Preparation And Electrochemical Performance Of Some Transition Metal Organic Frameworks Derivatives

Energy density of supercapacitor depends on the voltage window and specific capacitance of the electrode material,while the specific capacitance relys on intrinsic physical and chemical properties of the active materials including the theoretical capacitance,electrochemical activity,composition,structure,morphology and so on.Due to their particular pore structure and rich active sites,the Metal Organic Frameworks(MOFs)have become a research hotspot in the field of energy storage in recent years.Their poor conductivity and stability have severely limit their application for electrochemical energy storage.Therefore,these works aim to study the preparation of different nanocomposites using MOFs as precursors to enhance number of exposed surface active sites for improving their electrical conductivity and stability.And by assembling hybrid supercapacitors with these materials as positive electrode and activated carbon as negative one,it is expected that the voltage window can be further expanded and the energy density increased.This thesis consists of the following three parts:1.A Ni/Go-MOF was successfully prepared by a simple hydrothermal reaction,and successfully canbonized and vulcanized at different temperatures to obtain bimetal sulfide/nitrogen doped porous carbon composite materials.After high-temperature pyrolysis,the pores occupied by the organic ligands in the porous carbon framework material derived from the Ni/Co-MOF self-sacrificial template precursor were opened,which provided a convenient channel for charge transfer.At the same time,the formation of a carbon skeleton reduced the internal resistance of the precursor.The introducing of the S element strengthened the precursor’s skeleton structure,and the formation of sulfides also provided an important guarantee for the penetration of the electrode interface.As a result,the prepared materials delivered outstanding electrochemical performance.Particularly,NiS2/CoS2/NC-500 obtained at 500℃ had the highest specific capacitance of 1,325 F· g-1 at current density of 1 A· g-1 and a high capacitance retention rate of 75%after 5,000 cycles.The assembled NiS2/CoS2/NC-500//AC hybrid supercapacitor had an energy density of 53.93 Wh· kg-1 at power density of 800 W· kg-1.After 20,000 charge/discharge cycles,the specific capacitance still remained 85.71%of the initial value.2.A series of M-MOF-74(M=Ni,Co,NiCo)with different ratios of Ni to Co were prepared by a simple hydrothermal method.Then,by selenizing the M-MOF-74 precursor,CoSe2,NiSe2,and NiCoSe(NiCoSe-X)with different ratios of Ni to Co were successfully fabricated.It was found that the bimetal selenide possessed better electrochemical performance than the single metal selenides,and the electrochemical performance is the best when the molar ratio of Ni to Co is 4:1(NiCoSe-4).NiCoSe-4 and activated carbon were assembled to obtain an aqueous hybrid supercapacitor.The assembled NiCoSe-4//AC showed a high energy density of 61.24 Wh·kg-1 at the power density of 800 W· kg-1.At a current density of 10 A· g-1,the NiCoSe-4//AC capacitance retention and coulomb efficiency were 91%and 89%after 12,000 cycles,respectively.These results suggest that the synthesized NiCoSe-4 is a promising electrode material with a good application potential.3,A new type of Mn/Ni-MOF-74 was successfully synthesized by a simple hydrothermal method.At the same time,a bimetallic hydroxide composite with special morphology was prepared by a simple alkalization procedure using Mn/Ni-MOF-74 as a self-sacrifice template.By rationally controlling the alkalizing conditions,a novel structure with smaller particle size and rich micropores was prepared.The resultant MnNiDH composite demonstrated a high specific capacitance of 2,498 F· g-1 at a current density of 1 A· g-1 with a retention rate of 85.29%after 5,000 cycles.In addition,the aqueous hybrid supercapacitor assembled with MnNiDH and activated carbon had an energy density of up to 58.53 Wh· kg-1 and a maximum power density of 16 kW· kg-1.It is worth noting that the voltage window of the assembled solid-state hybrid device reached 2.1 V.These excellent performances demonstrate that the obtained bimetallic hydroxide is very hopeful electrode in practical application.