Facile synthesis of NiCo2O4 quantum dots for asymmetric supercapacitor

Binary metal oxides have great potential as electrode materials for supercapacitors. Three-dimensional flower-like nickel-cobalt oxide (NiCo2O4) nanostructures have been obtained by a simple and cost-effective hydrothermal synthesis followed by annealing at distinct temperatures. The effect of calcination temperature, on the structure and the electrochemical behaviour of the nanostructures, has also been investigated. Highly porous, hollow and continuous structures of NiCo2O4 quantum dots (NCO-QDs), formed at the calcination temperature of 300 °C, delivered a specific capacitance of 362 F g−1 at a current density of 0.5 A g−1. The good electrochemical behaviour of these nanostructures may be related to their unique, highly porous, integrated nanostructures that provide a good electroactive surface for faradaic redox reactions to occur. Also, an asymmetric-supercapacitor with NCO-QDs as positive electrode and reduced graphene oxide (rGO) as negative electrode has been fabricated which exhibits a good charge storage capacity (81 F g−1 at the scan rate of 5 mV s−1) along with very good cycling stability (86% capacitance retention after 1000 cycles). The energy density and power density of the supercapacitor have been checked at a potential window of 2.5 V after 1000 charge-discharge cycles. The device has shown a very good energy density of 69.5 W h kg−1 along with high power density of 2.22 kW kg−1 at a current density of 1.5 A g −1. So, this study suggests that the prepared NCO-QDs are prospective candidates for fabricating supercapacitor electrodes with good electrochemical performance in an extended potential window.