Study On The Capacitive Performance Of Molybdenum Disulfide/Reduced Graphene Oxide Composite For Supercapacitor

In order to solve the increasingly serious energy demand crisis,there is an urgent need to develop and utilize renewable energy and new storage technologies.In many energy storage systems,supercapacitors are considered as an important energy storage device between batteries and conventional capacitors due to their fast charging-discharging and high magnification characteristics.Electrode material is an important part of supercapacitors and plays a key role in improving the performance of supercapacitors.Therefore,it is very important to develop and design new electrode materials with outstanding electrochemical properties.At the same time,the structure of electrode material is also one of the key factors affecting its electrochemical properties,that is,the special microstructure of electrode material is conducive to the improvement of its electrochemical properties.The electrode materials used in supercapacitors include carbon-based materials,conductive polymers,transition metal oxides and transition metal sulfides.Among them,transition metal sulfide is considered as a potential electrode material due to its wide source,low price and unique physical and chemical properties.Molybdenum disulfide（MoS₂）has a two-dimensional layered structure similar to graphene,and its edge is in a high-energy state due to the absence of atoms.It has a high chemical activity and is widely used in the electrode materials of supercapacitors.MoS₂ nanosheets dispersion was prepared by liquid exfoliation method.GO was prepared by an improved Hummers method,and then MoS₂ nanosheets were grown on rGO（MoS₂/rGO）via hydrothermal method.The effects of different mass ratios on the morphology and performance of as-prepared MoS₂/rGO composites were also studied.The scanning electron microscope（SEM）,Fourier transform infrared spectroscopy（FT-IR）spectrum,X-ray diffraction analysis（XRD）and X-ray photoelectron spectroscopy（XPS）were employed the analyze the structure and composition,and electrochemical workstation was adopted to analyze the electrochemical performances.The structure test results show that the morphology of the composite changes with the increase of MoS₂ load.When the mass ratio of MoS₂ to rGO was 1:5（MG-5）,MoS₂ nanosheets were grown uniformly on the surface of rGO.The structure can increase the contact area between the electrode material and the electrolyte,which is beneficial to the electron transfer between them.As a result,MG-5composite material showed excellent electrochemical properties with a high specific capacitance of 331 F g^-1 at a current density of 0.75 A g^-1 and an excellent cycling stability with capacitance 110.7%capacitance retention after15,000 continuous charge-discharge cycles at a high current density of 5 A g^-1.In addition,the asymmetric supercapacitor（ASC）was assembled using MG-5composite material as the positive electrode and active carbon（AC）as negative electrode.The device shows high energy density and high power density.When the power density of the device is 449.8 W kg^-1,its energy density is 29.2 Wh kg^-1.When the energy density is 6.4 Wh kg^-1,the power density is 4517.7 W kg^-1.Moreover,the assembled devices have excellent cycling stability with capacitance 80%capacitance retention after 6,000 continuous charge-discharge cycles at a current density of 2 A g^-1.These results indicate that MoS₂/rGO composite material as electrode material has an important application potential in supercapacitor.