Controllable shell thickness of Co/CoO core-shell structure on 3D nickel foam with high performance supercapacitors

Co/CoO core-shell nanostructure on the 3D nickel foam has been synthesized by a hydrothermal method following by annealing the precursor in hydrogen atmosphere and air respectively. Different shell thicknesses of the CoO are designed and controlled by annealing the nanostructured Co in the air at 50 degrees C, 100 degrees C, 150 degrees C, 200 degrees C for 2 h, which were characterized by X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectronspectroscopy (XPS). As a result, Co/CoO core-shell nanostructure annealed at 150 degrees C achieved the best electrochemical performance (ultrahigh areal capacitance of 6.08 F cm(-2)), which was superior to those treated in other temperatures. An asymmetric supercapacitor device was assembled by using the Co/CoO core-shell nanostructure (positive electrode) and the active carbon (negative electrode), which can deliver a working voltage of 1.5 V, and display a high energy density of 0.51 mWh cm(-2) at a power density of 2.03 mW cm(-2). The results show that the Co/CoO core-shell nanostructure has potential application prospect in the pseudocapacitor. (C) 2017 Elsevier B.V. All rights reserved.