CN108823597B - Method for preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method and its application - Google Patents

Abstract

The invention belongs to the technical field of electrocatalysis hydrogen evolution, and relates to a method for preparing a nitrogen-doped nickel sulfide hydrogen evolution catalyst by an annealing method. The prepared catalyst is used as a working electrode to electrolyze water under an alkaline condition to generate hydrogen. The invention takes foam nickel as a substrate, thiourea as a sulfur source and a nitrogen source, and the nitrogen-doped nickel sulfide electrocatalyst synthesized by a one-step annealing method obviously changes Ni₃S₂The morphology and electronic structure of the material expose more surface active sites, increase the conductivity and enhance the hydrogen evolution reaction activity. The invention solves the defects of low conductivity, few surface active sites and the like of various sulfides of nickel, improves the electrocatalytic hydrogen evolution performance, has excellent stability in alkalinity, and is expected to be industrialized.

Description

Method for preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method and its application

technical field

The invention belongs to the technical field of electrocatalytic hydrogen evolution, relates to the preparation of a hydrogen evolution catalyst, in particular to a method for preparing a nitrogen-doped nickel sulfide hydrogen evolution catalyst by an annealing method and an application thereof.

Background technique

The development of today's society is overly dependent on fossil fuels, and the excessive consumption of fossil fuels exacerbates environmental pollution and energy crisis. Therefore, it is urgent to develop clean, renewable and environmentally friendly alternative energy sources. Compared with various alternative energy sources, hydrogen is considered to be the most promising energy carrier to replace traditional fossil fuels due to its high combustion value and only water as the combustion product. Hydrogen production from water electrolysis is considered as a green and sustainable hydrogen production method. Precious metals such as platinum-based catalysts have excellent hydrogen evolution reaction (HER) activity, but their applications are greatly limited due to their high cost and low reserves. Therefore, there is an urgent need to find cheaper and easily available hydrogen evolution reaction catalysts.

In recent years, various nickel-based catalysts have been widely used in the field of electrocatalytic hydrogen evolution, typical examples are various sulfides, selenides, oxides, hydroxides and various nickel alloys of nickel. Various sulfides of nickel are considered as promising hydrogen evolution reaction (HER) catalysts due to their good electrical conductivity and high stability in alkaline media. However, the catalytic activity of various nickel sulfides reported so far is still low. Studies have shown that the activity of nickel sulfide is highly correlated with the coordination number of surface S atoms and the charge depletion of neighboring Ni atoms. Therefore, nitrogen (N) doping can increase the free energy of hydrogen adsorption and thus improve the hydrogen evolution reaction activity of nickel sulfide.

There is no research report on the electrocatalytic hydrogen evolution performance of nitrogen-doped nickel sulfide (N _{- Ni3S2} /NF) nanomaterials in alkaline.

SUMMARY OF THE INVENTION

The purpose of the present invention is to disclose a method for preparing a nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF) hydrogen evolution catalyst by an annealing method.

Technical solutions:

The method for preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method, the specific steps are as follows:

According to the ratio of 0.5-2 g thiourea to a piece of pretreated nickel foam, weigh thiourea in a porcelain boat, transfer it to the upstream of the temperature-programmed tube furnace, and then take the pretreated nickel foam and place it in another porcelain boat. The boat was moved to the downstream of the temperature-programmed tube furnace, heated to 300-500 °C under the protection of inert gas, calcined for 30-100 min, and taken out after it was naturally cooled to room temperature.

In the preferred disclosure example of the present invention, the pretreated nickel foam is cut into a certain size, and ultrasonically cleaned with hydrochloric acid and acetone for 15 to 30 minutes in turn to remove oxides on the surface, and then use anhydrous ethanol. and deionized water for 2 to 3 times respectively, each time for 5 to 10 minutes, and finally vacuum drying to obtain pretreated nickel foam.

In a preferred embodiment of the present invention, the inert gas is nitrogen.

In a preferred disclosure example of the present invention, the heating rate is 5°C/min.

In the preferred disclosed example of the present invention, it is preferred that 1 g of thiourea corresponds to a piece of pretreated nickel foam, which is calcined at 400°C for 90 minutes under the protection of inert gas.

For the convenience of comparison, the present invention discloses a preparation method for synthesizing nickel sulfide hydrogen evolution electrocatalyst by hydrothermal method, comprising: preparing a solution according to the ratio of 15-25 mL deionized water and adding 2-2.5 g thiourea, ultrasonically dispersing and transferring to 50 mL of Teflon-lined reaction kettle, then take a piece of pretreated nickel foam and put it into the reaction kettle and immerse it in the solution, keep the reaction kettle at 100 ~ 150 ℃ for 4 ~ 6 hours, and cool it to room temperature , take out the sample, wash several times with deionized water and absolute ethanol, and finally vacuum dry to obtain nickel sulfide (Ni ₃ S ₂ /NF), preferably 2.2 g of thiourea is dispersed in 20 mL of deionized water, and kept at 150 ℃ 5h.

Another object of the present invention is to use the prepared catalyst as a working electrode for electrolysis of water for hydrogen evolution under alkaline conditions.

The present invention utilizes X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and takes potassium hydroxide (KOH) solution as the target to carry out the experiment of electrocatalytic decomposition of water and hydrogen evolution. Chemical polarization curves (LSV) and Tafel plots to evaluate their electrocatalytic activity for water splitting and hydrogen evolution.

₃₂ Electrocatalytic activity experiments of electrocatalysts:

(1) Prepare a KOH solution with a concentration of 1 mol/L, seal the prepared solution and place it in a dark place;

(2) CHI760 electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.) was used to test the electrochemical properties of the samples in a three-electrode system. The carbon rod was used as the counter electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the N-Ni ₃ S ₂ material was used as the working electrode. The electrochemical properties of the electrode materials were tested by linear sweep voltammetry (LSV) in 1 mol/L KOH electrolyte.

The advantages of the present invention are:

(1) Using porous nickel foam as the conductive substrate and nickel source, and thiourea as the sulfur source and nitrogen source, the nickel sulfide nanowires are directly grown on the surface of the foamed nickel through a one-step annealing method, and nitrogen is introduced into the nickel sulfide at the same time. The method is simple;

(2) Directly growing nickel sulfide on nickel foam, and doping nickel sulfide with nitrogen can accelerate electron transport. At the same time, the strong interaction between nickel sulfide and nickel foam can improve the stability of the catalyst in alkaline medium;

(3) The Ni ₃ S ₂ material obtained in the present invention is used for electrocatalytic hydrogen evolution catalyst. The optimized N-Ni ₃ S ₂ NWs material has an overpotential of 105 mV when the current density is 10 mA/cm ² under alkaline conditions. , and its Tafel slope is only 108mV dec ^-1 .

beneficial effect

Due to the unique three-dimensional structure of porous nickel foam (NF), as a conductive substrate and nickel source, not only the surface area is increased, but the product is also simple and easy to obtain. The invention uses foamed nickel as the substrate, thiourea as the sulfur source and nitrogen source, and a nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF) electrocatalyst synthesized by a one-step annealing method, which significantly changes the Ni ₃ S ₂ . The morphology and electronic structure expose more surface active sites and increase the electrical conductivity, which in turn enhances the hydrogen evolution reaction activity. The nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF) electrocatalyst synthesized in the present invention solves the shortcomings of various nickel sulfides, such as low electrical conductivity and few surface active sites, and improves the electrocatalytic hydrogen evolution. performance, and excellent stability in alkaline.

Description of drawings

Figure 1(a) shows the SEM images of Ni ₃ S ₂ /NF NRs at high resolution and low resolution;

(b) SEM images of N-Ni ₃ S ₂ /NF NWs at high resolution and low resolution.

Figure 2(a) is the longitudinal cross-sectional SEM image of N-Ni ₃ S ₂ /NF NWs at low resolution;

(b) is the longitudinal cross-sectional SEM image of N-Ni ₃ S ₂ /NF NWs at high resolution.

Figure 3(a) is the XRD pattern of blank nickel foam (NF);

(b, c, d) EDS images of NF, Ni ₃ S ₂ /NF NRs and N-Ni ₃ S ₂ /NF NWs, respectively.

Figure 4(a) shows the XRD patterns of Ni ₃ S ₂ /NF NRs and N-Ni ₃ S ₂ /NF NWs;

(b, c, d) are the XPS images of Ni 2p, S 2p, and N 1s in N-Ni ₃ S ₂ /NF NWs, respectively.

Figure 5. Hydrogen evolution activity test of N-Ni ₃ S ₂ /NF NWs electrocatalytic material in alkaline medium (1.0M KOH):

where (a) are the polarization curves of NF, Ni ₃ S ₂ /NF NRs and N-Ni ₃ S ₂ /NF NWs and Pt/NF in 1.0 M KOH;

(b) is the Tafel slope of NF, Ni ₃ S ₂ /NF NRs and N-Ni ₃ S ₂ /NF NWs and Pt/NF in 1.0 M KOH;

(c) is the electrochemical impedance diagram of NF, Ni ₃ S ₂ /NF NRs and N-Ni ₃ S ₂ /NF NWs in 1.0 M KOH;

(d) Polarization curves of Ni ₃ S ₂ /NF NRs and N-Ni ₃ S ₂ /NF NWs after 2000 cycles in alkaline (1.0 M KOH), the inset is the stability test at a certain current density .

Detailed ways

The present invention will be further described below in conjunction with specific implementation examples, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following examples.

Comparative Test

To synthesize nickel sulfide hydrogen evolution electrocatalyst by hydrothermal method, weigh 2-2.5 g of thiourea into a beaker, add 15-25 mL of deionized water, ultrasonically disperse it and transfer it to a 50-mL polytetrafluoroethylene-lined reaction kettle, and then take A piece of pretreated nickel foam was tilted into the reaction kettle and immersed in the solution. The reaction kettle was placed in a 100-150 °C oven for 4-6 hours, cooled to room temperature, and the sample was taken out and washed with deionized water and anhydrous Wash with ethanol for several times, and finally vacuum dry to obtain nickel sulfide (Ni ₃ S ₂ /NF). Preferably, 2.2 g of thiourea is dispersed in 20 mL of deionized water, and kept in an oven at 150 °C for 5 h.

Example 1

The method for preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method. Weigh 0.5 g of thiourea and place it in a porcelain boat, transfer it to the upstream of the temperature-programmed tube furnace, and then take a piece of treated nickel foam and place it in another. A porcelain boat was transferred to the downstream of the temperature-programmed tube furnace. Under the protection of nitrogen, the temperature-programmed tube furnace was heated to 400 °C at a heating rate of 5 °C/min, and then kept for 90 min, and then cooled to room temperature naturally. , take out to obtain nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF).

Example 2

The method of preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method. Weigh 1.0 g of thiourea and place it in a porcelain boat, transfer it to the upstream of the temperature-programmed tube furnace, and then take a piece of treated nickel foam and place it in another. A porcelain boat was transferred to the downstream of the temperature-programmed tube furnace. Under the protection of nitrogen, the temperature-programmed tube furnace was heated to 400 °C at a heating rate of 5 °C/min, and then kept for 90 min, and then cooled to room temperature naturally. , take out to obtain nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF).

Example 3

The method for preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method. Weigh 1.5 g of thiourea and place it in a porcelain boat, transfer it to the upstream of the temperature-programmed tube furnace, and then take a piece of treated nickel foam and place it in another. A porcelain boat was transferred to the downstream of the temperature-programmed tube furnace. Under the protection of nitrogen, the temperature-programmed tube furnace was heated to 400 °C at a heating rate of 5 °C/min, and then kept for 90 min, and then cooled to room temperature naturally. , take out to obtain nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF).

Example 4

The method of preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method is to weigh 2.0 g of thiourea and place it in a porcelain boat, transfer it to the upstream of the temperature-programmed tube furnace, and then take a piece of treated nickel foam and place it in another. A porcelain boat was transferred to the downstream of the temperature-programmed tube furnace. Under the protection of nitrogen, the temperature-programmed tube furnace was heated to 400 °C at a heating rate of 5 °C/min, and then kept for 90 min, and then cooled to room temperature naturally. , take out to obtain nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF).

Example 5

The method of preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method. Weigh 1.0 g of thiourea and place it in a porcelain boat, transfer it to the upstream of the temperature-programmed tube furnace, and then take a piece of treated nickel foam and place it in another. A porcelain boat was transferred to the downstream of the temperature-programmed tube furnace. Under the protection of nitrogen, the temperature-programmed tube furnace was heated to 300 °C at a heating rate of 5 °C/min, and then kept for 90 min, and then cooled to room temperature naturally. , take out to obtain nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF).

Example 6

The method of preparing nitrogen-doped nickel sulfide hydrogen evolution catalyst by annealing method. Weigh 1.0 g of thiourea and place it in a porcelain boat, transfer it to the upstream of the temperature-programmed tube furnace, and then take a piece of treated nickel foam and place it in another. A porcelain boat was transferred to the downstream of the temperature-programmed tube furnace. Under the protection of nitrogen, the temperature-programmed tube furnace was heated to 500 °C at a heating rate of 5 °C/min, and then kept for 90 min, and then cooled to room temperature naturally. , take out to obtain nitrogen-doped nickel sulfide (N-Ni ₃ S ₂ /NF).

Characterization of the prepared electrocatalyst and experimental analysis of electrocatalytic activity:

As shown in Figure 1, it can be seen from Figure a that the Ni ₃ S ₂ /NF morphology is rod-like with a length of about 1 μm and a diameter of about 300 nm, and it can be seen from Figure b that the N-Ni ₃ S ₂ /NF shape appearance is linear;

It can be seen from Figure 2 that the length of N-Ni ₃ S ₂ /NFNWs is about 5.89 μm and the diameter is 30-80 nm;

As shown in Figure 3, it can be seen from Figure c that the rod-shaped Ni ₃ S ₂ /NF synthesized by the hydrothermal reaction does not contain nitrogen, while from Figure d it can be seen that the linear Ni ₃ S ₂ synthesized by the annealing reaction Nitrogen is introduced into /NF;

As shown in Fig. 4, the diffraction peaks at 21.8°, 31.1°, 37.8°, 44.3°, 50.1°, and 55.3° and Ni ₃ S ₂ (JCPDF# 44-1418) can be seen from (a) , and at 44.8°, 52.2° and 76.8° are consistent with those of blank nickel foam (JCPDF# 03-1051); as can be seen from Figure (b), the peaks at 856.1 eV and 874.2 eV are Ni2p _3/2 and the spin-orbit doublet of Ni p _1/2 , the sharp peak at 852.9 eV may be the peak of the foamed nickel substrate; from figure (c), it can be seen that the double peak at 162.7 eV and 163.5 eV may be the peak of S 2p _3/2 and S 2p _1/2 ; the peak at 161.7 eV may be the peak of S-Ni in Ni ₃ S ₂ ; the peak at 398 eV in panel (d) and 870.2 eV in panel (b) The peaks of may be Ni-N peaks, which indicate that nitrogen was successfully introduced into Ni ₃ S ₂ ;

As shown in Fig. 5, the N _{- Ni3S2} /NFNWs electrocatalytic material has excellent electrocatalytic hydrogen evolution performance in alkaline conditions, which can be clearly seen in figure (a) at current densities of ¹⁰ mA/cm and 100 mA/ The overpotential of cm ² is significantly lower than that of NF and Ni ₃ S ₂ /NF NRs; Figure (b) shows that the Tafel slope of N-Ni ₃ S ₂ /NFNWs electrocatalytic material is smaller than that of NF and Ni ₃ S ₂ /NF NRs , indicating that the reaction kinetics is accelerated; (c) it can be seen that the electrochemical impedance of N-Ni ₃ S ₂ /NFNWs electrocatalytic material is smaller than that of NF and Ni ₃ S ₂ /NFNRs, indicating that the electron transport rate is fast; (d) It can be seen from the figure that in the alkaline medium, after 2000 CV cycles, the N-Ni ₃ S ₂ /NF NWs electrocatalytic material exhibits better stability, while the stability of Ni ₃ S ₂ /NF NRs It is relatively poor; it can also be seen from the it curve that the current density of the N-Ni ₃ S ₂ /NFNWs electrocatalytic material has no obvious attenuation.

The above descriptions are only the embodiments of the present invention, and are not intended to limit the scope of the patent of the present invention. Any equivalent structure or equivalent process transformation made by the description of the present invention, or directly or indirectly applied in other related technical fields, are the same as The principles are included in the scope of patent protection of the present invention.

Claims (7)

1. Preparation of nitrogen-doped Ni by annealing₃S₂The method for the hydrogen evolution catalyst is characterized by comprising the following specific steps: weighing thiourea into a porcelain boat according to the proportion of 0.5-2 g thiourea to one piece of pretreated foamed nickel, transferring the porcelain boat to the upstream of a programmed heating tube furnace, then placing one piece of pretreated foamed nickel into another porcelain boat, transferring the porcelain boat to the downstream of the programmed heating tube furnace, heating to 300-500 ℃ under the protection of inert gas, calcining, preserving heat for 30-100 min, and taking out after naturally cooling to room temperature.

2. The annealing process of claim 1 to produce nitrogen-doped Ni₃S₂Hydrogen evolution catalystThe method is characterized in that the pretreated foamed nickel is obtained by cutting the foamed nickel into 2 × 3 cm, carrying out ultrasonic cleaning for 15-30 min by using 3 mol/L hydrochloric acid and acetone in sequence, removing oxides on the surface of the foamed nickel, carrying out ultrasonic cleaning for 2-3 times by using absolute ethyl alcohol and deionized water respectively, carrying out 5-10 min each time, and carrying out vacuum drying at 60 ℃ to obtain the pretreated foamed nickel.

3. The annealing process of claim 1 to produce nitrogen-doped Ni₃S₂A method of evolving a hydrogen catalyst, characterized in that: the inert gas is nitrogen.

4. The annealing process of claim 1 to produce nitrogen-doped Ni₃S₂A method of evolving a hydrogen catalyst, characterized in that: the heating rate is 5 ℃/min.

5. The annealing process of claim 1 to produce nitrogen-doped Ni₃S₂A method of evolving a hydrogen catalyst, characterized in that: calcining at 400 ℃ for 90min under the protection of inert gas according to the proportion that 1 g of thiourea corresponds to one pretreated foamed nickel.

6. Nitrogen doped Ni obtainable by the process according to any one of claims 1 to 5₃S₂A hydrogen evolution catalyst.

7. The nitrogen-doped Ni of claim 6₃S₂The application of the hydrogen evolution catalyst is characterized in that: the water is electrolyzed and hydrogen is separated out under the alkaline condition by taking the electrode as a working electrode.

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