Designed roadblock for oxygen evolution through construction of stack structure during Ti anodization

Although many researches have involved oxygen generation to clarify the self-assembling growth of anodic TiO₂ nanotubes, none convincing evidence has been provided to prove oxygen evolution during anodization. Herein, a special stack structure has been designed to restrain the digging behaviors of field-assisted dissolution theory. The stack structure looks like just a sandwich, made of lower porous layer, middle compact layer and upper porous layer, through anodizations for three times in different electrolytes. After the third anodization, the middle layer formed by the second anodization tends to an interlaced nanotube link layer, without any observation of one-to-one through-hole evidence from the cross-section FESEM images. The stack sandwich structure effectively rejects the digging manners of the traditional field-assisted dissolution theory, since the middle compact layer should be one-to-one through-hole after the fluorine dissolution process. Actually, the plastic oxide flow grows under the mould effects of oxygen bubbles and then results in the porous structure. (paper)