CN116145184A - Preparation method and application of graphene-based composite binary metal sulfide electrocatalyst - Google Patents

Abstract

The invention relates to the technical field of electrocatalysis, in particular to a preparation method and application of a graphene-based composite binary metal sulfide electrocatalyst. Using graphene as the substrate for the preparation reaction, the composite electrocatalyst was prepared by realizing the in-situ growth of nanosheets and the metal sulfidation reaction by a hydrothermal one-step method. By adjusting the doping amount of Fe element, the nanostructure of the composite catalyst can be effectively improved, which can not only increase the catalytic activity and reaction sites of the _MoS2 electrocatalyst, but also maintain the stability of the catalyst for hydrogen evolution reaction for a long time. The method can effectively improve the problems of low catalytic activity and poor kinetic rate of single-component catalysts in the process of electrolysis of water; through graphene compounding, the conductivity of the catalyst can be improved and the stability of the catalytic process can be increased. This method is simple, easy to operate, economical and environmentally friendly, and can be produced on a large scale and applied to the preparation of other metal sulfide electrocatalysts to realize the application of electrolyzed water.

Description

A kind of preparation method of graphene-based composite binary metal sulfide electrocatalyst and its application

technical field

The invention belongs to the technical field of electrocatalysis, and specifically relates to a preparation method and application of a graphene-based composite binary metal sulfide electrocatalyst. Using graphene as a reaction substrate, the in-situ growth of nanosheets and metal Sulfurization reaction to prepare a composite electrocatalyst.

Background technique

In order to cope with the impact of the energy and environmental crisis and reduce the use of fossil energy, my country has carried out a lot of exploratory work on the application of clean energy in recent years. Among them, hydrogen energy, as an energy carrier with an energy density greater than that of petroleum, has the most development prospects. It has a wide range of sources and low cost, and the consumption process can achieve zero carbon emissions. It is the most ideal primary energy substitute at this stage. There are many methods for industrial hydrogen production, among which water is used as raw material for hydrogen production by electrolysis, the process is clean and no pollutants are produced, and the product has high purity, which is one of the most effective methods of hydrogen production. Due to the existence of overpotential in the process of water electrolysis, the voltage required for the electrolysis process increases, which greatly increases energy consumption. Therefore, it is necessary to explore efficient and stable electrocatalysts that can reduce the overpotential.

Compared with conventional noble metal electrocatalysts, two-dimensional metal sulfides are considered to be a promising electrocatalyst due to their unique electronic structure, good multi-doping coexistence and excellent material properties. However, in the electrocatalytic hydrogen evolution reaction, although metal sulfides have good reactivity, their poor conductivity and easy agglomeration lead to poor stability, which limits their further practical applications. It is an effective means to improve the catalytic properties of metal sulfides by increasing the active sites of metal sulfides, enhancing the conductivity of materials and further improving their stability.

Contents of the invention

The invention relates to a preparation method and application of a graphene-based composite binary metal sulfide electrocatalyst. This method uses thin-layer graphene as the substrate for the reaction, and realizes the in-situ growth of nanosheets and metal sulfidation reaction through a hydrothermal one-step method, and prepares a graphene-based composite binary metal sulfide electrocatalyst, named rGO@FeS ₂ MoS ₂ . The catalyst has the advantages of high activity, good stability, low cost and the like, and has good application prospects.

In order to achieve the above object, the present invention adopts the following technical solutions:

A preparation method of a graphene-based composite binary metal sulfide electrocatalyst, comprising the following steps:

Add ferrous chloride, ammonium heptamolybdate, and thin-layer graphene sheets into deionized water, and disperse uniformly (preferably ultrasonically for 3 hours) to obtain solution A; stir and dissolve thiourea in glycerin to obtain solution B; then dissolve solution A Put the graphene attached to the upper layer after layering (preferably place it for 3 hours), then mix the graphene attached to the upper layer and solution B evenly and place it in a high-pressure reactor, seal it and carry out hydrothermal reaction at 180-260°C 10-30h (preferably hydrothermal reaction at 220°C for 18h), after the reaction is complete, cool naturally to room temperature, centrifuge the obtained solid to wash (preferably wash with absolute ethanol and water in sequence), filter and vacuum dry to obtain graphene based composite binary metal sulfide electrocatalysts.

In the present invention, metal salt and graphene are ultrasonically dispersed into deionized solution A to form solution A. This step enables metal ions to be evenly adsorbed on the surface of graphene, which can effectively avoid the subsequent reaction of nanosheet agglomeration, and realize the uniformity of nanosheets on both sides of graphene. In situ growth and uniform control of morphology.

By dissolving thiourea in glycerol in solution B, glycerin can effectively increase the defects of nanosheets and increase the active sites of catalytic reactions.

Preferably, the vacuum drying condition is vacuum drying at 60° C. for 12 hours.

Preferably, the thin-layer graphene sheet is: a graphene sheet with a thin-layer structure obtained after the graphene oxide powder prepared by the traditional hummers method is subjected to ultrasonic and aging treatments;

The traditional hummers method is carried out with reference to the following documents: Hummers, W.S.; Offeman, R.E.Preparation of Graphitic Oxide.J.Am.Chem.Soc.1958,80,1339-1339.

More preferably, the steps of ultrasonication and aging treatment are as follows: uniformly disperse the graphene oxide powder by ultrasonication, leave it to age overnight, take the supernatant liquid and centrifuge the solid and dry it at 40°C.

Preferably, the molar ratio of ferrous chloride to ammonium heptamolybdate is (1-4):1.

Preferably, the ratio of ferrous chloride, thin-layer graphene oxide sheets and thiourea is (0.25-1) mmol: 0.1 g: (0.1-1.0) g.

The present invention also provides the application of the catalyst obtained by the above preparation method in electrolyzing water for hydrogen evolution.

The present invention utilizes the means of binary metal co-doping and graphene carbon material compounding to realize the preparation of high-efficiency and stable graphene-based composite binary metal sulfide electrocatalysts, avoid particle agglomeration caused by high-temperature sintering, and effectively improve the performance of two-dimensional metal sulfides. Electron transfer ability, and further enhance its catalytic activity and stability, has a good application prospect.

Compared with prior art, advantage and beneficial effect of the present invention are as follows:

(1) By adjusting the doping amount of Fe element, the nanostructure of the composite catalyst can be effectively improved, which can not only increase the catalytic activity and reaction sites of the _MoS2 electrocatalyst, but also maintain the stability of the catalyst for the long-term hydrogen evolution reaction.

(2) Graphene has an adjustable two-dimensional structure and good electrical conductivity. It can not only provide metal coordination points, realize the uniform in-situ generation of two-dimensional metal sulfides, and effectively avoid the agglomeration of active catalysts; and graphene as an interlayer The material can provide the catalyst with lower charge transfer resistance and further increase the HER activity of the catalyst.

(3) This method is simple and easy, economical and environmentally friendly, and can be produced on a large scale and applied to the preparation of other metal sulfide electrocatalysts such as Ni and Co to realize the application in electrolysis of water.

Description of drawings

Fig. 1 is the X-ray diffraction spectrum (XRD) of embodiment 1 gained catalyst;

Fig. 2 is the scanning electron micrograph (SEM) of embodiment 1 gained catalyst;

Fig. 3 is the electrode polarization curve of embodiment 1-3 and comparative example gained catalyst in electrolyte;

Fig. 4 is the Tafel slope corresponding to the electrode polarization curve of the catalyst obtained in Examples 1-3 and Comparative Examples;

Figure 5 is a TEM image of the graphene oxide sheet with a thin layer structure obtained in Example 1.

Detailed ways

The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments.

In the following examples, the traditional hummers method is used to prepare graphene oxide with reference to the following documents: Hummers, W.S.;

Glycerol used in the following examples is anhydrous glycerol;

The concentrations of the used concentrated sulfuric acid and hydrochloric acid are mass percent concentrations.

Embodiment 1: a kind of preparation method of graphene-based composite binary metal sulfide electrocatalyst comprises the steps:

(1) Prepare graphene oxide by the traditional hummers method and carry out initial centrifugal drying: under the condition of ice-water bath, assemble a 250mL reaction bottle, add 10mL concentrated sulfuric acid with a concentration of 95% to it, add 2g graphite powder and 1g nitric acid under stirring Sodium solid mixture, then add 6g potassium permanganate in 3 times, control the reaction temperature not to exceed 20°C, stir for 30min, then raise the temperature to about 35°C, continue stirring for 30min, then slowly add 100mL deionized water, continue stirring for 20min Afterwards, 2 mL of hydrogen peroxide was added to reduce the residual oxidant, making the solution turn bright yellow. Filtrate while hot and wash with 5% HCl solution and deionized water until no sulfate is detected in the filtrate. Finally, the filter cake was fully dried in a vacuum oven at 60°C to obtain graphite oxide powder, which was stored for future use.

Disperse the obtained graphite oxide powder into deionized water, sonicate with 60W power for 3 hours, settle overnight, take the supernatant and centrifuge the solid into an oven, and dry at 40°C for 3 hours to obtain graphene oxide with a thin layer structure The sheet is ready for use, and its TEM image is shown in Figure 5;

(2) 0.25mmol ferrous chloride, 0.25mmol ammonium heptamolybdate, 0.1g step (1) prepared thin-layer graphene oxide sheets were added to 30mL deionized water, and ultrasonically dispersed for 3 hours under 60W to obtain solution A ( This step enables metal ions to be evenly adsorbed on the graphene surface at first, which can effectively avoid the subsequent reaction of nanosheets from agglomeration, and realize the uniform in-situ growth of nanosheets on both sides of the graphene and the uniform control of the shape), stirring and dissolving 0.571g of thiourea in Solution B was obtained in 5 mL glycerol (dissolving thiourea in glycerin, glycerin can effectively increase the defects of nanosheets and increase the catalytic reaction active sites). Place solution A for 3 hours and take the graphene attached to the upper layer, then mix it with solution B and stir under ultrasound for 30 minutes to ensure that the raw materials are evenly dispersed, and transfer the uniformly mixed solution to a 50mL autoclave. Hydrothermal reaction at 220°C for 18 hours (hydrothermal reaction can realize metal vulcanization and graphene reduction), then naturally cool to room temperature and centrifuge, the obtained solid is washed with absolute ethanol and water for 4 times each, and the washed solid is placed in a vacuum at 60°C After drying for 12 hours, the product-highly efficient and stable graphene-based composite binary metal sulfide electrocatalyst was obtained.

Embodiment 2: Prepare efficient and stable graphene-based composite binary metal sulfide electrocatalyst according to the method of embodiment 1, the difference is: the consumption of ferrous chloride is changed to 0.5mmol, other raw material types and consumption, reaction conditions and The parameters are all unchanged.

Example 3: Prepare efficient and stable graphene-based composite binary metal sulfide electrocatalyst according to the method of Example 1, the difference is: the amount of ferrous chloride is changed to 1 mmol, other raw material types and amounts, reaction conditions and parameters are unchanged.

Comparative example: Add 0.5mmol ferrous chloride and 0.25mmol ammonium heptamolybdate into 30mL deionized water, ultrasonically disperse for 3 hours, and record it as solution A, while stirring and dissolving 0.571g thiourea in 5mL glycerin, record it as solution B. After solution A was left for 3 hours, it was mixed with solution B, stirred under ultrasonic for 30 minutes to ensure that the raw materials were uniformly dispersed, and the mixed solution was transferred to a 50mL autoclave, sealed and hydrothermally treated at 220°C for 18 hours. After the end, it was naturally cooled to room temperature and then centrifuged, and the obtained solid was washed with ethanol and water four times in sequence, and the centrifuged solid was vacuum-dried at 60°C for 12 hours to obtain the product composite binary metal sulfide electrocatalyst.

Fig. 1 is the XRD spectrogram of the catalyst obtained in Example 1, as can be seen: the obtained catalyst is composed of _FeS2 (PDF74-1051) and _MoS2 (PDF 86-2308), and it is proved that the introduction of _FeS2 does not change the structure of _MoS2 characteristic.

Figure 2 is a scanning electron microscope image of the catalyst obtained in Example 1. It can be seen from the figure that the metal sulfide nanosheets with a uniform structure in the obtained electrocatalyst grow uniformly on both sides of the catalyst with a thin layer of graphene as a template, showing a sandwich sandwich structure . This structure can provide a large number of active sites, which can greatly promote the catalytic activity and efficiency. At the same time, the surface chemical bonds between metal sulfide nanosheets and graphene are cross-linked, which effectively reduces the resistance of electron transfer in the catalytic process and enhances the stability of the process.

Electrolytic hydrogen activity and stability test:

The catalyst prepared in Example 1 was tested for electrolysis of hydrogen: on the electrochemical workstation, a three-electrode test system was adopted, and the working electrode was a catalyst electrode (4 mg of the catalyst obtained in Example 1 was dispersed in 1 mL of dehydrated alcohol with a volume ratio of 95:5 and Nafion solution mixed solution to obtain a dispersion, get 14 μ L of the resulting dispersion and evenly drop it on a glassy carbon electrode to make a catalyst electrode), the counter electrode is a graphite electrode, and the reference electrode is an Ag/AgCl (3.5M KCl) electrode. The test electrolyte is 25°C, 1mmol/L potassium hydroxide aqueous solution. During the test, high-purity nitrogen gas is passed through for saturation treatment, and the test temperature is room temperature. When testing the linear sweep voltammetry curve, the sweep rate is 5mV/s.

Tests of other catalysts and comparative examples were carried out in the manner described above.

Fig. 3 is the electrode polarization curve of embodiment 1-3 gained product in electrolytic solution, as can be seen from curve, embodiment 1-3 gained catalyst is in 10mA. At the current density of cm ^-2 , the overpotentials were 163mV, 93mV, and 166mV, respectively, showing good HER activity, while the comparative example had an overpotential of 300mV at the same current density due to the fact that graphene was not compounded, indicating that graphene has a good HER activity. The increase in catalyst activity plays an important role.

Fig. 4 is the Tafel slope corresponding to the electrode polarization curve of the product obtained in the embodiment, as can be seen from the curve, the Tafel slope of the catalyst obtained in Examples 1-3 is 70.250mV. dec ^-1 、50mV． dec ^-1 、79.150mV． dec ^-1 , it can be seen that the HER kinetic performance of the electrocatalyst can be effectively enhanced by adjusting the doping ratio. The Tafel slope of the comparative example is 71.30mV. dec ^-1 , indicating that graphene can effectively enhance the kinetic properties of metal sulfides.

The present invention utilizes the means of binary metal co-doping and graphene carbon material compounding to realize the preparation of high-efficiency and stable graphene-based composite binary metal sulfide electrocatalysts, avoid particle agglomeration caused by high-temperature sintering, and effectively improve the performance of two-dimensional metal sulfides. Electron transfer ability, and further enhance its catalytic activity and stability, has a good application prospect.

It should be noted that those skilled in the art can make improvements or transformations based on the above description, and these improvements or transformations should fall within the protection scope of the appended claims of the present invention.

Claims (7)

1. A preparation method of a graphene-based composite binary metal sulfide electrocatalyst comprises the following steps:

adding ferrous chloride, ammonium heptamolybdate and a thin-layer graphene sheet into deionized water, and uniformly dispersing by ultrasonic to obtain a solution A; stirring thiourea to dissolve in glycerol to obtain a solution B; and then placing the solution A to be layered, taking the graphene attached to the upper layer, uniformly mixing the graphene attached to the upper layer with the solution B, placing the mixture into a high-pressure reaction kettle, sealing, carrying out hydrothermal reaction at 180-260 ℃ for 10-30h, naturally cooling to room temperature after the reaction is completed, centrifuging the obtained solid, washing, filtering, and vacuum drying to obtain the graphene-based composite binary metal sulfide electrocatalyst.

2. The method according to claim 1, wherein the vacuum drying condition is vacuum drying at 60 ℃ for 12 hours.

3. The method of claim 1, wherein the thin graphene sheets are: graphene oxide powder prepared by the traditional hummers method is subjected to ultrasonic and aging treatment to obtain the graphene sheet with the thin-layer structure.

4. A method of manufacture according to claim 3, wherein the step of ultrasound and aging treatment comprises: and (3) after uniformly dispersing graphene oxide powder by ultrasonic waves, standing for overnight for aging, and drying the solid obtained after centrifuging the supernatant at 40 ℃.

5. The preparation method according to claim 1, wherein the molar ratio of ferrous chloride to ammonium heptamolybdate is (1-4): 1.

6. the preparation method of claim 5, wherein the dosage ratio of the ferrous chloride, the thin graphene oxide sheets and the thiourea is (0.25-1) mmol:0.1g: (0.1 to 1.0 g).

7. Use of the catalyst obtained by the preparation method of any one of claims 1 to 6 in hydrogen evolution of electrolyzed water.

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