Preparation Of Metal Sulfide Hollow Nanostructures And Study On Electrochemical Properties

All the time,the energy problem is closely related to our life,and it is also animportant issue that has been concerned in the world.Traditional energy of fossil fuels have been unable to meet the needs of society because of its serious pollution and non-regeneration.Therefore,exploring new environmentally and efficient energy sources is an urgent problem.Lithium ion batteries have been considered as one of the most promising energy storage and conversion device because of clean no pollution,high energy density and long cycle life,which are widely used in portable electronic products.And electrode material is the key to the performance of the lithium ion battery.At present,the commercialized graphite materials have relatively low specific capacity(approximately 372 mAh g^-1)and security problems.Therefore,it is urgent to explore new anode materials with high energy density and high performance to meet the demand of lithium ion battery for electrode materials.While the transition metal sulfides and their nanocomposites with low price,wide source,high specific capacity,good cycle performance,safety performance and other advantages,are the ideal substitutes for the commercialization of graphite materials.However,they are suffered from the problems of poor conductivity,low initial coulomb efficiency,large irreversible capacity,and large volume change during charging and discharging process,which result in poor cycling stability.In response to this problem,the researchers find out that nanostructure materials,the morphology control and the carbon coating and doping can effectively improve the conductivity of the material,relieve the volume effect during the charge and discharge process and further improve the performance of electrochemical lithium storage.In addition,hydrogen energy as another kind of highly efficient clean energy source has received people's attention,and electrolysis hydrogenation?HER?is an effective way to obtain high purity hydrogen.Precious metals?Pt?Pd?are used as catalysts for the electrolysis hydrogenation.But their price limits the large-scale application in production.So it is urgent to find a kind of high efficient and economic catalysts.Although transition metal sulfides are poor electrical conductivity and catalytic activity of a small number of defects,the study found that the synthesis of materials with special morphologies or doping with other nanomaterials can obviously improve the catalytic activity,which are expected to replace the noble metal catalyst.Therefore,it is of great significance to study the electrochemical properties of transition metal sulfides and their composites.This paper prepared by hydrothermal method of transition metal sulfide nano FeMo₄S₆,MoS₂/BNG and CoMoS_3.13@BN-CNT,analyzed the structure morphology and physical characteristics of materials by XRD,SEM,TEM,Raman and other technical means,and studied the electrochemical performance of lithium ion storage and electro-catalytic performance.The specific contents are as follows:1.We firstly develop FeMo₄S₆ nanosheets via one step hydrothermal process as advanced energy materials for energy storage and conversion.TEM and XRD characterizations reveal that FeMo₄S₆ nanosheets possess distinctive layered structure with an interlayer distance of 0.64 nm and 10–14 layers in thickness.Rooted in the intriguing layered 2D structural advantages and multicomponent effect,the sample exhibits large and stable lithium storage properties when it is used as anode material for lithium-ion batteries.It is also evaluated as electrocatalyst for water splitting and shows promising catalytic activity for hydrogen evolution,including low onset overpotential and after 1000 cycles,the cathode current density has no obvious attenuation,showing a good cycle stability.2.Two-dimensional?2D?nanostructures and their hybrids have triggered intensive attention in energy storage and conversion field owing to their structural benefits.We have prepared for the first time the two-dimensional nanocomposite MoS₂/BNG of MoS₂ nanosheets grown on B,N co-doped graphene sheets,which is used as advanced anode materials for lithium ion batteries.The rational use of 2D nanomaterials can supply a large surface area for the storage of lithium ion and shorten Li⁺diffusion length.The design of this special structure can not only effectively enhance the electrical conductivity of composite electrode,but also relax the volume change of MoS₂ upon electrochemical cycling process.Due to the structural and compositional advantages,MoS₂/BNG delivers the initial discharge capacity of 1203 mAh g^-1 at a current density of 0.2 A g^-1,and a high initial Coulombic efficiency?CE?of 80%.After100 cycles,achieving excellent cyclic stability with high capacity retention of 96.7%.When the current density turns back to 0.2 A g^-1,capacity of 913 mAh g^-1 is recovered,further confirming good rate performance and high reversible stability.3.Transition metal sulfides have attracted intensive interests as cost-effective catalysts for water electrolysis.However,demands for their active catalytic activity towards hydrogen evolution reaction?HER?,and especially oxygen evolution reaction?OER?are still urgently needed and challenging.We rationally select B,N co-doped graphene nanotubes?BN-CNT?as active substrate to support CoMoS_3.13 nanosheets to fabricate bifunctional catalyst for overall water electrolysis.The test results show that the doping of B and N species in the active substrate can effectively improve the HER and OER activity of the transition metal sulfide.Moreover,BN-CNT substrate not only assures the edge terminated texture of CoMoS_3.13 nanosheets for more active sites,but also acts as“highway”to accelerate the charge transfer for enhanced reaction kinetics.Therefore,remarkably enhanced HER and OER catalytic activities are obtained from the hybrid catalyst,including decreased overpotential,increased catalytic current density,improved reaction kinetics,and superior stable durability.