Enhanced activity of highly ordered pristine and black anodic TiO2 nanotubes for high performance supercapacitors

For energy storage systems such as supercapacitors, it is a huge challenge to achieve high energy density. Here we report on the effect of either tube ordering manipulated by two-step anodisation or electrolytic surface reduction of TiO2 nanotubes (TNTs) on the supercapacitor performance. The microstructure, crystallinity, morphology and chemical composition of TNTs were examined, compared by using X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDX) and field emission scanning electron microscopy (FE-SEM). Electrochemical investigations were performed using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The GCD curves recorded for TNTs grown in different conditions confirmed the quasi-capacitive behaviour of the produced titanium oxide nanotubes. The galvanostatic charge-discharge showed an increase in the value of specific capacitance rising from 22 mu F cm(-2) to 3672 mu F cm(-2) at a current density of 50 mu A cm(-2) in a solution of 1 M KCl. The highest value corresponds to the black TiO2 owing to a decrease in charge transfer resistance as evidenced by the Nyquist plots. This study reveals the feasibility of one-pot electrochemical production of efficient TiO2 nanotubes as efficient nanoporous electrodes for supercapacitors.