Preparation method of composite electrocatalyst of molybdenum disulfide loaded platinum nanoclusters for hydrogen production by alkaline water electrolysis

Abstract

The present invention belongs to the technical field of electrocatalysis for hydrogen production by electrolysis of water, and discloses a method for preparing a composite electrocatalyst of molybdenum disulfide loaded with platinum nanoclusters for hydrogen production by alkaline electrolysis of water. 2 In the process, the size of the precious metal platinum is reduced to atomic size and loaded on the surface of the carrier, which can minimize the cost of the catalyst while maintaining the catalytic performance of the material. The substrate of the prepared nanocomposite material is MoS 2 Nanosheets, this sheet structure has a large specific surface area and can load more Pt atomic clusters, thereby providing more active centers and improving the catalytic activity of the material in water electrolysis; the prepared nanomaterial has good catalytic performance in an alkaline environment, and MoS 2 The substrate has good catalytic activity in acidic environment, so the prepared material has potential applications in different pH environments.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalysis for producing hydrogen through electrolysis of water, and specifically relates to a method for preparing a nanocomposite electrocatalyst of flaky molybdenum disulfide loaded with platinum atomic clusters. Background Art

[0002] Hydrogen energy, or hydrogen, has a high unit mass combustion value and its combustion product is the cleanest water. It is considered to be the most ideal energy-containing energy and fuel to replace fossil energy. In addition, hydrogen energy can be obtained by decomposing water, making the entire process an atomic-economical green process.

[0003] Whether hydrogen energy can be widely used, the choice of hydrogen production method is crucial. At present, the electrolysis of water is a method for preparing hydrogen widely used in industrial production due to its simple process equipment, and it is also an important research direction in the field of scientific research. Pt, Pd and other precious metals are the best catalysts for hydrogen production by electrolysis of water found so far, but due to their high price, low reserves, easy poisoning and other reasons, it is difficult to be widely used in large-scale industrial production. Therefore, finding alternative electrolysis catalysts for water has become an important topic in this field. In recent years, more and more hydrogen evolution catalysts have been developed, mainly alloy materials, carbon materials, carbides, sulfides, phosphides, nitrides, etc. Among them, NiMo alloy catalysts in alkaline systems and MoS2-based catalysts in acidic systems have shown efficient hydrogen evolution catalysts and are expected to become new alternative catalysts. Although the development of alternative hydrogen evolution catalysts has achieved certain results, Pt is still the best electrolysis catalyst for water. In summary, the key problems hindering the development of hydrogen production technology by electrolysis of water are insufficient catalyst activity and the use of high-load precious metals leading to high energy consumption and hydrogen production costs. Due to their unique geometric (electronic) structure, clear active sites and excellent catalytic performance, single atom catalysts and single cluster catalysts have shown excellent catalytic performance in many reactions. Therefore, in order to improve the activity and utilization of electrocatalysts and reduce the cost of electrocatalysts, it is one of the current research hotspots to develop highly active and durable supported noble metal single atom or atomic cluster electrocatalysts for water electrolysis to produce hydrogen, reduce the amount of noble metals used, and achieve higher activity at a lower cost, and promote the large-scale production of water electrolysis to produce hydrogen.

[0004] Unlike the acidic HER process, the alkaline HER kinetic process is 2-3 orders of magnitude slower than the acidic HER due to the significant decrease in proton concentration. On the one hand, as the simplest cathode reaction in a high pH environment, alkaline HER plays a fundamental and important role. On the other hand, due to the increasing maturity of the anion exchange membrane fuel cell process and the rapid kinetics of the OER half-reaction in alkaline electrolytes, the study of alkaline HER systems is very important. At present, there are few catalysts for alkaline hydrogen evolution. Finding a suitable carrier and preparing single-atom catalysts for hydrogen evolution under alkaline conditions are urgent issues to be solved. In addition, many scientific research works have reported that treating catalysts by nano-sizing, arraying, doping, and composite with carbon materials can increase the surface area of ​​the catalyst, increase the number of catalytically active sites, and enhance the conductivity of the catalyst, thereby further improving the catalytic activity of existing catalysts. Summary of the invention

[0005] In view of the above problems, the present invention uses MoS2 with good catalytic performance in acidic media as a carrier and proposes a method for preparing a MoS2-loaded Pt atomic cluster nanocomposite material. The prepared nanomaterial has excellent performance in hydrogen production by water electrolysis in alkaline electrolyte.

[0006] The technical solution of the present invention:

[0007] A method for preparing a composite electrocatalyst of molybdenum disulfide loaded with platinum nanoclusters for hydrogen production by alkaline water electrolysis, comprising the following steps:

[0008] (1) Preparation of MoS2: Under stirring conditions, ammonium molybdate and thiourea in a mass ratio of 1:10-1:15 were dissolved in secondary water to obtain a mixed solution. The concentration of ammonium molybdate in the mixed solution was 0.1 g L -1 ; After reacting for 10-50 minutes, the mixed solution is transferred to a reactor and subjected to hydrothermal reaction at 160-200°C for 20-28 hours; after cooling naturally, the solid samples are collected by centrifugation with anhydrous ethanol and secondary water, and after vacuum drying overnight, the samples are heat treated in an inert atmosphere; the heat treatment temperature is 450-550°C, and the heating rate is 1-5°C min -1 , heat treatment time is 1-3h, and MoS2 is obtained;

[0009] (2) Preparation of MoS2-loaded platinum atomic clusters: MoS2 was dissolved in secondary water, and a 1.5-2.5 mM chloroplatinic acid solution was added under stirring. The concentration of MoS2 in the reaction system was 1.25 g L -1 The concentration of chloroplatinic acid in the reaction system is 0.65 g L -1The mixed solution was reacted in a water bath at 30-60°C for 2-4h, cooled naturally, and then centrifuged and washed with anhydrous ethanol and secondary water, respectively, and vacuum dried to obtain a composite electrocatalyst of molybdenum disulfide-loaded platinum nanoclusters.

[0010] Application of MoS2-loaded Pt nanoclusters composite electrocatalyst in hydrogen production by alkaline water electrolysis.

[0011] Beneficial effects of the present invention: Compared with the prior art, the nanocomposite material of platinum atomic clusters loaded on two-dimensional MoS2 nanosheets synthesized by the method adopted by the present invention has a uniform morphology of the substrate MoS2, a small thickness, and can be cross-linked to form a three-dimensional network structure. Using it as a substrate to load platinum nanoclusters can not only provide a large specific surface area, but also effectively improve the electron transmission speed in the process of electrolysis of water to produce hydrogen. During the heat treatment process, the heat treatment temperature has a great influence on the structure of the material. When the temperature is too high, the structure of MoS2 is prone to collapse, and the three-dimensional network structure is destroyed, while when the temperature is low, the precursor cannot completely form MoS2 nanomaterials. In the Pt@MoS nanocomposite prepared by the present invention, the platinum atomic clusters can be evenly dispersed on the surface of MoS2, and the reproducibility is good, and the synthesis method is simple and easy. During the preparation process, the amount of chloroplatinic acid used has a great influence on the performance and cost of the material. The Pt@MoS2 nanocomposite material obtained when the concentration of chloroplatinic acid is too low has fewer active centers and poor performance of the material. When the concentration of chloroplatinic acid is too high, the active centers of the prepared Pt@MoS2 nanocomposite material will accumulate together, resulting in not only failure to improve the activity of the material but also an increase in the cost of the catalyst material. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the X-ray diffraction pattern of the prepared Pt@MoS2 nanomaterial.

[0013] Figure 2 This is a scanning electron microscope photo of MoS2-600 nanomaterial.

[0014] Figure 3 Scanning electron microscope photos of MoS2 and Pt@MoS2 nanomaterials.

[0015] Figure 4 This is the X-ray electron energy spectrum of Pt@MoS2 nanomaterials.

[0016] Figure 5 High-resolution XPS spectrum of Pt 4f

[0017] Figure 6 Linear voltammetric hydrogen production curves of bare carbon paper, MoS2 and Pt@MoS2 nanomaterials.

[0018] Figure 7This is a test diagram of the hydrogen production cycle stability of MoS2 and Pt@MoS2 nanomaterials. DETAILED DESCRIPTION

[0019] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0020] Preparation of MoS2: Dissolve a certain amount of ammonium molybdate and thiourea (mass ratio of 1:10) in 30mL of secondary water under stirring. After 30 minutes, transfer the mixed solution to the reactor. Hydrothermal reaction at 180°C for 20 hours. After natural cooling, collect solid samples by centrifugation with anhydrous ethanol and secondary water respectively. After vacuum drying overnight, heat treat the samples in an inert atmosphere. The heat treatment temperature is 500°C, and the heating rate is 2°C min -1 , the heat treatment time is 2h, and MoS2-500 is obtained. In order to investigate the effect of heat treatment temperature on the microstructure of MoS2, the annealing temperature is set to 400 and 600℃ at the same time, and two samples of MoS2-400 and MoS2-600 are obtained respectively.

[0021] Preparation of MoS2-loaded platinum atomic clusters: Dissolve 50 mg MoS2-500 in 20 mL secondary water, and add 20 mL of a certain concentration of chloroplatinic acid solution (2 mM) under stirring. The mixed solution was reacted in a 40 ° C water bath for 3 hours. After natural cooling, it was centrifuged and washed with anhydrous ethanol and secondary water respectively. Pt@MoS2 was obtained after vacuum drying. In order to investigate the effect of chloroplatinic acid concentration on the catalytic performance of the material, we prepared two comparative samples with chloroplatinic acid concentrations adjusted to 1 and 3 mM, namely Pt@MoS2-1 and Pt@MoS2-3.

[0022] For electrochemical hydrogen production performance testing

[0023] (1) Hydrogen production performance test by water electrolysis

[0024] Test instrument: Electrochemical workstation

[0025] Preparation of working electrode: Weigh 10 mg of the prepared samples (MoS2, Pt@MoS2-1, Pt@MoS2-2, Pt@MoS2-3) respectively, add water and isopropanol (volume ratio of 4:1) in turn, the total volume is 1 mL, and then add 50 μL of 5% Nafion solution. After ultrasonication for 10 min, take 15 μL of the mixed solution and drop it onto carbon paper and dry it naturally. The sample loading is 0.6 mg cm -2 .

[0026] (2) Hydrogen production performance test of water electrolysis

[0027] Test method: Three-electrode system, the sample electrode prepared above, saturated calomel electrode, graphite rod are working electrode, reference electrode and counter electrode respectively, and the electrolyte is 1M KOH solution. After nitrogen is passed for 30 minutes, the linear voltammetric curve of the test material (scan rate 2mVs -2 ), electrochemical impedance curve (voltage is open circuit voltage, frequency range is 0.1Hz~100KHz, amplitude is 5mV), stability curve (current density is 10mA cm -2 , time is 10h). The test potential is converted to standard hydrogen electrode, the formula is: E(RHE)=E(SCE)+0.242V+0.059pH

[0028] The results show that: from the XRD pattern of the sample ( Figure 1 ) It can be seen that we prepared MoS2 by hydrothermal method, and successfully loaded platinum atom clusters on MoS2 by impregnation method, and finally obtained Pt@MoS2 nanocomposite material. When the heat treatment temperature of the hydrothermal product was 400℃, the precursor was not completely converted into MoS2. From the scanning electron microscope image of the sample, it can be seen that when the heat treatment temperature of the hydrothermal product was 600℃, the microstructure of MoS2 collapsed ( Figure 2 ). Scanning electron microscope image ( Figure 3 ) shows that the prepared Pt@MoS2 nanocomposite material is a two-dimensional sheet structure, and the nanosheets are cross-linked to form a network structure. The thickness of the sheet structure is about 10nm. The cross-linked structure of the material is conducive to the transmission of electrons in the hydrogen production process, and can improve the catalytic activity of the material to a certain extent. Figure 4 This is the X-ray photoelectron spectroscopy (XPS) diagram of the Pt@MoS2 nanocomposite material. It can be seen that the composite material contains molybdenum, sulfur, carbon, platinum and oxygen elements. Figure 5 This is a high-resolution XPS image of Pt 4f. It can be seen from the figure that platinum exists in the form of metal in the Pt@MoS2 nanocomposite. Figure 6 The linear voltammetric curve of the sample is shown in Figure 2. As can be seen from the figure, the nanomaterial loaded with platinum atomic clusters exhibits the best activity for hydrogen production by water electrolysis. -2 When the overpotential is 0.21V, it is much larger than the overpotential of MoS2 and bare carbon cloth. Similarly, when the concentration of chloroplatinic acid is too small, the activity of the prepared electrode material (Pt@MoS2-1) is also lower than that of Pt@MoS2. On the contrary, when the concentration of chloroplatinic acid is too large, the activity of the electrode material (Pt@MoS2-3) decreases. The above performance test results prove that the amount of chloroplatinic acid cannot be increased indefinitely in the process of preparing molybdenum disulfide-loaded platinum atomic cluster nanocomposites. From the stability curve of the sample ( Figure 7 ) shows that at a current density of mA cm -2Under the above conditions, the activity of the Pt@MoS2 nanocomposite material did not change significantly after 10 hours of reaction. This shows that the Pt@MoS2 nanocomposite material we prepared has good stability.

Claims

1. A method for preparing a composite electrocatalyst of molybdenum disulfide loaded with platinum nanoclusters for hydrogen production by alkaline water electrolysis, characterized in that: Here are the steps: (1) Preparation of MoS2: Under stirring conditions, ammonium molybdate and thiourea in a mass ratio of 1:10-1:15 are dissolved in secondary water to obtain a mixed solution, wherein the concentration of ammonium molybdate in the mixed solution is 0.1 g / L; after reacting for 10-50 min, the mixed solution is transferred to a reactor and subjected to a hydrothermal reaction at 160-200°C for 20-28 h; after natural cooling, the solid samples are collected by centrifugation with anhydrous ethanol and secondary water, and after vacuum drying overnight, the samples are heat treated in an inert atmosphere; the heat treatment temperature is 450-550°C, the heating rate is 1-5°C / min, and the heat treatment time is 1-3 h to obtain MoS2; (2) Preparation of MoS2-loaded platinum atomic clusters: MoS2 was dissolved in secondary water, and a 1.5-2.5 mM chloroplatinic acid solution was added under stirring, wherein the concentration of MoS2 in the reaction system was 1.25 g / L, and the concentration of chloroplatinic acid in the reaction system was 0.65 g / L; the mixed solution was reacted in a 30-60°C water bath for 2-4 h, and after natural cooling, it was centrifugally washed with anhydrous ethanol and secondary water respectively, and vacuum dried to obtain a composite electrocatalyst of molybdenum disulfide-loaded platinum nanoclusters.

2. The method for preparing the composite electrocatalyst of molybdenum disulfide loaded with platinum nanoclusters for hydrogen production by alkaline water electrolysis according to claim 1, characterized in that: In step (1), the heat treatment temperature is 500°C.

3. The method for preparing the composite electrocatalyst of molybdenum disulfide loaded with platinum nanoclusters for hydrogen production by alkaline water electrolysis according to claim 1, characterized in that: In step (2), the concentration of the chloroplatinic acid solution is 2 mM.

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