Layered Molybdenum Disulfide And Its Nanocomposites For Supercapacitor Applications

Energy crisis has become a global problem and has attracted widespread attention. To search new materials has been proved to be an important task for scientists for dealing with the energy problems. As a new kind of energy storage device, supercapacitor has many excellent advantages such as great power density, high energy density, long cycle life, short charge/discharge time and no harm to the environment. Recently, it has been the research focus in the area of clean energy and attracted more and more attention from both academia and industry. To develop the supercapacitor, the most effective way is to find a kind of electrode material with outstanding performances. Due to its unique two-dimensional layer structure and larger specific surface area, layered molybdenum disulfide nanoparticles have higher intrinsic fast ionic conductivity and higher theoretical capacity, which have attracted considerable attention over the past decades. However, the electronic conductivity of MoS2is still lower compared to carbon materials such as graphene, and the specific capacitance of MoS2is still very limited in alone for energy storage applications. In order to overcome these deficiencies, we design several nanocomposites based on MoS2and graphene, carbon aerogel, carbon nanotubes and polyaniline to obtain good supercapacitor characteristics. The main works are listed as follows:(1) MoS2/graphene (MoS2/Gr) composite is synthesized by hydrothermal method. The morphology of the MoS2/Gr composites was characterized and the electrochemical properties were evaluated. The layered MoS2coated on the surfaces of Gr nanosheets forms the loose-formed open structure, which can facilitates fast electron transfer between the active materials and the charge collector. The integration of Gr into the composites provides relatively large areas to loading MoS2sheets, which can make full use of electrochemical active MoS2during the charge and discharge processes. The maximum specific capacitance of MoS2/Gr composites reachs up to243F/g at a discharge current density of1A/g and the capacitance only decreases by about7.7%of the initial capacitance after1000cycles, which indicates good supercapacitor characteristics. (2) MoS2/Carbon aerogel composite is synthesized by a simple hydrothermal method. The morphology of the MoS2/Carbon aerogel composite was characterized and the electrochemical properties were evaluated. The Carbon Aerogel anchored onto the surfaces of MoS2nanosheets can effectively decrease the stacking of MoS2, resulting in the higher specific surface area of the composites. Furthermore, carbon aerogel coating on the surfaces of MoS2nanosheets accumulate to form pores for ion-buffering reservoirs to improve the diffusion rate of ions within the bulk of the prepared materials. The maximum specific capacitance of MoS2/carbon aerogel composite reachs up to260F/g at a discharge current density of1A/g, and there is only4%decrease in specific capacitance after500cycles.(3) MoS2/MWCNTs composite is prepared by hydrothermal method. The morphology of the MoS2/MWCNTs composite was characterized and the electrochemical properties were evaluated. The MWCNTs insert and entwine the MoS2nanosheets can form a3D architecture, which is helpful to increase the specific area of the composites. Furthermore, the overlapping or coalescing of the MoS2in the3D MoS2/MWCNT composites would form an interconnected conducting network, which facilitates rapid electronic transport in electrode reactions. The maximum specific capacitance of MoS2/MWCNTs composites reachs up to452.7F/g at a discharge current density of1A/g, and there is only4.2%decrease in specific capacitance after1000cycles, which displays good supercapacitor characteristics.(4) MoS2nanosheet is synthesized by hydrothermal method, and its morphology was characterized. A facile strategy was then used to synthesize polyaniline (PANI)/MoS2via in situ polymerization of aniline monomer in the presence of2D MoS2suspension. The morphology the MoS2/PANI composites was characterized and its electrochemical properties were carefully studied. The PANI anchored onto the surfaces of MoS2nanosheets can effectively decrease the stacking of MoS2, resulting in the higher specific surface area of the composites; Furthermore, PANI coating on the surfaces of MoS2nanosheets accumulate to form pores for ion-buffering reservoirs to improve the diffusion rate of ions within the bulk of the prepared materials. The maximum specific capacitance of MoS2/PANI composites reachs up to575F/g at a discharge current density of1A/g. MoS2sheets intercalated by PANI undertake some mechanical deformation in the redox process of PANI, which avoid destroying the electrode material and leads to an outstanding stability. For PANI/MoS2composite electrodes, there is only2%decay in the specific capacitance after500cycles, which exhibits good supercapacitor characteristics.