Preparation Of Transition Bimetallic Compound/Carbon Nanofiber Composites And Theirs Application In Supercapacitors

With the rapid development of science&technology and social productivity,automobiles have become an indispensable energy-consuming necessity in daily life.Considering the consumption of oils and the protection of the environment,more and more attention is devoted to the development and application of new energy sources,which can be widely used in new energy vehicles,special and daily equipments.As a new energy storage device,supercapacitor has been a research hotspot because of its green environmental protection,long life and high power density.At present,there have been a lot of studies on different types of electrode materials for supercapacitors.Among them,transition metal compounds/carbon-based material composites are the important ones.Among all carbon-based materials,carbon nanofibers can be used directly as electrode materials or as substrates for active materials of transition metal compound,which can be used directly as electrode materials without any binders and collectors,it can significantly improve the electrochemical performance of the materials.This thesis explores the controlled preparation and electrochemical performance of self-supporting carbon nanofiber/transition metal（Ni,Co,Mo）compound composites.The specific research contents are as follows:（1）Carbon nanofibers were used as substruate for active materials of the transition bimetallic compounds CoMoO₄,NiMoO₄,NiCo₂S₄,and the carbon fiber-based composites electrode was prepared by hydrothermal method.During the preparation process,the structure and morphology of the composite electrode were controlled by the reaction conditions,finally the self-supporting composite materials（CNFs/CoMoO₄,CNFs/NiMoO₄,CNFs/NiCo₂S₄）with uniform and fine structure were prepared.The effects of preparation conditions on electrode material morphology and electrochemical performance were studied in detail.The electrochemical performance of the composites are as follows:（1）The specific capacitance of CNFs/CoMoO₄ is 1407.1 F·g^-1 at current density of 1 A·g^-1,and the specific capacitance retention is 78.7%after 3000 cycles at current density of 10 A·g^-1.（2）The specific capacitance of CNFs/NiMoO₄ is 1295.1 F·g^-1 at a current density of 1 A·g^-1,and the specific capacitance retention is 87.6%after 3000 cycles(10 A·g^-1).（3）The specific capacitance of CNFs/NiCo₂S₄ at is 1940.67 F·g^-1 the current density of 1 A·g^-1,and the specific capacitance retention is 86.4%after 3000 cycles(10 A·g^-1)cycles.Therefore,CNFs/NiCo₂S₄ shows best electrochemical performance among the three composits（2）On the basis of the above research,hollow carbon nanofibers（HCNFs）and hollow porous carbon nanofibers（HCNFs）were prepared by coaxial electrospinning.Three composites CNFs/NiCo₂S₄,HCNFs/NiCo₂S₄,HPCNFs/NiCo₂S₄ were prepared by hydrothermal method.Due to hollow multi-channel structure in HPCNFs/NiCo₂S₄,which can effectively increase the specific surface area of the electrode material,promote the rapid penetration of the electrolyte and effectively buffer the volume change during charge and discharge.The research results show that the HPCNFs/NiCo₂S₄ composite electrode exhibits excellent electrochemical performance:the specific capacitance of HPCNFs/NiCo₂S₄ at a current density of 1 A·g^-1 is 2328 F·g^-1,and the capacitance retention rate is 90.5%after 3000 cycles at current density of 10 A·g^-1.