Synthesis And Supercapacitive Properties Of 2D Layered MoS₂ Nanocomposites

Social development and progress cannot be separated from energy and the main energy currently consumed is fossil energy.However,fossil fuels not only have limited reserves,but also cause irreversible pollution due to massive use of the environment,which seriously threatens human survival.Therefore,the production of renewable energy and the corresponding energy storage and conversion equipment have received increasing attention.From the point of view of energy density and power density,the supercapacitor fills the gap between the capacitor and the battery,and has an irreplaceable position in the energy storage field.The research of supercapacitors is now focused on further increasing their energy density without sacrificing their power density.The selection of electrode material and the preparation of the electrode are the key factors affecting the performance of the supercapacitor.In recent years,two-dimensional molybdenum disulfide nanomaterials have been discovered due to their unique physical,optical,electronic and electrochemical properties,and have shown good application prospects in various fields such as catalysis,energy storage and conversion,and sensing.However,there are no reports on high-stable transparent MoS₂nanofilms as supercapacitors electrode.In addition,the method steps for preparing the molybdenum disulfide-based composite material in many literature reports are relatively complicated,and the obtained material is usually a powder and it is necessary to add a non-conductive adhesive to fix it on the electrode.In view of the above problems,molybdenum disulfide-based electrode materials were prepared by electrostatic layer-by-layer self-assembly or electropolymerization using two-dimensional molybdenum disulfide as the research object.Characterization techniques such as scanning electron microscopy and transmission electron microscopy X-ray photoelectron spectroscopy were used.The morphology and structure of the electrode were analyzed,and the electrochemical performances were studied.The detailed study is as follows:?1?A single layer or few layers of molybdenum disulfide?MoS₂?nanosheets with negative charge on the surface were prepared by chemical lithium ion intercalation.Based on the principle of positive and negative charge attraction,ITO/?PDDA/MoS₂?_x?x=1-20?electrodes with super-long stability anchored on the indium tin oxide?ITO?glass by a simple alternate layer-by-layer?LBL?self-assembly of a highly charged cationic poly?diallyldimethylammonium chloride??PDDA?and negative molybdenum disulfide?MoS₂?nanosheets.The ITO/?PDDA/MoS₂?₂₀ electrode shows a transmittance of 52%at 550 nm and obviously exhibits excellent transparency by naked eye observation.Ultrasonic damage test validates that the?PDDA/MoS₂?₂₀ film with the average thickness about 50 nm is robustly anchored on ITO substrate.Additionally,the electrochemical results indicate that the ITO/?PDDA/MoS₂?₂₀ film shows areal capacitance of 1.1 mF cm^-2 and volumetric capacitance of 220 F cm^-3 at the current of0.04 mA cm^-2,and 130.6%retention of the original capacitance value after 5000 cycles.Further experiments indicate that the formation of transparent?PDDA/MoS₂?_x nanofilm by LBL selfassembly can be extended to other substrates,e.g.,slide glass and flexible polyethylene terephthalate?PET?.Thus,the easily available?PDDA/MoS₂?x nanofilm electrode has great potential for application in transparent and/or flexible optoelectronic and electronics devices?2?The nanocomposites based on MoS₂ and conducting polymer?CPs?are mainly prepared by the chemical oxidation polymerization of monomers with the presence of MoS₂ nanosheets.The disadvantage is that the aggregation and re-stacking of monolayered MoS₂ occur easily.In the electrosynthesis of CPs,monolayered MoS₂with negative charges can be uniformly doped into CPs film,thus avoiding the above disadvantage.Herein,a direct electrochemical deposition method is used to incorporate the exfoliated monolayered MoS₂ into BF₄^--doped poly?3,4-ethylenedioxythiophene??PEDOT?BF₄^-??film,forming PEDOT?BF₄^-?/MoS₂ nanocomposite.The as-prepared monolayered MoS₂,PEDOT?BF₄^-?and PEDOT?BF₄^-?/MoS₂ nanocomposite are characterized by AFM,SEM,TEM,EDX and electrochemical means.The results indicate that PEDOT?BF₄^-?/MoS₂ nanocomposite has specific capacitance of 149.8 mF cm^-2 at 1.0 mA cm^-2,which is 4.3 times higher than PEDOT?BF₄^-?(35 mF cm^-2).And the specific capacitance of PEDOT?BF₄^-?/MoS₂ nanocomposite remains about 85%of the initial capacitance after 1000 cycles at 8 mA cm^-2.Therefore,the monolayered MoS₂ doped into PEDOT?BF₄^-?film can further improve the capacitance performance of PEDOT?BF₄-?,which is attributed to the porous nano-network structure of composite and the synergistic effect between MoS₂ and PEDOT in the composite.?3?In order to further study the performance of the MoS₂ nanosheets as a dopant.At the same molar concentration,the MoS₂ nanosheets were respectively compared with a typical inorganic electrolyte,lithium perchlorate?LiClO₄?and an organic electrolyte,tetrabutylammonium tetrafluoroborate?Bu₄NBF₄?,the ability of electropolymerize indole were studied in indole acetonitrile systems.Meanwhile,the capacitance properties of the individual polyindole?PIn?prepared were compared.The morphology analysis results show that the MoS₂/PIn nanocomposites obtained a more rough morphology and it was a more complete film.SEM-Mapping and XPS were adapted to analysis the distribution and composition of elements,showing molybdenum disulfide nanosheets were not only inserted into the interior of the polyindole,but also composited uniformly.At the same time,the electrochemical results show that when the molar ratio of molybdenum disulfide to indole monomer is1:2,the maximum specific capacitance achieved(35 mF cm^-2).In addition,the capacitance of the polyindole prepared by doping the molybdenum disulfide nanosheets was respectively 7 times than that of doping with LiClO₄ and 9 times than doping with the Bu₄NBF₄.At a current density of 1 mA cm^-2 and circulating 5000 times,the capacity retention rate of the MoS₂/PIn composite was 88%.