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

Abstract

The present application relates to the technical field of electrocatalysis, and in particular to a preparation method and application of a graphene-based composite binary metal sulfide electrocatalyst. Graphene is used as a substrate for the preparation reaction, and through a one-step hydrothermal method, nanosheet in-situ growth and metal sulfide reaction are realized to prepare a composite electrocatalyst. By adjusting the doping amount of Fe elements, the nanostructure of the composite catalyst can be effectively improved, not only the catalytic activity and reaction sites of the MoS2 electrocatalyst can be increased, but also the stability of the catalyst in the long-term catalytic hydrogen evolution reaction can be maintained. The method can effectively improve the problems of low catalytic activity and poor kinetic rate of single-component catalysts in the water electrolysis reaction process; through graphene compounding, the conductivity of the catalyst is improved and the stability of the catalytic process is increased. The method is simple, easy to implement, economical and environmentally friendly, can be produced on a large scale and applied to the preparation of other metal sulfide electrocatalysts to realize the application of water electrolysis.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, specifically relating to a method for preparing and applying a graphene-based composite binary metal sulfide electrocatalyst. Using graphene as the reaction substrate, a one-step hydrothermal method is used to achieve in-situ growth of nanosheets and metal sulfidation reaction to prepare the composite electrocatalyst. Background Technology

[0002] To address the impact of the energy and environmental crisis and reduce the use of fossil fuels, my country has conducted extensive exploratory work on the application of clean energy in recent years. Among these, hydrogen energy, with its higher energy density than petroleum, shows the greatest potential. It is widely available, inexpensive, and its consumption process can potentially achieve zero carbon emissions, making it the most ideal primary energy substitute at present. There are many methods for industrial hydrogen production, among which water electrolysis, using water as a raw material, is a clean process with no pollutants and produces high-purity products, making it one of the most efficient methods. However, the presence of overpotential during water electrolysis increases the voltage required for the process, significantly increasing energy consumption. Therefore, it is essential to explore efficient and stable electrocatalysts that can reduce overpotential.

[0003] Compared to conventional noble metal electrocatalysts, two-dimensional metal sulfides are considered promising electrocatalysts due to their unique electronic structure, good multi-doped coexistence, and excellent material properties. However, in the electrocatalytic hydrogen evolution reaction, although metal sulfides exhibit good reactivity, their poor conductivity and tendency to aggregate lead to poor stability, limiting their further practical applications. Increasing the active sites of metal sulfides to enhance material conductivity and further improve their stability are effective means to improve the catalytic properties of metal sulfides. Summary of the Invention

[0004] This invention relates to a method for preparing and applying a graphene-based composite binary metal sulfide electrocatalyst. The method uses thin-layer graphene as the reaction matrix and achieves in-situ growth of nanosheets and metal sulfidation reaction via a one-step hydrothermal process to prepare a graphene-based composite binary metal sulfide electrocatalyst, named rGO@FeS2MoS2. This catalyst exhibits advantages such as high activity, good stability, and low cost, and shows promising application prospects.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0006] A method for preparing a graphene-based composite binary metal sulfide electrocatalyst includes the following steps:

[0007] Ferrous chloride, ammonium heptamolybdate, and thin-layer graphene sheets are added to deionized water and ultrasonically dispersed (preferably for 3 hours) to obtain solution A. Thiourea is dissolved in glycerol by stirring to obtain solution B. Solution A is then left to separate into layers, and the graphene attached to the upper layer is taken (preferably left to stand for 3 hours). The graphene attached to the upper layer and solution B are then mixed evenly and placed in a high-pressure reactor. After sealing, a hydrothermal reaction is carried out at 180-260℃ for 10-30 hours (preferably at 220℃ for 18 hours). After the reaction is complete, the mixture is naturally cooled to room temperature, and the solid obtained by centrifugation is washed (preferably with anhydrous ethanol and water in sequence), filtered, and vacuum dried to obtain a graphene-based composite binary metal sulfide electrocatalyst.

[0008] This invention involves ultrasonically dispersing metal salts and graphene into a deionized medium to form solution A. This step allows metal ions to be uniformly adsorbed onto the graphene surface, effectively preventing the subsequent agglomeration of nanosheets and achieving uniform in-situ growth and morphological control of nanosheets on both sides of the graphene.

[0009] By dissolving thiourea in glycerol in solution B, glycerol can effectively increase the defects in the nanosheets and increase the number of active sites for catalytic reaction.

[0010] Preferably, the vacuum drying conditions are vacuum drying at 60°C for 12 hours.

[0011] Preferably, the thin-layer graphene sheet is a graphene sheet with a thin-layer structure obtained by ultrasonic and aging treatment of graphene oxide powder prepared by the traditional Hummers method.

[0012] The traditional Hummers method is described in the following references: Hummers, WS; Offeman, REPreparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80, 1339-1339.

[0013] More preferably, the ultrasonic and aging treatment steps are as follows: after ultrasonically dispersing the graphene oxide powder evenly, it is left to age overnight, and the solid after centrifugation of the upper liquid is dried at 40°C.

[0014] Preferably, the molar ratio of ferrous chloride to ammonium heptamolybdate is (1-4):1.

[0015] Preferably, the ratio of ferrous chloride, thin-layer graphene oxide sheet and thiourea is (0.25-1) mmol: 0.1 g: (0.1-1.0) g.

[0016] This invention also provides the application of the catalyst obtained by the above preparation method in hydrogen evolution through water electrolysis.

[0017] This invention utilizes binary metal co-doping and graphene-carbon material composites to achieve the preparation of highly efficient and stable graphene-based composite binary metal sulfide electrocatalysts. This avoids particle agglomeration caused by high-temperature sintering, effectively improves the electron transfer capability of two-dimensional metal sulfides, and further enhances their catalytic activity and stability, showing promising application prospects.

[0018] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0019] (1) By adjusting the amount of Fe doping, the nanostructure of the composite catalyst can be effectively improved, which can not only increase the catalytic activity and reaction sites of MoS2 electrocatalyst, but also maintain the stability of the catalyst for long-term hydrogen evolution reaction.

[0020] (2) Graphene has a tunable two-dimensional structure and good conductivity. It can not only provide metal coordination sites to achieve uniform in-situ generation of two-dimensional metal sulfides and effectively avoid the aggregation of active catalysts; but also, as a sandwich material, graphene can provide the catalyst with a lower charge transfer resistance and further increase the HER activity of the catalyst.

[0021] (3) This method is simple, economical and environmentally friendly. It can be mass-produced and applied to the preparation of other metal sulfide electrocatalysts such as Ni and Co, and can be used in water electrolysis. Attached Figure Description

[0022] Figure 1 The X-ray diffraction (XRD) pattern of the catalyst obtained in Example 1 is shown below.

[0023] Figure 2 The image shown is a scanning electron microscope (SEM) image of the catalyst obtained in Example 1.

[0024] Figure 3 The electrode polarization curves of the catalysts obtained in Examples 1-3 and the comparative examples in the electrolyte are shown.

[0025] Figure 4 The Tafel slopes are the electrode polarization curves of the catalysts obtained in Examples 1-3 and the comparative examples.

[0026] Figure 5 This is a TEM image of the graphene oxide sheet with a thin-layer structure obtained in Example 1. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0028] The following examples demonstrate the preparation of graphene oxide using the conventional Hummers method, referring to the following literature: Hummers, WS; Offeman, RE Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80, 1339-1339.

[0029] The glycerol used in the following examples is anhydrous glycerol;

[0030] The concentrations of the concentrated sulfuric acid and hydrochloric acid used are both mass percentage concentrations.

[0031] Example 1: A method for preparing a graphene-based composite binary metal sulfide electrocatalyst, comprising the following steps:

[0032] (1) Preparation of graphene oxide using the traditional Hummers method followed by initial centrifugal drying: A 250 mL reaction flask was assembled under ice-water bath conditions. 10 mL of 95% concentrated sulfuric acid was added, followed by stirring. A solid mixture of 2 g of graphite powder and 1 g of sodium nitrate was then added, followed by 6 g of potassium permanganate in three portions. The reaction temperature was controlled to not exceed 20°C, and the mixture was stirred for 30 min. The temperature was then raised to approximately 35°C, and stirring continued for another 30 min. 100 mL of deionized water was slowly added, and stirring continued for another 20 min. Finally, 2 mL of hydrogen peroxide was added to reduce the residual oxidant, turning the solution a bright yellow. The solution was filtered while hot and washed with 5% HCl solution and deionized water until no sulfate ions were detected in the filtrate. The filter cake was then thoroughly dried in a vacuum drying oven at 60°C to obtain graphene oxide powder, which was stored for later use.

[0033] The obtained graphene oxide powder was dispersed in deionized water and sonicated at 60W for 3 hours. After precipitation overnight, the solid from the supernatant was centrifuged and placed in an oven to dry at 40℃ for 3 hours, thus obtaining graphene oxide sheets with a thin-layer structure for later use. TEM images are shown below. Figure 5 ;

[0034] (2) Add 0.25 mmol ferrous chloride, 0.25 mmol ammonium heptamolybdate, and 0.1 g of the thin-layer graphene oxide sheet prepared in step (1) to 30 mL of deionized water and sonicate at 60 W for 3 hours to obtain solution A (this step allows metal ions to be uniformly adsorbed on the graphene surface, which can effectively avoid the aggregation of nanosheets in subsequent reactions, and achieve uniform in-situ growth and morphology control of nanosheets on both sides of the graphene). Dissolve 0.571 g of thiourea in 5 mL of glycerol to obtain solution B (dissolving thiourea in glycerol can effectively increase the defects of the nanosheets and increase the active sites for catalytic reaction). After 3 hours of standing, the graphene adhering to the upper layer of solution A was collected and then mixed with solution B and stirred under ultrasound for 30 minutes to ensure uniform dispersion of the raw materials. The uniformly mixed solution was transferred to a 50 mL high-pressure reactor, sealed, and subjected to hydrothermal reaction at 220 °C for 18 hours (hydrothermal reaction can achieve metal sulfidation and graphene reduction). After natural cooling to room temperature, the solution was centrifuged. The obtained solid was washed 4 times each with anhydrous ethanol and water. The washed solid was then vacuum dried at 60 °C for 12 hours to obtain the product - a highly efficient and stable graphene-based composite binary metal sulfide electrocatalyst.

[0035] Example 2: A highly efficient and stable graphene-based composite binary metal sulfide electrocatalyst was prepared according to the method of Example 1, except that the amount of ferrous chloride was changed to 0.5 mmol, while the types and amounts of other raw materials, reaction conditions and parameters remained unchanged.

[0036] Example 3: A highly efficient and stable graphene-based composite binary metal sulfide electrocatalyst was prepared according to the method of Example 1, except that the amount of ferrous chloride was changed to 1 mmol, while the types and amounts of other raw materials, reaction conditions and parameters remained unchanged.

[0037] Comparative Example: 0.5 mmol ferrous chloride and 0.25 mmol ammonium heptamolybdate were added to 30 mL of deionized water and ultrasonically dispersed for 3 hours, denoted as solution A. Simultaneously, 0.571 g thiourea was dissolved in 5 mL of glycerol and denoted as solution B. After solution A was left to stand for 3 hours, it was mixed with solution B and stirred ultrasonically for 30 min to ensure uniform dispersion of the raw materials. The mixed solution was transferred to a 50 mL high-pressure reactor, sealed, and hydrothermally treated at 220 °C for 18 h. After natural cooling to room temperature, the mixture was centrifuged. The resulting solid was then washed four times sequentially with ethanol and water. The centrifuged solid was vacuum dried at 60 °C for 12 h to obtain the product, a composite binary metal sulfide electrocatalyst.

[0038] Figure 1 The XRD pattern of the catalyst obtained in Example 1 shows that the catalyst is composed of FeS2 (PDF74-1051) and MoS2 (PDF86-2308), which also proves that the introduction of FeS2 did not change the structural characteristics of MoS2.

[0039] Figure 2 The image shows a scanning electron microscope (SEM) image of the catalyst obtained in Example 1. As can be seen, the uniformly structured metal sulfide nanosheets in the obtained electrocatalyst are uniformly grown on both sides of a thin layer of graphene, exhibiting a sandwich structure. This structure provides a large number of active sites, which can greatly promote catalytic activity and efficiency. Simultaneously, the surface chemical bonds of the metal sulfide nanosheets and graphene undergo cross-linking, effectively reducing electron transfer resistance in the catalytic process and enhancing process stability.

[0040] Electrolytic hydrogen activity and stability tests:

[0041] Electrochemical hydrogen evolution test was performed on the catalyst prepared in Example 1: A three-electrode test system was used on an electrochemical workstation. The working electrode was the catalyst electrode (4 mg of the catalyst obtained in Example 1 was dispersed in 1 mL of a 95:5 volume ratio mixture of anhydrous ethanol and Nafion solution to obtain a dispersion, and 14 μL of the resulting dispersion was uniformly dropped onto a glassy carbon electrode to obtain the catalyst electrode), the counter electrode was a graphite electrode, and the reference electrode was an Ag / AgCl (3.5 M KCl) electrode. The test electrolyte was a 1 mmol / L potassium hydroxide aqueous solution at 25 °C. High-purity nitrogen gas was purged during the test, and the test temperature was room temperature. The linear sweep voltammetry curve was performed at a scan rate of 5 mV / s.

[0042] Other catalysts and comparative samples were tested in the same manner as described above.

[0043] Figure 3 The figures show the electrode polarization curves of the products obtained in Examples 1-3 in the electrolyte. The curves indicate that the catalysts obtained in Examples 1-3 exhibit electrode polarization at 10 mA·cm⁻¹. -2 At the given current density, the overpotentials were 163mV, 93mV, and 166mV, respectively, demonstrating good HER activity. In contrast, the overpotential of the control sample without graphene composite was 300mV at the same current density, indicating that graphene plays an important role in improving catalyst activity.

[0044] Figure 4 The figure shows the Tafel slope corresponding to the electrode polarization curves of the products obtained in the examples. As can be seen from the curves, the Tafel slope of the catalysts obtained in Examples 1-3 is 70.250 mV·dec. -1 50mV·dec -1 79.150mV dec -1 It can be seen that by controlling the doping ratio, the HER kinetics of the electrocatalyst can be effectively enhanced. The Tafel slope of the comparative example is 71.30 mV·dec. -1 This indicates that graphene can effectively enhance the kinetic properties of metal sulfides.

[0045] This invention utilizes binary metal co-doping and graphene-carbon material composites to achieve the preparation of highly efficient and stable graphene-based composite binary metal sulfide electrocatalysts. This avoids particle agglomeration caused by high-temperature sintering, effectively improves the electron transfer capability of two-dimensional metal sulfides, and further enhances their catalytic activity and stability, showing promising application prospects.

[0046] It should be noted that those skilled in the art can make improvements or modifications based on the above description, and such improvements or modifications should all fall within the protection scope of the appended claims.

Claims

1. A method for preparing a graphene-based composite binary metal sulfide electrocatalyst, comprising the following steps: Ferrous chloride, ammonium heptamolybdate, and thin-layer graphene sheets were added to deionized water and ultrasonically dispersed to obtain solution A. Thiourea was dissolved in glycerol by stirring to obtain solution B. Solution A was then allowed to separate into layers, and the graphene attached to the upper layer was taken. The graphene attached to the upper layer and solution B were then mixed evenly and placed in a high-pressure reactor. After sealing, a hydrothermal reaction was carried out at 180-260℃ for 10-30 hours. After the reaction was complete, the mixture was naturally cooled to room temperature, centrifuged, washed, filtered, and vacuum dried to obtain a graphene-based composite binary metal sulfide electrocatalyst. The thin-layer graphene sheet is a graphene sheet with a thin-layer structure obtained by ultrasonic and aging treatment of graphene oxide powder prepared by the traditional Hummers method. The ultrasonic and aging treatment steps are as follows: after ultrasonically dispersing the graphene oxide powder evenly, it is left to age overnight, and the solid after centrifugation of the upper liquid is dried at 40°C. The molar ratio of ferrous chloride to ammonium heptamolybdate is (1 ~ 4): 1, and the ratio of ferrous chloride, thin-layer graphene oxide sheet and thiourea is (0.25 ~ 1) mmol: 0.1 g: (0.1 ~ 1.0) g.

2. The preparation method according to claim 1, characterized in that, The vacuum drying conditions are as follows: vacuum drying at 60°C for 12 hours.

3. The application of the graphene-based composite binary metal sulfide electrocatalyst obtained by the preparation method according to any one of claims 1-2 in the electrolysis of water to produce hydrogen.

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