阅读说明：本技术 铜基纳米催化剂及其制备方法和应用 (Copper-based nano catalyst and preparation method and application thereof ) 是由 胡章贵 黄聪 沈丽丽 于 2019-09-27 设计创作，主要内容包括：本发明涉及铜基纳米催化剂及其制备方法和应用。通过铜掺杂金属有机框架(ZIF-8)为前驱体,在惰性气氛下高温热解,形成一种无需后续处理可以直接使用的过渡金属铜基纳米团簇催化剂,晶粒尺寸处于纳米级别且尺寸均一,其中铜以团簇的形式存在,充分暴露了活性中心,使催化性能大大提升,具有良好的循环稳定性和甲醇耐受性,可以很好的适用于燃料电池、金属-空气电池等多种新型能源催化体系中。(The invention relates to a copper-based nano catalyst, a preparation method and application thereof. The transition metal copper-based nanocluster catalyst which can be directly used without subsequent treatment is formed by taking a copper-doped metal organic framework (ZIF-8) as a precursor and performing high-temperature pyrolysis in an inert atmosphere, the crystal grain size is in a nanometer level and uniform in size, wherein copper exists in a cluster form, an active center is fully exposed, the catalytic performance is greatly improved, and the catalyst has good circulation stability and methanol tolerance and can be well applied to various novel energy catalytic systems such as fuel cells, metal-air cells and the like.)

1. A preparation method of a copper-based nano catalyst is characterized by comprising the following steps:

step one, mixing 2-methylimidazole and methanol and stirring to form a uniform solution A;

mixing zinc nitrate hexahydrate, copper acetylacetonate and an organic solvent, and stirring to obtain a uniform solution B;

adding the solution A into the solution B, fully stirring, transferring the stirred solution into a polytetrafluoroethylene lining, and placing the polytetrafluoroethylene lining into an air-blowing drying oven for hydrothermal treatment;

step four, centrifuging the product obtained in the step three by using methanol and adopting a high-speed centrifuge, and drying the centrifuged product in a vacuum drying oven;

and step five, putting the product dried in the step four in vacuum into a magnetic boat, and carrying out high-temperature pyrolysis in an inert atmosphere to form the copper-based nano catalyst.

2. The method of claim 1, wherein: in the second step, the organic solvent is methanol or N, N-dimethylformamide.

3. The method according to claim 1 or 2, characterized in that: in the third step, the hydrothermal temperature is 90-180 ℃, and the temperature is kept for 1-24 hours.

4. The method of claim 3, wherein: in the fourth step, the product obtained by centrifugation is placed in a vacuum drying oven for drying for 8 hours at 60 ℃.

5. The method of claim 4, wherein: in the fifth step, the pyrolysis temperature is 300-1200 ℃, the heat preservation time is 1-8 hours, and the heating rate is 1-10 ℃ per minute.

6. A copper-based nanocatalyst, characterized in that: prepared by the process of any one of claims 1 to 5.

7. Use of the copper-based nanocatalyst of claim 6 in an electrocatalytic oxygen reduction reaction of a fuel cell.

8. A preparation method of a fuel cell electrode material is characterized by comprising the following steps: adding the copper-based nano catalyst of claim 6 into a mixed solution of water and ethanol (the volume ratio of water to ethanol is 4: 6), adding a Nafion solution, performing ultrasonic preparation to obtain a mixed solution, dripping the mixed solution onto the surface of an electrode, and naturally drying.

Technical Field

The invention relates to a transition metal copper nano catalyst, in particular to a copper-based nano catalyst for fuel cell cathode oxygen reduction reaction and a preparation method and application thereof.

Background

The conventional power generation technology mainly depends on the large consumption of fossil fuel, causing serious environmental pollution, which greatly affects the life and health of human beings. The fuel cell is a device for directly converting chemical energy into electric energy, and compared with the dry cell principle used in daily life, the fuel cell solves the problems of limited capacity, fast consumption, short service life and difficult recycling of the dry cell. The fuel cell can continuously supply electric energy to the outside by supplying fuel and a catalyst to continuously perform an electrochemical reaction in principle. Because the fuel cell directly converts chemical energy into electric energy without undergoing a combustion process, the fuel cell is not limited by Carnot cycle, has the advantages of higher energy conversion rate, low reaction noise, no pollution of reaction products and the like, has very wide application prospect, and becomes one of the high-quality energy accepted by countries in the 21 st century.

Typically, the cathode of the fuel cell is an Oxygen Reduction Reaction (ORR), the slow kinetics of which greatly impede the commercialization of this technology. Therefore, the cathode catalyst is one of the most important factors currently restricting the fuel cell. Currently, cathodic oxygen reduction catalysts rely primarily on platinum (Pt), iridium (Ir), rhodium (Rh), or ruthenium (Ru) based catalysts for catalysis. However, in view of the high cost and scarcity of these noble metal catalysts, their use in related clean energy technologies is greatly limited. Therefore, the development of a low-cost electrocatalyst with high activity, high durability and low cost is very important for realizing a clean energy device.

The search for inexpensive and highly catalytically active electrocatalysts that can replace commercial platinum carbon has focused mainly on the study of nanomaterials such as transition metal oxides and chalcogenides, non-noble metal composite catalysts and non-metallic catalysts. Particularly, the non-noble metal catalyst has the advantages of low cost, no pollution, good catalytic performance and the like, but the material has poor catalytic stability, so that breakthrough development cannot be realized.

In recent years, copper catalysts have attracted much attention, and most of the reported copper catalysts are used for hydrogenation and dehydrogenation reactions, reduction of carbon dioxide, and adsorption of gases. The copper catalyst is low in price, rich in content, high in electronic conductivity and low in overpotential of oxygen reduction, so that the copper catalyst is rarely reported to be used for catalyzing the cathode oxygen reduction reaction of the fuel cell. In the current reports, the Cu-N-C coordination has more types, and some show better oxygen reduction catalytic activity. For example, Lifuzhi et alPreparing KB loaded Cu-N by using copper salt, nitrogen-containing organic matter and conductive carbon black (KB) through hydrothermal and twice calcination methods_x-C_yThe catalyst of active site has certain catalytic activity. However, the preparation method of the catalyst is complex, and the catalyst can show catalytic activity only by two times of high-temperature treatment and has poor cycle stability. The metal nanoclusters have high surface activity due to the unique atom stacking structure, and have important application value in catalytic reactions. Reports on metal nanoclusters have mainly focused on noble metals such as gold, platinum, palladium, silver, and the like. In addition, the copper nanoclusters also give a positive initial potential of-0.07V in oxygen reduction, together with the reported Au₁₁And some platinum-based catalysts. Also, with respect to the size effect of the metal nanoclusters, it has been found that smaller-sized copper nanoclusters have better catalytic activity for oxygen reduction. However, it is worth noting that the currently reported electrocatalytic oxidation and reduction of copper nanoclusters mainly proceeds through a two-electron reaction, which is beneficial to the generation of hydrogen peroxide. In addition, most of the copper-containing oxygen reduction electrocatalysts reported at present have low catalyst activity and poor stability under an alkaline environment, and are still far away from the target of commercial application.

Disclosure of Invention

The invention aims to provide a copper-based nano catalyst capable of improving the catalytic performance of an electrocatalytic oxygen reduction reaction, and a preparation method and application thereof.

According to an aspect of the present invention, there is provided a method for preparing a copper-based nanocatalyst, including:

step one, mixing 2-methylimidazole and methanol and stirring to form a uniform solution A;

mixing zinc nitrate hexahydrate, copper acetylacetonate and an organic solvent, and stirring to obtain a uniform solution B;

adding the solution A into the solution B, fully stirring, transferring the stirred solution into a polytetrafluoroethylene lining, and placing the polytetrafluoroethylene lining into an air-blowing drying oven for hydrothermal treatment;

step four, centrifuging the product obtained in the step three by using methanol and adopting a high-speed centrifuge, and drying the centrifuged product in a vacuum drying oven;

and step five, putting the product dried in the step four in vacuum into a magnetic boat, and carrying out high-temperature pyrolysis in an inert atmosphere to form the copper-based nano catalyst.

Further, in the second step, the organic solvent is methanol or N, N dimethylformamide.

And further, in the third step, the hydrothermal temperature is 90-180 ℃, and the temperature is kept for 1-24 hours.

Further, in the fourth step, the product obtained by centrifugation is placed in a vacuum drying oven for drying for 8 hours at 60 ℃.

Further, in the fifth step, the pyrolysis temperature is 300-1200 ℃, the heat preservation time is 1-8 hours, and the heating rate is 1-10 ℃ per minute.

According to another aspect of the present invention, there is provided a copper-based nanocatalyst prepared by the above-described method. In addition, the invention also claims the application of the copper-based nano catalyst in the electrocatalytic oxygen reduction reaction of the fuel cell.

According to another aspect of the invention, a preparation method of the fuel cell electrode material is provided, the copper-based nano catalyst is added into a mixed solution of water and ethanol (the volume ratio of water to ethanol is 4: 6), a Nafion solution is added, then a mixed solution is prepared by ultrasonic treatment, the mixed solution is dripped on the surface of an electrode, and the electrode is naturally dried.

The preparation process of the copper-based nano catalyst provided by the invention is simple and easy to operate, the preparation raw materials are cheap and easy to purchase, no pollution is caused to the environment, and the preparation is convenient for large-scale preparation.

According to the invention, a transition metal copper-based nanocluster catalyst which can be directly used without subsequent treatment is formed by taking a copper-doped metal organic framework (ZIF-8) as a precursor and performing high-temperature pyrolysis in an inert atmosphere, the grain size is in a nanometer level and uniform in size, wherein copper exists in a cluster form, so that an active center is fully exposed, and the catalytic performance is greatly improved. The oxygen reduction catalytic performance under alkaline conditions is superior to that of a commercial platinum-carbon catalyst, the performance is almost unchanged after 10000 cycles of cyclic voltammetry scanning, and the catalyst has good cyclic stability and methanol tolerance and can be well applied to various novel energy catalytic systems such as fuel cells, metal-air cells and the like.

Drawings

FIG. 1 is a high resolution TEM image of a catalyst prepared in example 2 of the present invention;

FIG. 2 is a transmission electron micrograph of a catalyst prepared in example 2 of the present invention;

FIG. 3 is a linear voltammogram (LSV) of the catalysts prepared in examples 1, 2, 3 of the present invention in an oxygen-saturated 0.1 mol/L KOH solution;

FIG. 4 is a linear voltammogram (LSV) of the catalysts prepared in examples 2, 4, 5 of the present invention in an oxygen-saturated 0.1 mol/L KOH solution;

FIG. 5 is a linear voltammogram (LSV) of the catalysts prepared in examples 2, 6, and 7 of the present invention in an oxygen-saturated 0.1 mol/L KOH solution;

FIG. 6 is a linear voltammogram (LSV) of a catalyst prepared in example 2 of the present invention before and after 10000 cycles of Cyclic Voltammogram (CV) in 0.1 mol/L KOH saturated with oxygen;

FIG. 7 is a graph of methanol resistance in 0.1 mol/L KOH solution saturated with oxygen for the catalyst prepared in example 2 of the present invention;

FIG. 8 is an X-ray photoelectron spectroscopy (XPS) nitrogen peak spectrum of the catalyst prepared in example 2 of the present invention.

Detailed Description

The preparation method of the copper-based nano catalyst provided by the typical embodiment of the invention comprises the following steps:

step one, mixing 2-methylimidazole and methanol and stirring to form a uniform solution A.

And step two, mixing zinc nitrate hexahydrate, copper acetylacetonate and an organic solvent, and stirring to obtain a uniform solution B. Preferably, the organic solvent is methanol. The mass ratio of 2-methylimidazole, zinc nitrate hexahydrate and copper acetylacetonate is preferably 1.314: 1.190: (0.21-1.05), more preferably 1.314: 1.190: 0.628.

and step three, adding the solution A into the solution B, fully stirring, transferring the stirred solution into a polytetrafluoroethylene lining, and placing the polytetrafluoroethylene lining into an air-blowing drying oven for hydrothermal treatment. Preferably, the temperature of the hydrothermal treatment is 90-180 ℃ and the heat preservation is carried out for 1-24 hours.

And step four, centrifuging the product obtained in the step three by using methanol and adopting a high-speed centrifuge, and drying the centrifuged product in a vacuum drying oven. Preferably, drying is carried out in a vacuum drying oven for 8 h at 60 ℃.

And step five, putting the product dried in the step four in vacuum into a magnetic boat, and carrying out high-temperature pyrolysis in an inert atmosphere to form the copper-based nano catalyst. The pyrolysis temperature is 300-1200 ℃, the heat preservation time is 1-8 hours, and the heating rate is 1-10 ℃ per minute.

The above embodiment provides a simple and effective method, and the ZIF-derived Cu nanocluster and nitrogen co-doped carbon nanocatalyst with definite definition and excellent performance is prepared by introducing Cu in the ZIF-8 synthesis process through one-step high-temperature pyrolysis. The copper-based nano catalyst is a nano catalyst with copper nanoclusters embedded in a carbon nitrogen material, has a good rhombic dodecahedron shape, can be directly used without subsequent treatment, and mainly has catalytic activity derived from the exposed copper nanoclusters and high contents of pyridine nitrogen and graphitized nitrogen.

The copper-based nano catalyst has better oxygen reduction catalytic performance, methanol fuel cross effect resistance and good cycle stability, has good catalytic activity in alkaline oxygen reduction reaction, and has half-wave potential and limiting current density which are both equal to those of commercial platinum carbon. The reaction is mainly carried out through four-electron reaction, which is beneficial to the generation of water. Besides, the catalyst also has good methanol tolerance and cycle stability.

The technical solution and the technical effects of the present invention are further illustrated by some examples.

The transition metal copper-based catalyst prepared according to the following example was applied to an electrocatalytic oxygen reduction reaction. The copper-based catalyst uses a rotating disc electrode to test the catalytic performance of the copper-based catalyst, uses a three-electrode system,Ag/AgCl as reference electrode and carbon rod as counter electrode at 0.1 mol/LThe NaOH solution is tested by using an electrochemical workstation to catalyze the oxygen reduction reaction, the half-wave potential is 0.84V, and the limiting current density is 5.6 mA.cm^-2。