Effect of Potential and Aqueous Electrolyte In Different Anode Coating Steps on the Structure and Specific Capacitance of Titanium Dioxide Nanotubes
Abstract
We report the fabrication and electrochemical properties of anodic TiO2 nanotube arrays (TNA) formed on Ti-alloy substrate as supercapacitor electrode. Physical or chemical cleaning method was applied for surface pretreatment of Ti-alloy sheet. The single-step and triple-step of anodization were carried out in ethylene glycol electrolyte containing 0.5wt % NH4F under the applied potential of 40 and 50 V, and anodizing time for the last coating of 3 and 5 h. The influence of aqueous ethylene glycol electrolyte containing 0.5wt % NH4F and 5wt% distilled water on the morphology of TNA was compared. Annealing the as-grown TNA at 500°C transformed an amorphous phase to crystalline phase. Morphologies, crystal structure and supercapacitor performances of samples were investigated by scanning electron microscopy, X-ray diffraction and electrochemical measurement, respectively. Cyclic voltammetry was measured in 1 M H2SO4 electrolyte at -0.7 V to -0.1 V with different scan rate from 5 to 60 mV/s. Electrochemical impedance spectroscopy was investigated with the frequency ranging of 0.01 Hz to 100 kHz in the same electrolyte. Results showed that triple-step anodization of chemical-cleaned Ti-alloy sheet with 5 h of the final coating in aqueous electrolyte under applied potential of 50 V flowed by air annealing gave the well-porous dense structured TNA. Moreover, its capacitance was up to 63.73 F/g at the scan rate of 5 mV/s corresponded to the electrochemical impedance behavior.