Electrochemical impedance analysis of TiO2 nanotube porous layers based on an alternative representation of impedance data

• Alternative EIS data representation allows more accurate information about nanotubes.
• Double-structured nanotubes and barrier layers show three relaxation processes.
• A three time constants equivalent circuit is held to account for these relaxations.

A new direct approach for model identification is proposed. It allows a more accurate survey of the different relaxation processes yielding distinct time constants in electrochemical impedance spectroscopy. With the help of self-organized TiO2 nanotubes layers grown in pure Ti substrates, it is shown that the conventional impedance data representation methods are susceptible to miss some information that is made accessible by the frequency survey of αeff, the effective CPE exponent parameter. In the specific case of the present work, the alternative representation proposed here shows that the electrochemical behavior of the TiO2 layers exposed to Ringer physiological solution is characterized by up to three time constants related to a simple double-layered structure composed by a dense barrier and the porous nanotubes one, instead of the ubiquitous two time constants mentioned in the literature for the same systems.