INFLUENCE OF TEMPERATURE ON ZNO/CO3O4 NANOCOMPOSITES FOR HIGH ENERGY STORAGE SUPERCAPACITORS
For the fabrication of ZnO/Co3O4 nanocomposites, we applied a two-step chemical bath deposition process followed by calcination. ZnO nanotubes were densely grown on a three dimensional nickel foam in aqueous reactions, and then flat nanosheets of Co3O4 developed and produced a porous thin layer. The presence of ZnO nanotubeson Ni-foam with robust adhesion, which endows fast ion and electron transport, large electroactive surface area, and excellent structural stabilityincreased the aspect ratio and conductivity of the Co3O4nanosheets, whereas bath deposition from a mixture of Zn/Co precursors (one-step approach) resulted in a wrinkled plate of Zn/Co oxides. Such nanoarchitecture shows significant electrochemical performance with high capacitance and remarkable cycle life. When test as an electrode material for supercapacitors, the ZnO/Co3O4nanosheets electrode is able to deliver maximum specific capacitance of940 F g-1at a scan rate of 5 mV s-1in 1M KOH aqueous solution after being calcined at 450 °C.Because this value was much larger than that of single-component electrodes Co3O4 (785 F g-1) and ZnO (200 F g-1), a synergistic effect was suggested. The specific capacitance of ZnO/Co3O4 calcined at 450 °C was calculated to be 740 F g-1 at a current density of 0.75 A g-1 based on the charge/discharge curves,and the electrode also exhibits excellent cycling stability by retaining 85.7% of the maximum capacitance over 1000 charge-discharge cycles.
Assembling ZnO/Co3O4@450 nanocomposite as symmetrical electrode in 1 M KOH delivered high energy density of 36.6 Wh kg-1at a power density of 356 W kg-1withgood cycling stability of 89.9% and coulombic efficiency of 99.6% over 1000 cycles. Thus, the ZnO/Co3O4 nanocomposite fabricated with two step CBD method presented here is facile, cost-effective, and can offer a way for energy storage device applications. Furthermore, this approach can be applied to other metal oxide nanocomposites with intricate structures to extend the design possibility of active materials for electrochemical devices.