Synthesis Of Ternary Oxides Electrode Materials On Conductive Substrates And Their Application In Supercapacitors

Achieving a secure,sustainable energy future is one of the most challenging issues in 21st century science and engineering.In the present age of electric and hybrid vehicles,smart electricity grid systems,and advanced consumer electronics,electrical energy storage plays a crucial role in providing the required high energy and power density for these systems.With the depletion of fossil fuels,electricity generated from renewable natural sources,such as solar and wind,will be critical to meeting future energy demands.However,these energy sources are intermittent in time and localized in space,requiring higher efficient electrical energy storage devices.Supercapacitors?SCs?which can temporarily store a large amount of charges and then release them when necessary,have attracted much attention for their high power density,fast charging/discharging rate and long cycle life.Unfortunately,to some extent,the practical applications of SCs have been restricted by their low energy densities.Therefore,numerous efforts have been devoted to developing high-performance electrode materials for SCs.The purpose of this thesis is to design and synthesize electrode materials with high capacitance and excellent cycling stability.We rationally design and fabricate transition metal oxides?mainly ternary oxides?with unique nanostructures grown directly on conductive substrates as an advanced binder-free electrode for SCs.The research results obtained are as follows:1.An integrated electrode of CoMoO₄ nanosheet arrays/Ni foam has been successfully synthesized via a one-step hydrothermal method followed by calcination treatment.The formation process of CoMoO₄ nanosheet arrays was discussed.The as-obtained CoMoO₄ electrode exhibited a specific capacitance of 737.6 F g^-1 at current density of 10 mA cm^-2,and excellent cyclic stability?after 3000 cycles 99%retention of specific capacitance?.2.We have rationally designed and synthesized hierarchical CoMoO₄@MnO₂core-shell nanosheet arrays on nickel foam by a facile hydrothermal process followed by annealing.Nanosheet arrays of cobalt molybdenum precursors are synthesized first by a mild hydrothermal reaction and used as the“core”.After the second facile hydrothermal process with a successive annealing,the Co-Mo precursors aretransformed into the 3D hierarchical CoMoO₄@MnO₂ core-shell nanostructure.The CoMoO₄@MnO₂ electrode exhibited excellent electrochemical properties,which were superior to CoMoO₄ electrode.The as-synthesized electrode delivered high specific capacitance of 1704.8 F g^-1 at 10 mA cm^-2 as well as markedly enhanced cycle stability with 93%retention after 3000 cycles.3.Hierarchical CoMoO₄@NiMoO₄ core-shell nanosheet arrays were successfully grown on nickel foam via a facile two-step hydrothermal method followed by calcination treatment.With an ordered core-shell nanostructure and a desired composition,the optimized CoMoO₄@NiMoO₄ composite electrode exhibited a high specific capacitance of 1639.8 F g^-1(at 10 mA cm^-2)and an excellent cycling stability with a 95%retention rate at a high current density of 20 mA cm^-2 after 3000 cycles.Additionally,an asymmetric supercapacitor?ASC?was assembled with CoMoO₄@NiMoO₄ nanosheet arrays/Ni foam as the positive electrode and activated carbon?AC?as the negative electrode,which displayed an energy density of 28.7 W h kg^-1 at a power density of 267 W kg^-1.Two ASC devices in series can successfully light a 5 mm diameter red LED.The remarkable electrochemical performance indicated that the CoMoO₄@NiMoO₄ composite was a promising electrode material and had great application potential for energy storage.4.A facile hydrothermal approach with annealing posttreatment was developed to construct the porous ZnCo₂O₄ nanoribbon arrays/nickel foam electrode for high-performance SCs and LIBs.The defined nanoribbon array structure with high porosity based on 3D nickel foam substrate exhibited an excellent cycling stability and rate capability.More importantly,the electrode not only yielded an extraordinary specific capacitance of 1957.7 F g^-1 at a current density of 3 m A cm^-2 for SCs,but also gave 1422 mA h g^-1 at 200 mA g^-1 after 80 cycles for LIBs.The constructed porous ZnCo₂O₄ nanoribbon arrays can serve as a versatile binder-free electrode for electrical energy storage devices,and bring remarkably enhancement in their electrochemical performance.