution A is dripped into the bottom of a glass bottle, 2mL of the solution B is placed on the upper layer of the solution A to form a middle layer solution, 3mL of the solution C is placed on the upper layer of the solution B, and the glass bottle which is obviously layered is placed in a low-temperature environment and is kept stand to react for 24 hours. And then centrifuging at 10000 rpm for 20min, repeatedly washing with N, N dimethylformamide/chloroform solvent for 3 times, and drying the obtained precipitate at room temperature for 12h to obtain NiFe-MOF powder which can be used as an oxygen evolution reaction electrocatalyst.
Example 2: preparation of NiCo-MOF oxygen evolution catalyst
Weighing 80 mg of 1, 4-terephthalic acid powder, dissolving in a mixed solvent consisting of 16mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring and dissolving at room temperature for 2 hours to obtain a solution A; measuring 8mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring at room temperature for 2h to obtain a solution B; weighing a proper amount of nickel acetate tetrahydrate and cobalt acetate tetrahydrate, dissolving the nickel acetate tetrahydrate and the cobalt acetate tetrahydrate in a mixed solvent consisting of 8mL of N, N-dimethylformamide and 16mL of acetonitrile, and fully stirring the mixture for 2 hours at room temperature to obtain a solution C. And then in the stirring process, 3mL of the solution A is dripped into the bottom of a glass bottle, 2mL of the solution B is placed on the upper layer of the solution A to form a middle layer solution, 3mL of the solution C is placed on the upper layer of the solution B, and the glass bottle which is obviously layered is placed in a low-temperature environment and is kept stand to react for 24 hours. And then centrifuging at 10000 rpm for 20min, repeatedly washing with N, N dimethylformamide/chloroform solvent for 3 times, and drying the obtained precipitate at room temperature for 12h to obtain NiCo-MOF powder which can be used as an oxygen evolution reaction electrocatalyst.
Example 3: preparation of NiCu-MOF oxygen evolution catalyst
Weighing 80 mg of 1, 4-terephthalic acid powder, dissolving in a mixed solvent consisting of 16mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring and dissolving at room temperature for 2 hours to obtain a solution A; measuring 8mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring at room temperature for 2h to obtain a solution B; weighing a proper amount of nickel acetate tetrahydrate and copper acetate monohydrate, dissolving in a mixed solvent consisting of 8mL of N, N-dimethylformamide and 16mL of acetonitrile, and fully stirring for 2h at room temperature to obtain a solution C. And then in the stirring process, 3mL of the solution A is dripped into the bottom of a glass bottle, 2mL of the solution B is placed on the upper layer of the solution A to form a middle layer solution, 3mL of the solution C is placed on the upper layer of the solution B, and the glass bottle which is obviously layered is placed in a low-temperature environment and is kept stand to react for 24 hours. And then centrifuging at 10000 rpm for 20min, repeatedly washing with N, N dimethylformamide/chloroform solvent for 3 times, and drying the obtained precipitate at room temperature for 12h to obtain NiCu-MOF powder which can be used as an oxygen evolution reaction electrocatalyst.
Example 4: preparation of NiMn-MOF oxygen evolution catalyst
Weighing 80 mg of 1, 4-terephthalic acid powder, dissolving in a mixed solvent consisting of 16mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring and dissolving at room temperature for 2 hours to obtain a solution A; measuring 8mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring at room temperature for 2h to obtain a solution B; weighing a proper amount of nickel acetate tetrahydrate and manganese acetate tetrahydrate, dissolving the nickel acetate tetrahydrate and the manganese acetate tetrahydrate in a mixed solvent consisting of 8mL of N, N-dimethylformamide and 16mL of acetonitrile, and fully stirring the mixture for 2 hours at room temperature to obtain a solution C. And then in the stirring process, 3mL of the solution A is dripped into the bottom of a glass bottle, 2mL of the solution B is placed on the upper layer of the solution A to form a middle layer solution, 3mL of the solution C is placed on the upper layer of the solution B, and the glass bottle which is obviously layered is placed in a low-temperature environment and is kept stand to react for 24 hours. And then centrifuging at 10000 rpm for 20min, repeatedly washing with N, N dimethylformamide/chloroform solvent for 3 times, and drying the obtained precipitate at room temperature for 12h to obtain NiMn-MOF powder which can be used as an oxygen evolution reaction electrocatalyst.
Example 5: preparation of NiZn-MOF oxygen evolution catalyst
Weighing 80 mg of 1, 4-terephthalic acid powder, dissolving in a mixed solvent consisting of 16mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring and dissolving at room temperature for 2 hours to obtain a solution A; measuring 8mL of N, N-dimethylformamide and 8mL of acetonitrile, and fully stirring at room temperature for 2h to obtain a solution B; weighing a proper amount of nickel acetate tetrahydrate and zinc acetate dihydrate, dissolving the nickel acetate tetrahydrate and the zinc acetate dihydrate in a mixed solvent consisting of 8mL of N, N-dimethylformamide and 16mL of acetonitrile, and fully stirring the mixture for 2 hours at room temperature to obtain a solution C. And then in the stirring process, 3mL of the solution A is dripped into the bottom of a glass bottle, 2mL of the solution B is placed on the upper layer of the solution A to form a middle layer solution, 3mL of the solution C is placed on the upper layer of the solution B, and the glass bottle which is obviously layered is placed in a low-temperature environment and is kept stand to react for 24 hours. And then centrifuging at 10000 rpm for 20min, repeatedly washing with N, N dimethylformamide/chloroform solvent for 3 times, and drying the obtained precipitate at room temperature for 12h to obtain NiZn-MOF powder which can be used as an oxygen evolution reaction electrocatalyst.
Application example 1
Before use, the carbon cloth is firstly respectively subjected to ultrasonic treatment for 20min by acetone (30 ml), deionized ethanol (30 ml) and deionized water (30 ml) in an ultrasonic instrument, and then is placed in a vacuum oven at 50 ℃ for 24 h. Simultaneously, catalyst ink was prepared according to the following steps: 5 mg of the prepared MOF powder in the solution was dispersed in a mixed solvent of water/isopropanol/Nafion in a volume ratio of 4/1/0.1, and uniformly dispersed ink was obtained by ultrasonic treatment. Finally, will50 μ L of the above catalyst suspension was dropped onto the surface of a carbon cloth electrode, and then dried at room temperature using an infrared lamp, followed by conducting an oxygen evolution reaction test. The mass loading was calculated to be 1 mg/cm for all samples2. Then, taking the prepared Fe/Ni-MOF catalyst as an example, the performance of the oxygen evolution catalytic reaction was tested on the catalyst modified electrode by using the NiFe-MOF catalyst obtained in example 1 as a working electrode, a saturated Hg/HgO electrode as a reference electrode, a carbon rod as a counter electrode, and a chenhua CHI-660E electrochemical workstation.
In 1.0M KOH alkaline solution, the modified electrode of the obtained NiFe-MOF catalyst has optimal oxygen evolution catalytic activity. At a current density of 10 mA/cm2When the overpotential is 217 mV, the Tafel slope is 50.5 mV dec-1While at a high current density of 500 mA/cm2When the overpotential is 297 mV, the standard of industrial application is met (the current density is 500 mA/cm)2Overpotential less than 300 mV), far beyond commercial RuO2The performance of the catalyst and the performance of most sheet-shaped transition metal-based metal organic framework catalysts prepared by the traditional method have important significance for promoting the commercialization process of hydrogen production by water electrolysis. Example 1 NiFe-MOF catalyst modified electrode at 10 mA/cm2Long-term stability test was performed, no significant performance degradation occurred after 40 h, whereas commercial RuO2The catalyst has obvious performance decay change, which shows that the NiFe-MOF catalyst prepared by the method has good stability.
The above description is only for the purpose of creating a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can substitute or change the technical solution and the inventive concept of the present invention within the technical scope of the present invention.