Synthsis Of Novel Nanostrctures And Their Application In The Electrochemical Storage Of Lithium And Electrochemical Hydrogen Evolution

In recent years,Energy issues are the focus of the world's attention,with the energy demand increasing,there is an urgent need to explore and study new green energy to solve this problem.The emergence and maturing of nanomaterials is expected to be very useful in energy problems,especially the new transition metal sulfide nanomaterials and their composites.These nanomaterials are widely available,inexpensive,environmentally friendly.They both have high specific surface area and good chemical stability.So they are widely used in lithium ion secondary batteries and electrochemical catalytic hydrogen evolution reactions.However,the transition metal sulfide itself possesses very poor conductivity,low diffusion rate of lithium ions,high hydrogen evolution potential,and larger volume change in the lithium ion embedded-deinterleaving process,and the resulting poor rate performance and cycle performance when it is applied in lithium-ion batteries.The overpotential is high and the energy loss is serious,when it is applied as the catalyst in electrocatalytic hydrogen evolution reaction.All these shortcomings limit its application in real life.To overcome these shortcomings,the transition metal sulfide with special morphology and composite nanomaterials with carbon can be prepared.The material with special morphology has a large specific surface area,thus expanding the contact area of the electrolyte and the activematerial;The carbon material in the compound can increase conductivity of the compound,and ease the volume effect of transition metal sulfide.So the compound has better electrochemical performance in the lithium-ion battery and electrochemical catalytic hydrogen reaction.In this paper,we mainly study the preparation of MoS₂-G,SnS₂-G and PB-MoS₂-G,and their electrochemical properties,including lithium storage and electrochemical hydrogen evolution.1)In this work,a two-dimensional structure of molybdenum disulfide nanosheets and CoMo₂S₄ nanosheets was prepared by in-situ hydrothermal method on the graphene matrix.The novel catalyst was prepared for electrochemical hydrogen evolution.Due to the conductivity of the graphene structure,the electrochemical synergism between MoS₂ and CoMo₂S₄ and the 2D structural advantages,MoS₂-CoMo₂S₄ / graphene composite catalyst shows good hydrogen evolution performance.The overpotential is as low as 110 mV with a high cathode current density of 85 mAcm-2at ?= 300 mV,and the Tafel slope is 42 mVdec-1.The hydrogen evolution efficiency in the 1000 th cycle has no attenuation compared with the firs cycle,showing a good durability.2)In this work,potassium ferrocyanide,molybdenum disulfide and graphene were prepared by one step hydrothermal method to synthesize MoS₂-PB-GO composites.The unique PB cube binds tightly to graphene in the composite material.The synthetic materials have both unique structural and compositional advantages,exhibit good catalytic performance in electrochemical hydrogen evolution.The 3D composite catalyst shows an overpotential as low as160 mV and a corresponding current density of 60 m A cm-2 at an overvoltage of 300 mV.After testing,the material also has a large electrochemical active surface area?ECSA?,and each active site has a high electrocatalytic activity,which played a very important role in the improment of composite material's catalytic performance.3)Based on MoS₂-G mixed nanosheets,3D strcture was synthesized by hydrothermal method,in which the MoS₂ nanosheets and the graphene substrates were tightly connected.The special 3D architecture combined structure and combination,and improved the electrochemical performance in both of lithium-ion batteries and HER.At a current density of 200 mA g^-1,the capacity remains at 904mAhg^-1after 200 cycles,compared with the 910 m Ah g^-1after 2 cycles.The capacity retention rate was 99%,indicating good cycle performance.When cycled at a high current density of 1 A g^-1and 2 A g^-1,the material still maintained a highcapacity of 706 mAh g^-1 and 581 mAh g^-1,respectively.When the current density returns to 100 mAg^-1,the capacity is restored to 898 mAhg^-1,showing good structural stability and reversibility.In the hydrogen evolution reaction,MoS₂-G exhibits an overpotential as low as 110 mV,with a Tafel slope of 47 mV dec-1.The electrochemical hydrogen evolution performance did not decrease after 1000 cycles,showing good cycling stability.4)The 3D structure composed of 2D SnS₂ nanosheets and graphene composites was synthesized by hydrothermal method,and the excellent lithium ion storage performance was exhibited due to the structural advantages of SnS₂-G.2D sheet structure provided a large surface area and structural stability,but also eases the volume effect.The tight connection of SnS₂ and graphene ensured fast electron exchange,so the composite material capacity was up to 933 mAh g^-1when used as the negative electrode material.After cycled for 200 cycles at a current density of500 mA g^-1,the capacity remained at 826 mAh g^-1,showing good cycle stability.At a high current density of 8 A g^-1,the capacity is 498 mAhg^-1,exhibiting excellent magnification performance.