Hydrothermal Preparation Of Co₃O₄ Nanomaterials And Study On Energy Storage Mechanism Of Supercapacitors

In recent years,with the increasing environmental pollution and the intensification of natural resource consumption,it has became crucial to seek for green sustainable and renewable energy.Among various electrochemical energy storage devices,supercapacitors have attracted widespread attention due to their high capacitance,environmental friendliness and rapid charge-discharge.At present,supercapacitors have been applied to various hybrid vehicles,portable electronic devices and micro/nano energy storage device.Transition metal oxides stand out in various electrode materials due to their high specific capacitance,high power density,abundant resources,and low cost.However,most transition metal oxides exhibits large volume expansion or contraction during charging and discharging process.Therefore,it is important to design and develop hybrid electrode materials that possess large specific surface area and more active sites.In this thesis,various Co₃O₄ nanostructures as electrode materials and their electrochemical performance were studied.Several devices were assembled.The main contents are as follows:Firstly,Co₃O₄ nanoneedle arrays with uniform morphology and size were prepared by a facile hydrothermal method.Reaction time dependent shapes was studied.Co₃O₄ nanoneedle arrays as electrode materials show specific capacitance of 2178.4 mF cm^-22 at 10 mA cm^-22 and a cycle stability of 85.4%of initial capacitance after 6000 cycles.Secondly,we synthesized Co₃O₄@NiO nanowire arrays grown on nickel foam by using a two-step method.The Co₃O₄@NiO nanowire arrays delivers a specific capacitance 2018 mF cm^-22 at 2 mA cm^-2.the supercapacitor device was assembled by using the Co₃O₄@NiO nanowire arrays as a positive electrode and the activated carbon as negative electrode.The voltage window of the device can reach 1.5 V.The device delivers an energy density of 0.152mW h cm^-33 at a power density of 5.242 W cm^-3.Its capacitance retention can reach at 73.5%after 10,000 cycles.Finally,Co₃O₄ nanosheets were synthesized on Ni foam by a solution growth route.Heterogeneous structured Co₃O₄@Co₉S₈ nanowalls were prepared through vulcanizing the Co₃O₄ precusors.A Flexible asymmetric supercapacitor was assembled through Co₃O₄@Co₉S₈nanowall structures and activated carbon as the positive and negative electrodes,respectively with a voltage window of 1.5 V.It shows excellent mechanical properties and long cycle life（capacitance retention rate of 86.5%）.the device delivers an energy density of 0.416 mWh cm^-3at a power density of 14.99 W cm^-3.Three devices in series can light one LED（3.2 V）for 5min.