The Synthesis Of Cobalt-based Self-support Nanoarrays With Secondary Structure For Supercapacitor Application

Supercapacitors are recognized as suitable choices for applications which require pulse charge-discharge characteristics due to their desirable properties including high power density,long cycle life,and safe operation.Core/shell self-supported nanoarray is a promising type of electrode materials for high-performance supercapacitors.The inner core materials could provide an efficient electron transfer pathway,and the outer shell materials could offer large amount of active sites as well as work as a protective layer.In addition,the self-supported materials could achieve the highly efficient transport of electrons by directly growing the active materials on the conductive current collector.The“dead volume”could be minimized because the extra binder/conductive agents are absent in the electrode materials.In this thesis,the core/shell configuration and the self-supported materials are combined to prepare self-supported nanoarrays with secondary structures.Main contents of this thesis are as follows:The Co-based nanoarrays?NAs?are first grown on the nickel foam via a hydrothermal method which are then transformed into Co₃O₄ NAs through calcination under ambient atmosphere.Subsequently,Ni²⁺ions are electrochemically deposited on the Co₃O₄ NAs,and are finally converted into Ni₃S₂ nanosheets by hydrothermal sulfurization.The Co₃O₄@Ni₃S₂ could achieve an areal capacitance of(5.5 F/cm² at a current density of 2 mA/cm².And the sample could demonstrate good cycling stability by maintaining a stable capacitance of 1.5 F/cm² after 10000 cycles at 50 mA/cm².When coupling with activated carbon in an asymmetric supercapacitor,it shows a good cycle performance over 10000 cycles with promising potential for practical use by lighting up12 red LEDs.MOFs derived Co₉S₈ is used as secondary structure to reinforce the Co₃O₄ NAs,forming a 1D Co₉S₈ hierarchical structure.When the Co₉S₈ NAs were applied for supercapacitor,it delivers a areal capacitance of 4.48 F/cm² at 2 mA/cm².In addition,the sample exhibits negligible capacitance loss over 100000 cycles at 25 mA/cm².Furthermore,the sample is assembled into an asymmetric supercapacitor with activated carbon,and this device shows a stable capacitance of 416 mF/cm² for 100000 cycles at25 mA/cm²,giving rise to a capacitance loss of only 2.8×10^-4%per cycle.Moreover,a quasi-solid-state asymmetric supercapacitor is constructed used Aluminum-plastic packaging.The device demonstrates excellent cycling stability under flat-bend-flat alternating states over 5000 cycles,and it could light up 16 commercial red LEDs under both flat and bending states.The superior performance suggests its promising capability for practical applications.