Electrical and Proton Conduction Properties of Amorphous TiO2 Nanotubes Fabricated by Electrochemical Anodization

Electrolyte contacts were used to investigate the properties of pure and N-doped titania nanotubes (ntTiO(2)). Mott-Schottky analysis gave a flat-band potential E-fb = -0.57V vs. Ag/AgCl for pure ntTiO(2) and E-fb = -0.22V vs. Ag/AgCl for N-doped ntTiO(2). The charge carrier density was N-D = 6.7 10(20) cm(-3) for pure ntTiO(2) and ND = 3.9 10(20) for N-doped ntTiO(2). This investigation also allowed estimation of the apparent diffusion coefficient of H+ in ntTiO(2). Following the Randles-Sevcik method, the effective proton diffusion coefficient in ntTiO(2) is (2 +/- 1).10(-11) cm(2)s(-1) while in N-doped ntTiO(2) it is (4 +/- 1).10(-11) cm(2)s(-1). Using the Warburg diffusion element determined by electrochemical impedance spectroscopy, the proton diffusion coefficient is (2 +/- 1).10(-11) cm(2) s(-1) for pure ntTiO(2) while for nitrogen-doped ntTiO(2) a value of (7 +/- 3).10(-11) cm(2) s(-1) is found. These values are consistent with those of the Randles-Sevcik method.