Fabrication of TiO-Nanotube-Array-Based Supercapacitors.

In this work, a simple and cost-effective electrochemical anodization technique was adopted to rapidly grow TiO nanotube arrays on a Ti current collector and to utilize the synthesized materials as potential electrodes for supercapacitors. To accelerate the growth of the TiO nanotube arrays, lactic acid was used as an electrolyte additive. The as-prepared TiO nanotube arrays with a high aspect ratio were strongly adhered to the Ti substrate. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed that the TiO nanotube arrays were crystallized in the anatase phase. TEM images confirmed the nanotublar-like morphology of the TiO nanotubes, which had a tube length and a diameter of ~16 and ~80 nm, respectively. The electrochemical performance of the TiO nanotube array electrodes was evaluated using the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) measurements. Excellent electrochemical response was observed for the electrodes based on the TiO nanotube arrays, as the cells delivered a high specific capacitance of 5.12 mF/cm at a scan rate of 100 mV/s and a current density of 100 µA/cm. The initial capacity was maintained for more than 250 cycles. Further, a remarkable rate capability response was observed, as the cell retained 88% of the initial areal capacitance when the scan rate was increased from 10 to 500 mV/s. The results suggest the suitability of TiO nanotube arrays as electrode materials for commercial supercapacitor applications.