Study On Preparation And Electrochemcial Properties Of Transition Metal Sulfide And Its Composites

The continual increase demand for energy,the reduce of finite reserved fossil fuel and the increase of serious environmental pollution in the world have become a topic of great concern to the scientific community.The resulting growing requirement for renewable energy and environmental protection has driven research and development of effective clean energy and energy storage strategies.Hydrogen energy and supercapacitors are considered clean,green energy technologies due to their high efficiency and environmentally friendly properties.In order to improve the electrochemical performance of electrocatalytic hydrogen evolution and supercapacitors,the development of low-cost,high-efficiency electrode materials has become a trend of efforts.In this paper,the preparation and electrochemical properties of transition metal sulfides and its composites were investigated.The main content is divided into three parts:?1?Hollow polypyrrole spheres?PPY?were prepared by copolymer?PMMA- PMAA-PBMA?template method and expansion effect.Then,PPY@?NH₄?₂MoS₄ was prepared by reflux.Finally,the precursor was subjected to high temperature treatment to obtain the carbon hollow sphere coated with molybdenum disulfide?NHCS@MoS₂?.XRD,Raman,XPS,SEM and TEM showed that the molybdenum disulfide was uniformly wrapped on the NHCS.The electrocatalytic hydrogen evolution performance was tested by electrochemical measurement.When the current density reached 10 mA cm^-2,the overpotential is corresponding to 190 mV.When the overpotential is increased to 250 mV,the current density reaches 34 mA cm^-2.The tafel slope of NHCS@MoS₂ is 96 mV/dec,while the tafel slope of MoS₂ is as high as 226mV/dec.Compared with the initial LSV curve,the LSV curve of NHCS@MoS₂ did not change much after 1000 cycles.This shows that the stability of NHCS@MoS₂ is still high even after a long period of electrochemical treatment.The C_dll value of NHCS@MoS₂(20.08 mF cm^-2)is almost five times that of NHCS(4.4 mF cm^-2).As can be seen from the Nyquist plot,the charge transfer resistance?Rct?of NHCS@MoS₂ is only 140 ohm.The addition of carbon material enhances the conductivity of NHCS@MoS₂,which further enhances the electrocatalytic hydrogen evolution capability of the sample.?2?Polypyrrole hollow spheres?PPY?were treated with polyvinylpyrrolidone?PVP?which is as the surface stabilizer and growth regulator.The modified PPY was mixed with sulfur source and molybdenum source,and MoS₂ shell and PPY core were prepared by hydrothermal method.The core-shell heterostructure material PPY@MoS₂.XRD,Raman,XPS,SEM and TEM characterization showed that MoS₂ grew in situ on PPY and formed a hollow nanoflower-like structure of PPY@MoS₂.By measuring the performance of the supercapacitor by electrochemical,when the current density is 1 A g^-1,the specific capacitance of PPY@MoS₂ is as high as 297 F g^-1.At the current density of 5 A g^-1,after 500 cycles,the specific capacitance is retained at 71%.?3?Firstly,NiCo₂S₄ was synthesized by two-step hydrothermal method,then NiCo₂S₄ was mixed with MoS₂ and graphene oxide?GO?,respectively,and then NiCo₂S₄/MoS₂ and NiCo₂S₄/RGO composite structures were formed by hydrothermal.Their electrochemical properties were studied and the synergistic effects of the two were analyzed.MoS₂ and RGO have greatly improved the electrochemical performance of the supercapacitor electrode,with high specific capacitance and remarkable cycle stability.The supercapacitor performance was tested electrochemically.When the current density is 1 A g^-1,the specific capacitance of NiCo₂S₄/MoS₂ and NiCo₂S₄/RGO was 959 F g^-1and 579 F g^-1,respectively;when the current density is 20 A g^-1,The specific capacitance of NiCo₂S₄/MoS₂ and NiCo₂S₄/RGO was 726 F g^-11 and 480 F g^-1,respectively.In addition,at the current density of 15 A g^-1,after 2000 cycles,the specific capacitance of NiCo₂S₄/MoS₂ and NiCo₂S₄/RGO is retained at 80%and 79%.