CN110729486A

CN110729486A - Preparation method of elemental cobalt composite nitrogen-doped carbon high-efficiency oxygen reduction/oxygen precipitation catalyst

Info

Publication number: CN110729486A
Application number: CN201910961930.6A
Authority: CN
Inventors: 李光达; 葛怀云; 孟宪赓; 盖志鹏
Original assignee: Qilu University of Technology
Current assignee: Qilu University of Technology
Priority date: 2019-10-09
Filing date: 2019-10-09
Publication date: 2020-01-24

Abstract

The invention combines the fields of catalysis and nano materials, and discloses a method for preparing and synthesizing dodecahedral ZIF-67 with uniform appearance and controllable size by firstly dissolving cobalt nitrate hexahydrate and polyether F127 in a methanol solution, independently dissolving 2-methylimidazole in the methanol solution, then mixing and stirring the mixture and standing the mixture at 60 ℃, obtaining a nitrogen-doped carbon material derived from the ZIF-67 through high-temperature calcination, embedding simple substance cobalt particles in the carbon material, finally further calcining the nitrogen-doped carbon material in ammonia gas to improve the content of N doping, and testing the oxygen reduction and oxygen precipitation performance of the prepared slurry in 0.1M KOHIn noble metal catalyst RuO₂。

Description

Preparation method of elemental cobalt composite nitrogen-doped carbon high-efficiency oxygen reduction/oxygen precipitation catalyst

Technical Field

The invention relates to the field of electrocatalysis and nano materials, in particular to a preparation method of a metal cobalt embedded nitrogen-doped carbon material and application thereof in the field of oxygen reduction/oxygen precipitation.

Background

Safe, clean and renewable energy storage systems are central to current energy research because of their ability to do soCan effectively reduce environmental pollution and the dependence on fossil fuel at present. Among them, metal-air batteries are due to their inherent high energy density (about 1084 Whkg)^-1) And the advantages of abundant reserves in nature, low cost, environmental friendliness, safety and the like, thereby being widely concerned. However, before practical applications are considered, many challenges remain, the main limitation being the slow kinetics of the oxygen reduction reaction and oxygen evolution reaction. The traditional oxygen reduction/oxygen evolution reaction catalysts are mainly the noble metal materials Pt/C and RuO2, which are also the internationally recognized catalyst materials with the most excellent performance, however, the serious scarcity, high cost and limited electrochemical stability of the noble metals hinder the practical application of the noble metals. Therefore, the development of a stable and low-cost noble metal-free bifunctional catalyst is the key to solve the problem. The invention reports a simple method for preparing a Co nanoparticle embedded nitrogen-doped porous carbon material by carbonization and controllable nitridation of Metal Organic Frameworks (MOFs) and briefly describes the application of the Co nanoparticle embedded nitrogen-doped porous carbon material in the field of oxygen reduction/oxygen precipitation catalysis.

Carbon materials doped with heteroatoms (e.g., N, P, S, B, etc.) have attracted considerable attention over the past decade and although most of these materials have excellent oxygen reduction activity comparable to platinum carbon, their oxygen evolution performance is significantly lower than that of IrO₂/RuO₂In recent years, studies have shown that a great improvement in oxygen evolution performance can be achieved by adjusting the electronic structure. The metal-organic frameworks (MOFs) are used as precursors to be pyrolyzed at high temperature to obtain the nitrogen-doped carbon material embedded with the nano cobalt particles, and the nitrogen-doped carbon material has a large specific surface area, high porosity and a uniform pore channel structure. The carbon material derived from the metal organic framework can effectively inhibit the aggregation and growth of metal particles in the oxygen reduction/oxygen evolution reaction process. After the material is further treated in ammonia gas, a catalyst with higher nitrogen doping content and rich defects can be obtained, an electrocatalytic performance test is carried out, and a test result shows that the Co @ CN oxygen reduction/oxygen precipitation performance obtained through high-temperature carbonization and ammonia gas treatment regulation can be comparable to that of a noble metal catalyst.

Disclosure of Invention

The present invention proposes the following solutions based on the above research problems:

(1) weighing cobalt nitrate and 0.625g F127 with different mol numbers, dissolving the cobalt nitrate and the 0.625g F with different mol numbers in 25ml of methanol, separately dissolving 8mmol of 2-methylimidazole in 25ml of methanol, stirring for one hour, rapidly mixing the two solutions, and standing in an oven at 60 ℃ to prepare a ZIF-67 precursor

(2) And (2) calcining the ZIF-67 precursor prepared in the step (1) at a high temperature under the protection of nitrogen.

(3) And (3) further calcining the product obtained in the step (2) in an ammonia atmosphere to obtain a final product.

In the first step, the amount of cobalt nitrate was 1mmol, 2mmol, 3mmol, 4 mmol. Dissolving 0.625g of F127 in 25ml of methanol, separately dissolving 8mmol of 2-methylimidazole in 25ml of methanol, stirring for one hour, quickly mixing the two solutions, stirring for 30 minutes, standing for 4 hours in an oven at 60 ℃ to obtain a ZIF-67 precursor

In the second step, the calcination temperature is 800 ℃, 900 ℃, 1000 ℃, and the temperature rise speed is 5 ℃/min.

In the third step, the temperature is kept for one hour in the ammonia atmosphere, and the temperature rise speed is 3 degrees/min.

Drawings

FIG. 1 is an X-ray diffraction pattern of a catalyst prepared in an embodiment example.

Fig. 2 is a transmission electron microscope picture of a Co nanoparticle embedded nitrogen doped porous carbon catalyst material prepared in the embodiment example.

FIG. 3 is a scanning electron microscope image of a nitrogen-doped porous carbon catalyst material with embedded Co nanoparticles prepared in the example of the embodiment

Fig. 4 is a polarization curve of oxygen reduction/oxygen evolution reaction of nitrogen-doped porous carbon catalyst material embedded with prepared Co nanoparticles under 0.1M potassium hydroxide basic condition in embodiment example.

Detailed Description

The following patent of the present invention is described in detail with reference to specific experimental schemes for further understanding of the present invention, and the following specific examples are not limited to one experimental scheme.

Examples

0.291 g of cobalt nitrate hexahydrate and 0.625g F127 g of the mixed solution are weighed and dissolved in 25ml of methanol, then 0.627 g of 2-methylimidazole is separately dissolved in 25ml of methanol, after stirring for one hour, the two solutions are quickly mixed and stirred for 30 minutes, and then the mixture is placed in an oven at 60 ℃ and kept stand for 4 hours, thus obtaining the precursor of ZIF-67.

And (3) calcining the prepared ZIF-67 precursor at high temperature under the protection of nitrogen, wherein the calcining temperature is 800 ℃, 900 ℃, 1000 ℃, the heating speed is 5 ℃/min, and the heat preservation time is 3 hours.

And further calcining the product in an ammonia atmosphere at the calcining temperature of 350 ℃, the heating rate of 2 ℃/min and the heat preservation time of 1 hour to obtain the final product Co @ NC.

The electrode manufacturing process comprises the following steps:

weighing 2 mg of Co @ NC catalyst material, 2 mg of VXC-72 carbon material and 5 microliter of 5% Nafion, dissolving in 200 microliter of isopropanol, carrying out ultrasonic treatment for 30 minutes, dripping 10 microliter of slurry on a glassy carbon electrode, and drying at room temperature for 10 hours.

And (3) testing oxygen precipitation performance:

the performance test is carried out by using a Co @ NC catalyst material, and the method is characterized by comprising the following steps: before analyzing the oxygen precipitation performance, oxygen is introduced into 0.1M potassium hydroxide electrolyte for half an hour to ensure that the oxygen in the solution is saturated, a Chenghua electrochemical workstation is used for testing, a glassy carbon electrode is tested in the electrolyte at the rotating speed of 1600r/min, and the scanning speed is 5 mV/s. The test data shows that the Co @ NC catalyst material has the same half-wave potential (0.83V) as platinum carbon and reaches 10mA cm^-2Only a voltage of 1.56V is required for the current density of (a).

As shown in fig. 1, the X-ray diffraction peaks of the Co @ NC catalyst material have 3 distinct diffraction peaks at angles of 44.2, 51.5 and 75.9, which correspond to the diffraction peaks of Co simple substance, and have amorphous carbon peaks at about 24 °.

As shown in FIG. 2, a transmission electron micrograph of the Co @ NC material shows that Co @ NC is a regular dodecahedron and small particles with the composition Co are uniformly dispersed in the carbon material of the dodecahedron.

As shown in FIG. 3, CoThe SEM picture of @ NC material reflects that Co @ NC is a uniform dodecahedron. As shown in FIG. 4, the Co @ NC catalyst material has a half-wave potential (0.83V) as that of platinum-carbon up to 10mA cm in terms of an oxygen reduction/oxygen evolution catalytic curve measured under alkaline conditions^-2Only a voltage of 1.56V is required for the current density of (a).

Claims

1. A preparation method of a simple substance cobalt composite nitrogen-doped carbon high-efficiency oxygen reduction/oxygen precipitation catalyst is characterized by comprising the following steps: the sample is prepared by taking cobalt nitrate, 2-methylimidazole and polyether F127 as raw materials.

2. The method for preparing the elemental cobalt composite nitrogen-doped carbon high-efficiency oxygen reduction/oxygen precipitation catalyst as claimed in claim 1, wherein the method comprises the following steps: controlling the ratio of cobalt nitrate to 2-methylimidazole affects the size of the rhombohedral.

3. The preparation method of the elemental cobalt composite nitrogen-doped carbon high-efficiency oxygen reduction/oxygen precipitation catalyst as claimed in claim 1, comprising the following steps:

(1) the method for preparing the elemental cobalt composite nitrogen-doped carbon high-efficiency oxygen reduction/oxygen precipitation catalyst as claimed in claim 1, wherein the method comprises the following steps: cobalt nitrate (1mmol, 2mmol, 3mmol, 4mmol) and 0.625g F127 in different moles are weighed and dissolved in 25ml of methanol, then 8mmol of 2-methylimidazole is separately dissolved in 25ml of methanol, after stirring for one hour, the two solutions are quickly mixed and stirred for 30 minutes, and then placed in an oven at 60 ℃ for standing for 4 hours, thus obtaining the precursor ZIF-67.

(3) And (3) further calcining the product in the step (2) in an ammonia atmosphere to obtain a final product.

4. The high efficiency oxygen evolution catalyst as claimed in claim 1 consisting of nitrogen doped porous carbon and elemental cobalt.

5. The calcination temperature range under nitrogen protection of claim 2 is 700, 800, 900 ℃.

6. The tube furnace of claim 2 having a holding time of 3 hours.

7. The calcination in ammonia gas as claimed in claim 2, wherein the calcination temperature is 350 ℃ and the temperature is kept for 1 hour.