Comparative supercapacitance performance of CuO nanostructures for energy storage device applicationsElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ra00035a

In the present study, three different morphologies of copper oxide (CuO) nanostructures; bud-, flower- and plate-shaped CuO structures were synthesized by a simple chemical method. Binder-included pseudocapacitor electrodes were prepared using bud- and flower-shaped CuO structures whereas, directly grown CuO-nanoplates on Ni foam were used as a binder-free electrode in a three-electrode setup for electrochemical studies. Remarkably, the binder-free CuO nanoplates electrode exhibited excellent specific capacitance of 536 F g −1 at a current density of 2 A g −1 , whereas the binder-included electrodes of bud- and flower-shaped CuO exhibited 230 F g −1 and 296 F g −1 , respectively, at a current density of 0.7 A g −1 in a 6 M KOH electrolyte. The cycling retention test and charge/discharge stability for the binder-free CuO nanoplates electrode showed 94% capacity retention after 2000 cycles and capacitance loss of only 11.3% over ∼1000 cycles at a current density of 4 A g −1 from charge/discharge measurements. Also, the binder-free CuO electrode showed higher energy and power densities of 29.4 W h kg −1 and 12.7 W kg −1 , respectively, at 1.96 A g −1 in an asymmetrical device, when compared to the binder-included electrode of flower-shaped CuO. (a)-(c) FE-SEM images of CuO nanoplates on Ni foam, flower-shaped CuO and bud-shaped CuO. (d) Specific capacitance and (d) and (e) Ragone plots of power density vs. energy density according to CuO electrodes in an asymmetrical device.