Enhanced charge storage by the electrocatalytic effect of anodic TiO₂nanotubes

Ordered titania nanotube (TNT) arrays were fabricated by anodization of titanium with a very fast voltage ramp speed. Co(OH)2/TNT nanocomposite was synthesized by cathodic deposition using the as-anodized TNT as the substrate. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology, crystalline structure and chemical state. The capacitive characteristics were investigated by cyclic voltammetry (CV), charge-discharge tests, and electrochemical impedance spectroscopy (EIS). Thanks to the electrocatalytic effect of the as-anodized TNTs on the reduction of Co(OH)2, the Co(OH)2/TNT composite electrode exhibits a significantly enhanced charge storage capacity (an increase of 73%) when compared with Co(OH)2/Ti (titanium as the deposition substrate). The occurrence of such an electrocatalytic effect is suggested to be related to the nano-sized TiO2crystals (rutile) embedded in organized amorphous TNTs. Co(OH)2/TNT demonstrates enhanced specific energy, high rate capability and good cyclability, and can be a potential electrode of choice for supercapacitors.