Electrochemical and photoelectrical properties of titania nanotube arrays annealed in different gases

Titania nanotube arrays fabricated by anodic oxidation of titanium foil were calcined in dry nitrogen, air, and argon at various temperatures for varied period of time. Changes in morphology and crystallinity of the nanotube arrays were studied by means of SEM and XRD. The influences of annealing conditions on the electrochemical and conductivity were investigated by electrochemical impedance spectroscopy (EIS), and the results showed that the electrical conductivities of TiO2 nanotube arrays calcined in nitrogen for 3 h were improved greatly as compared to the as-grown titania nanotube arrays or annealed in air or argon. Well defined oxidation and reduction peaks were observed during the cyclic voltammetric scan at 0.1 V/s in 10 mM K3[Fe(CN)6] solution. Photocurrent response in TiO2 nanotube arrays calcined in nitrogen was significantly enhanced. Reduction of tetravalent titanium cations and the formation of oxygen vacancies were ascribed to explain the improved electrochemical and photoelectrical properties of titania nanotube arrays.