Study of highly porous ZnO nanospheres embedded reduced graphene oxide for high performance supercapacitor application

Design and fabrication of different metal oxide nanosphere with hierarchically porous structure is important for developing the performance of energy storage devices. In this present work, we have reported the fabrication of ZnO nanosphere decorated reduced graphene oxide (rGO) composite and its electrochemical performance for supercapacitive applications. The porous ZnO nanosphere embedded on rGO (ZnO@rGO) has been synthesized by a simple ex-situ wet chemical process. The specific capacitance of the composite material is investigated by using two-electrode configuration and from the galvanostatic charge-discharge plot the specific capacitance is obtained 949 F g-1 at 1 Ag-1. Integrating the pseudo-capacitive effect of porous ZnO nanosphere, and the electrochemical double layer of the reduced graphene oxide, the maximum energy and power density of 74 Wh kg−1 and 374 W kg−1 are achieved respectively at 1 Ag-1. The ZnO@rGO composite is also observed to exhibit high cyclic stability and it retains 91% capacitance value even after 10,000 cycles, demonstrating good long-term stability. Increased specific surface area and presence of additional active sites due to the porous structure of ZnO nanosphere are proposed to be the primary factor for the superior electrochemical performance of ZnO@rGO based supercapacitor devices.