CN111450851A - A kind of preparation method of sulfur-doped cobalt-based nanometer oxygen evolution electrocatalyst - Google Patents

Abstract

The invention belongs to the field of electrocatalytic materials, in particular to a preparation method of a sulfur-doped cobalt-based nanometer oxygen evolution electrocatalyst. The electrocatalyst is a composite material made of cobalt-based sulfide doped with cobalt tetroxide nanocubes; the steps are as follows: first, a cobalt-based hydroxide is synthesized by hydrothermal reaction, and after calcination, a cobalt tetroxide material with a nanocube structure is obtained, The oxygen evolution electrocatalyst can be prepared by hydrothermal reaction with previously prepared cobalt tetroxide by using thioacetamide as a sulfur source. Due to the special nano-cube structure and chemical composition, the electrocatalyst of the present invention provides more active sites, increases the electrochemical active area, and has higher oxygen evolution activity and stability; and the preparation method is simple and convenient. It is simple, easy to operate, easy to control the morphology of the sample, rich in raw materials and low in price, which is conducive to large-scale synthesis and popularization and lays a good foundation for the development and industrial application of new energy.

Description

A kind of preparation method of sulfur-doped cobalt-based nanometer oxygen evolution electrocatalyst

technical field

The invention belongs to the field of electrocatalytic materials, in particular to a preparation method of a sulfur-doped cobalt-based nanometer oxygen evolution electrocatalyst.

Background technique

Energy is an important material basis for human survival and development, and it is also a hot spot of international, economic, military and diplomatic attention today. The current energy crisis and environmental pollution have become increasingly severe, and the development of renewable and clean energy has become the focus of scholars from all over the world. Hydrogen energy is recognized as the most potential ideal energy carrier in the future due to its clean and efficient characteristics. Hydrogen production by electrolysis of water is favored by researchers because of its simple process principle. Electrolysis voltage is an important criterion for judging the energy consumption of electrolyzed water. Because of the existence of high overpotential and large ohmic voltage drop, the actual voltage required for electrolysis of water is often much higher than the theoretical one. The key to improving the energy conversion efficiency and the performance of the electrolyzed water system is to reduce the reaction resistance or overpotential. Therefore, it is necessary to find anode catalysts with low overpotentials to accelerate the reaction rate of oxygen evolution electrodes to improve energy conversion efficiency. At present, the best catalysts for water electrolysis for hydrogen production and oxygen reduction are still Pt noble metals, while RuO ₂ and IrO ₂ are considered to be the best OER electrocatalysts. However, these precious metals have limited reserves in the earth's crust, are expensive and have poor stability, which are not conducive to large-scale production for electrocatalytic reactions. Therefore, the controllable preparation of inexpensive, efficient, durable and green catalysts has become one of the current research hotspots.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art and to solve the above problems. Therefore, a preparation method of an oxygen evolution electrocatalyst with certain catalytic activity, simple preparation process, low price of raw materials and abundant oxygen evolution electrocatalyst has been invented.

In order to achieve the above object, the concrete steps of the present invention are as follows:

The present invention is made of cobalt nitrate hexahydrate, sodium hydroxide, thioacetamide and ethanol, and its concrete steps are as follows:

(1) respectively disperse cobalt nitrate hexahydrate and sodium hydroxide in water and carry out ultrasonic wave, obtain the aqueous solution of sodium hydroxide and the aqueous solution of cobalt nitrate;

(2) the aqueous solution of sodium hydroxide is then uniformly added dropwise to the aqueous solution of cobalt nitrate, and stirred to obtain a mixed solution;

(3) hydrothermally reacting the mixed solution in step (2), centrifuging, washing, and drying to obtain precursor powder after the reaction;

(4) calcining the precursor powder in the step (3) in a muffle furnace to obtain cobalt tetroxide powder; then disperse the cobalt tetroxide powder and thioacetamide in absolute ethanol respectively and carry out ultrasonication to obtain an ethanolic solution of cobalt tetroxide and sulfuric acid Then, the ethanol solution of cobalt tetroxide and the ethanol solution of thioacetamide are mixed to obtain a mixed solution; after stirring, a hydrothermal reaction is performed; the precipitate obtained after the reaction is centrifuged, washed and freeze-dried. The desired prepared sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution was obtained.

Preferably, in step (1), the dosage ratio of the cobalt nitrate hexahydrate to water is 0.388 g: 1 mL.

Preferably, in step (1), the dosage ratio of the sodium hydroxide to water is 0.04 g: 1 mL.

Preferably, in step (2), during the dropwise mixing, the dosage ratio of sodium hydroxide in the aqueous solution of sodium hydroxide to cobalt nitrate in the aqueous solution of cobalt nitrate is 0.04g: 0.388g; the stirring time 30 to 40 minutes.

Preferably, in step (3), the temperature of the hydrothermal reaction is 150-180°C, and the time is 5h.

Preferably, in step (4), the dosage ratio of the cobalt tetroxide powder to absolute ethanol is 1.5 mg: 1 mL;

Preferably, in step (4), the dosage ratio of the thioacetamide to water is 1.2-14.4 mg: 1 mL;

Preferably, in step (4), when the ethanolic solution of described cobalt tetroxide and the ethanolic solution of thioacetamide are mixed, the thioacetamide dosage ratio in the ethanolic solution of cobalt tetroxide and the ethanolic solution of thioacetamide is 1.5mg: 1.2～14.4mg.

Preferably, in step (4), the temperature of the hydrothermal reaction is 120-150° C., and the time is 12 h.

The beneficial effects of the present invention are as follows:

(1) The present invention adopts an anion regulation strategy, which adjusts the electronic structure of the active site through the doping of sulfide ions, increases the exposure of the catalytic active site, accelerates the electron transfer rate, and reduces the adsorption and desorption of OER intermediates with the catalyst surface. related ΔG to improve the overall performance of the OER catalyst. Due to its special nanocube structure and chemical composition, the material exposes more active sites and increases the electrochemical active area compared with cobalt tetroxide monomer catalysts; compared with other transition metal electrocatalysts , the material exhibits higher oxygen evolution activity and stability, and only requires an ^{overpotential} as low as 292 mV to reach a current density of 10 mA cm in 1 M KOH. In addition, the preparation method is simple, the steps are simple, the operation is easy, and the sample morphology is easy to control; it is beneficial to large-scale preparation in industrial production, and has considerable industrial application potential.

(2) The present invention has demonstrated a simple and cost-effective strategy to prepare sulfur-doped cobalt-based nano-electrocatalysts for oxygen evolution, which can easily control the microstructure and morphology of materials by controlling the reaction conditions, Thereby improving catalyst performance.

Description of drawings

FIG. 1 is a scanning electron microscope picture of the cobalt tetroxide monomer prepared in Example 1 of the present invention.

2 is a scanning electron microscope picture of the electrocatalytic material prepared in Example 1 of the present invention.

FIG. 3 is the X-ray diffraction pattern of the cobalt tetroxide monomer prepared in Example 1 of the present invention.

FIG. 4 is the X-ray diffraction pattern of the electrocatalytic materials prepared in Examples 1-4 of the present invention.

FIG. 5 is the linear scanning voltammogram of the oxygen evolution reaction of the electrocatalytic materials with different sulfur doping contents prepared in Examples 1-4 of the present invention.

Detailed ways

In order for those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention. Some examples of the invention are not limiting. All other embodiments based on the following should belong to the protection scope of the present invention.

Example 1:

(1) solvothermal reaction;

Dissolve 11.64g of cobalt nitrate hexahydrate and 0.4g of sodium hydroxide in 30mL and 10mL of water respectively, and stir for 10min to obtain an aqueous solution of sodium hydroxide and an aqueous solution of cobalt nitrate; then add the sodium hydroxide solution dropwise to the stirred solution. In the cobalt nitrate solution, after stirring for 30min, it was transferred to a 50mL PTFE-lined stainless steel reaction kettle, and then the reaction kettle was placed in a 180°C constant temperature oven for 5h; after it was naturally cooled to room temperature, it was taken out for use Centrifuge with a high-speed rotary centrifuge, wash the precipitate three times with deionized water and twice with ethanol, and place it in a vacuum drying box at 60 °C for 24 h. After the sample is dried, it is fully ground, and it is placed in a crucible and placed in a muffle furnace for calcination at a temperature of 2 °C/min to 500 °C for 3 hours to obtain cobalt tetroxide powder with nanocube cube structure.

(2) vulcanization reaction;

Using 96 mg of thioacetamide as the sulfur source, dissolved in 20 mL of absolute ethanol to obtain an ethanolic solution of thioacetamide; then 60 mg of cobalt tetroxide powder was dispersed in 40 mL of ethanol and sonicated for 30 min, and then an ethanolic solution of thioacetamide was added , stir, transfer it to a 100mL PTFE-lined stainless steel reaction kettle after 30min, put the reaction kettle into a 140 ℃ constant temperature oven for 12h; let it cool to room temperature naturally, take it out and use a high-speed rotary centrifuge for centrifugation , the precipitate was washed three times with deionized water and twice with ethanol, and then taken out after freeze-drying for 24 h to obtain a sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution.

Characterization Analysis:

The scanning electron microscope pictures of the obtained cobalt tetroxide monomer catalyst and sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution are shown in Figures 1 and 2. It can be seen from the scanning results shown in Figure 1 that the cubic structure of cobalt tetroxide has been successfully prepared, and the cubes are uniform in size and about 200 nm in length. From the scanning results shown in Figure 2, it can be seen that the morphology of the sulfur-doped cobalt-based nano-electrocatalyst material for oxygen evolution has changed, and the sulfide has a nano-flower-like structure, which can greatly increase the specific surface area of the electrocatalyst and provide more the active site.

From the analysis of the X-ray diffraction spectrum of the cobalt tetroxide single catalyst, it can be seen that the prepared cobalt tetroxide is in a cubic phase, which is in complete agreement with the standard card of cobalt tetroxide (JCPDS No.50-0653), which means that the cobalt tetroxide can pass through one step Hydrothermal synthesis, no impurity peaks were detected, indicating that the prepared cobalt tetroxide was of high purity; the X-ray diffraction pattern 4 of the sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution showed some noise, which may be due to the due to a complex multivariate composition. Diffraction peaks can be marked with a mixture of two cobalt sulfide phases, CoS _1.097 and Co ₃ S ₄ , respectively.

Performance Testing:

The sulfur-doped cobalt-based nano-electrocatalysts for oxygen evolution with different sulfur doping contents were prepared by the same method as a comparison.

All performance tests were performed on a CHI 760E electrochemical workstation equipped with a typical three-electrode system, and the electrocatalyst material was tested for oxygen evolution performance in the electrolyte of 1 mol/L potassium hydroxide solution. Among them, the platinum wire electrode was used as the counter electrode, and the Ag/Agcl electrode was used as the reference electrode, and 4 mg of the prepared electrocatalyst powder was weighed and added to the mixed solution of 980 ul of isopropanol and 20 ul of nafion solution. Needle drop 10ul to 3mm on the glassy carbon electrode to dry as the working electrode. The scan rate is 5mV/s. As shown in Fig. 5, when the current density is 10 mA/cm ² , the overpotential of the prepared sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution is reduced to 292 mV, while the overpotential of the single cobalt tetroxide catalyst is 425 mV, indicating that its precipitation Oxygen performance has been significantly improved. To sum up the above results, a sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution was successfully prepared by this method, and the catalyst has excellent catalytic activity for oxygen evolution reaction.

Example 2:

The preparation method of the sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution is basically the same as that in Example 1, except that 24 mg of thioacetamide was used as the sulfur source in the sulfurization step, and dissolved in 20 mL of anhydrous ethanol to obtain sulfur The ethanol solution of acetamide is replaced with the same steps as the other steps; further characterization analysis and performance test are carried out on it, and the purpose of the invention can be achieved in Example 2.

Example 3:

The preparation method of the sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution is basically the same as that in Example 1, except that 192 mg of thioacetamide was used as the sulfur source in the sulfurization step, dissolved in 20 mL of absolute ethanol, and the remaining steps The same; further characterization analysis and performance test were carried out, and Example 3 could achieve the purpose of the invention.

Example 4:

The preparation method of the sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution is basically the same as that in Example 1, except that 288 mg of thioacetamide was used as the sulfur source in the sulfurization step, dissolved in 20 mL of anhydrous ethanol, and the remaining steps The same; further characterization analysis and performance test were carried out, and Example 4 could achieve the purpose of the invention.

Test results: The sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution was prepared by changing the amount of sulfur doping, and X-ray diffraction was performed on it. The results of scanning electron microscopy showed that the sulfurization was successful, and the electron microscope test showed that The degree of vulcanization shows a progressive relationship. The linear voltammetry test was carried out, as shown in Figure 3, Example 2 shows that when the current density is 10mA/cm ² , the overpotential of the prepared sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution is reduced to 332mV, Example 3 shows that when the current density is 10 mA/cm ² , the overpotential of the prepared sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution is reduced to 307 mV, and Example 4 shows that when the current density is 10 mA/cm ² , the prepared The overpotential of the sulfur-doped cobalt-based nanoelectrocatalyst for oxygen evolution is reduced to 305 mV. It can be seen that the oxygen evolution performance of sulfur-doped cobalt-based nano-electrocatalysts for oxygen evolution with different sulfur doping amounts is greatly improved on the basis of cobalt tetroxide single catalyst, which may be caused by sulfur doping. The increase of active sites and the electronic structure of the composite were effectively tuned. This is more conducive to the adsorption of hydroxide, and improves the electron transfer rate, and accelerates the kinetic process of the oxygen evolution reaction. With the different doping amount of sulfur, it presents different overpotentials, indicating that the content of sulfur doping is not the better, and the performance of the electrocatalyst will be optimal only when the amount of doping is appropriate.

According to the above results, it can be seen that the method proposed in the present invention avoids the complicated preparation process, and successfully prepares sulfur with high electrocatalytic oxygen evolution performance at a relatively low temperature (140° C.) and a simple and easy preparation method. The doped cobalt-based nano-electrocatalyst for oxygen evolution effectively improves the cumbersome preparation of transition metal-based electrocatalytic materials and the defects of poor oxygen evolution performance. The sulfur-doped cobalt-based nano-electrocatalyst for oxygen evolution prepared by this method can also be used in metal-air batteries, new capacitors, and new energy fields.

Matters not addressed in the present invention are known in the art. Unless otherwise specified, the reagents and equipment used in the present invention are conventional reagents and equipment in the technical field; the reagents and materials used are commercially available.

Explanation: The above embodiments are only used to illustrate the present invention rather than limit the technical solutions described in the present invention; therefore, although this specification has described the present invention in detail with reference to the above-mentioned embodiments, those of ordinary skill in the art should It should be understood that the present invention can still be modified or equivalently replaced; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims (10)

1. A preparation method of a sulfur-doped cobalt-based nano oxygen evolution electrocatalyst is characterized by comprising the following specific steps of:

(1) respectively dispersing cobalt nitrate hexahydrate and sodium hydroxide in water for ultrasonic treatment to obtain an aqueous solution of sodium hydroxide and an aqueous solution of cobalt nitrate;

(2) then dropwise adding the aqueous solution of sodium hydroxide into the aqueous solution of cobalt nitrate, and stirring to obtain a mixed solution;

(3) carrying out hydrothermal reaction on the mixed solution in the step (2), centrifuging, washing and drying after the reaction to obtain precursor powder;

(4) calcining the precursor powder in the step (3) in a muffle furnace to obtain cobaltosic oxide powder; then respectively dispersing cobaltosic oxide powder and thioacetamide in absolute ethyl alcohol for ultrasonic treatment to obtain an ethanol solution of cobaltosic oxide and an ethanol solution of thioacetamide; then mixing the ethanol solution of cobaltosic oxide and the ethanol solution of thioacetamide to obtain a mixed solution; stirring and then carrying out hydrothermal reaction; and centrifuging, washing, freeze-drying and drying the precipitate obtained after the reaction to obtain the sulfur-doped cobalt-based nano oxygen evolution electrocatalyst required to be prepared.

2. The preparation method of the sulfur-doped cobalt-based nano oxygen evolution electrocatalyst according to claim 1, wherein in the step (1), the dosage ratio of the cobalt nitrate hexahydrate to the water is 0.388 g: 1m L.

3. The method for preparing a sulfur-doped cobalt-based nano oxygen evolution electrocatalyst according to claim 1, wherein in step (1), the amount ratio of sodium hydroxide to water is 0.04 g: 1m L.

4. The preparation method of the sulfur-doped cobalt-based nano oxygen evolution electrocatalyst according to claim 1, wherein in the step (2), during the dropwise mixing, the dosage ratio of sodium hydroxide in the aqueous solution of sodium hydroxide to cobalt nitrate in the aqueous solution of cobalt nitrate is 0.04 g: 0.388 g; the stirring time is 30-40 min.

5. The preparation method of the sulfur-doped cobalt-based nano oxygen evolution electrocatalyst according to claim 1, wherein in the step (3), the temperature of the hydrothermal reaction is 150-180 ℃ and the time is 5 h.

6. The preparation method of the sulfur-doped cobalt-based nano oxygen evolution electrocatalyst according to claim 1, wherein in the step (4), the dosage ratio of the cobaltosic oxide powder to the absolute ethyl alcohol is 1.5 mg: 1m L.

7. The preparation method of the sulfur-doped cobalt-based nano oxygen evolution electrocatalyst according to claim 1, wherein in the step (4), the dosage ratio of thioacetamide to water is 1.2-14.4 mg: 1m L.

8. The method for preparing a sulfur-doped cobalt-based nano oxygen evolution electrocatalyst according to claim 1, wherein in the step (4), when the ethanol solution of cobaltosic oxide and the ethanol solution of thioacetamide are mixed, the dosage ratio of cobaltosic oxide in the ethanol solution of cobaltosic oxide to thioacetamide in the ethanol solution of thioacetamide is 1.5 mg: 1.2-14.4 mg.

9. The preparation method of the sulfur-doped cobalt-based nano oxygen evolution electrocatalyst according to claim 1, wherein in the step (4), the temperature of the hydrothermal reaction is 120-150 ℃ and the time is 12 h.

10. The sulfur-doped cobalt-based nano oxygen evolution electrocatalyst cobalt prepared by the method according to any one of claims 1 to 9 is applied to the fields of metal-air batteries, novel capacitors or novel energy sources.

Images