Hierarchical NiO@Ni(OH)2 nanoarrays as high-performance supercapacitor electrode material

Abstract

A binary metal oxide/hydroxide as a hierarchical NiO@Ni(OH)2 nanoarrays was synthesized through several steps. Firstly, ZnO nanorods were prepared through a facile electrodeposition method on Ni foam (NF), and then the obtained ZnO nanorods were used as sacrificed template to deposit NiO nanotubes around them. The obtained nanotubes served as ideal 1D superhighways for charge storage and ion delivery. After that, chemical bath deposition was used to decorate Ni(OH)2 nanoflakes on top of NiO nanotubes acting as an ion reservoir. The prepared electrodes were evaluated by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) methods. More advanced characterizations of the NF/NiO nanotubes and NF/NiO@Ni(OH)2 nanoarrays were performed using Fourier transform infrared (FT-IR) and Raman spectroscopy, Thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. Compared with the single NiO nanotubes or Ni(OH)2 nanoflakes, the NiO@Ni(OH)2 nanoarrays exhibited a high specific capacitance (Csp) of 2509 mA cm-2 at 1 mA cm-2. Long term cycling stability observed over 5000 cycles without negligible loss of Csp. This study shows that hierarchical covering metal oxide channels with the metal hydroxide flakes can open up new strategies for the design of high-performance supercapacitor electrode materials.