CN110841658A

CN110841658A - Preparation method of cobalt-based sulfide nanorod array

Info

Publication number: CN110841658A
Application number: CN201810949909.XA
Authority: CN
Inventors: 姜炜; 郭小雪; 吴方; 王宁; 郝嘎子; 胡玉冰; 谈玲华
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2018-08-20
Filing date: 2018-08-20
Publication date: 2020-02-28

Abstract

The invention discloses a preparation method of a cobalt-based sulfide nanorod array. The method comprises the steps of automatically growing a cobalt-based precursor with a nanorod array structure on nickel foam by a simple hydrothermal method, adding the precursor into a sodium sulfide solution, and preparing the cobalt-based sulfide nanorod array through ion exchange. The method is simple, the raw material cost is low, the industrial production is facilitated, the cobalt-based sulfide nanorod array is effectively controlled and synthesized under a mild condition, and the prepared cobalt-based sulfide nanorod array has good self-supporting capacity, oxygen evolution reaction activity and oxygen evolution stability.

Description

Preparation method of cobalt-based sulfide nanorod array

Technical Field

The invention belongs to the technical field of oxygen evolution catalysts, and relates to a preparation method of a cobalt-based sulfide nanorod array.

Background

Hydrogen energy is a green, environment-friendly and nontoxic clean energy, and has attracted attention due to its advantages of wide sources, environmental friendliness, high calorific value, and the like. The hydrogen production by water electrolysis is regarded as a hydrogen production technology with great potential due to the advantages of high hydrogen production purity, simple preparation process and wide raw material source. However, the oxygen evolution process occurring at the anode as a half-reaction of electrolyzed water involves transfer of 4 electrons, and the poor oxygen evolution kinetic reaction and the high oxygen evolution overpotential lead to an increase in energy consumption and a decrease in water decomposition efficiency. Therefore, under the condition of keeping other conditions unchanged, the development of the high-efficiency oxygen evolution catalyst can effectively reduce the reaction overpotential, which is the key for improving the hydrogen production efficiency/reducing the energy consumption. Although noble metal oxide catalysts have high catalytic activity, their large-scale use is limited due to the expensive and low reserves of noble metals. Therefore, the development of an efficient, cheap and easily-obtained oxygen evolution catalyst becomes the key of the real large-scale hydrogen production by water electrolysis.

Research shows that cobalt-based sulfides have better OER activity in alkaline solution (J. alloys Compd.,2017,723(5): 772-778). However, the nickel-cobalt-based sulfide oxygen evolution catalyst prepared by the method reported in the literature may cause the problem of tail gas treatment in the preparation process by adopting a high-temperature vulcanization method (J.Mater.chem.A., 2018,6(26), 12506-12514). In the method of preparing cobalt-based sulfide by adopting the two-step method, the synthesis time of some precursors is longer, which is not beneficial to the requirement of practical production (Electrochimica Acta,2018,278, 219-. In addition, the cobalt-based sulfide catalyst prepared by the hydrothermal method is powdery, and a nafion reagent is needed to adhere the cobalt-based sulfide catalyst to an electrode in the electrocatalysis process, so that the catalytic performance of the catalyst is limited. Therefore, the key point for expanding the application of the cobalt-based sulfide oxygen evolution catalyst is to select a safe, environment-friendly, simple and easily-obtained method to prepare the cobalt-based sulfide oxygen evolution catalyst with higher oxygen evolution activity.

Disclosure of Invention

The invention aims to provide a preparation method of a cobalt-based sulfide nanorod array capable of improving the catalytic activity of an oxygen evolution reaction.

The technical scheme for realizing the purpose of the invention is as follows:

the preparation method of the cobalt-based sulfide nanorod array takes nickel foam as a substrate, prepares a cobalt-based precursor with a nanorod array structure by using a hydrothermal method, and then prepares a self-supporting cobalt-based sulfide nanorod array catalyst with high catalytic activity by using a simple hydrothermal vulcanization method, and comprises the following specific steps:

immersing foamed nickel into a mixed solution of cobalt nitrate, urea and ammonium fluoride, carrying out hydrothermal reaction at 100-150 ℃, washing with water after the reaction is finished, and adding Na₂And (3) reacting the S solution at 90-140 ℃, washing with water after the reaction is finished, and drying to obtain the cobalt-based sulfide nanorod array, wherein the concentration of cobalt nitrate in the mixed solution is 0.02-0.07 mol/L.

Preferably, in the mixed solution, the concentration of urea is 0.25-0.29 mol/L, the concentration of ammonium fluoride is 0.1-0.28 mol/L, and Na is added₂The concentration of the S solution is 7-9 mmol/L.

Preferably, the hydrothermal reaction time is 10-14 hours.

Preferably, the vulcanization reaction time is 8-10 hours.

Compared with the prior art, the invention has the following advantages:

(1) the method is simple, the cost of raw materials is low, the industrial production is facilitated, and the cobalt-based sulfide nanorod array is effectively controlled and synthesized under a mild condition;

(2) the prepared cobalt-based sulfide nanorod array has good self-supporting capacity, and the influence of using Nafion and other binders is effectively avoided;

(3) the prepared cobalt-based sulfide nanorod array has good oxygen evolution reaction activity, and oxygen evolution reaction is carried out in 1M KOH electrolyte to reach 100mA cm^-2The required overpotential is only 328mV, in addition to 20mA cm^-2The current density of the catalyst is tested by constant current, the reaction time is 15 hours, the overpotential is increased by only 10mV, and the catalyst has good oxygen evolution stability.

Drawings

FIG. 1 is a scanning electron microscope image of a cobalt-based precursor (a) and a cobalt-based sulfide nanorod array (b) in a rod array structure in example 1.

FIG. 2 is a linear sweep voltammogram of the cobalt based sulfide oxygen evolution catalyst of examples 1, 2, 3.

FIG. 3 is a graph of the stability of the cobalt-based sulfide oxygen evolution catalyst of example 1 in promoting oxygen evolution reactions.

FIG. 4 is a linear scanning voltammogram of the cobalt-based sulfide oxygen evolution catalysts of example 1 and comparative example 1.

FIG. 5 is a linear scanning voltammogram of the cobalt-based sulfide oxygen evolution catalysts of example 1 and comparative example 2.

Detailed Description

The present invention will be described in more detail with reference to the following examples and the accompanying drawings.

Example 1

Step 1, preparing a mixed solution of cobalt nitrate, urea and ammonium fluoride, wherein the concentrations of the cobalt nitrate, the urea and the ammonium fluoride are respectively 0.0475mol/L, 0.25mol/L and 0.1mol/L, and transferring the mixed solution into a reaction kettle;

step 2, immersing the washed foam nickel into the mixed solution, and carrying out hydrothermal reaction for 12 hours at 120 ℃;

step 3, washing the nickel foam with the cobalt-based precursor with water, and then transferring the nickel foam to Na with the concentration of 0.007mol/L₂And (3) reacting in the S aqueous solution at 100 ℃ for 12 hours, and after the reaction is finished, washing with water and drying in vacuum to obtain the cobalt-based sulfide nanorod array.

FIG. 1(a) is a cobalt-based precursor with a rod-like array structure prepared by a hydrothermal method, and FIG. 1(b) is a scanning electron microscope image of a cobalt-based sulfide nanorod array obtained after hydrothermal vulcanization. As can be seen from the figure, after hydrothermal vulcanization, the structure of the array still appears, and the morphology is favorable for providing more electrocatalytic active area. In 1mol/L KOH electrolyte, 100mA cm is reached^-2The overpotentials required for examples 1, 2 and 3 were 328mV, 346mV and 356mV, respectively (FIG. 2). It can be seen that example 1 exhibits excellent oxygen evolution performance under alkaline conditions. Testing stability by constant current methodPerforming oxygen evolution reaction on KOH with the electrolyte of 1mol/L and the current density of 20mA cm^-2And when the test is carried out for 15 hours, the overpotential change is less than 10mV (figure 3), which shows that the cobalt-based sulfide nanorod array prepared by the method has higher oxygen evolution stability.

Example 2

This example is substantially the same as example 1 except that the cobalt nitrate concentration was 0.07mol/L and the ammonium fluoride concentration was 0.12mol/L, and other conditions were kept the same.

Example 3

This example is substantially the same as example 1 except that the cobalt nitrate concentration was 0.02mol/L and the urea concentration was 0.28mol/L, and the other conditions were kept the same.

Comparative example 1

This example is substantially the same as example 1 except that the cobalt nitrate concentration was 0.095mol/L and the other conditions were kept the same.

Comparative example 2

This example is substantially the same as example 1 except that the cobalt nitrate concentration was 0.006mol/L and the other conditions were kept the same.

Fig. 4 and 5 are linear scanning voltammograms of the cobalt-based sulfide oxygen evolution catalysts of comparative example 1 and comparative example 2, respectively. As can be seen from the figure, 1mol/L KOH is used as electrolyte, oxygen evolution reaction is carried out, and the oxygen evolution reaction reaches 100mA cm^-2The overpotentials required for comparative example 1 and comparative example 2 were 420mV and 380mV, respectively.

Claims

1. The preparation method of the cobalt-based sulfide nanorod array is characterized by comprising the following specific steps of:

2. The method according to claim 1, wherein the concentration of urea in the mixed solution is 0.25 to 0.29 mol/L.

3. The method according to claim 1, wherein the concentration of ammonium fluoride in the mixed solution is 0.1 to 0.28 mol/L.

4. The method according to claim 1, wherein said Na is₂The concentration of the S solution is 7-9 mmol/L.

5. The preparation method according to claim 1, wherein the hydrothermal reaction time is 10 to 14 hours.

6. The method according to claim 1, wherein the vulcanization reaction time is 8 to 10 hours.