Research On The Electrochemical Performance Of Molybdenum Disulfide-based Composite Materials And Supercapacitor Devices

The two-dimensional layered materials have an enormous application in the information processing,energy storage,biomedical treatment and other fields,due to their unique morphological structure and excellent physicochemical properties.Molybdenum disulfide?MoS₂?,as a new kind of supercapacitor material,has the advantages of high specific surface area,strong adsorption capacity and high reactivity.However,there are still some problems which restrict the application of MoS₂,such as the poor conductivity of semiconductor materials,the agglomeration during the cycle process,the volume expansion and shrinkage under different forces.Nowadays,the research on improving the electrochemical performance of MoS₂ is mainly focused on two aspects,one is the optimization of the atomic structure and surface properties of MoS₂ nanosheets,and another is the novel designs of the composition and structure of MoS₂-based composites.In this paper,bismuthous sulfide nanorods?Bi₂S₃?,carbon cloth?CC?,polypyrrole?PPy?were combined with MoS₂ to improve the electrochemical performance of electrode materials and their supercapacitor devices.The results provide an important reference for further expanding the application of MoS₂ in energy storage devices.The MoS₂/Bi₂S₃ nanocomposite was successfully prepared by a two-step hydrothermal method.Two-dimensional MoS₂ nanosheets were grown directly on the surface of one-dimensional Bi₂S₃ nanorods.At the current density of 1 A g^-1,MoS₂/Bi₂S₃ can retain 87.7%of its initial capacitance after 2000 cycles test,but Bi₂S₃and MoS₂ only maintain 64.5%and 60.4%,respectively.The unique 2D/1D structure and the synergistic effect between two different kinds of metal sulfides accelerate the charge transfer between the interfaces of the active materials and improve the capacitance performance and cycle stability of MoS₂/Bi₂S₃ nanocomposite.The MoS₂/CC nanocomposite was successfully prepared by a one-step hydrothermal method.The temperature of preparation affects the morphology,charge transfer characteristics and electrochemical properties of the electrode material.When the reaction temperature arrives 200 ^oC,MoS₂ nanosheets are cross-linked and grow vertically on the surface of carbon cloth.The structure of the nanosheets array is conducive to the participation of more edge active sites of MoS₂ in the electrochemical reaction.The carbon cloth is not only the support substrate of the nanosheets,but also accelerates the transmission of electrons in MoS₂/CC.MoS₂/CC-200 shows a high specific capacitance of 2236.6 mF cm^-2 at a current density of 10 mA cm^-2.The symmetrical all-solid-state supercapacitor is assembled with MoS₂/CC-200 as positive and negative electrodes,which both have excellent electrochemical performance and cycle stability.The PPy/MoS₂/CC nanocomposite was obtained by combining hydrothermal method and electrochemical polymerization method.The MoS₂ nanosheets array was grown on the surface of carbon cloth,and then conductive polymer PPy was uniformly deposited on the surface of MoS₂ nanosheets.The coating of conductive polymer PPy improve the structural stability of electrode material,which has barely fallen off even after ultrasonic treatment for 1.5 h.The specific capacitance of PPy/MoS₂/CC still maintains 64.2%even with increasing to 50 times of the initial measured density,and keeps 87.2%capacitance retention after 5000 cycles,which proves that PPy/MoS₂/CC has excellent rate performance and cycle performance.The symmetrical flexible all-solid-state supercapacitor,assembled with PPy/MoS₂/CC as the positive and negative electrodes,can maintain stable electrochemical performance after long times of bending or twisting,and reach the maximum energy density of 0.706 mWh cm^-3.In this paper,MoS₂/Bi₂S₃,MoS₂/CC and PPy/MoS₂/CC nanocomposites were successfully prepared based on two-dimensional MoS₂ nanosheets.Through the methods of composition design,structure design and electrode material interface optimization,the agglomeration and stacking of MoS₂ nanosheets are effectively prohibited,the internal impedance of nanocomposites is reduced,and the structure stability of electrode materials is stable.Therefore,the electrochemical properties of MoS₂ based electrode materials and their supercapacitor devices are significantly improved.