Controllable Preparation Of MoS₂/C Composites And Their Application In Energy Storage And Conversion

With the progress of society and the development of science and technology,energy demand has increased rapidly.Because of the increasing depletion of fossil fuels and the emissions of harmful gas caused by the excessive combustion of the fossil fuels,there is an urgent need to find a new strategy to deal.with the energy crisis.Hydrogen energy from water decomposition and efficient energy storage systems,such as ion batteries,are considered to be a feasible solution.Therefore,it has become a research hotspot to develop catalytic materials with strong catalytic activity for water decomposition reaction and materials with the ability of efficiently store energy.Molybdenum disulfide(MoS2)as a typical two-dimensional transition metal sulfide which has versatile utilization and application potential in many fields such as optoelectronics,catalysis,sensors,energy storage and conversion due to its special structure and unique properties.In this paper,we synthesized a series of MoS2/C materials by adjusting the corresponding morphology and structure.The catalytic performance of hydrogen evolution and energy storage properties were studied as well The main contents are as follows:1.An annealing-followed self-etched template method was developed to prepare MoS2/C hollow microspheres,which are composed of thin-layered MoS2 nanosheets radially growing on the surfaces of carbon hollow spheres.The electrical conductivity of the composite can be obviously improved,which is favorable for electron transport in the electrochemical reaction process.The hollow and thin-layered nanostructures can enhance the ion diffusion in them and alleviate volume effect during the discharge-charge process.In addition,because SiO2 spherical templates are etched in the hydrothermal reaction,no extra template-removed treatment is required.Based on features mentioned above,the electrochemical studies of MoS2/C hollow microspheres,as an anode of lithium ion batteries,demonstrate that they can deliver a reversible discharge capacity of 924 mAh g-1 at 200 mA g-1 after 100 cycles.When the current density was improved to 1 A g"1,the discharge capacity maintained 576 mAh g-1 after 300 cycles without obviously decay.This research suggests that the sample possesses good cyclic stability and rate performance.2.A novel annealing-followed soft-template approach was designed to obtain interlayer-expanded MoS2 ultrathin-layered hollow nanospheres in a high-pressure hydrothermal reaction system(m-C/MoS2).N-doped carbon monolayers were alternately intercalated into the adjacent MoS2 monolayers to realize ideal atomic contact between them and expand the interlayer distance.The ultrathin-layered hollow nanostructures not only increase the contact area between the electrolyte and electrode,but also provide sufficient void space to buffer volume variation upon repeated insertion/exaction of lithium/sodium ions.The expanded interlayer spacing can improving ion diffusion mobility,shortening ion diffusion paths.As a consequence,the superstructure delivers high reversible discharge capacity of?900 mAh g-1 at 1000 mA g-1 after 220 cycles for LIBs.Furthermore,the hollow nanospheres can also deliver a reversible discharge capacity of 401 mAh g-1 at 200 mA g-1 after 150 cycles and excellent rate capacity of 211 mAh g-1 at 10000 mA g-1 for SIBs.More importantly,it can still maintain 262 mAh g-1 at 2000 mA g-1 after 600 cycles which exhibits high reversible capacity,outstanding cyclic stability and excellent rate performance.3.An annealing-followed chemistry-intercalated strategy was developed to synthesize novel MoS2 tubular porous architectures(MoS2/m-C),which are assembled from few-layered nanosheets,deviated to the tube-axis direction,resulting in high specific surface area and mesopores.These nanosheets are constructed of alternate intercalation of MoS2 and N-doped carbon monolayers to achieve atomic contact between them and interlayer expansion from 0.62 nm to 0.96 nm.Combining of the hollow-porous structure,the MoS2/m-C hybrid is expected to facilitate fast ion diffusion throughout the electrode and electron-expedited transfer along plentiful atomic interfaces,abundant ion storage as well as mitigating volume variation upon cycling.As a positive consequence,the porous tubular MoS2/m-C architectures exhibit excellent electrochemical properties in terms of high reversible discharge capacity,long cycle stability,and high rate capability as anode host of LIBs which deliver a reversible discharge capacity of 951 mAh g-1 at 1.25 A g-1 after 350 cycles.Furthermore,the superstructure also delivers high reversible discharge capacity of 350 mAh g-1 at 500 mA g-1 after 500 cycles.4.A high-pressure hydrothermal reaction approach was designed to obtain reduced graphene oxide loaded interlayer-expanded MoS2 ultrathin-layered superstructure(RGO@MoS2/C).Due to the intercalation of N-doped carbon monolayers,the interlayer expansion from 0.62 nm to 0.96 nm and the internal conductivity of particles is significantly improved.The introduction of RGO improves the conductivity between MoS2/C particles.Attributed to the synergetic effect of RGO and carbon monolayers,electrons can be transferred and transferred rapidly in the materials.The radial MoS2 with ultra-thin and interlayer-expanded structure can expose more active sites at the edge.As a result,the high electric conductivity and pronounced catalytically active sties give the catalyst an outstanding electrocatalytic performance with small overpotential of 162 mV at 10 mA cm-1,low Tafel slope of 54 mV dec-1.5.The MoS2/C operates as a fast saturable absorber for the formation of MoS2/C Q-switched pulse.The stable Q-switching operation has been achieved through using the MoS2/C saturable absorber mirrors in both 2 ?m Tm:BYF laser and 2.8 ?m Er:YSGG laser.The output power were 1.3 and 0.17 W in 2 and 2.8 ?m,respectively.The corresponding pulse width were 206 and 138 ns.While the repetition rate were as high as 53 and 148 KHz.Moreover,the optical-optical conversion slope efficiencies were 32.5%and 33.8%in 2 ?m.The results show that MoS2/C saturable absorber mirrors has potential application value as Q-switched device of laser.