Design,Pieparation And Electrochemical Energy Storage Applications Of Several MOFs Based Nanocomposite Materials

At the same time that the rapid development of society brings material richness and convenience to human life,the large amount of consumption of fossil fuels and the increasing environmental pollution issues caused by its increasing environmental pollution have been increasingly worse,prompting people to find promising clean energy and new energy storage devices.As an efficient energy storage equipment,supercapacitors have received widespread attention due to their high power density,fast charging and discharge rate,excellent circulating life and environmental friendship.Electrical materials are an important part of supercapacitors and have a decisive effect on the performance of super capacitors.According to the energy density formula E=0.5CV²,energy density of a supercapacitor largely depends on the specific capacitance and voltage window of the electrode material.Therefore,adjusting the inherent characteristics of the electrode material and improving the electrochemical performance of the materials are the key to the preparation of high-performance supercapacitor devices.Metal-organic frameworks（MOFs）have received much attention as a promising crystalline porous material.Due to their advantages of adjustable aperture,high porosity,topological diversity and high specific surface area,MOFs hav been widely used in the field of supercapacitors.However,low conductivity and poor structural stability lead to low specific capacity and poor cyclic stability.Therefore,in this paper,by using MOFs materials as precursors,several nano-composites are prepared by combining them with conductive matrix or converting them into different derivatives,and the influences of materials,structure and morphology,the impact of chemical composition and charge storage mechanism on the electrochemical performance of composite materials.On this basis,the related preparation strategies of the electrode materials were optimized.At the same time,by constructing hybrid supercapacitors with these materials as positive electrode and activated carbon as negative electrode,their practical application performances were further evaluated.The thesis mainly includes three parts as follows:1.At first Co-MOF（ZIF-67）was successfully synthesized through a simple hydrothermal reaction,and then ZIF-8 was in situ grown on the surface of the pre-synthesized ZIF-67 to prepare ZIF-67@ZIF-8 composition structure by controlling the reaction temperature and time.This structure was further carbonized as carbon nanotube-interlinked Co-doped nitrogen-containing carbon nanostructure（Co-NC）.At last,Ni S was coated on its surface to form a Ni S encapsulated Co-doped N-containing nanostructural carbon material（Co-NC@Ni S）.The obtained Co-NC@Ni S delivered the largest specific capacitance of 1116.6 F·g^-1 at the current density of 1A·g^-1 and the assembled hybrid supercapacitor Co-NC@Ni S//AC HSC device,in which AC was activated carbon,possesses an energy density of 33.9 Wh·kg at a power density of 799.9W·kg^-1.And when the power density is increased to 7999 W·kg^-1,it still remains 14.22Wh·kg^-1.In addition,the HSC still showed good cyclic performance with a specific capacitanceretention 89.85%after 5000 charge and discharge cycles.2.A novel iron-nickel selenide nanostructure Fe Ni-Se was synthesized by employing Ni-MOF as self-sacrificing template through a simple ion-exchange process followed by hydrothermal selenization.Fe Ni-Se showed the biggest specific capacitance of 1,688 F·g^-1 at a current density of 1 A·g^-1and a good cyclic stability with a capacitance retention of80.6%after 5000 cycles at 10 A·g^-1.Meantime,the assembled Fe Ni-Se//AC HSC had an ultrahigh energy density of 60.5Wh·kg^-1 at the power density of 787.2 W·kg^-1 and even when the power density was rosen to 16.1 k W·kg^-1 the energy density still reached35.6Wh·kg^-1,which are much bigger than those of most reported similar materials.In addition,the material also exhibited an excellent cyclic performance and the capacitance was maintained at 91.1%of the original value after 5000 cycles at 5 A·g^-1.3.A carbon nanotube（CNTs）-interlinked accordion morphological Ni Co-MOFs（Ni Co-MOF/CNTs）were successfully prepared by controlling Ni/Co molar ratio in the presence of CNTs using a simple hydrothermal procedure.This particular structure not only realized the rapid diffusion of the electrolyte ions,enhanced the electrical conductivity of the material,but also enhanced the electrochemical performance and structural stability of the resulted composite.The prepared composition material displayed the largest specific capacitance at 1 A·g^-1.And the assembled Ni Co-MOF/CNTs HSC device delivered a high energy density of 33.2 Wh·kg^-1 at a power density of375W·kg^-1.In particular,the device also had a good cyclic stability with a capacitance retention rate of 91.35%after 5000 consecutive charge-discharge cycles at a current density of 5 A·g^-1.Notably,the preparation procedure of this material is simple enough and environment-friendly without further carbonization and heteroatom dopping.