Microstructures Of Tungsten Disulfide And Applications Of Energy Devices

Tungsten disulfide,as a member of two-dimensional materials,has attracted a lot of attentions in energy field for application of such as Li-ion battery,supercapacitor and hydrogen evolution due to the abundant and tunable microstructures.The shortage of fossil fuels,and the environmental pollution and climate anomalies caused by unreasonable utilization of fossil fuels have threatened the persistence of human society.The development of new energy sources is imminent,and the establishment of new energy system is the only way to solve the energy crisis.Lithium ion battery,as a kind of high performance battery,would be indispensable in the new energy system.These energy storage device could help adjust the configuration of the grid system and support the development of portable electronic devices and new energy vehicles.Developing suitable electrode materials is one of the key issues of lithium ion battery.Hydrogen,as an efficient clean energy source,can be obtained through the simple form of water splitting,although the industrial production of H2 is currently limited by the cost of precious metal catalysts.The development of efficient catalyst is an important part to realize the effective utilization of hydrogen and even solar energy.In this dissertation,we discussed the lithium ion battery cathode material and hydrogen evolution catalyst applications of tungsten disulfides?WS2?,according to the influence of microstructure on electrochemical mechanism of nano materials.Tungsten disulfide has a two-dimensional layered structure similar to graphene,which is suitable for the intercalation/deintercalation of lithium ions.However,challenges in the synthesis of phase-pure WS2,restacking between WS2 nanosheets,low electronic conductivity,and the brittle nature of WS2,severely limit its use in Li-ion battery and other applications.The presence of active sites at the edges and the higher specific surface area make WS2 considered as a promising Hydrogen Evolution Reaction?HER?catalyst to replace noble metal?such as Pt and Pd?,but limited by inert in-plane atoms and poor electrical properties.Mass synthesis of WS2 by hydrothermal method were further physically or chemically treated.Surface impurities and defects were regulated and controled,to realize the optimization of the performance of lithium ion batteries and electrochemical activity of hydrogen evolution,respectively.The conclusions of this dissertation are summarized as follows:?1?We have developed a facile low temperature solution sulfuration process towards WS2 to improve battery performance dramatically.The sulfuration process is demonstrated to be effective in converting WO3 impurities to WS2,and in repairing the sulfur vacancies,to improve cyclability and rate capability.Lithium-ion battery measurements demonstrate that the stable capacity of the WS2 anode could be enhanced by 48.4%via sulfuration reprocessing,i.e.,from 381.7 to 566.8 mAh/g at a relatively high current density of 0.8 A/g after 50 cycles.We further show that the sulfuration process can be readily extended to other dichalcogenides,and may provide a class of versatile electrode materials for lithium-ion batteries with improved electrochemical characteristics.A one-pot method for synthesizing of WS2/reduced Graphene Oxide?rGO?composite has been adopted to improve the battery performance dramatically.The WS2/rGO anode shows a stable discharge capacity of 431.2 mAh/g,at a current density of 0.1 A/g after 100 cycles.The added graphene oxide is reduced to rGO in reaction process and constitute stable composite with WS2,not only avoiding the restacking between WS2 nanosheets and improving the conductive properties,but also promoting the reduction of WO3 effectively.?2?We have combined a one-pot synthesis with a wet chemical etching to realize the controlled cobalt doping and tuneable morphology in WS2.The etched products composed of porous WS2,CoS2 and a part of oxide,showed a low overpotential and small Tafel slope in 0.5 M H2SO4 solution.The overpotential could be optimized to-134 mV?at 10 mA/cm2?with a Tafel slope of 76 mV/dec at high loadings?5.1 mg/cm2?.Compared with original WS2 sample,the treated sample shows increasing macropore?>50 nm?distributions,which may promote efficience of HER activity.We also found a low surface electrostatic potential in Co-doped region by the electron hologram.This work may provide further understanding of HER mechanism at nanometer sacle,and open up new avenues for designing catalysts based on other transition metal dichalcogenides for highly efficient HER.?3?WS₂ nanodots have been successfully synthesized by using a combination of grinding and sonication techniques.The morphology of the nanodots was observed,using transmission electron microscopy and an atomic force microscope,to have uniform sizes of-4 nm.Photoelectrochemical?PEC?measurements show that the current density of WS2 nanodots under illumination is almost two times higher than that of pristine WS2.Furthermore,these high-quality WS2 nanodots may have various applications in optoelectronics,solar cells,and biomedicine.