CN113122872B

CN113122872B - Cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst and preparation method and application thereof

Info

Publication number: CN113122872B
Application number: CN202110382962.8A
Authority: CN
Inventors: 谢建晖; 刘慧婧; 李懿君
Original assignee: Hefei University of Technology
Current assignee: Hefei University of Technology
Priority date: 2021-04-09
Filing date: 2021-04-09
Publication date: 2022-07-12
Anticipated expiration: 2041-04-09
Also published as: CN113122872A

Abstract

The invention discloses a cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst and a preparation method and application thereof, belonging to the field of electrocatalytic materials, and the method comprises the steps of taking 2, 4-diamino-6- (2-pyridyl) -1,3, 5-triazine as a carbon source, carrying out coordination reaction with cobalt salt, and then carrying out high-temperature pyrolysis in an inert atmosphere to obtain the target electrocatalyst. The catalyst of the invention has excellent and stable hydrogen evolution performance under both acidic and alkaline conditions, and the preparation method of the invention is simple, the raw materials are cheap, the yield is high, the repeatability is good, and the mass production is easy.

Description

Cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst and preparation method and application thereof

Technical Field

The invention belongs to the field of catalyst material preparation and electrochemical catalysis, relates to preparation of an electrocatalyst applied to electrochemical hydrogen evolution reaction, and particularly relates to a preparation method of a cobalt and nitrogen doped carbon nanotube/carbon electrocatalytic hydrogen evolution catalyst.

Background

Hydrogen is considered a sustainable ideal energy source to replace fossil fuels due to its environmentally friendly, zero carbon emissions, and high quality energy density characteristics. However, at present, over 95% of hydrogen is generated from fossil fuel through methane steam reforming, hydrocarbon partial oxidation, autothermal reforming, coal gasification, water gas shift, and other reactions, and these hydrogen production processes waste a large amount of energy and cause serious environmental problems. The method for producing high-purity hydrogen by electrolyzing water by utilizing renewable energy sources such as wind energy, hydroenergy and solar energy is an ideal hydrogen production and energy storage means, but the hydrogen preparation by water electrolysis needs to use an efficient electrochemical catalyst to overcome the energy barrier of hydrogen production by water decomposition.

Generally, commercially available hydrogen evolution electrocatalysts are all noble metal platinum-based catalysts. Although platinum-based catalysts have extremely high hydrogen evolution activity, the scarcity and high cost of platinum have severely hampered their large-scale industrial application. And non-noble metals such as Mo, W, Co, Fe, Ni, Cu and the like have relatively high content in the crust and are cheaper. Therefore, it is important to design and manufacture non-noble metal catalysts that have excellent performance under both acidic and basic conditions. The carbon material has excellent conductivity, a large specific surface area and a high pore volume, and thus can support various transition metals as an excellent framework, thereby preparing an excellent metal/carbon composite electrocatalyst. However, it is difficult to ensure strong interaction between the metal and the carbon skeleton by directly loading the metal on the carbon skeleton, so that the catalytic effect of the metal active site is not high, and the catalyst is easy to aggregate in the catalytic process to cause the stability of the catalyst to be reduced. The method of high-temperature carbonization by using an organic carbon source and metal salt can generate a metal-doped carbon material in situ, can ensure strong interaction between metal and a carbon skeleton, but metal is easy to aggregate into large metal particles in the carbonization process, so that the metal utilization rate and the activity of the catalyst are low.

The transition metal complex is used as a precursor or a template, and the metal/carbon material catalyst is prepared by a high-temperature carbonization method. The chelation of organic ligand nitrogen atoms and the like can be used for limiting the domain in the in-situ conversion process of metal, so that the composite material with high metal dispersity and strong metal/carbon interaction is obtained. In addition, the metal center can also catalyze the pyrolysis process of the organic ligand, so that the morphology of the obtained carbon material is regulated and controlled, and catalysts with high specific surface area, such as nano sheets, nano tubes and the like, are used, and the catalytic performance of the obtained material is comprehensively improved.

Disclosure of Invention

The invention aims to provide a cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst and a preparation method thereof, so that the electrocatalyst can show excellent hydrogen evolution performance under both acidic and alkaline conditions.

The invention adopts the following technical scheme for realizing the purpose:

a method for preparing cobalt and nitrogen doped carbon nano tube/carbon electrocatalyst is characterized by comprising the following steps:

taking 2-cyanopyridine, dicyandiamide and potassium hydroxide as raw materials, heating and refluxing in ethylene glycol monomethyl ether to prepare precursor ligand 2, 4-diamino-6- (2-pyridyl) -1,3, 5-triazine; placing the precursor ligand and cobalt salt in acetonitrile, refluxing and stirring, and then drying in vacuum to obtain a precursor cobalt complex;

and pyrolyzing the precursor cobalt complex at the high temperature of 750-950 ℃ for 1-4 h under an inert atmosphere, cooling to room temperature, and carrying out acid washing, water washing and vacuum drying on the obtained solid material to obtain the cobalt and nitrogen doped carbon nano tube/carbon electrocatalyst.

Preferably, the cobalt salt is at least one of cobalt nitrate and cobalt acetate.

Preferably, the molar ratio of 2-cyanopyridine, dicyandiamide and potassium hydroxide in preparing the precursor ligand is 1: 1.1-1.3: 0.1-0.3, wherein the heating reflux temperature is 160-180 ℃, and the reflux time is 4-6 h.

Preferably, when the precursor cobalt complex is prepared, the mass ratio of the precursor ligand to the cobalt salt is 1-3: 1, the reflux stirring temperature is 100-120 ℃, and the reflux time is 6-10 hours.

Preferably, the high-temperature pyrolysis temperature is 800-900 ℃, and the inert atmosphere is nitrogen or argon.

Preferably, the acid washing is to add the solid material into 0.05-1M sulfuric acid and stir for 12h, and more preferably 0.1-0.5M sulfuric acid.

In the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst prepared by the preparation method, the mass doping amount of cobalt is 2-3%, and the mass doping amount of nitrogen is 5-6%, so that the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst can be used as an electrochemical hydrogen evolution catalyst to be applied to electrochemical reaction, and has excellent electrochemical hydrogen evolution effect and stability under acidic and alkaline conditions.

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

1. the invention takes the cobalt complex containing 2, 4-diamino-6- (2-pyridyl) -1,3, 5-triazine ligand as a precursor to prepare the cobalt and nitrogen-doped carbon nano tube/carbon electrocatalyst for the first time, and the ligand has abundant nitrogen atoms and can form a nitrogen-doped carbon material in the pyrolysis process. And because the cobalt nitrogen interaction can anchor cobalt atoms, the dispersity of cobalt is improved, the agglomeration of the cobalt atoms is limited, the electronic structure of the cobalt atoms is adjusted, and the catalytic activity and the stability of the catalyst are improved.

2. In the pyrolysis process of the precursor cobalt complex, the cobalt metal center can catalyze the pyrolysis process of the ligand, and finally the morphology of the carbon nano tube uniformly dispersed on the carbon sheet is obtained. The morphology has large specific surface area and porosity, and is beneficial to improving and exposing more catalytic active sites.

3. The invention has simple process, low cost, good repeatability and easy mass production.

4. The cobalt and nitrogen doped carbon nano tube/carbon electro-catalyst prepared by the invention can show excellent hydrogen evolution activity and stability under acidic and alkaline conditions only by lower metal cobalt loading, is expected to replace a noble metal platinum-based catalyst in the future and realizes commercial large-scale production.

Drawings

FIG. 1 is an SEM image of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 1;

FIG. 2 is an XRD pattern of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 1;

FIG. 3 is an XPS plot of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 1;

FIG. 4 is a graph showing the hydrogen evolution effect of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 1 in alkali;

FIG. 5 is a graph showing the hydrogen evolution effect of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 1 in acid;

FIG. 6 is a graph showing the hydrogen evolution effect of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 2 in alkali;

FIG. 7 is a graph showing the hydrogen evolution effect of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 2 in acid;

FIG. 8 is a graph showing the hydrogen evolution effect of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 3 in alkali;

fig. 9 is a graph showing the hydrogen evolution effect of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst obtained in example 3 in acid.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. The following disclosure is merely exemplary and illustrative of the inventive concept, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

The chemicals used in the following examples were all chemically pure and were freely available in the market.

Example 1

The preparation method of the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst in the embodiment is as follows:

step 1, adding 3.23g (0.031mol) of 2-cyanopyridine, 3.26g (0.0388mol) of dicyandiamide and 347.88mg (6.2mmol) of potassium hydroxide into 30mL of ethylene glycol monomethyl ether respectively, refluxing for 4h at 180 ℃, adding deionized water, filtering and drying to obtain a white ligand, namely 2, 4-diamino-6- (2-pyridyl) -1,3, 5-triazine. 570mg of 2, 4-diamino-6- (2-pyridyl) -1,3, 5-triazine ligand and 291mg of cobalt nitrate are weighed and uniformly mixed in 10mL of acetonitrile, refluxed for 6h, and then centrifuged and dried to obtain a precursor cobalt complex.

Step 2, placing the precursor Co complex obtained in the step 1 in a tube furnace under inert atmosphere, and keeping the temperature for 5 ℃ for min^-1The temperature rising rate is increased to 850 ℃, the pyrolysis is carried out for 2 hours, and the temperature is naturally cooled to the room temperature.

Step 3, dispersing the solid material obtained in the step 2 in 0.5M H₂SO₄And stirring for 12 hours at room temperature, then washing with deionized water, and drying in vacuum to obtain the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst.

The electrocatalyst obtained in this example had a specific surface area of 231.97m² g^-1Pore volume of 0.271cm³g^-1。

The mass doping amount of cobalt and the mass doping amount of nitrogen in the electrocatalyst obtained in this example were 2.6% and 5.3%.

The SEM image of the electrocatalyst obtained in this example is shown in fig. 1, and it can be seen that the carbon nanotubes are uniformly dispersed on the carbon sheet.

The XRD pattern of the electrocatalyst obtained in this example is shown in fig. 2, and it can be seen that the pattern contains carbon peaks and metallic cobalt peaks.

The XPS of the electrocatalyst obtained in this example is shown in fig. 3, and it can be seen that the catalyst contains Co, C, N and oxygen elements.

The electrocatalyst obtained in this example was electrochemically tested as follows:

3mg of the catalyst obtained in this example was weighed, 500. mu.L of methanol and 20. mu.L of Nafion solution were added, and the mixture was dispersed by sonication to uniformity. Dropping 5 μ L of the solution on a glassy carbon working electrodeDrying at room temperature, and the loading amount of the catalyst is 0.4mg cm^-2. The graphite electrode and the saturated mercury/mercury oxide electrode are respectively used as a counter electrode and a reference electrode.

Saturated with argon in 1M KOH solution at 5mV S^-1Electrochemical LSV testing was performed at rates ranging from-0.9 to-1.6V voltage window, followed by 10mA cm^-2Stability tests were performed at current density. As shown in FIG. 4, the catalyst of this example reached 10mA cm in 1M KOH at room temperature^-2The current density only needs 130mV overpotential and has good stability.

At 0.5M H₂SO₄The solution was saturated with argon and 5mV S^-1Electrochemical LSV testing was performed at a rate in the voltage window 0-0.6V, followed by 10mA cm^-2Stability tests were performed at current density. As shown in FIG. 5, the catalyst of this example was at 0.5M H at room temperature₂SO₄To 10mA cm in^-2The current density only needs 140mV overpotential and has excellent stability.

Example 2

This example prepares a cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst according to the same method as in example 1, except that the pyrolysis conditions in step 2 were changed to: at 5 ℃ for min^-1The temperature rise rate of (2) is increased to 750 ℃ and the pyrolysis is carried out for 2 h.

The electrocatalyst obtained in this example was electrochemically tested in the same manner as in example 1.

As shown in FIG. 6, the catalyst of this example reached 10mA cm in 1M KOH at room temperature^-2The current density only needs 176mV overpotential. As shown in FIG. 7, the catalyst of this example was at 0.5M H at room temperature₂SO₄To 10mA cm in^-2The current density only needs 245mV overpotential.

Example 3

This example prepares a cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst according to the same method as in example 1, except that the pyrolysis conditions in step 2 were changed to: at 5 ℃ for min^-1The temperature rising rate of the reaction kettle is increased to 950 ℃ and the pyrolysis is carried out for 2 hours under the condition of heat preservation.

As shown in FIG. 8, the catalyst of this example reached 10mAcm in 1M KOH at room temperature^-2The current density only needs 169mV overpotential. As shown in FIG. 9, the catalyst of this example was at 0.5M H at room temperature₂SO₄To 10mA cm in^-2The current density only needs 180mV overpotential.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. A preparation method of a cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst is characterized by comprising the following steps:

taking 2-cyanopyridine, dicyandiamide and potassium hydroxide as raw materials, heating and refluxing in ethylene glycol monomethyl ether to prepare a precursor ligand 2, 4-diamino-6- (2-pyridyl) -1,3, 5-triazine;

placing the precursor ligand and cobalt salt in acetonitrile according to the mass ratio of 1-3: 1, refluxing and stirring for 6-10 h at 100-120 ℃, and then drying in vacuum to obtain a precursor cobalt complex; the cobalt salt is at least one of cobalt nitrate and cobalt acetate;

and pyrolyzing the precursor cobalt complex at the high temperature of 800-900 ℃ for 1-4 h under nitrogen or argon, cooling to room temperature, and carrying out acid washing, water washing and vacuum drying on the obtained solid material to obtain the cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst.

2. The method of claim 1, wherein: when the precursor ligand is prepared, the molar ratio of the 2-cyanopyridine to the dicyandiamide to the potassium hydroxide is 1: 1.1-1.3: 0.1-0.3, the temperature of heating reflux is 160-180 ℃, and the reflux time is 4-6 h.

3. The method of claim 1, wherein: and in the acid washing step, the solid material is added into 0.05-1M sulfuric acid and stirred for 12 hours.

4. A cobalt and nitrogen doped carbon nanotube/carbon electrocatalyst prepared by the preparation method of any one of claims 1 to 3.

5. The cobalt, nitrogen doped carbon nanotube/carbon electrocatalyst according to claim 4, wherein: in the electrocatalyst, the mass doping amount of cobalt is 2-3%, and the mass doping amount of nitrogen is 5-6%.

6. Use of the cobalt-nitrogen doped carbon nanotube/carbon electrocatalyst according to claim 4 or 5 as an electrochemical hydrogen evolution catalyst in electrochemical reactions.

7. Use according to claim 6, characterized in that: the cobalt and nitrogen doped carbon nano tube/carbon electro-catalyst has excellent electrochemical hydrogen evolution effect and stability under both acidic and alkaline conditions.