Freeze Drying Assisted Synthesis Of Metal Sulfide/Carbon Composites And Their Application In Supercapacitor

As a promising energy storage and conversion equipment,Supercapacitors are critical in solving the problems of greenhouse effect and energy crisis.The transition metal sulfides(TMDCs)gain much attention due to its layered structure.However,the poor conductivity and instability seriously hinder its further application.In this project,the layered TMDCs are supported on the carbon matrix via a simple freeze drying method.As expected,the above problems could be improved or restrained by the carbon matrix.The well electrochemical performance is obtained by using structural control,surface modification and composition regulation.Specific research contents are as follows:(1).The WS2/graphene aerogel(WGA)is prepared by direct freeze and low temperature activation method.The optimal electrochemical performance of WGA is obtained by adjusting the mass loading of WS2 on graphene aerogel.Through scanning electron microscopy(SEM)characterization,it is found that the hierarchical porous 3D structure is obtained by the assistance of ice template directing that the layered graphene nanosheets are self-assembled.Specially,the amount of WS2 can significantly influence the 3D graphene architecture and also influence their specific surface area.It is found that the WGA exhibits the best electrochemical performance when 8%WS2 supported on the graphene architecture.(2).The spherical S-MoS2/GA composite is synthesized by freeze-spraying and thermal activation.It is found that the graphene nanosheets self-assembled in the direction of ice template to form hierarchical porous spherical structure.Specifically,the thiourea is acted as a bridge agent to closely connect layered MoS2 and graphene nanosheets.In addition,the pyrolysis of thiourea agent could efficiently inhibit the oxidation of MoS2 interface.Moreover,it could serve as a dopant to adjust the electronic state of the graphene surface.Therefore,the S-MoS2/GA microspheres have well specific capacitance of 402.4 F g-1 at the scan rate of 5mV s-1,good rate capability of 77.8%and good cyclic stability of 97.1%after 5000 cycles.(3).The oxidized carbon nanotubes(OCNT)are obtained by ozone treatment;the layered molybdenum sulfide(MoS2)with single or few layers is obtained by ultrasonic-assisted lithium exfoliation method.Then,the MoS2/O-CNT composites are obtained by using spray freezing and low temperature activation method.It has the well-defined morphology of spherical that with open porous.Moreover,the well distribution of layered MoS2 on OCNT networks are determined by transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).It is found that they are closely connected by Mo-O bonds.Through electrochemical characterization,the specific capacitance of the MoS2/OCNT is 406.5 F g-1 at the current density of 0.5 A g-1.