Impact of Nanosize on Supercapacitance: Study of 1D Nanorods and 2D Thin-Films of Nickel Oxide

We synthesized unique one-dimensional (1D) nanorods and two-dimensional (2D) thin-films of NiO on indium–tin-oxide thin-films using a hot-filament metal-oxide vapor deposition technique. The 1D nanorods have an average width and length of ∼100 and ∼500 nm, respectively, and the densely packed 2D thin-films have an average thickness of ∼500 nm. The 1D nanorods perform as parallel units for charge storing. However, the 2D thin-films act as one single unit for charge storing. The 2D thin-films possess a high specific capacitance of ∼746 F/g compared to 1D nanorods (∼230 F/g) using galvanostatic charge–discharge measurements at a current density of 3 A/g. Because the 1D NiO nanorods provide more plentiful surface areas than those of the 2D thin-films, they are fully active at the first few cycles. However, the capacitance retention of the 1D nanorods decays faster than that of the 2D thin-films. Also, the 1D NiO nanorods suffer from instability due to the fast electrochemical dissolution and high nanocontact ...