Direct growth of bundle-like cobalt selenide nanotube arrays on Ni foam as binder-free electrode for high-performance supercapacitors

Freestanding bundle-like Co0.85Se nanotube arrays on nickle foam were prepared through a facile ion-exchange reaction and directly used as electrodes for supercapacitors. The morphology and structure of the obtained Co0.85Se nanotube arrays were studied by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). The electrochemical properties of the obtained Co0.85Se electrodes were studied by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS) in a three-electrode system. The Co0.85Se nanotube array/Ni foam electrode exhibited remarkable pseudocapacitive performance with high specific capacitance (1394 F g−1 at 4 A g−1) as well as good cycling performance and rate capability. The good electrochemical properties were due to the hollow nanostructure of the bundle-like Co0.85Se nanotube arrays and the three-dimensional (3D) conductive Ni foam, which can increase the contact between electrode and electrolyte and improve the conductivity of the whole electrode.