Facile synthesis of NiSnO3/graphene nanocomposite for high-performance electrode towards asymmetric supercapacitor device

Potentially, active nickel stannate (NiSnO3)/graphene nanosheets (GNS) composite was prepared using facile hydrothermal method. From XRD analysis, the average crystallite size of NiSnO3 nanoparticles and NiSnO3/GNS nanocomposite was found to be 5 and 3 nm, respectively. XPS analysis revealed chemical species and oxidation state of elements present on the surface of the samples. HRSEM analysis showed the formation of elongated shape of NiSnO3/graphene nanocomposite with size of similar to 6 nm. Moreover, the internal structure and interactions between stannate and graphene were examined using transmission electron microscope analysis. BET analysis revealed the significant increase in surface area of 162 m(2)/g in NiSnO3/GNS nanocomposite, whereas bare NiSnO3 nanoparticles showed 101 m(2)/g. Electrochemical performance of bare NiSnO3 and NiSnO3/GNS nanocomposite was studied using cyclic voltammetry and charge-discharge techniques. Cyclic voltammetry of NiSnO3/GNS resulted in maximum specific capacitance of 891 F/g at a scan rate of 5 mV/s which is higher than that of NiSnO3 alone 570 F/g at same scan rate. Electrochemical impedance spectra show negligible charge transfer resistance of 1.6 and 1.5 Omega for NiSnO3 and NiSnO3/GNS, respectively. Enhancement in the electrochemical performance of NiSnO3/GNS is mainly due to graphene incorporation which provided high surface area, thereby offering high interfacial sites, electrical conductivity and improved redox activity. Further, an asymmetric supercapacitor was constructed using NiSnO3 /GNS nanocomposite and activated carbon acted as positive and negative electrodes within an operating potential window of 0-0.8 V. Fabricated asymmetric device delivered a high energy density of 42.54 Wh/kg at a power density of 0.34 kW/kg. Moreover, this device exhibited excellent charge-discharge cycling stability with 88.3% capacitance retention even after 4000 cycles.