Preparation Of MoS₂ Nanosheets By Chemical Vapor Deposition And Catalytic Performance Investigation

Since the graphene was successfully prepared in 2004,two-dimensional materials have received extensive attention due to its exotic properties which were totally different from the bulk material.Molybdenum disulfide?MoS₂?is a typical transition metal sulfide and becomes a hot topic.MoS₂ shows many excellent properties,such as:a typical layered material can be used as lubricants;compared with the zero bandgap graphene,MoS₂ with adjustable band gap exihibits greater prospects in electronic device;theoretical calculations point out that MoS₂ possesses comparable catalytic properties to Pt and can be used for electrocatalytic hydrogen evolution reaction?HER?.Among all these excellent performances,hydrogen evolution reaction has received particular attention due to the country's demand for green energy and policy support.Since the single-layer MoS₂ was successfully prepared in 2005,researchers have explored various preparation methods for MoS₂ films systhesis,which can be divided into two types:"top-down"and"bottom-up".The"top-down"preparation methods mainly include micromechanical exfoliation,lithium ion intercalation exfoliation,and liquid ultrasonic exfoliation.The"bottom up"preparation methods mainly include:hydrothermal,chemical vapor deposition.Among these preparation methods,the chemical vapor deposition?CVD?is suitable for industrial production because of its simple preparation,high growth speed,good film quality,controllable morphology and size of the sample.In this paper,vertically standing MoS₂ nanosheets were prepared by CVD techniques,the effect of various deposition parameters on growth characteristics of MoS₂ was investigated.Also the relationship between the structure characteristics of MoS₂ and its catalytic performance for HER was elucidated.The main research contents are as follows:?1?The influence of deposition parameters such as deposition pressure,hydrogen flow rate,deposition time,deposition position,and deposition temperature on the vertically standing MoS₂ nanosheets were systematically investigated.The phase composition,crystal structure and crystal quality of the prepared samples were characterized by X-ray diffraction?XRD?and laser Raman.The surface and cross-section morphology were observed by scanning electron microscopy?SEM?.The average length and density of the nanosheets was calculated by using the measurement software;the average peak-to-valley depth of the nanosheets was obtained by AFM.Finally,the maximum size of the nanosheets was obtained when the deposition pressure was 250 Pa,the hydrogen flow rate was 500 sccm,the deposition time was 5 min,and the deposition position was 5.5 cm.?2?The growth mechanism of vertically standing nanosheets was analyzed based on the extrusion growth mode.As the deposition time increases,the morphology of the sample changes from a small triangular nanosheet to a nanosheet with two or three triangles.It can be concluded that:within a certain range of deposition time,as the deposition time increases,the density and the size of the triangular nano-sheets gradually increase,and the adjacent nanosheets fuse into one nanosheet during the growth process,thereby forming a nanosheet with two or three triangles.?3?All of the electrochemical measurements were performed in 0.5 mol/L H2SO4solution using a three-electrode setup on an electrochemical workstation.The variation of electrocatalytic properties of samples deposited on Au substrates with different deposition parameters were studied.At the deposition pressure of 250 Pa,the hydrogen flow rate of 500 sccm,the deposition time of 5 min,the deposition position of 5.5 cm,and the deposition temperature of 600°C,the sample had the lowest Tafel value(?IR correction data showed 119.6 mV/decade?,indicating the best catalytic performance.In addition,the sample was subjected to a linear voltammetry scan cycle of 1000 cycles and showed good catalytic stability.